This document summarizes a study that evaluated buriti fruit by-products as sources of dietary fiber and natural antioxidants. Buriti is a fruit native to South America that is commercially processed for its oil. The processing generates by-products including peels, endocarp, and pulp bran. The study produced flours from these by-products and analyzed their chemical composition and antioxidant properties. The results showed that all the flour samples were high in dietary fiber and contained antioxidants such as polyphenols and carotenoids. The peels flour in particular had very high levels of non-extractable proanthocyanidins. The study concluded that buriti by-product flours have potential as sources of dietary fiber and

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Food Chemistry
journal homepage: www.elsevier.com/locate/foodchem
Buriti (Mauritia flexuosa L. f.) fruit by-products flours: Evaluation as source
of dietary fibers and natural antioxidants
Laís M. Resendea,⁎
, Adriana S. Francab,⁎
, Leandro S. Oliveirab
a
PPGCA/Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil
b
DEMEC/Universidade Federal de Minas Gerais, Av. Antônio Carlos, 6627, 31270-901 Belo Horizonte, MG, Brazil
A R T I C L E I N F O
Keywords:
Agricultural waste valorization
Buriti
Dietary fiber
Antioxidant potential
Non-extractable proanthocyanidins
A B S T R A C T
Buriti by-products flours were evaluated as sources of dietary fibers and natural antioxidants. All flours pre-
sented chemical characteristics that allowed classification as high dietary fiber powders. Presence of pectic
polysaccharides, arabinoxylans and xyloglucans was inferred by the neutral monosaccharides profile. Peels and
defatted pulp flours are highlighted as those with higher antioxidant potential (total extractable polyphenols and
antioxidant activities by DPPH and FRAP) compared to endocarp and manually-produced bran flours.
Carotenoids content were also higher in the peels flours. All produced flours showed expressive amounts of total
non-extractable proanthocyanidins (NEPA). Buriti peels flours NEPA levels are among the highest values pre-
viously described in the literature. Blanching preserved the extractable polyphenols but not carotenoids or
NEPA. Technological properties were influenced mainly by the size of the particles. Buriti by-products flours
have potential to be used as sources of dietary fiber and natural antioxidants in food.
1. Introduction
Buriti (Mauritia flexuosa L. f.), from the Arecaceae family (Fig. 1), is a
fruit native to South America, and over 10,000 tons are produced yearly
in Brazil (IBGE, 2018). It is a small fruit, of the size of a plum, with
reddish brown peel and a thin layer of yellow pulp, which is consumed
in the processed forms of sweets, ice creams, juices, jams and wine
(Sampaio & Carrazza, 2012). The fruit pulp has been reported to pre-
sent significant levels of total phenolics and carotenoids as well as high
antioxidant capacity (Candido, Silva, & Agostini-Costa, 2015). The fatty
acids and beta-carotene types and contents in the oil extracted from the
pulp are considered relevant for applications in the pharmaceutical and
cosmetics industries (Garcia-Quiroz et al., 2003).
Industrial extraction of the oil generates residues such as peels
(∼2500 tons/year), endocarp and pulp bran (∼6000 tons/year). Local
producers also extract the oil directly from the fruit, generating a re-
sidue, namely manually-produced bran (MB). These residues are either
discarded or used by local artisans (baskets, furnitures, toys, etc.) or as
animal feed (Sampaio & Carrazza, 2012). However, they present a
potential use for human food, since they can be viewed as sources of
dietary fiber and antioxidant compounds. Ayala-Zavala et al. (2011)
argue that exotic fruit by-products can present higher contents of
bioactive compounds (e.g. dietary fiber, phenolic constituents and
carotenoids) than the edible portion of the fruits, and that these by-
products could be used by the food industry as colorants, texturizer
additives, antimicrobials, flavoring and antioxidants, in the control of
lipid oxidation and as functional food ingredients. Saura-Calixto (1998)
commented that dietary fiber from fruits are better than dietary fiber
from cereals, because they contain more associated bioactive com-
pounds, better soluble/insoluble fiber ratio and higher fat retention
capacity, with lower energy value. Fruit by-products have been ex-
tensivelty identified and characterized as potential food ingredients,
sources of dietary fibers and bioactive compounds. Examples include
grape peels (Saura-Calixto, 1998), pequi peels (Leão, Franca, Oliveira,
Bastos, & Coimbra, 2017) and others. However, even though fruit by-
products are produced worldwide in large quantities and have been
already established as rich sources of functional compounds, they are
also scarcely profitably exploited, with only a handful of by-products
such as citrus peel, tomato waste and apple pomace being currently
industrially processed (Galanakis, 2012).
Fiber-rich flours produced from fruit by-products are an ingredient
that can be added to different food products, improving the nutritional
value and properties of processed foods. Food fibers can influence hy-
dration, solubility and viscosity properties of foods. Also, they con-
tribute to slow glucose absorption, to decrease total cholesterol and
LDL, to stimulate intestinal fermentation and production of short chain
fatty acids, among other functions (Dhingra, Michael, Rajput, & Patil,
2012). Furthermore, dietary fibers from by-products of fruits that are
https://doi.org/10.1016/j.foodchem.2018.07.079
Received 29 December 2017; Received in revised form 9 July 2018; Accepted 11 July 2018
⁎
Corresponding authors.
E-mail addresses: laismaia@ymail.com (L.M. Resende), adriana@demec.ufmg.br (A.S. Franca).
Food Chemistry 270 (2019) 53–60
Available online 17 July 2018
0308-8146/ © 2018 Elsevier Ltd. All rights reserved.
