3

LWT - Food Science and Technology 152 (2021) 112338
Available online 20 August 2021
0023-6438/© 2021 Elsevier Ltd. All rights reserved.
Advanced konjac glucomannan-based films in food packaging:
Classification, preparation, formation mechanism and function
Yongsheng Ni a
, Yilin Liu a
, Wentao Zhang a
, Shuo Shi a
, Wenxin Zhu a
, Rong Wang a
,
Liang Zhang a
, Linrang Chen a
, Jing Sun b
, Jie Pang c,**
, Jianlong Wang a,*
a
College of Food Science and Engineering, Northwest A&F University, Yangling, 712100, Shaanxi, China
b
Qinghai Provincial Key Laboratory of Qinghai-Tibet Plateau Biological Resources, Northwest Institute of Plateau Biology, Chinese Academy of Sciences, Qinghai,
810008, China
c
College of Food Science, Fujian Agriculture and Forestry University, Fuzhou, 350002, China
A R T I C L E I N F O
Keywords:
Polysaccharides
Konjac glucomannan
Food packaging
Biodegradable films
Bio-nanocomposite
A B S T R A C T
Konjac glucomannan-based (KGM-based) films are new promising alternative materials for solving white
pollution and food safety concerns induced by traditional petroleum-based packaging materials. This paper re
views the current situation, the bottlenecks and the trend of future research of KGM-based films. Natural KGM-
based films including biopolymer composite films, bio-nanocomposite films, emulsion films and physically or
chemically modified films are summarized. Fabrication methods including solvent casting, microfluidic spinning
and electrospinning are introduced. Functions of films including active packaging, intelligent packaging and
edible packaging are summarized. Finally, the film formation mechanisms and promising trend of research are
comprehensively analyzed and discussed. The upsurge of films research based on KGM is coming. Based on the
comparison and analysis for published literatures, the key points for research primarily cover the following
aspects: actual preservation effect and activity mechanisms of KGM-based films should be emphasized; new
strategies need to be explored to improve the antibacterial activity of KGM-based films; various novel methods
should be found to deal with the issue that KGM-based films have strong water solubility.
1. Introduction
Konjac, which belongs to the category of potato and taro in culti
vation, is a general name of amorphopha llus blume in araceae (Zhu,
2018). It is widely distributed in warm and humid areas in Asia (mainly
includes China and Japan) and Southeast Asia, such as hilly areas in
southern provinces, Daba mountain area in Qinling mountains, Sichuan
basin and Taiwan (Behera & Ray, 2016). Konjac is composed of leaves,
branches and tubers. Its tubers are the main edible part and the source of
income (Huang et al., 2016). Konjac glucomannan (KGM) can be
extracted from dry konjac tubers and purified by the precipitation
method. The content of glucomannan in dry tuber is approximately
60%, and is varied in different types. Other ingredients (approximately
40%) mainly include starches, proteins, vitamins, celluloses and alka
loids (Chen et al., 2016). The origin of KGM and the formation process of
KGM-based films are shown in Fig. 1A.
KGM is a water-soluble neutral macromolecular polysaccharide. Its
main chain and side chain are respectively linked by β-1,4 glycosidic
bonds and β-1,3 glycosidic bonds. There is one acetyl group for every 9
to 19 sugar units in the molecule chains (C-6 position) (Zhang, Chen, &
Yang, 2014). The chemical structure of KGM is shown in Fig. 1B. KGM
has excellent film-forming, hydrophilia and swelling properties as well
as edibility and biodegradability. It also has slight antioxidant activity
and extraordinary controlled release ability for functional substances.
Especially, the films with KGM as raw materials have huge application
potentials in the field of food, which primarily ascribe to the following
points: 1) KGM is abundant, accessible and cost-effective; 2) it is easy to
be biodegraded and recycled; 3) it is a neutral non-ionic polysaccharide
without charge and has good physical and chemical inertness so it will
not threaten the stability of the packaged food; 4) KGM has an excellent
slow-release ability, which lays the firm foundation for the preparation
of active films.
In recent year, KGM-based food packaging films are gaining mo
mentum, primarily driven by consumer preferences to low-cost, safe and
* Corresponding author.
** Corresponding author.
E-mail addresses: pang3721941@163.com (J. Pang), wanglong79@nwsuaf.edu.cn (J. Wang).
Contents lists available at ScienceDirect
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journal homepage: www.elsevier.com/locate/lwt
https://doi.org/10.1016/j.lwt.2021.112338
Received 26 April 2021; Received in revised form 23 July 2021; Accepted 19 August 2021

LWT 152 (2021) 112338
2
biodegradable food packaging materials. Various efforts have been
made to develop KGM-based novel packaging films, including innova
tion of preparation method, exploration of films forming mechanisms
and design of multipurpose food-packaging system (Xiang et al., 2021).
The rapid development of KGM-based films provides useful guidance for
other neutral polysaccharide films in this field. Unfortunately, the
research on many neutral polysaccharide films (such as guar gum,
ginseng neutral polysaccharide and allium macrostemon poly
saccharide) represented by KGM-based films is relatively less than other
charged polysaccharide-based films (Devaraj, Reddy, & Xu, 2019). This
may be due to the following two major challenges in the preparation of
advanced KGM-based films: 1) there are abundant hydroxyl groups in
the surface of KGM molecule, which endow KGM with strong water
absorption performance. One volume of KGM can absorb 100 times its
own volume of water, which can lead to easy dissolution of the formed
KGM-based films; 2) KGM has a large molar mass ranging from hundreds
of thousands to one million, which increases the difficulty preparing and
processing the films.
In order to stimulate the research and the development of KGM-
based films and expand its applications in the food field, a review is
needed to guide the research of KGM-based films by giving a summary of
the existing new attempts and then putting forward the bottleneck
problems for researchers. To the best of our knowledge, the overview on
KGM-based films has not been reported. Now that significant advances
have been made in KGM-based films (Zhu, 2018). This review illustrates
the development status and application prospects of KGM-based films in
the food packaging. This work is expected to make full use of the
abundant KGM resources in the world and stimulate the development of
KGM-based films, thereby meeting the demands of human beings for
high food quality, improving food safety and creating green living
environment. Firstly, the types and formation mechanisms of
KGM-based films are summarized. Secondly, the fabrication methods
and formation mechanisms of KGM-based films in recent years are
introduced. Thirdly, the packaging functions of KGM-based films are
articulated. Finally, the promising trend of research of KGM-based films
are summarized and discussed. It is hoped that this review will arouse
the attention of researchers on studying the polysaccharide-based films.
2. Types and formation mechanisms of KGM-based films
2.1. Film-forming solution
KGM has natural film-forming property and can form stable film-
forming solution by itself. Its film-forming solution is a typical pseudo-
plastic fluid (Wang et al., 2012). Although the crude extract of konjac
tuber also can form films, the appearance of the films is poor. There are
Fig. 1. (A) The origin of KGM and the formation process of KGM-based films. (B) Chemical structure of KGM (adapted from Zhang et al., 2014).
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many black spots visible to the naked eye on the films. Therefore, the
crude extract needs to be purified before used to prepare films. Firstly,
fresh konjac tuber is washed, sliced, dried and grounded to obtain crude
powder. Then the impurities are removed by washing crude powder
through mechanical ways or/and alcohol. Finally, the refined konjac
flour is obtained (Huang et al., 2016). Researchers used refined konjac
flour which contains 80–98% of KGM as the raw materials to prepare
films. The corresponding films formed by refined konjac flour are uni
form and transparent. The film-forming solution concentration of
refined konjac flour is generally below 3%, while higher concentration
of solution will form konjac gum which is usually used to prepare
KGM-based gel products (Guo, Yokoyama, Chen, & Zhong, 2021). In
recent years, films prepared by researchers can be summarized into the
following two categories: 1) films formed by the refined konjac flour as
matrix and incorporating with various functional substances and/or
mechanical reinforcements; 2) films prepared by modified film-forming
solution.
2.2. Natural KGM-based films
Natural KGM with high molar mass and strong water solubility can
be obtained from the tuber of konjac. Many researchers have directly
constructed polysaccharide films by utilizing unmodified KGM (Liu
et al., 2021a, b). These studies directly used natural KGM as a carrier to
form films. Those films mainly include biopolymer composite films
based-KGM, bio-nanocomposite films based-KGM and emulsion films
based-KGM.
2.2.1. Biopolymer composite films based-KGM
Polysaccharides are one of the suitable materials to combine with
KGM to form films. Typical polysaccharides are curdlan, starch and
sodium alginate. Curdlan, an extracellular polysaccharide produced by
bacteria, has wide applications in food such as noodles, bean curd and
meat products owing to its unique bioactivity. Wu, Wan, et al. (2020)
utilized curdlan to prepare KGM/curdlan blend films. KGM improved
the poor film-forming property of curdlan. The impact of heating tem
perature (from 60 ◦
C to 90 ◦
C) on the mechanical properties of
KGM/curdlan blend films as well as the relationship between structure
and properties was investigated. They found that high heating temper
ature (90 ◦
C) could enhance molecular interaction in the films due to the
stretched structure of curdlan and dissociation of curdlan bundles or
triple-helix structure. This film had the excellent mechanical property
(tensile strength = 85.5 MPa, elongation at break = 48.7%) and low
swelling and solubility (dissolution ratio = 40%, swelling ratio = 25%).