T

2. rich in antioxidants usually present high levels of polyphenols and
carotenoids, thus combining the beneficial effects of both dietary fiber
and antioxidants, e.g., antioxidant dietary fiber (Leão et al., 2017).
Different studies are found in the scientific literature about the
buriti fruit, oil and pulp (Candido et al., 2015; Cordeiro, de Almeida, &
Iacomini, 2015; Medeiros et al., 2015; Lima et al., 2017; Milanez,
Neves, Colombo, Shahab, & Roberto, 2018), with a wide variety of
applications including food (fruit, pulp), cosmetics and biofuels (oil).
However, no studies were found on the nutritional potential of buriti
processing by-products. Thus, the hypothesis of our study is that buriti
by-product-based flours can be considered potential sources of anti-
oxidant dietary fibers for food applications. The composition of the
polysaccharide fraction of dietary fiber matrix of buriti by-product
flours is characterized, together with the total phenolic and proantho-
cyanidin contents and associated antioxidant capacity. The technolo-
gical properties of the by-product flour are also determined in order to
evaluate their potential use as functional ingredient in food formula-
tions.
2. Materials and methods
2.1. Materials
Buriti (Mauritia flexuosa L. f.) fruits were collected in Três Marias/
Brazil, a subhumid tropical savannah area, in the Cerrado biome. The
fruits were stored in boxes for seven days until complete maturation.
The following chemicals were employed: acetone, butanol, hexane,
hydrochloric acid, iron(III) chloride, methanol, petroleum ether and
sodium carbonate (acquired from Synth, São Paulo, Brazil); alpha
amylase, dichloromethane, 1,1-diphenyl-2-picrylhydrazyl radical
(DPPH), dimethylsulfoxide, Folin-Ciocalteu reagent, gallic acid, 1-me-
thylimidazole, pancreatin, pepsin, sodium borohydride, trifluoroacetic
acid, and 2,4,6-Tri(2-pyridyl)-s-triazine (TPTZ) (acquired from Sigma-
Aldrich, São Paulo, Brazil).
2.2. Flours preparation
The process steps are summarized in a flowchart (Fig. 2). Graded
fruits were washed and sanitized. Some fruits were broken down into
their constituent parts (peels, pulp and endocarp), and the seeds were
discarded. Another part was destined for oil extraction by a manual
process. The manual process for oil extraction was based on reports of
the procedure employed by traditional extractive communities
(Sampaio and Carrazza, 2012), with minor modifications. The fruits
were macerated and boiled with water until the oil floated to the sur-
face. The oil was collected and the remaining solid part (herein labled
manually-produced bran) was separated. The manually-produced bran,
peels, pulp and endocarp were stored at −18 °C. The pulp bran was
defatted by the Soxhlet method, using hexane, as an alternative to the
method of oil extracting by screw-pressing the pulp. Some of the sam-
ples were submitted to blanching (immersion in hot water at 75 °C for
3 min followed by immersion in cold water at 2 °C for 2 min).
Six different types of processed by-products were employed for
production of flours: blanched peels (BP); unblanched peels (UP);
blanched endocarp (BE); unblanched endocarp (UE); manually-pro-
duced bran (MB); and bran of defatted pulp obtained by solvent ex-
traction (PB). Except for PB, the samples were mixed with water for
wet-milling, and dried in a convective oven (model 420-1DE, Nova
Ética, Brazil) at 60 °C for 24 h. Subsequently, the samples were ground,
sieved (425-µm) and stored at room temperature in tightly sealed
plastic containers. PB was already in powder form so it was just sieved
and stored.
2.3. Chemical composition
Moisture, fat content, ash and proteins were analyzed according to
the methodologies recommended by AOAC (1998): moisture content
was evaluated by oven drying at 105 °C until constant weight; fat was
evaluated by the Soxhlet method, with petroleum ether as a solvent
(4.5.05); ash was quantified after incineration at 550 °C for 20 h
(942.05); and protein was determined by the Kjeldahl method (960.52).
Carbohydrate content was obtained by difference. Total, insoluble and
soluble dietary fiber were determined by the enzymatic gravimetric
method, in which the samples were digested with alpha amylase, pepsin
and pancreatin enzymes (Asp, Johansson, Hallmer, & Siljestrom, 1983;
Leão et al., 2017).
The neutral monosaccharides composition was evaluated by gas
chromatography (Melton & Smith, 2001). The neutral sugars in the
samples (5 mg sample) were hydrolysed with trifluoroacetic acid 2 mol/
L (0.5 mL), reduced with sodium borohydride (1 mL, 0.5 mol/L) in di-
methylsulfoxide, and derivatized with acetic anhydride (2 mL) in the
presence of 1-methylimidazole (200 µL) to their alditol acetates. Di-
chloromethane (1 mL) was used to extract the alditol acetates. The se-
paration of the alditol acetates was performed on a Varian 3900 gas
chromatograph with flame ionization detector, through a BPX-70 ca-
pillary column (30 m × 0.32 mm × 0.25 μm; SGE Chromatography
Products) and nitrogen as carrier gas (1.5 mL/min). Injector and de-
tector temperatures were 230 °C and 280 °C, respectively. The total run
time was 38 min (30 s at 38 °C, temperature increased to 170 °C at a rate
of 50 °C/min, then increased to 230 °C at a rate of 2 °C/min, then
maintained for 5 min).
The relation between the concentration of each monosaccharide and
the peak areas of their respective alditol acetates in the chromatograms
was calculated by means of the monosaccharide molar ratio relative to
the internal standard used, in this case, allose:
⎜ ⎟⎜ ⎟= ⎛
⎝
⎞
⎠
⎛
⎝
⎞
⎠
RMR
A MM
m
m
A MM
m a
m m
m
a
a a
/
(1)
where RMRm/a is the monosaccharide molar ratio relative to allose, A is
the chromatogram peak area, m is the mass of the sugar (g), MM is the
molar mass, and the subscripts m and a represent monosaccharide and
allose, respectively. The molar composition of each monosaccharide (%
mol) was then calculated by
⎜ ⎟= × ⎛
⎝ ∑
⎞
⎠=
mol A
RMR
A
% ( 100)i m
m a
i
n
m
/
1
i
i
i (2)
where the subscript i represents a specific monosaccharide and n is the
total number of monosaccharides in the chromatogram.
2.4. Total phenolics, carotenoids and in vitro antioxidant capacity
For total phenolics, DPPH, and FRAP analyses, extracts of the
samples were prepared with methanol and acetone as described in the
literature (Pérez-Jiménez et al., 2008), with minor modifications. The
flours (1 g) were placed in test tubes, sequentially extracted with me-
thanol (50% v/v) and acetone (70% v/v), 40 mL each. After each ex-
traction, the mixture was centrifuged at 3500 rpm for 15 min. The su-
pernatants were afterwards combined and the total volume completed
exocarp (peel)
mesocarp (pulp)
endocarp
endosperm (seed)
Fig. 1. Buriti fruit (Mauritia flexuosa L. f.).
L.M. Resende et al. Food Chemistry 270 (2019) 53–60
54

3. to 100 mL with distilled water (Larrauri, Ruperez, Borroto & Saura-
Calixto, 1996).
Total extractable phenolics (TEP) were evaluated by the Folin-
Ciocalteau method with minor modifications (Singleton, Orthofer, &
Lamuela-Raventos, 1999; Leão et al., 2017). In summary, 1 mL of ex-
tract was added to 5 mL of Folin–Ciocalteu reagent and 4 mL of sodium
carbonate solution. The resulting solution was stirred and then let to
rest for 120 min, in the absence of light. Absorbance values were
measured in a UV/Vis spectrophotometer (Micronal AJX 1900, SP,
Brazil) at 765 nm. A calibration curve was built employing gallic acid,
at concentrations ranging from 2 to 7 μg/mL, and the results were ex-
pressed as gallic acid equivalents (mg GAE per g of dry matter).
Non-extractable phenolics (proanthocyanidins, NEPA) assay was
performed according to Zurita, Diaz-Rubio and Saura-Calixto (2012).
Residues obtained from the preparation of extracts for DPPH, FRAP and
total phenolic analyses were dried at 35 °C for 16 h and reacted with
butanol solution acidified with hydrochloric acid (95:5 v/v) containing
FeCl3 at 100 °C, for 1 h. The remaining material was centrifuged, the
supernatants were recovered and the volume completed to 25 mL with
the butanol solution. 500μL of this mixture was diluted to 10 mL. Ab-
sorbance values were measured at 450 nm and 550 nm, and the sum of
absorbance readings at both values were plotted against NEPA con-
centration. Polymeric proanthocyanidin concentrate isolated from
carob pod (Ceratonia siliqua L.) was used as a standard (Zurita et al.,
2012). Results were expressed as mg NEPA/100g flour.
Total carotenoids were evaluated according to the method described
by Lichtenthaler and Buschmann (2001). Extracts of the samples were
prepared with acetone (3 g:5 mL for endocarp flours and 3 g:10 mL for
the others) and then centrifuged. Absorbance values were measured at
470 nm, 644 nm and 661 nm. Chlorophylls A and B were calculated for
determination of total carotenoid (Leão et al., 2017). Results were ex-
pressed as µg total carotenoids/100 g flour.
The antioxidant activity was evaluated by DPPH and FRAP assays.
DPPH assay was performed as described in the literature (Brand-
Williams, Cuvelier & Berset, 1995), with minor modifications. In sum-
mary, 3.9 mL of DPPH methanolic solution (0.06 mM) were added to
0.1 mL of different dilutions of the extracts in methanol (3:1, 1:1, 1:3 v/
v). A control sample (water/methanol/acetone) was also prepared as
previously described. The tubes were incubated at room temperature in
the dark. Variations in the absorbance of the samples were measured at
515 nm using a UV–Vis spectrophotometer (Micronal AJX 1900, SP,
Brazil) until absorbance readings became stable. IC50 (the amount of
dry sample required to decrease 50% of the initial DPPH concentration)
was determined by linear regression. Results were expressed in grams of
sample per grams of DPPH (Leão et al., 2017).
FRAP assay was performed according to Pulido, Bravo and Saura-
Calixto (2000), with modifications. Samples extracts of four with dif-
ferent concentrations were reacted with FRAP solution (acetate buffer,
Fruit picking
zFLOURS PREPARATION
Washing and
sanitizing
Separation of structures Selection of part
of whole fruits
shell pulp seed
Oil extraction
by
handmade
process
Oil extraction
by solvent
extraction
method
Bran of
defatted
pulp (PB)
Handmade
bran (HB)
Discard
Bleaching
Unbleache
d shells
(US)
Bleached
shell (BS)
Wet-milling
Drying and
grinding
BS
Flour
US
Flour
PB
Flour
HB
Flour
endocarp
Bleaching
Unbleached
endocarp
(UE)
Bleached
endocarp
(BE)
BE
Flour
UE
Flour
Drying,
grinding
and sifting
Wet-milling
Drying
grinding,
and sifting
Wet-milling
Drying
grinding,
and sifting
Wet-milling
Drying
grinding,
and sifting
Wet-milling
Drying,
grinding,
and sifting
Drying
grinding,
and sifting
Fig. 2. Flour preparation flowchart.