These phenomena could be related to the greater molecular interaction
and closer molecular distance as curdlan bundles or triple-helixes
structure was dissociated.
Starch, a renewable polysaccharide raw material with low-cost
attribute, is promising in agriculture applications, food hydrocolloids
and packaging materials. Zou et al. (2021) prepared high amylose corn
starch (HCS)/KGM composite films. The addition of KGM enhanced the
crystallinity and short-range order structure of HCS. This composite film
showed the highest tensile strength value (9.35 ± 0.43 MPa) and elon
gation at break value (54.11%) with 0.5% content of KGM. Meanwhile,
the water resistance was significantly improved by incorporating KGM.
The reason for those enhanced properties was the phase separation and
acceleration of dispersion with low addition concentrations of KGM. The
linkage inhibition played the leading role when KGM was at high
addition concentrations. A new strategy for the development of alter
native packaging film using HCS and KGM was provided. Sodium algi
nate, a natural polysaccharide derived from brown algae or bacterial
sources, can form insoluble alginate films by divalent ionic crosslinking.
Santos et al. (2020) prepared KGM/alginate films enriched with sugar
cane vinasse. This blended film was continuous and homogeneous.
Vinasse addition decreased the water resistance and light transmittance
of KGM/alginate films. The visual appearance and transparency of film
are shown in Fig. 2A. Blended films showed characteristic properties of
the two biopolymers and appropriate compatibility. They found that
blending KGM with alginate (with and without vinasse) could enhance
mechanical properties (including tensile strength, elongation at break
and Young’s modulus) of pure KGM films due to the intramolecular and
intermolecular hydrogen-bonding forces based on the abundant hy
droxyl groups in KGM.
Blending films obtained from mixing KGM and proteins includes zein
and whey protein isolate are detailly summarized in this part. Zein, a
major storage protein of corn, has good film-forming ability, relatively
low price and abundant sources. The mechanical properties of pure zein
films are poor, but they have lots of non-polar amino acids which are
beneficial for the formation of films with high water barrier perfor
mance. Wang et al. (2017) successfully fabricated various KGM/zein
blend films. The hydrophobicity of blend films was significantly stronger
than pure KGM film, indicated by the increased water contact angle.
Meanwhile, this blend films also showed excellent thermal (onset
decomposition temperature was 248 ◦
C), mechanical (tensile strength
was 65 MPa, elongation at break was 15%) and oxygen barrier prop
erties (peroxide value was 50 m mol kg− 1
), which resulted from
hydrogen bond interactions and Maillard reactions between KGM and
zein molecules. This research revealed the great potential of KGM/zein
blend films as biodegradable food packaging materials. To understand
the film-forming mechanism of KGM/zein blend films during drying, Li,
Xiang, Wu, Jiang, and Ni (2020) systematically investigated the
microstructure and rheological properties of KGM/zein blend
film-forming solution by scanning electron microscopy and confocal
laser scanning microscopy. They found that KGM chains in the blend
solution aggregated into thicker chains and formed a molecular network
with larger pores due to molecular entanglement. Zein particles grew
larger but were homogeneously distributed during drying. This infor
mation was important for understanding the film-forming mechanism.
In addition, the heat seal also is one of the great obstacles for developing
polysaccharide packaging films because of its rigid structures. Due to the
excellent heat-sealable property of whey protein isolate (WPI),
Leuangsukrerk, Phupoksakul, Tananuwong, Borompichaichartkul, and
Janjarasskul (2014) utilized WPI to prepare KGM/WPI blend films. It
was found that WPI significantly altered the properties of pure KGM
film. With the increase of WPI concentration, the transparency, water
insolubility and flexibility of blend films were improved. Meanwhile, the
tensile strength and elastic modulus decreased. In addition, this blend
films can be heat-sealed at 175 ◦
C. The heat-sealed ability of pure KGM
films was significantly enhanced.
2.2.2. Bio-nanocomposite films based-KGM
The bio-nanocomposite films, mainly composed of nanoparticles and
natural biomass materials, are a new type of polysaccharide films in
recent years (Azizi-Lalabadi & Jafari, 2021). Jafarzadeh, Nafchi, Sale
habadi, Oladzadabbasabadi, and Jafari (2021) had reviewed the ad
vantages of bio-nanocomposite in extending shelf life of fresh fruits and
vegetables. For example, bio-nanocomposite films can decrease the
color changes, respiration rate, weight loss and delay ripening of fruits
and vegetables. The film matrix is composed of natural biopolymers
which are safe, environmental-friendly and renewable. Also, the incor
porated nanoparticles in the films owns unique nano size effect and large
specific surface area (Ni et al., 2021). These properties of nanoparticles
further confer functional activity onto films. KGM-based films will form
a water membrane around the bacteria when the polysaccharide swells,
which are difficult for natural active substances to pass through the
water membrane, thus the antibacterial activity of those films is limited.
One of the best ways to solve this problem is loading nanoparticles into
the polysaccharide films. Firstly, nanoparticles have good nano size ef
fect, which are conducive to pass through the water membrane around
the bacteria thereby increasing the antibacterial effect of polysaccharide
films. Secondly, the large specific surface area of nanoparticles is
beneficial for them to contact with bacteria. Nanoparticles which are
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LWT 152 (2021) 112338
4
used to prepare KGM-based films can be categorized into organic and
inorganic groups. Up to now, the organic nanoparticles mainly include
cellulose nanocrystals (CNs) and chitosan/gallic acid nanoparticles
(CGNPs). The inorganic nanoparticles mainly include cadmium sulfide
(CdS) nanoparticles, silver nanoparticles and montmorillonite clay.
CNs, organic nanoparticles particles prepared by Zhao, Zhang,
Lindstrom, and Li (2015) who utilized three methods (enzymatic
treatment, TEMPO-mediated oxidation and acid hydrolysis) to improve
the film formation processability of cellulose, were a kind of abundant
natural polymers with excellent availability and renewability. CNs were
used to fabricate KGM-based bio-nanocomposite films with good ther
mal, mechanical and optical properties. The chemical and morpholog
ical structures of films were systematically investigated and the results
indicated that they had application potentials in food or pharmaceutical
industries as substitutes for non-biodegradable films. Similarly, Wu et al.
(2019) further synthesized CGNPs through ionic gelation and then
loaded them into KGM-based matrix. The homogeneous dispersion of
CGNPs in KGM-based matrix can reduce the free space of the composite
system. The properties of this film including water resistance and me
chanical performance were reinforced due to the hydrogen bonds
interaction between CGNPs and KGM. The antibacterial activity of this
film also was improved by loading gallic acid. In addition, this film also
had a broad antibacterial activity against food-borne pathogens.
KGM-based bio-nanocomposite films incorporated with inorganic
CdS nanoparticles was firstly reported by Zhang et al., in 2007. This film
exhibited low infrared emissivity. Emissivity is the ratio of the infrared
energy actually emitted by an object to its theoretical value. Its value is
between 0.000 and 1.000. KGM/CdS bio-nanocomposite films showed
infrared emissivity value of 0.011 due to the strong synergism of KGM
and CdS nanoparticles. This study illustrated the potential of KGM/CdS
bio-nanocomposite film as stealth materials (Zhang, Zhou, Cao, & Chen,
2007). Similarly, chitosan was further chosen to prepare chito
san/KGM/CdS bio-nanocomposite films that have excellent mechanical
performances, thermo-stability properties and water swelling capacity.
The feasibility of preparing bio-nanocomposite films by utilizing KGM as
the main raw materials was further confirmed (Zhang et al., 2010).
According to the investigation, silver nanoparticles are the func
tional inorganic nanoparticles, commonly used in food packaging films.
For example, Lin, Ni, and Pang (2020) prepared food packaging films by
loading silver nanoparticles into KGM fiber films. They increased the
release of silver nanoparticles with the assist of good swelling property
of KGM. This fiber film shows excellent antibacterial activity. In such a
design, silver nanoparticles have good size effect and large specific
surface area, which are beneficial for them to pass through water
membranes and efficiently kill bacteria. However, two main challenges
hinder the practical application of silver nanoparticles: 1) the aggrega
tion of silver nanoparticles will decrease their surface energy and surface
area, which can weaken the antimicrobial activity; 2) the sudden release
Fig. 2. (A) Visual appearance and transparency of crosslinked/deacetylated KGM and alginate films without and with vinasse addition (adapted from Santos et al.,
2020). (B) The preparation process schematic diagram of KGM/montmorillonite/glycerin blend films (adapted from Li et al., 2021).