L.M. Resende et al. Food Chemistry 270 (2019) 53–60
55

4. TPTZ and FeCl3) at 37 °C for 30 min. Absorbance values were measured
at 595 nm. Ferrous sulphate was used for the calibration curve. Results
were expressed as µmol Fe2SO4/g flour.
2.5. Technological properties
The parameters luminosity L*
, a*
and b*
were measured using a
tristimulus colorimeter (ColorFlex, Hunter Associates Laboratory, VA)
with standard 10° observer angle and daylight. Polar coordinates c*
(chroma) and h (angle) were calculated.
Water and oil-retention capacities (WRC and ORC), water solubility
index (WSI) and swelling capacity (SC) were evaluated according to the
methods described by Wang, Xu, Yuan, Fan and Gao (2015) with minor
modifications. For the evaluation of the water and oil-retention capa-
cities, the samples (1 g) were mixed with water or oil separately
(20 mL), shaken and centrifuged; the supernatant with oil was dis-
carded and the supernatant with water was reserved. The final mass
was measured and divided by the mass of the samples. The reserved
supernatant (from WRC determination) was dehydrated (12 h, 105 °C)
and WSI determined as the percent mass ratio between the dehydrated
and original samples. For evaluation of the swelling capacity, the
samples (150 mg) were shaken with water (200 mL), and then set for
decantation (12 h); the final volume (mL) occupied by the sample was
recorded and expressed in mL/g of sample.
2.6. Statistical analysis
All assays were carried out in triplicates with mean and standard
deviation. The normality of the data was verified by the Shapiro-Wilk
method. Data were statistically analyzed using ANOVA and Tuckey
tests, with 95% confidence (p < 0.05), using IBM SPSS Statistics soft-
ware, version 19.
3. Results and discussion
3.1. Flour preparation and chemical analysis
The values obtained for chemical composition and yield of the buriti
by-product flours are shown in Table 1. All the prepared flours pre-
sented moisture levels below the recommended limit of 9 g/100 g
(Larrauri, 1999), assuring adequate conditions for product storage.
Yields of the flours productions calculated from the fresh matter (fruit)
were below 12%. However, yield values will be significantly higher if
based on a specific residue. Lipid levels were low for all samples, as
expected for commercially available as well as residue-based flours
(Larrauri, 1999; Leão et al., 2017). Ash contents ranged from about 1 g/
100 g (bran of defatted pulp and peels samples) to about 3 g/100 g
(endocarp samples). All the prepared flours had protein levels below
7 g/100 g dry matter, with the larger values corresponding to the flours
based on bran. Statistical differences were not observed in the chemical
composition between blanched and unblanched samples, indicating
that the treatment did not interfere in the analyzed compounds, with
exception of the ash content in the peel-based flours, probably due to
loss of minerals in the hot water during blanching (de Corcuera,
Cavalieri, & Powers, 2004).
The total dietary fiber content of all flours is also shown in Table 1,
with values ranging from 50.33 g/100 g (UE) up to 88.69 g/100 g (BP),
thus being all classified as high dietary fiber powders (Larrauri, 1999;
Saura-Calixto, 1998). Flours of peels and brans presented high insoluble
dietary fiber content and did not statistically differ. Flours of endocarp
presented lower insoluble dietary fiber content. Botanical functions of
the peel and endocarp justify the distribution of fiber. The peels have
the function of protecting the fruits of external agents and are more
fibrous while the endocarp protects the seed, being more or less fibrous
depending on the fruit. Soluble dietary fiber contents did not sig-
nificantly differ for all samples. TDF values are high in comparison to
Table1
Chemicalcompositionandyieldoftheburitiby-productsflours.
SampleMoisture(g/100g)Dietaryfiber(drymatterbasis)(g/100g)Proximatecomposition(drymatterbasis)(g/100g)
IDFSDFTDFLipidsAshProteinCarbohydrates
BP(blanchedpeels)3.57±0.36b
87.76±7.19a
0.94±0.45cd
88.690.52±0.09ab
1.02±0.04d
2.59±0.20c
95.87
UP(unblanchedpeels)4.21±0.58ab
88.06±5.41a
0.86±0.21d
88.910.55±0.08a
1.88±0.15b
3.17±0.20c
94.40
BE(blanchedendocarp)4.08±0.20ab
47.91±0.80b
2.70±0.66ab
50.610.71±0.17a
3.40±0.03a
2.71±0.01c
93.18
UE(unblanchedendocarp)4.29±0.13ab
49.21±0.04b
1.12±0.68bcd
50.330.71±0.09a
3.45±0.02a
2.95±0.53c
92.89
MB(manually-producedbran)4.26±0.93ab
84.22±0.16a
3.17±0.31a
87.390.78±0.09a
1.46±0.03c
4.62±0.25b
93.14
PB(defattedpulpbran)5.32±0.03a
80.88±0.14a
2.51±0.09abc
83.390.20±0.02b
1.01±0.06d
6.20±0.01a
92.59
SampleYield(%)Rhamnose(%mol)Fucose(%mol)Arabinose(%mol)Xylose(%mol)Mannose(%mol)Galactose(%mol)Glucose(%mol)
BP(blanchedpeels)11.490.000.008.8875.561.804.189.57
UP(unblanchedpeels)11.340.000.0010.5557.022.144.3725.92
BE(blanchedendocarp)2.530.360.7310.729.672.3511.5464.63
UE(unblanchedendocarp)3.260.280.6311.098.822.3010.4766.41
MB(manually-producedbran)11.840.430.9410.6064.362.655.4215.59
PB(defattedpulpbran)8.500.952.7741.5024.439.487.6313.24
Mean±standarddeviation(n=3).Differentlettersinthesamecolumnindicatethatvaluesaresignificantlydifferent(p>0.05).IDF=insolubledietaryfiber;SDF=solubledietaryfiber;TDF=totaldietaryfiber.
L.M. Resende et al. Food Chemistry 270 (2019) 53–60
56

5. other types of fruit by-products such as pequi (39.8–43.3 g/100 g),
mango (38.9–40.51 g/100 g) and orange (49.0–50.8 g/100 g) peels
(Leão et al., 2017; Tejada-Ortigoza, Garcıa-Amezquita, Serna-Saldıvar,
& Welti-Chanes, 2017). Insoluble fiber (IDF) values ranged from 49.2 to
88.1 g/100 g, representing over 95% of TDF in all samples. Thus, the
majority of DF in the prepared flours corresponds to IDF. Physiological
effects associated to IDF include the ability to increase faecal bulk and
decrease intestinal transit (Leão et al., 2017). Although the IDF/SDF
ratio is quite high in comparison to other studies using fruit byproducts,
this could be improved by further treatment, for example employment
of high hydrostatic pressure (HPP) as proposed by Tejada-Ortigoza
et al. (2017). These authors observed an increase in the SDF content of
mango peels after pressure treatment (at 55 °C), with SDF/TDF values
increasing from 37.4% (control) up to to 45.7% (HPP).
In the non-cellulosic neutral monosaccharide profile of the buriti by-
products flours, xylose (peels and manually-produced bran), glucose
(endocarps) and arabinose (bran of defatted pulp) were dominant
(Table 1). Xylose was also reported as the major carbohydrate of other
fruit by-products such as coconut husk, defatted grape seeds and
pressed palm fiber (Prado et al., 2014). Glucose was reported as the
major carbohydrate in flours obtained from pequi peels (Leão et al.,
2017), similar to the flours based on buriti endocarp. However, pequi
based flours presented higher ammounts of galactose and higher SDF
values. Additionally, galactose, mannose, fucose and rhamnose were
the minor constituents of the buriti by-products flours, with the last two
not detected in the peel-based flours. Larrauri et al. (1996) reported the
same major and minor monosaccharides in mango peel dietary fiber,
but also detected erythrose. These authors determined the contents of
arabinose to be higher in the soluble fiber fraction than in the insoluble
one, whereas the contents of glucose were higher in the insoluble fiber
fractions The presence of rhamnose, arabinose, galactose, glucose, xy-
lose and mannose were also determined in orange, grapefruit and
lemon peels by Wang et al. (2015).
It is noteworthy to mention that polysaccharides are found mainly
in the cell wall of plants, whose characteristics change according to the
botanical origin of the species. Buriti is a palm tree (Arecaceae) and
therefore it is a monocotyledons commelinoid plant. However, studies
have shown that the cell wall of the palms differs from the walls of
other commelinoid monocotyledons, such as Poaces (e.g., cereals such
as oats and wheat), and their composition are somewhat intermediate
to those of the walls of dicotyledons plants and non-commelinoid
monocotyledons and of the walls of the monocotyledons commelinoid.
Thus, palm trees may have a significant amount of pectic poly-
saccharides and xyloglucans similar to those of non-commelinoid
monocotyledons and dicotyledons (the latter with more xylose and
galactose, and presence of fucose) and also contain glucuronoar-
abinoxylans like the monocotyledons commelinoid (Carnachan &
Harris, 2000; Harris, Kelderman, Kendon, & Mckenzie, 1997; Hayashi,
1989).
The non-cellulosic monosaccharide analysis of the buriti by-product
flours confirmed the expectations in regard to the characteristics of
palm trees. The presence of arabinose, galactose and rhamnose may
indicate presence of pectic polysaccharides, such as pectic arabinans,
pectic galactans and rhamnogalacturonans. Expressive levels of arabi-
nose and xylose may indicate the presence of arabinoxylan, the main
hemicellulose of typical commelinoid monocotyledons, such as Poaces
(e.g., oats and wheat) (Harris et al., 1997). The identification of glu-
cose, xylose and galactose may indicate the presence of xyloglucans
similar to those of dicotyledons. It is known that xyloglucans play an
important role as softener during fruit maturation. The small amount of
fucose induces the inference of the presence of fucosylated xyloglucans.
The presence of mannose induces the inference of the presence of
glucomannans or galactoglucomannans, which were also present in
pineapple cell walls, as reported by Smith and Harris (1995). In the
defatted buriti pulp, a small amount of glucose, xylose and arabinose
may be associated with the linear polysaccharides (1 → 5)-α-L-Ara-
binan, (1 → 3) – (1 → 4)-α-D-glucan and (1 → 4)-β-D-xylan found in
small amounts in buriti pulp by Cordeiro et al. (2015). Ultimately it is
inferred that part of the glucose may be product of sucrose hydrolysis,
highlighting the large amount of this monosaccharide in the endocarp
samples. Sundram, Sambanthamurthi and Tan (2003) report the pre-
sence of carbohydrate reserves for the embryo in palm fruit, which
reinforces this hypothesis.