Y. Ni et al.

LWT 152 (2021) 112338
5
of silver nanoparticles might have harmful effects on normal cells. The
KGM can prevent the aggregation of nanoparticles and is helpful for
their slow-release. Thus, embedding silver nanoparticles into KGM
matrix can not only solve the problem of self-aggregation of silver
nanoparticles and decrease the toxicity, but also increase the antibac
terial properties of KGM-based films.
In addition, KGM has many oxygen-containing functional groups
which are beneficial for forming hydrogen bonds. Montmorillonite clay
(MMT), a kind of earth-like mineral, is composed of silicate sheets with
nano-scale-thickness and is negatively charged. Glycerin (Gly) is a kind
of common plasticizers which can form hydrogen bonds with hydro
philic polymers. Obtaining packaging films with high strength and
toughness is still a challenge. Inspired by nacre, Li, Liu, Liang, Shu, and
Wang (2021) fabricated KGM/MMT/Gly blend films. Dynamic small
molecular hydrogen bonds were the main film-forming mechanism. The
schematic diagram of preparation process is shown in Fig. 2B. This film
had a tensile strength of 214.9 MPa and a toughness of up to 12.3 MJ
m− 3
due to the hydrogen-bonded small molecule. It also had high
transparency and UV shielding performance because of the ordered
layered structure and the incorporated MMT nanosheet. This study also
expanded the application of KGM-based films in another field. The Eu
ropean Food Safety Authority (EFSA) mandates the upper limits of silver
ions immigrate from packages to food of no more than 0.05 mg/kg. The
risk of disease as a consequence of silver ion migration from packages
has not been fully assessed so far (Kumar et al., 2021). The safety of CdS
nanoparticles, silver nanoparticles and montmorillonite clay need to be
further evaluated.
2.2.3. Emulsion films based-KGM
KGM emulsion films are the novel kind of film, which combine the
properties of hydrocolloid and lipid compounds to further enhance the
moisture barrier properties of pure KGM films. Compared with pure
hydrocolloid films and bilayer films, emulsion films are stable, smooth
and uniform (Liu, Shen, et al., 2021). In this respect, Liu, Lin, Shen, and
Yang (2020) constructed novel high-barrier KGM emulsion films by
incorporating high internal phase pickering emulsions (HIPEs) which
were fabricated by bacterial cellulose nanofibers/soy protein isolation.
The addition of HIPEs increased the surface roughness and decreased the
hydrophilicity of pure KGM films. This emulsion film (emulsion ratio
was 50% based on the weight of KGM) displayed excellent thermal
stability, mechanical properties (tensile strength was 44.23 MPa, elon
gation at break was 14.62%) as well as water and oxygen barrier per
formances (water vapor permeability was 1.82 × 10− 11
g m/Pa s m2
,
oxygen permeability was 2.46 × 10− 3
g/m s Pa). Similarly, Zhou et al.
(2021) used emulsified camellia oil as the dispersed phase of
KGM/carrageenan matrix to fabricate emulsified films. This emulsified
film showed excellent hydrophobicity, water-resistant properties, ther
mal stability, optical properties and mechanical properties. They
concluded that the incorporation of camellia oil by emulsification was
an effective and promising pathway to improve the properties of
KGM-based film.
2.3. Modified KGM-based films
In order to improve the performance of films based on natural KGM
Fig. 3. (A) The modification methods of KGM-based films. (B) Two-step casting method for the production of bilayer films. *Photograph of the bilayer film; **SEM
magnification of the cryofracture section of the bilayer film (adapted from Gomes-Neto et al., 2019).
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LWT 152 (2021) 112338
6
and broaden their application scope, many researchers fabricated
modified KGM-based films. The way of modifying KGM were divided
into physical and chemical methods based on the change of groups in
molecular. Physical method means the change of molar mass, water
solubility and viscosity of natural KGM. While the chemical one refers to
the change of groups on natural KGM or/and molecular chain.
The main physical methods include extrusion and gamma irradiation
(Fig. 3A). Extrusion is one of the best methods to modify material
structure by breaking polymer chains. KGM film-forming solution can be
extruded before forming films. Tatirat, Charoenrein, and Kerr (2012)
offered a representative example. They fabricated the slightly larger and
rougher KGM particles by extrusion. The molar mass, water solubility
and viscosity of natural KGM were decreased. Meanwhile, the crystal
linity property was increased. This research illustrated the possibility of
extrusion for modifying KGM-based films. Gamma irradiation, an ionic
and no-heat process, was a useful method to degrade the molar mass of
KGM (Prawitwong, Takigami, & Phillips, 2007). Li et al. (2011) found
that the tensile strength and breaking elongation of KGM/chitosan blend
films (weight ratio of KGM to chitosan was 8:2) were enhanced about
40% and 30% under 25 KiloGray (kGy, radation unit of measure) dose of
gamma irradiation. The primary groups including hydroxyl and acetyl of
the blend films were stable. This study provided an efficient modifica
tion method for enhancing the properties of KGM/chitosan blend films.
Chemical methods include alkali modification, carboxymethyl, graft
copolymerization and nitrogen plasma treatment (Fig. 3A). Alkali
modification mainly focuses on the deacetylation of KGM which is
closely related to the water solubility, micro-structural properties of the
films. Jin et al. (2015) explored the influences of deacetylation degree
on phase separation of KGM/xanthan gum blended systems. They
offered a new sight to study phase separation between two macromol
ecules through film forming process. They concluded that the 52.34%
deacetylation degree of KGM can improve the transparency, mechanical
properties and moisture absorption of films. More importantly, the
hydrogen bonds between KGM and xanthan gum can be enhanced with
the increased deacetylation degree. A smooth and flat surface in
KGM-based films can be realized by modulating the deacetylation de
gree. Carboxymethyl konjac glucomannan (CMKGM), an important de
rivative of KGM, was used to prepare the composite film with soy protein
(SPI) because it was an amphiphilic anionic polysaccharide with excel
lent film forming ability, water resistance, mechanical properties,
biocompatibility and biodegradability. SPI was a plant protein with
superior film-forming ability, relatively low cost, wide availability, and
complete biodegradability. Wang et al. (2014) employed CMKGM to
improve the poor mechanical properties and relatively high moisture
sensitivity of pure SPI films. The results showed that the water adsorp
tion, oxygen permeability and roughness of the CMKGM/SPI films
progressively decreased while tensile strength, elongation at break and
surface wettability of the CMKGM/SPI films improved, which could be
attributed to the Maillard reactions, hydrogen bond interactions and
well compatibility in the blend films between CMKGM and SPI.
In addition, thermoplastic konjac glucomannan (TKGM) was fabri
cated by graft copolymerization of vinyl acetate and methyl acrylate
onto KGM. Polylactide (PLA) is a biodegradable polymer produced from
annually renewable resources. Since its intrinsic drawbacks such as high
cost and low mechanical properties, PLA has not been widely used. In
order to broaden the application scope of PLA, Xu, Luo, Lin, Zhuo, and
Liang (2009) built a new degradable PLA/TKGM blend films. They were
committed to reducing the cost of the materials and improving
comprehensive mechanical properties of PLA and TKGM. The misci
bility, thermal properties, phase morphology and mechanical properties
of PLA/TKGM blend films were investigated. This study offered an
interesting blend method by which the property range of PLA and KGM
can be expanded. Nitrogen plasma treatment is also an effective
approach for incorporating functional groups onto KGM. Pang et al.
(2012) enhanced the surface property of KGM-based films by nitrogen
plasma modification from ion beam injection machine. The acetyl in
KGM was removed and hydroxyl was replaced partly based on X-ray
photoelectron spectroscopy analysis. These results illustrated that
plasma treatment was an effective method to modify KGM-based films
by introducing new functional groups and degrading the molecular
chain.
2.4. Summary on types, unique properties and formation mechanisms
In general, the existing KGM-based films can be divided into natural
and modified films. In the early stage of research on preparing KGM-
based films, formation of the film mainly relies on the natural struc
ture and properties of KGM. Blend films are the main types of those
natural films. Various emerging biopolymer composite films, bio-
nanocomposite films and emulsion films are gradually catching peo
ple’s attention. The formation mechanisms of those films mainly depend
on the abundant hydroxyl groups on KGM molecules which are used to
form different intramolecular and intermolecular hydrogen bonds. In
addition, nano-scale additives can fill in the free space between KGM
molecular chains, thus further increasing the strength of the films.
However, the characteristics of KGM on these films remain unchanged,
so they are easily dissolved. Therefore, various types of modified KGM-
based films have emerged. The modified KGM-based films are mainly
constructed by changing the molecular structure of KGM. Their forma
tion mechanisms can be summed up in two aspects. KGM can be nega
tively charged by modifying the hydroxyl groups on KGM molecules to
carboxyl or carboxymethyl groups, thus multiple types of films are
formed by electrostatic interaction and hydrogen bond interaction. Be
sides, the solubility of KGM-based films is greatly decreased by removing
the acetyl group in KGM. Various auxiliary functional substances,
unique properties and formation mechanisms of KGM-based films are
summarized in Table 1.
3. Fabrication methods and formation mechanisms of KGM-
based films
3.1. Solvent casting
Solvent casting is considered as a common, simple and low-cost
preparation method of KGM-based films. The preparation of KGM-
based films by solvent casting method is achieved by pouring film-
forming solution onto the substrate followed by solvent natural vola
tilization and solidification into films. The film formation mechanisms
are mainly the intermolecular and intramolecular hydrogen bonds
interaction. This method is simple, but it is difficult to control the uni
formity of film formation solution and separate films from matrix as well
as prevent the formation of bubbles in the film formation process. The
inventive work for this end recently had been reported by Gomes-Neto
et al. (2019). They prepared a transparent chitosan/KGM bilayer film via
the two-step casting method. Firstly, the chitosan solution was cast on a
polystyrene plate and then the KGM solution was cast onto the partially
dried chitosan layer. The preparation process of bilayer film is shown in
Fig. 3B. Through this elaborate design, the intrinsic properties of each
polymer were retained. Differing from blends, this bilayer film exhibited
a suitable mechanical property, good thermostability and barrier prop
erties owing to the formation of strong hydrogen bonds.
It is found that drying temperatures are the main factors affecting the
properties of the solvent casting films. For example, Li et al. (2019)
successfully prepared KGM/zein blend films at different drying tem
peratures. Based on its structure, thermal stability and water barrier
properties, 60 ◦
C was preferred for KGM/zein blend film preparation.
This blend film showed compact and smooth surface and zein particles
were homogeneously dispersed in KGM continuous matrix. This
research indicated that drying temperature would contribute to modu
late the physical properties of the film. The deep mechanism of this
phenomenon was that the drying temperatures can affect the compati
bility of film component. The strong intermolecular interaction between
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Table 1
Auxiliary functional substances, unique properties and formation mechanisms of KGM-based films.
KGM-based films Auxiliary functional substances Unique
properties
Formation mechanisms References
KGM/zein/curcumin nanofiber films Curcumin and zein Hydrophobicity,
antibacterial and
antioxidant
activity
Intramolecular hydrogen bonds Wang et al. (2019)
KGM/bacterial cellulose nanofiber
films
Bacterial cellulose Thermal
stability,
enhanced
mechanical
strength
Intermolecular hydrogen bonds Liu, Lin, Lopez-Sanchez,
and Yang (2020)
KGM/chitosan bilayer films Chitosan Thermal
stability,
enhanced
mechanical
strength, barrier
properties
Intermolecular hydrogen bonds Gomes-Neto et al. (2019)
KGM/polyvinylpyrrolidone/
epigallocatechin gallate films
Polyvinylpyrrolidone,
epigallocatechin gallate
Thermal
stability,
antibacterial
activity,
transparency
Intermolecular hydrogen bonds Ni et al. (2019)
KGM/gellan gum composite films Gellan gum, gallic acid Thermal
stability,
antioxidant and
antimicrobial
activity
Electrostatic self-assembly Du et al. (2019)
KGM/pectin/tea polyphenol films Pectin, tea polyphenol Antioxidant and
antimicrobial
activity,
enhanced
mechanical
strength
Intermolecular hydrogen bonds Lei et al. (2019)
KGM/poly (methyl methacrylate)/
chlorogenic acid films
Poly (methyl methacrylate),
chlorogenic acid
Thermal
stability,
enhanced
mechanical
strength,
hydrophobicity,
antibacterial
activity
Hydrophilic and hydrophobic interactions Lin, Ni, and Pang (2019)
KGM/oxidized chitin nanocrystals/red
cabbage anthocyanins films
Oxidized chitin nanocrystals, red
cabbage anthocyanins
UV-barrier,
antioxidant and
antimicrobial
activity, pH-
sensitive
Electrostatic interactions Wu, Li, et al. (2020)
KGM/polylactic acid/trans-cinnamic
acid microfilms
Polylactic acid, trans-cinnamic acid Thermal
stability,
enhanced
moisture barrier,
mechanical
strength and
antimicrobial
activity
Intermolecular hydrogen bonds Lin, Ni, Liu, Yao, and
Pang (2019)
KGM/polycaprolactone/silver
nanoparticles fiber films
Polycaprolactone, silver
nanoparticles
Thermal
stability,
antioxidating
activity,
enhanced
hydrophobicity
and mechanical
strength
Intermolecular hydrogen bonds Lin et al. (2020)
KGM/zein blend films Zein Enhanced
hydrophobicity
and mechanical
strength
Intermolecular interactions Li et al. (2019)
KGM/whey protein isolate blend films Whey protein isolate Enhanced
hydrophobicity
Intermolecular interactions Leuangsukrerk et al.
(2014)
Deacetylated konjac glucomannan/
shellac/stearic acid films
Shellac, stearic acid Enhanced
moisture barrier,
mechanical
strength, optical
transparency
Intimate interfacial adhesion between the
coating layer and deacetylated konjac
glucomannan substrate
Wei et al. (2015)
xanthan gum blend films
Xanthan gum Enhanced
mechanical
Intermolecular hydrogen bonds Jin et al. (2015)
(continued on next page)
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KGM and zein was realized. This film was uniform and smooth. Also, the
zein aggregate size was the smallest, which was conducive to imparting
the films with high mechanical performance and big water contact
angle. This research will help to understand the molecular interaction in
KGM/zein blend films and optimize the function of the films.
Cross-linking is also a mechanism for forming films by solvent cast
ing method. KGM is not a poly-anionic polymer, so KGM needs to be
mixed with a poly-anionic polymer such as alginate or gellan gum to
form films with calcium ion (Ca2+
). In this respect, Du et al. (2019)
prepared KGM/gellan gum/gallic acid films by Ca2+
crosslinking. After
structure characterization and determination of films properties, they
concluded that the incorporation of KGM improved mechanical
strength, thermal stability, release ability, antibacterial and antioxidant
property of films. Similarly, Li, Ma, Chen, He, and Huang (2018) pre
pared calcium alginate/deacetylated konjac glucomannan
(Ca-SA/DKGM) blend films via Ca2+
crosslinking. Schematic diagram of
preparation process is shown in Fig. 4A. This blend films showed
enhanced thermal stability, surface hydrophobicity, and tensile strength
Table 1 (continued)
KGM-based films Auxiliary functional substances Unique
properties
Formation mechanisms References
strength,
moisture
absorption,
thermal stability
KGM/zein blend films Zein Enhanced
hydrophobicity,
mechanical
strength, thermal
stability, oxygen
barrier
Intermolecular hydrogen bonds and Maillard
reaction
Wang et al. (2017)
KGM/carboxylation cellulose
nanocrystal/grape peel extracts
films
Carboxylation cellulose
nanocrystal, grape peel extracts
Enhanced water
vapor barrier,
light barrier,
mechanical
strength,
antioxidant
activity, thermal
stability
Intermolecular hydrogen bonds Tong et al. (2020)
calcium alginate blend films
Sodium alginate, CaCl2 Enhanced
thermal stability,
surface
hydrophobicity,
mechanical
strength
Electrostatic adsorption and hydrogen bonds Li et al. (2018)
KGM/chitosan blend films Chitosan Enhanced
mechanical
strength
Intermolecular hydrogen bonds Li et al. (2011)
Carboxymethyl KGM/soy protein
isolate films
Soy protein isolate Enhanced
mechanical
strength, oxygen
barrier
Maillard reactions and hydrogen bonds
interactions
Wang et al. (2014)
KGM/chitosan/CdS nanocomposite
films
Chitosan, CdS Low infrared
emissivity
Intermolecular hydrogen bonds Zhang et al. (2010)
KGM/cellulose nanocrystals composite
films
Cellulose nanocrystals Enhanced optical
transparency,
thermal stability,
mechanical
strength
Intermolecular hydrogen bonds Zhao et al. (2015)
KGM/CdS nanocomposite films CdS Low infrared
emissivity
Intermolecular hydrogen bonds Zhang et al. (2007)
Fig. 4. (A) Schematic diagram of preparation process of the alginate/konjac glucomannan (SA/KGM), calcium alginate/konjac glucomannan (Ca-SA/KGM), and
calcium alginate/deacetylated konjac glucomannan (Ca-SA/DKGM) films (adapted from Li et al., 2018). (B) The microfluidic spinning process of the films. (C)
Schematic representation of KGM/zein/curcumin (KGM/Zein/Cur) nanofiber films fabricated via electrospinning.
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LWT 152 (2021) 112338
9
resulting from Ca2+
crosslinking and intermolecular hydrogen bonds.
This study provided a novel way to prepare Ca-SA/DKGM films.