3.2. Total phenolics, carotenoids and in vitro antioxidant capacity
Total extractable phenolics results are displayed in Table 2. The
flours produced from peels presented the highest values, followed by
bran of defatted pulp, manually-produced bran and endocarp.
Blanching preserved the polyphenols from peels, but this behavior was
not observed in endocarp samples. Blanching is an essential step in the
processing of fruits and vegetables in order to inactivate certain en-
zymes including polyphenoloxidase, which causes deleterious effects in
the polyphenolic fractions and in their associated antioxidant proper-
ties. Low-temperature short-time blanching can have a diversity of ef-
fects on the polyphenol fraction depending on the nature of its con-
stituents. Although the time–temperature combination herein
employed could cause underblanching, therefore with the adverse ef-
fect of speeding up the activity of the deleterious enzymes, it seems that
only the polyphenols in the endocarp were susceptible to that, sug-
gesting that these polyphenols were more easily extracted from the
endocarp cells than those of the peel cells. Peels and endocarp have
distinct cell wall compositions and this could constitute a factor to
promote differences in the sensitivity to blanching, with the cell walls
in the peel being tougher to break than those in the endocarp under the
blanching conditions herein employed (Abu-Ghannam and Jaiswal,
2015). Another factor that might have contributed to this difference
could be that the types of polyphenols present in the endocarp are more
soluble in the blanching environment than those in the peels and thus
are more heat-labile.
Flours based on buriti peels and brans presented higher amounts of
extractable phenolics in comparison to buriti pulp (435.08 mg GAE/
100 g) (Candido et al., 2015), açaí pulp (454 mg GAE/100 g), jaboti-
caba (Myrciaria cauliflora) (440 mg GAE/100 g), mangaba (Hancornia
speciosa) (169 mg GAE/100 g) and others tropical fruits (Rufino et al.,
2010). These results confirm the potential of the produced flours as
Table 2
Total extractable phenolics, proanthocyanidins (NEPA), carotenoids and antioxidant capacity of buriti by-products flours.
Sample TEP (mg GAE/100 g) NEPA (mg/100 g) Carotenoids (µg/100 g) DPPH IC50 (g/g DPPH) FRAP (µmol Fe2SO4/g)
BP (blanched peels) 934.6 ± 34.0a
4085.3 ± 474.0b
1040.1 ± 11.3b
413.1 ± 14.9a
155.5 ± 4.6b
UP (unblanched peels) 785.1 ± 21.4b
5008.1 ± 116.0a
1186.7 ± 22.0a
1036.7 ± 143.8c
88.9 ± 2.3c
BE (blanched endocarp) 114.9 ± 7.7d
1272.2 ± 159.9de
150.5 ± 38.5d
1915.2 ± 99.9d
ND
UE (unblanched endocarp) 93.2 ± 5.1e
1195.2 ± 118.3e
291.2 ± 17.3c
ND ND
MB (manually-produced bran) 676.8 ± 26.7c
2285.9 ± 311.0c
ND 835.9 ± 63.4b
88.6 ± 14.5c
PB (defatted pulp bran) 740.1 ± 26.5b
1907.3 ± 134.0cd
ND 447.0 ± 60.0a
205.8 ± 5.7a
Mean ± standard deviation (n = 3). Different letters in the same column indicate that values are significantly different (p > 0.05). ND = Not detected. TPE = Total
extractable phenolics; NEPA = Non-extractable phenolics (proanthocyanidins).
L.M. Resende et al. Food Chemistry 270 (2019) 53–60
57

6. relevant sources of phenolics.
Total non-extractable proanthocyanidins (NEPA) results are also
shown in Table 2. In general, the flours based on buriti by-products
flours presented expressive amounts of total non-extractable proan-
thocyanidins. Again, the highest values were determined for the peels,
followed by brans and endocarps. However, the contents of non-ex-
tractable proanthocyanidins were significant in the endocarps, corre-
sponding to approximately 50% of the amount that has been de-
termined for red grape pomace, one of the major sources of NEPA
reported in the literature (Zurita et al., 2012). This observation shows
that buriti, a native fruit of the Brazilian Cerrado, is rich in these
compounds. Candido et al. (2015) observed that the buritis from the
Cerrado region had higher phenolic contents than the buritis from the
Amazon region. The authors evaluated only extractable polyphenols. It
could have been even more significant if the non-extractable poly-
phenols were also evaluated.
Blanching had a negative effect on the total non-extractable
proanthocyanidins content in flours based on peels, but did not affect
the content in samples based on the endocarp. As discussed by Zurita
et al. (2012), non-extractable proanthocyanidins form complexes with
protein and cell wall polysaccharides. Bindon, Smith, Holt and Kennedy
(2010) complement that the nature of cell wall structure has influence
in the interaction with the proanthocyanidins. They reported greater
affinity of xyloglucans and pectins for proanthocyanidins and weaker
surface interaction with limited binding sites on cellulose. From the
neutral monosaccharide profile analysis, it is inferred that the peels
contained higher amounts of xyloglucans and pectins than the endocarp
samples. Peels and endocarp samples have distinct cell wall composi-
tions and this difference can be responsible for the sensitivity to
blanching.