3.2. Microfluidic spinning
Microfluidic spinning technology is considered as a new preparation
technology which has a good development prospect in fabricating
polysaccharide-based films relying on their green characteristics and
flexibility control. Microfluidic spinning can be used in forming KGM-
based films whose successful formation relies on the interactions be
tween fluids. It has potential in large-scale industrial production.
However, it is necessary to prepare KGM-based films assisted with
spinning aid because KGM has poor tensile strength. Microfluidic spin
ning system is composed of a syringe pump, frame receiver, forward and
reverse step process, and an immobilization device. The spinning solu
tion is ejected by syringe pump, and then the microfiber is stretched and
twined by frame receiver. The forward and reverse step process are used
to guide microfibers to form films, and the corresponding film is dried by
immobilization device. The microfluidic spinning process of the films is
shown in Fig. 4B. The privilege of microfluidic spinning is that a large
number of films with micro-structure or multi-functions can be pre
pared. The preparation process can be realized under room temperature
and normal pressure, so the destruction for thermally unstable active
substances can be reduced. The negative point is that the preparation of
the films requires specific equipment. Compared with the common
methods such as solvent casting, films prepared by microfluidic spinning
technology are relatively uniform. This technology can also be used to
design some new types of multi-functional films but that needs skilled
operators. Therefore, a lot of time and energy need to be put into ma
chine learning in the early stage. Pure KGM can not be made into films
by microfluidic spinning technology. Combining KGM with other poly
mers is necessary. For example, Lin, Ni, and Pang (2019) constructed a
novel KGM-based active food packaging film with high performance by
microfluidic spinning technology, in which the activities of natural
compound were remained due to the green and mild processing.
Meanwhile, benefiting from the interesting and unique fluid character in
tiny channels of microfluidic spinning, hydrophilic-hydrophobic theory
was utilized to furtherer enhance functional activity of films. They uti
lized hydrophilic KGM to improve the release of hydrophobic chloro
genic acid, thereby the antibacterial activity of KGM-based films was
enhanced. In addition, this film showed excellent thermal stabilities,
moisture barrier properties (water contact angle was 89.2◦
, water vapor
permeability was 1.47 × 10− 5
g/(m.h.kPa)) and mechanical properties
(tensile strength was 14.94 MPa, elongation at break was 4.88%).
3.3. Electrospinning
Electrospinning is a special technology for fiber films preparation, in
which polysaccharide-based solution is jet spun in strong electric field.
The droplets at the tip of the needle will change from a sphere to a cone,
and the filaments will be obtained from the tip of the cone assisted by the
electric field. In this way, polysaccharide fibers at nanometer scale can
be obtained. Nanofibers are deposited on the receiver to form nanofiber
films. The advantage of this method is that the films with nano-structure
can be prepared. The disadvantages are that the yield is small and spe
cial equipment is required. Electrospinning mainly is driven by voltage
to form KGM-based films. This method requires the processing raw
materials to have conductivity. So conductive spinning additives mate
rials needs to be added for the uncharged KGM. The production of films
is small, which only can meet the demands of scientific research. For
example, Wang et al. (2019) constructed a biodegradable and bioactive
KGM/zein/curcumin nanofiber film via electrospinning technology.
Zein was chosen as an electrospinning auxiliary to form stable homo
geneous nanofiber films. The solution was loaded into a syringe capped
with a 23-gauge stainless steel needle and then nanofiber films were
collected on a metal plate. The spinning parameters were as follow:
solution velocity was 1 mL/h, voltage was 15.0 kV, electrospinning
temperatures was kept at 55 ◦
C and the humidity was 50%. Schematic
representation of nanofiber films fabricated via electrospinning was
shown in Fig. 4C. The thermal properties and hydrophobicity of films
were increased as the addition amount of zein. This nanofiber film also
showed excellent antibacterial activity (a large inhibitory zone of 12–20
mm) against food-borne pathogens and antioxidant functions. This work
possible opened a facile pathway to fabricate KGM-based nanofiber
films.
3.4. Coated KGM films
Coated KGM films also is one of the methods to enhance the per
formance of KGM-based films. For example, Wei et al. (2015) prepared
various moisture-resistant KGM-based films via coating shellac/stearic
acid emulsion on deacetylated konjac glucomannan films. They inves
tigated the effect of stearic acid content in the coating layer on inter
facial and surface structure and properties of the coated films. They
concluded that intimate interfacial adhesion of stearic acid in the
coating layer and its uniform mixing played a significant role in
enhancing moisture barrier properties and mechanical properties. The
detailed fabrication methods and characterization measures of
KGM-based films were shown in Table 2.
4. KGM-based films for food packaging function
4.1. Active packaging function
As well known, the traditional food packaging films which have poor
activity cannot meet consumer’s demands for safe foods. Compared with
traditional packaging films, active packaging films can effectively
maintain food safety and extend the shelf-life of foods by releasing
functional substances to packaging microenvironment. Common KGM-
based active packaging films are those with antibacterial and antioxi
dant properties. For KGM-based antibacterial films, the active agent as
an auxiliary can increase the antibacterial activity relies on excellent
water absorption, swelling and slow-release properties of KGM. For
KGM-based antioxidant films, KGM can offer slight antioxidant activity.
The antioxidant activity decreased as its molar mass increased. There
fore, many researches have focused on the degradation of KGM.
4.1.1. Antibacterial packaging function
KGM has a lot of hydroxyl groups on its surface, which is beneficial
for KGM to form connections with the functional groups of antibacterial
active substances. Meanwhile, KGM has excellent loading and slow-
release functions, thus, antimicrobial food packaging is the main form
of active KGM-based films. The commonly used antibacterial active
substances mainly are divided into two categories: natural and synthetic
antibacterial agents. Natural compounds mainly include curcumin
(Cur), epigallocatechin-3-gallate (EGCG) and gallic acid. Cur, a yellow-
colored and low molar mass natural polyphenol, was a hydrophobic di-
phenolic substance extracted from the root of Curcumin longa. It had
good biocompatible and biodegradable properties. Cur which had
excellent antibacterial activities was utilized to enhance the antibacte
rial properties of KGM-based films. This film showed excellent disin
fection efficiency for E. coli and S. aureus (Wang et al., 2019). A
polyphenolic EGCG compound extracted from green tea was used to
prepare antibacterial packaging films. EGCG possessed many hydroxyl
groups in its molecular structure. The intermolecular hydrogen bond
interactions can contribute to form a strong biocomposite matrix. It was
remarkable that hydrophilic KGM and polyvinylpyrrolidone had good
compatibility with EGCG, which can generate novel functional struc
tures by the “bridging” phenomenon. The as-produced films displayed
excellent antibacterial activity, transparency and equilibrium swelling
ratios (Ni et al., 2019). Similarly, gallic acid, also known as gallate, was a
polyphenolic compound. Du et al. (2019) used gallic acid to enhance the
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LWT 152 (2021) 112338
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thermal stability, mechanical property, hydrophily and antibacterial
activity of KGM-based films. The incorporated active agents in the
abovementioned three kinds of films are from plants. The synthetic
antibacterial agents are mainly poly (diallydimethylammonium chlo
ride) and silver nanoparticles. For example, Lu, Wang, and Xiao (2008)
used the synthetic poly (diallydimethylammonium chloride) in
enhancing the antibacterial performance of KGM-based films. Silver
nanoparticles are also used to prepare antibacterial films which have
been introduced in Part 2.2.2.
4.1.2. Antioxidant packaging function
KGM is an excellent carrier of natural antioxidant substances. In this
respect, Tong et al. (2020) utilized grape peels to increase the antioxi
dant activity of KGM-based films. Grape peels were discarded as a res
idue of abundant grapes. It contained many kinds of polyphenols such as
anthocyanins, flavonoids. The reason why grape peels had excellent
antioxidant activities was that these polyphenols in grape peels can act
as donors of hydrogen or electrons, thereby inhibiting the formation of
radicals. The research results demonstrated the successful construction
of KGM-based antioxidant films which had potential applications in food
packaging industry. Similarly, Lei et al. (2019) used tea polyphenol (TP)
to improve the antioxidant activity of the films. TP was compatible with
KGM and can be well dispersed in the KGM matrix due to the formation
of hydrogen bonds with them. In addition, the mechanical and
water-resistant properties of the films also were enhanced.
4.2. Intelligent packaging function
Intelligent food packaging relies on tracking the external and inter
nal conditions of the packaged food to communicate with consumers.
This innovative technology can extend the shelf life and monitor food
quality changes in real time. The core design concept of intelligent
packaging films is the construction of responsive system including pH,
color, transparency, etc. For example, Wu, Li, et al. (2020) prepared a
novel KGM-based film for intelligent food packaging by using anthocy
anins which can change chemical structures and colors at different pH
values. However, anthocyanins were unstable due to their hydrophi
licity and migration properties. Oxidized chitin nanocrystals were uti
lized to as the host complex to immobilize anthocyanins in the films
through electrostatic interactions. Therefore, the migration of the an
thocyanins was inhibited and the sensitivity of the intelligent films was
enhanced. In addition, the microstructural, basic properties and
slow-release performance of the films were investigated. These films
showed promising potentials in intelligent food packaging.
4.3. Edible packaging function
The outstanding feature of edible films is high safety. Although
plastic packaging films are widely applied in food industry based on its
easy molding, excellent barrier and mechanical properties, the migra
tion of toxic monomers into food possible cause potential harm to
human health. It also causes the white environmental pollution. With
the improvement of consumers’ demands for stable, safe, high-quality
food and ecological awareness, the research on edible food packaging
materials is booming. Edible films are a promising food packaging
because of its ability to provide barrier properties, enhance the me
chanical integrity of foods and reduce environmental impacts. Besides,
the ability to carry and release a variety of active compounds is the most
attractive features of edible films. In this respect, Liu, Lin,
Lopez-Sanchez, and Yang (2020) used a promising bacterial cellulose
Table 2
Fabrication methods and characterization measures of KGM-based films.
KGM-based films Fabrication
methods
Characterization measures References
KGM/zein/curcumin nanofiber films Electrospinning FTIR, TGA, XRD, XPS, SEM, WCA Wang et al. (2019)
KGM/bacterial cellulose nanofiber films Solvent casting TEM, SEM, AFM, FTIR, XRD, DSC, TGA, WCA, moisture content, water
solubility, water vapor permeability, oxygen permeability
Liu, Lin, Lopez-Sanchez, and
Yang (2020)
KGM/chitosan bilayer films Solvent casting SEM, FTIR, XRD, DSC, TGA, water vapor transmission rate, mechanical tests Gomes-Neto et al. (2019)
KGM/polyvinylpyrrolidone/epigallocatechin
gallate films
Microfluidic
spinning
SEM, FTIR, IR imaging, TGA, XRD Ni et al. (2019)
KGM/gellan gum composite films Solvent casting SEM, AFM, TGA, FTIR, XRD, WCA, WVP Du et al. (2019)
KGM/pectin/tea polyphenol films Solvent casting FTIR, SEM, TGA, WCA, WVP, moisture content Lei et al. (2019)
KGM/poly (methyl methacrylate)/
chlorogenic acid films
Microfluidic
spinning
FTIR, XRD, TGA, DSC, WVP, WCA, swelling degree, water solubility Lin, Ni, and Pang (2019)
KGM/oxidized chitin nanocrystals/red
cabbage anthocyanins films
Solvent casting SEM, FTIR, XRD, WVP, water solubility, UV-2600 spectrophotometer, CS-
200 spectrophotometer
Wu, Li, et al. (2020)
KGM/polylactic acid/trans-cinnamic acid
microfilms
Microfluidic
spinning
SEM, FTIR, IR imaging, XRD, DSC, TGA, WVP, WCA, swelling degree, water
solubility
Lin, Ni, Liu, et al. (2019)
KGM/polycaprolactone/silver nanoparticles
fiber films
Microfluidic
spinning
SEM, FTIR, XRD, TGA, WVP, WCA, swelling degree Lin et al. (2020)
KGM/zein blend films Solvent casting AFM, SEM, confocal laser scanning microscopy, tensile strength, WCA,
swelling and solubility
Li et al. (2019)
KGM/whey protein isolate blend films Solvent casting WVP, DSC, transparency, mechanical properties, solubility Leuangsukrerk et al. (2014)
Deacetylated konjac glucomannan/shellac/
stearic acid films
Coated SEM, FTIR, UV–Vis, WVP, water uptake measurement, WCA, mechanical
properties
Wei et al. (2015)
Deacetylated konjac glucomannan/xanthan
gum blend films
Solvent casting Transparency, moisture absorption capability, mechanical properties,
UV–Vis, FTIR, SEM, XRD, TGA
Jin et al. (2015)
KGM/zein blend films Solvent casting FTIR, XRD, DSC, TGA, CLSM, AFM, mechanical properties, water vapor
permeability, oxygen barrier
Wang et al. (2017)
KGM/carboxylation cellulose nanocrystal/
grape peel extracts films
Solvent casting Rheology, SEM, FTIR, TGA, UV–Vis, WVP Tong et al. (2020)
Deacetylated konjac glucomannan/calcium
alginate blend films
Solvent casting FTIR, XRD, TGA, WCA, SEM, UV–vis Li et al. (2018)
KGM/chitosan blend films Solvent casting FTIR, SEM, XRD, DSC, mechanical tests Li et al. (2011)
Carboxymethyl KGM/soy protein isolate
films
Solvent casting FTIR, XRD, DSC, SEM, water contact angle, mechanical properties, oxygen
permeability
Wang et al. (2014)
KGM/chitosan/CdS nanocomposite films Solvent casting IR spectra, TEM, SEM, FTIR Zhang et al. (2010)
KGM/cellulose nanocrystals composite films Solvent casting Size exclusive chromatography, SEM, TGA, FTIR, XRD, BET, UV–vis
transmittance, mechanical strength
Zhao et al. (2015)
KGM/CdS nanocomposite films Solvent casting IR spectra, TEM, SEM Zhang et al. (2007)
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LWT 152 (2021) 112338
11
nanofibers (BCNs) to prepare reinforced edible films based on KGM. The
effects of BCNs on the properties of the KGM-based films were investi
gated. This edible film showed excellent barrier properties and tensile
strength (82.01 MPa) due to the hydrogen-bonding interactions between
BCNs and KGM.
4.4. Discussion on the packaging function of KGM-based films
Obviously, KGM-based films with various functions have been
developed, including antibacterial, antioxidant, intelligent and edible
functions. Nonetheless, most of these films only have single function, so
exploring multifunctional films is still imperative. For example, the
mechanical strength and hydrophobicity of KGM-based films may be
decreased when the antibacterial activity was enhanced. Food is a
complex system, the effective packaging for a certain food requires
various packaging functions of films simultaneously. For example, the
films with good transparency can increase consumers’ cognition so they
can quickly obtain sensory information of packaged food. Under taking
excellent transparency of films into account, the barrier resistance of
films against oxygen and moisture which can accelerate the deteriora
tion of food should also be included. Meanwhile, some foods are sensi
tive to UV light, so it should be paid attention to reduce the damage of
UV on food components. The antioxidant activity of pure KGM films is
low, thus antioxidant substances are introduced into the KGM matrix to
meet the actual production requirements. KGM can not sense the
changes of the external environment because it mainly contains a large
number of hydroxyl and acetyl groups. Therefore, modifications on KGM
molecules or incorporating functional substances is needed in devel
oping intelligent KGM-based films. Also, the safety of the introduced
substances should be evaluated while meeting the above functions given
the edible function of KGM-based films. In addition, the cost of active
and intelligent substances should also be considered. Therefore,
comparative studies of functions among various films are furthered
needed, which will be of great significance to promote the industriali
zation of KGM-based films.
5. Conclusion and future prospects
In summary, this review highlights the recent trends and applications
of KGM-based films from its classification, preparation, formation
mechanisms and packaging function. Obviously, KGM have been proven
to be one of the most promising candidates suitable for designing and
fabricating advanced neutral polysaccharides-based films for food
packaging. Many methods to fabricate food packaging films such as
solvent casting, microfluidic spinning and electrospinning have been
explored. Many kinds of functional films based on KGM like antibacte
rial packaging films, antioxidant packaging films, intelligent packaging
films and edible packaging films have been successfully developed. As a
whole, the conclusions and future perspectives of KGM-based films can
be pictorially depicted in Fig. 5 as a mind map to all the readers for the
state-of-the-art research.
Challenges still remain in fabricating highly efficient KGM-based
films with low cost to be widely applied in complex food systems and
deeply understand the mechanisms of the enhanced functions and for
mation. There are still many problems and opportunities, thus further
investigations may be conducted referring to the following points.
Firstly, the research on the actual preservation effect of KGM-based
films is almost blank. The performances of current reported films fail
to meet the demand of practical applications in most occasions. In the
literature review, we do find that there are a few application cases of
KGM-based films. Although practical application test faced with inevi
table challenges like long testing period, difficult operation, various
influences from external environment, numerous researches need to be
conducted for the purpose of ensuring the efficient protecting effects of
packaging films on fruits, vegetables, eggs, meat products, aquatic
products and so on. This is expected to provide guidance for high value
development of neutral polysaccharide films. This work has great stra
tegic significance in research.
Secondly, the activities of KGM-based films mainly come from the
loaded natural active substances, but the cost of natural active sub
stances are high. On the premise of satisfying the food safety and quality
of KGM-based packaging films, it is imperative to find a new type of
active substitute with low cost.
Thirdly, compared with other cationic or anion polysaccharide films,
the preparation methods of KGM-based films are relatively few, which
still need to be explored by researchers.