It is noteworthy to point out that the terminology “polyphenol”
herein employed refers exclusively to those represented by the ex-
tractable fraction, i.e., the free polyphenols. The non-extractable poly-
phenols are mostly comprised of proanthocianidins, which are oligo-
meric flavonoids. Polyphenols tend to form complexes with proteins by
means of hydrophobic interactions (Siebert, Troukhanova & Lynn,
1996). Proanthocyanidins present larger chain sizes than their mono-
meric counterparts (e.g., gallic acid, catechin, etc), which are mostly
present in the extractable fraction. Thus, proanthocyanidins are more
hydrophobic than their respective monomers and consequently prone
to form complexes with proteins through the protein hydrophobic sites.
The endocarp presented a protein content similar to that of the peels,
but a lower content of polyphenols than the latter (both extractable and
non-extractable). The unblanched samples of the peels presented higher
content of non-extractable polyphenols than the blanched ones, sug-
gesting that the polyphenol-protein complexes with weaker hydro-
phobic interactions were broken down by the heat treatment. The same
was not true for the probable polyphenol-protein complexes in the
endocarp, which remained intact after blanching, suggesting a stronger
hydrophobic interaction and consequently a distinct monomeric com-
position for both the protein and the proanthocyanidin molecules.
Buriti pulp is an important source of carotenoids (Candido et al.,
2015), but there is no such information in the literature in regard to its
residues. Total carotenoids results are displayed in Table 2. As well as
other bioactives compounds, greater amounts of total carotenoids were
found in the peels and less amount in the endocarp. However, car-
otenoids were not detected in the flours based on bran samples. Prob-
ably the carotenoids were degraded during the boiling process
employed in the manual extraction of oil (MB) or were extracted to-
gether with the oil during degreasing with hexane by the Soxhlet
method (PB) (Boon, Mcclements, Weiss, & Decker, 2010).
Blanched samples presented lower total carotenoids content than
unblanched samples, probably due to leaching or degradation. de
Corcuera et al. (2004) argued that water blanching requires longer
processing times, resulting in increased leaching not only of minerals
but also vitamins. Buriti peel flours presented levels of total carotenoids
similar to those of avocado peels (930–1115 µg/100 g) (Wang, Bostic, &
Gu, 2010). However, values are low in comparison to flours prepared
from pequi residues (2117–3499 µg/100 g) (Leão et al., 2017).
Antioxidant activity results based on DPPH and FRAP are also dis-
played in Table 2. Flours based on blanched peels (BP) and on bran of
defatted pulp samples (PB) presented the highest values. Endocarp
samples showed low antioxidant activity, not detected by FRAP because
it was below the methodology sensitivity levels. The blanched samples
presented higher antioxidant potential in comparison to the unblanched
ones. Blanching is a pretreatment that inhibits polyphenoloxidase en-
zymes, which are responsible for the oxidation of polyphenols (Fante &
Noreña, 2012).
The manually-produced bran samples presented intermediate anti-
oxidant activity in comparison to BP and PB. It is known that the peels
have more antioxidants because they protect the fruits against external
aggressive agents such as bacteria and insects. Guo et al. (2003) also
observed higher antioxidant activity in the peels of different fruits
commonly consumed in China in comparison to those of the fruit seeds
and pulps. The palm endocarp is thick and woody to protect the small
embryo. Therefore, the presence of antioxidant compounds is not
prioritized in this structure, which justifies the results herein obtained.
The manually-produced bran was obtained from the whole fruits. Thus,
the intermediate antioxidant potential of bran manually-produced flour
is expected. However, the conservation of antioxidant compounds is
surprising, even after long-time exposure to boiling during the oil ex-
traction by the manual process.
The antioxidant capacity of buriti by-products flours was shown to
be high, ranging from 413 to 1915 g/g DPPH and from 89 to 206 µmol
Fe2SO4/g (FRAP). DPPH based values herein determined are higher
(and thus worse) than those for flours obtained for pequi by-products
(44.4–48 g/g DPPH), but similar to those for extracts obtained from
tropical fruits including açaí (Euterpe oleracea) (598 ± 164 g/g DPPH),
mangaba (Hancornia Speciosa) (890 ± 69.1 g/g DPPH) and yellow
mombim (Spondias mombin) (1064 ± 162 g/g DPPH) (Rufino et al.,
2010, Leão et al., 2017). Results based on FRAP were also similar to
these tropical fruits: yellow mombim (Spondias mombin) (97.6 µmol
Fe2SO4/g), umbu (Spondias tuberose) (143 µmol Fe2SO4/g) and açaí
(Euterpe oleracea) (220 µmol Fe2SO4/g) (Rufino et al., 2010). It is no-
teworthy to mention that antioxidant capacity values were determined
using the TEP extract, and thus the effect of NEPA and other substances
was not taken into account.
3.3. Technological properties
Images of the prepared flours can be seen in Fig. 3. Color parameters
of the buriti by-products flours results are displayed in Table 3. Lu-
minosity values (L*
) values ranged from 53.13 to 62.38. The lighter
powders were those produced from endocarp and bran of defatted pulp,
followed by peels and manually processed bran. As expected, the
blanched samples are lighter than the unblanched ones. Luminosity
UP BHEBPB BPEU
Fig. 3. Buriti by-products flours produced.
BP = bleached peels; UP = unbleached peels;
BE = bleached endocarp; UE = unbleached en-
docarp; HB = handmade bran; PB = bran of defatted
pulp by solvent extraction method.