Fourthly, many articles focus on activity test of KGM-based films and
preliminarily studying its formation mechanisms, lacking study on the
activity mechanisms of KGM-based films, which greatly reduces the
practical value of KGM-based films. A deep understanding of this issue is
necessary for further enhancing the activity of the films and regulating
the quality of the packaged food.
Fifthly, there are increasing trends to develop multifunctional KGM-
based films. For example, the films based on modified KGM have a
greater application potential due to the introduction of functional
groups on KGM. The bio-nanocomposite films with active and intelligent
properties are expected to replace non-degradable petroleum-based
packaging materials in the context of high concern for serious white
pollution and food safety issue.
Author contributions
Yongsheng Ni: Conceptualization, Data curation, Investigation,
Methodology, Resources, Writing - original draft, Visualization, Formal
analysis. Writing - review & editing. Yilin Liu: Investigation, Resources.
Wentao Zhang: Data curation, Software. Shuo Shi: Data curation,
Fig. 5. The conclusions and future perspectives of KGM-based films.
Y. Ni et al.

LWT 152 (2021) 112338
12
Methodology. Wenxin Zhu: Investigation. Rong Wang: Investigation.
Liang Zhang: Methodology. Linrang Chen: Language modification. Jing
Sun: Supervision. Jie Pang: Supervision, Methodology, Resources.
Jianlong Wang: Conceptualization, Supervision, Resources, Project
administration, Writing - review & editing.
Declaration of competing interest
The authors declare that there is no conflict of interest.
Acknowledgements
The authors thank the National Natural Science Foundation of China
(21675127), Shaanxi Provincial Science Fund for Distinguished Young
Scholars (2018JC-011), Qinghai Special Project of Innovation Platform
for Basic Conditions of Scientific Research of China (No. 2020-ZJ-T05),
Qinghai Provincial Key Laboratory of Qinghai-Tibet Plateau Biological
Resource (2021-ZJ-Y14).
References
Azizi-Lalabadi, M., & Jafari, S. M. (2021). Bio-nanocomposites of graphene with
biopolymers; fabrication, properties, and applications. Advances in Colloid and
Interface Science, 292, 102416. https://doi.org/10.1016/j.cis.2021.102416
Behera, S., & Ray, R. (2016). Konjac glucomannan, a promising polysaccharide of
Amorphophallus konjac K. Koch in health care. International Journal of Biological
Macromolecules, 92, 942–956. https://doi.org/10.1016/j.ijbiomac.2016.07.098
Chen, Y., Zhao, H., Liu, X., Li, Z., Liu, B., Wu, J., et al. (2016). TEMPO-oxidized konjac
glucomannan as appliance for the preparation of hard capsules. Carbohydrate
Polymers, 143, 262–269. https://doi.org/10.1016/j.carbpol.2016.01.072
Devaraj, R. D., Reddy, C. K., & Xu, B. (2019). Health-promoting effects of konjac
glucomannan and its practical applications: A critical review. International Journal of
Biological Macromolecules, 126, 273–281. https://doi.org/10.1016/j.
ijbiomac.2018.12.203
Du, Y., Sun, J., Wang, L., Wu, C., Gong, J., Lin, L., et al. (2019). Development of
antimicrobial packaging materials by incorporation of gallic acid into Ca2+
crosslinking konjac glucomannan/gellan gum films. International Journal of Biological
Macromolecules, 137, 1076–1085. https://doi.org/10.1016/j.ijbiomac.2019.06.079
Gomes-Neto, R. J., Genevro, G. M., Paulo, L. A., Lopes, P. S., Moraes, M. A., &
Beppu, M. M. (2019). Characterization and in vitro evaluation of chitosan/konjac
glucomannan bilayer film as a wound dressing. Carbohydrate Polymers, 212, 59–66.
https://doi.org/10.1016/j.carbpol.2019.02.017
Guo, L., Yokoyama, W., Chen, M., & Zhong, F. (2021). Konjac glucomannan molecular
and rheological properties that delay gastric emptying and improve the regulation of
appetite. Food Hydrocolloids, 120, 106894. https://doi.org/10.1016/j.
foodhyd.2021.106894
Huang, Q., Jin, W., Ye, S., Hu, Y., Wang, Y., Xu, W., et al. (2016). Comparative studies of
konjac flours extracted from Amorphophallus guripingensis and Amorphophallus
rivirei: Based on chemical analysis and rheology. Food Hydrocolloids, 57, 209–216.
https://doi.org/10.1016/j.foodhyd.2016.01.017
Jafarzadeh, S., Nafchi, A. M., Salehabadi, A., Oladzadabbasabadi, N., & Jafari, S. M.
(2021). Application of bio-nanocomposite films and edible coatings for extending
the shelf life of fresh fruits and vegetables. Advances in Colloid and Interface Science,
291, 102405. https://doi.org/10.1016/j.cis.2021.102405
Jin, W., Song, R., Xu, W., Wang, Y., Li, J., Shah, B. R., et al. (2015). Analysis of
deacetylated konjac glucomannan and xanthan gum phase separation by film
forming. Food Hydrocolloids, 48, 320–326. https://doi.org/10.1016/j.
foodhyd.2015.02.007
Kumar, S., Basumatary, I. B., Sudhani, H. P., Bajpai, V. K., Chen, L., Shukla, S., et al.
(2021). Plant extract mediated silver nanoparticles and their applications as
antimicrobials and in sustainable food packaging: A state-of-the-art review. Trends in
Food Science & Technology, 112, 651–666. https://doi.org/10.1016/j.
tifs.2021.04.031
Lei, Y., Wu, H., Jiao, C., Jiang, Y., Liu, R., Xiao, D., et al. (2019). Investigation of the
structural and physical properties, antioxidant and antimicrobial activity of pectin-
konjac glucomannan composite edible films incorporated with tea polyphenol. Food
Hydrocolloids, 94, 128–135. https://doi.org/10.1016/j.foodhyd.2019.03.011
Leuangsukrerk, M., Phupoksakul, T., Tananuwong, K., Borompichaichartkul, C., &
Janjarasskul, T. (2014). Properties of konjac glucomannan-whey protein isolate
blend films. Lebensmittel-Wissenschaft und -Technologie- Food Science and Technology,
59(1), 94–100. https://doi.org/10.1016/j.lwt.2014.05.029
Li, W., Liu, J., Liang, B., Shu, Y., & Wang, J. (2021). Small molecule hydrogen-bonded
toughen nacre-inspired montmorillonite-konjac glucomannan-glycerin film with
superior mechanical, transparent and UV-blocking properties. Composites Part B:
Engineering, 204, 108492. https://doi.org/10.1016/j.compositesb.2020.108492
Li, B., Li, J., Xia, J., Kennedy, J. F., Yie, X., & Liu, T. G. (2011). Effect of gamma
irradiation on the condensed state structure and mechanical properties of konjac
glucomannan/chitosan blend films. Carbohydrate Polymers, 83(1), 44–51. https://
doi.org/10.1016/j.carbpol.2010.07.017
Li, J., Ma, J., Chen, S., He, J., & Huang, Y. (2018). Characterization of calcium alginate/
deacetylated konjac glucomannan blend films prepared by Ca2+
crosslinking and
deacetylation. Food Hydrocolloids, 82, 363–369. https://doi.org/10.1016/j.
foodhyd.2018.04.022
Lin, W., Ni, Y., Liu, D., Yao, Y., & Pang, J. (2019a). Robust microfluidic construction of
konjac glucomannan-based micro-films for active food packaging. International
Journal of Biological Macromolecules, 137, 982–991. https://doi.org/10.1016/j.
Lin, W., Ni, Y., & Pang, J. (2019b). Microfluidic spinning of poly (methyl methacrylate)/
konjac glucomannan active food packaging films based on hydrophilic/hydrophobic
strategy. Carbohydrate Polymers, 222, 114986. https://doi.org/10.1016/j.
carbpol.2019.114986
Lin, W., Ni, Y., & Pang, J. (2020). Size effect-inspired fabrication of konjac
glucomannan/polycaprolactone fiber films for antibacterial food packaging.
International Journal of Biological Macromolecules, 149, 853–860. https://doi.org/
10.1016/j.ijbiomac.2020.01.242
Liu, Z., Lin, D., Lopez-Sanchez, P., & Yang, X. (2020b). Characterizations of bacterial
cellulose nanofibers reinforced edible films based on konjac glucomannan.
International Journal of Biological Macromolecules, 145, 634–645. https://doi.org/
10.1016/j.ijbiomac.2019.12.109
Liu, Z., Lin, D., Shen, R., & Yang, X. (2020a). Characterizations of novel konjac
glucomannan emulsion films incorporated with high internal phase pickering
emulsions. Food Hydrocolloids, 109, 106088. https://doi.org/10.1016/j.
foodhyd.2020.106088
Liu, Z., Lin, D., Shen, R., Zhang, R., Liu, L., & Yang, X. (2021). Konjac glucomannan-
based edible films loaded with thyme essential oil: Physical properties and
antioxidant-antibacterial activities. Food Packaging and Shelf Life, 29, 100700.
https://doi.org/10.1016/j.fpsl.2021.100700
Liu, Z., Shen, R., Yang, X., & Lin, D. (2021). Characterization of a novel konjac
glucomannan film incorporated with pickering emulsions: Effect of the emulsion
particle sizes. International Journal of Biological Macromolecules, 179, 377–387.
https://doi.org/10.1016/j.ijbiomac.2021.02.188
Li, C., Wu, K., Su, Y., Riffat, S. B., Ni, X., & Jiang, F. (2019). Effect of drying temperature
on structural and thermomechanical properties of konjac glucomannan-zein blend
films. International Journal of Biological Macromolecules, 138, 135–143. https://doi.
org/10.1016/j.ijbiomac.2019.07.007
Li, C., Xiang, F., Wu, K., Jiang, F., & Ni, X. (2020). Changes in microstructure and
rheological properties of konjac glucomannan/zein blend film-forming solution
during drying. Carbohydrate Polymers, 250, 116840. https://doi.org/10.1016/j.
carbpol.2020.116840
Lu, J., Wang, X., & Xiao, C. (2008). Preparation and characterization of konjac
glucomannan/poly(diallydimethylammonium chloride) antibacterial blend films.
Carbohydrate Polymers, 73(3), 427–437. https://doi.org/10.1016/j.
carbpol.2007.12.021
Ni, Y., Lin, W., Mu, R., Wu, C., Lin, Z., Chen, S., et al. (2019). Facile fabrication of novel
konjac glucomannan films with antibacterial properties via microfluidic spinning
strategy. Carbohydrate Polymers, 208, 469–476. https://doi.org/10.1016/j.
carbpol.2018.12.102
Ni, Y., Shi, S., Li, M., Zhang, L., Yang, C., Du, T., et al. (2021). Visible light responsive,
self-activated bionanocomposite films with sustained antimicrobial activity for food
packaging. Food Chemistry, 362, 130201. https://doi.org/10.1016/j.
foodchem.2021.130201
Pang, J., Jian, W., Wang, L., Wu, C., Liu, Y., He, J., et al. (2012). X-ray photoelectron
spectroscopy analysis on surface modification of konjac glucomannan membrane by
nitrogen plasma treatment. Carbohydrate Polymers, 88(1), 369–372. https://doi.org/
10.1016/j.carbpol.2011.12.013
Prawitwong, P., Takigami, S., & Phillips, G. (2007). Effects of γ-irradiation on molar mass
and properties of konjac mannan. Food Hydrocolloids, 21, 1362–1367. https://doi:10.
1016/j.foodhyd.2006.10.015.
Santos, N. L., Ragazzo, G. O., Cerri, B. C., Soares, M. R., Kieckbusch, T. G., & Silva, M. A.
(2020). Physicochemical properties of konjac glucomannan/alginate films enriched
with sugarcane vinasse intended for mulching applications. International Journal of
Tatirat, O., Charoenrein, S., & Kerr, W. L. (2012). Physicochemical properties of
extrusion-modified konjac glucomannan. Carbohydrate Polymers, 87(2), 1545–1551.
https://doi.org/10.1016/j.carbpol.2011.09.052
Tong, C., Wu, Z., Sun, J., Lin, L., Wang, L., Guo, Y., et al. (2020). Effect of carboxylation
cellulose nanocrystal and grape peel extracts on the physical, mechanical and
antioxidant properties of konjac glucomannan films. International Journal of
Wang, L., Mu, R.-J., Li, Y., Lin, L., Lin, Z., & Pang, J. (2019). Characterization and
antibacterial activity evaluation of curcumin loaded konjac glucomannan and zein
nanofibril films. Lebensmittel-Wissenschaft und -Technologie- Food Science and
Technology, 113, 108293–108302. https://doi.org/10.1016/j.lwt.2019.108293
Wang, K., Wu, K., Xiao, M., Kuang, Y., Corke, H., Ni, X., et al. (2017). Structural
characterization and properties of konjac glucomannan and zein blend films.
International Journal of Biological Macromolecules, 105(Pt 1), 1096–1104. https://doi.
org/10.1016/j.ijbiomac.2017.07.127
Wang, L., Xiao, M., Dai, S., Song, J., Ni, X., Fang, Y., et al. (2014). Interactions between
carboxymethyl konjac glucomannan and soy protein isolate in blended films.
Carbohydrate Polymers, 101, 136–145. https://doi.org/10.1016/j.
carbpol.2013.09.028
Y. Ni et al.

LWT 152 (2021) 112338
13
Wang, C., Xu, M., Lv, W., Qiu, P., Gong, Y., & Li, D. (2012). Study on rheological
behavior of konjac glucomannan. Physics Procedia, 33, 25–30. https://doi.org/
10.1016/j.phpro.2012.05.026
Wei, X., Pang, J., Zhang, C., Yu, C., Chen, H., & Xie, B. (2015). Structure and properties of
moisture-resistant konjac glucomannan films coated with shellac/stearic acid
coating. Carbohydrate Polymers, 118, 119–125. https://doi.org/10.1016/j.
carbpol.2014.11.009
Wu, C., Li, Y., Du, Y., Wang, L., Tong, C., Hu, Y., et al. (2019). Preparation and
characterization of konjac glucomannan-based bionanocomposite film for active
food packaging. Food Hydrocolloids, 89, 682–690. https://doi.org/10.1016/j.
foodhyd.2018.11.001
Wu, C., Li, Y., Sun, J., Lu, Y., Tong, C., Wang, L., et al. (2020b). Novel konjac
glucomannan films with oxidized chitin nanocrystals immobilized red cabbage
anthocyanins for intelligent food packaging. Food Hydrocolloids, 98, 105245. https://
doi.org/10.1016/j.foodhyd.2019.105245
Wu, K., Wan, Y., Li, X., Qian, H., Xiao, M., Ni, X., et al. (2020a). Impact of heating and
drying temperatures on the properties of konjac glucomannan/curdlan blend films.
International Journal of Biological Macromolecules. https://doi.org/10.1016/j.
Xiang, F., Xia, Y., Wang, Y., Wang, Y., Wu, K., & Ni, X. (2021). Preparation of konjac
glucomannan based films reinforced with nanoparticles and its effect on cherry
tomatoes preservation. Food Packaging and Shelf Life, 29, 100701. https://doi.org/
10.1016/j.fpsl.2021.100701
Xu, C., Luo, X., Lin, X., Zhuo, X., & Liang, L. (2009). Preparation and characterization of
polylactide/thermoplastic konjac glucomannan blends. Polymer, 50(15), 3698–3705.
https://doi.org/10.1016/j.polymer.2009.06.007
Zhang, C., Chen, J., & Yang, F. (2014). Konjac glucomannan, a promising polysaccharide
for OCDDS. Carbohydrate Polymers, 104, 175–181. https://doi.org/10.1016/j.
carbpol.2013.12.081
Zhang, F.-Y., Zhou, Y.-M., Cao, Y., & Chen, J. (2007). Preparation and characterization of
KGM/CdS nanocomposite film with low infrared emissivity. Materials Letters, 61(26),
4811–4814. https://doi.org/10.1016/j.matlet.2007.03.108
Zhang, F.-Y., Zhou, Y.-M., Sun, Y.-Q., Chen, J., Ye, X.-Y., & Huang, J.-Y. (2010).
Preparation and characterization of chitosan/konjac glucomannan/CdS
nanocomposite film with low infrared emissivity. Materials Research Bulletin, 45(7),
859–862. https://doi.org/10.1016/j.materresbull.2010.02.019
Zhao, Y., Zhang, Y., Lindstrom, M. E., & Li, J. (2015). Tunicate cellulose nanocrystals:
Preparation, neat films and nanocomposite films with glucomannans. Carbohydrate
Polymers, 117, 286–296. https://doi.org/10.1016/j.carbpol.2014.09.020
Zhou, X., Zong, X., Wang, S., Yin, C., Gao, X., Xiong, G., et al. (2021). Emulsified blend
film based on konjac glucomannan/carrageenan/camellia oil: Physical, structural,
and water barrier properties. Carbohydrate Polymers, 251, 117100. https://doi.org/
10.1016/j.carbpol.2020.117100
Zhu, F. (2018). Modifications of konjac glucomannan for diverse applications. Food
Chemistry, 256, 419–426. https://doi.org/10.1016/j.foodchem.2018.02.151
Zou, Y., Yuan, C., Cui, B., Liu, P., Wu, Z., & Zhao, H. (2021). Formation of high amylose
corn starch/konjac glucomannan composite film with improved mechanical and
barrier properties. Carbohydrate Polymers, 251, 117039. https://doi.org/10.1016/j.
carbpol.2020.117039
Y. Ni et al.

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