L.M. Resende et al. Food Chemistry 270 (2019) 53–60
58

7. values are high in comparison to other flours based on fruit residues
processing, including passion fruit peel flour (32.32–36.71) and pequi
residue flour (45.2–55.2) (Coelho et al., 2017; Leão et al., 2017).
Lighter flours are important because they can be added to a larger range
of products and in larger quantities without compromising the char-
acteristic color of food. All hue angles (h) were between orange and
yellow hues, without significant differences amongst the flours. As ex-
pected, color intensity (c*
) is slightly higher for the unblanched samples
compared to the blanched ones.
Results obtained for the technological properties are also displayed
in Table 3. The water retention capacity values ranged from 1.10 to
1.6 g/g, low in comparison to pequi peel flours (3.7–4.0 g/g) and
mango peel (11.4 g/g) (Larrauri et al., 1996; Leão et al., 2017), but just
slightly lower than the values reported for defatted rice bran flour
(1.9 g/g) (Wang, Suo, De Wit, Boom, & Schutyser, 2016). Oil retention
capacity is used in cooked foods to enhance their fat retention during
cooking, preserve the flavor and increase the technological yield
(Thebaudin, Lefebvre, Harrington, & Bourgeois, 1997). The oil reten-
tion capacity values for the buriti by-products ranged from 1.18 to
1.27 g/g, similar to those of dietary fibers from orange (1.76 g/g) and
pequi peels (1.23–1.35 g/g) (Wang et al., 2015; Leão et al., 2017), but
low in comparison to mango peel (2.7 g/g) (Larrauri et al., 1996)
Water solubility index (WSI) is used to define the quantity of water
soluble matter in a product. The water solubility index values ranged
from 4.46 to 23.61 g/100 g. Values obtained for buriti bran and peels
are low in comparison to those of pequi peels (Leão et al., 2017),
whereas values obtained for buriti endcarp are higher. Values are much
lower than those reported for orange peels (86.7–91.4 g/100 g), al-
though these correspond only to SDF (Wang et al., 2015). Swelling is
the first stage of the solubilization of polysaccharides, with water dif-
fusing into the product structure and dispersing the macromolecules, in
other words, swelling, may promote the solubilization (Thebaudin
et al., 1997). The swelling capacity values ranged from 3.70 to
11.36 mL water/g, similar to soluble dietary fiber from orange peel
(4.83 g/g) (Wang et al., 2015) and rice bran flour (4.4 g/g) (Wang et al.,
2016), but smaller than coconut fiber (20.00 mL water/g)
(Raghavendra et al., 2006).
According to Thebaudin et al. (1997) the hydration properties of
dietary fibers depend on different factors, such as chemical structure,
associations between molecules, effects of solvents and temperature,
porosity of the fibers and the size of the particles. Raghavendra et al.
(2006) highlighted the influence of particle size on water retention
capacity. The authors tested different particle sizes of coconut fiber and
observed an increase in hydration properties with the decrease in par-
ticle size from 1127 down to 550 µm. This increase was explained by
increase in total pore volume and theoretical surface area due to col-
lapse of matrix structure and shearing of the cell wall due to milling.
However, the authors also observed a decrease in hydration properties
with the decrease in particle size below 550 µm, possibly because of
damages to the fiber matrix and the collapse of the pores by milling.
Flours of the present study presented particle sizes less than or equal to
425 µm, being in the same range as commercial dietary fiber powders
(150–430 µm) (Larrauri, 1999).
Overall, blanching and the physico-chemical nature of the specific
residue did not significantly interfere in the technological properties.
The only exception were the flours based on the endocarp, that pre-
sented WSI significantly higher than those of the other residues flours.
Our results indicate that all produced flours can be viewed as po-
tential sources of antioxidant dietary fibers (mostly insoluble) for food
applications. The selection of a specific residue flour should be made
according to the desired end use for it. If the interest is in lighter flours,
with a better ratio of soluble and insoluble fibers and greater anti-
oxidant activity provided by extractable compounds, the bran of de-
fatted pulp should be selected for the production of such flour.
However, press extraction is suggested, as performed by the buriti
processing industry, as opposed to the manual process herein used. If
the interest is for higher amounts of non-extractable polyphenols and
lighter colors, with soluble fiber content not being a decisive criteria,
then unblanched peels should be selected. However, the use of manu-
ally processed bran, although less expressive in regard to the anti-
oxidant potential, should not be disregarded, mainly by extractivist
communities, which generate important volumes of this residue by
manual extraction of buriti oil.
4. Conclusions
Buriti by-products flours were prepared and characterized. Peel and
bran-based flours presented high contents of extractable and non-ex-
tractable polyphenols (proantocyanidins), although antioxidant capa-
cities were intermediate to those of other residues described in the
literature. Nonetheless, all produced flours presented high contents of
non-extractable polyphenols in comparison to similar types of by-pro-
ducts.
The composition of the polysaccharide fraction indicated xylose
(peels and manually-produced bran), glucose (endocarps) and arabi-
nose (bran of defatted pulp) as the main carbohydrates. The technolo-
gical properties were comparable to those reported for to similar types
of by-products. Therefore, this study shows that buriti by-products
flours can be deemed relevant sources of dietary fibers and natural
antioxidants, with differences in composition and antioxidant perfor-
mance of flours justified by the botanical functions of each part of the
fruit.
Acknowledgments
The authors acknowledge financial support from the Brazilian
agencies CNPq, Brazil and CAPES, Brazil. We would like to thank the
reviewers for their valuable comments and suggestions.
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Color parameters and technological properties of the buriti by-products flours.
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