food engineering

1. Non-thermal hybrid drying methods of
fruits and vegetables
Taha HİJAZİ (15570022)
Istanbul,05,2018
YILDIZ TEKNİK ÜNİVERSİTESİ
FEN BİLİMLERİ ENSTİTÜSÜ
GIDA MÜHENDİSLİĞİ BÖLÜMÜ

2. Contents:
 introduce
 Terminology used in This Presentation
 definition of Non-thermal hybrid drying
 Non-thermal hybrid drying methods used in fruits and vegetables
 Current status and challenges of combined NT and CHAD
 Conclusion
 References
 Thanks
2

3. 1-interduce
- the choice of the most appropriate drying technique depends on various factors such as:
 the product type, drying conditions, drying efficiency, and cost of drying operation.
 Other critical selection parameters include energy consumption, and quality of the final product.
 due to drying process conditions: temperature, air velocity, and relative humidity, important product
properties, such as texture, color, total carotenoid content, phenolic composition, total phenolic content,
antioxidant capacity and other bioactive compounds could be affected .
 Drying is the oldest and widely used method of postharvest food preservation. It involves the removal of
moisture from a product due to couple heat and mass transfer. Drying improves postharvest handling and
packaging, increases the ease of product transportation, for that remains an area of incessant interest for food
research. The most commonly used traditional methods for drying fruits and vegetables include vacuum
drying, solar drying, Sun drying, freeze drying, fluidized bed drying ,tray drying ,and hot-air drying.
3

4. Over the years
 Fruits and vegetables are very perishable that have enormous industrial and commercial
importance To: preserve its quality attributes, increase shelf life, and reduce transport weight.
 fruit and vegetable can be processed by drying. Over the years, drying techniques have been
widely applied, both industrially and commercially for the processing and preservation of its .
 most of the traditional techniques needs time and energy consuming, and affect important quality
attributes of final products.
 Different novel techniques that involve the application of some of these heating modes or a
combination thereof have recently been developed, specifically for drying of fruits and vegetables.
4

5. Recently
 There has been increased interest in the use of non-thermal drying methods in
combination with other conventional drying techniques for preserving fruits and
vegetables.
 These methods have been reported to enhance the quality attributes of dried products,
reduce drying time and energy demand, and increase the overall drying efficiency.
 In this regard, the development of a cost effective non-thermal hybrid drying systems,
such as combined ultrasound (US) and hot-air drying, ultraviolet (UV) and hot-air drying,
and pulse electric field (PEF) and hot-air drying have recently been researched on.
 These drying techniques have become potential substitute for traditional industrial and
commercial dryers, owing to their advantage of producing quality dried fruit and
vegetable products, with reduced drying time and energy consumption
5

6. in This Presentation
 definition of Non-thermal hybrid drying
 Focus on recent developments of the commonly used non-thermal combined
convective hot-air drying (CHAD) techniques for fruits and vegetables, with
emphasis on drying time, drying rate, quality attributes of products,
 Focus on the primary constraints for industrial application of this technology as the
inadequate medium of transmission for power ultrasound (US), cost of design and
installation, and the limited study on (UV) and PEF assisted CHAD, The necessity
for conducting more detailed studies on non-thermal assisted convective hot-air
drying of fruits and vegetables was emphasized.
6

7. Terminology used in This Presentation
CHAD convective hot-air-drying UVD ultraviolet drying UV ultraviolet
HAD hot-air-drying NT non-thermal technology USD ultrasound drying
UVP ultraviolet power (W) HA hot-air USP ultrasound power (W)
dus
distance between US transducers and
sample (cm)
Pd power density (W) t time (s)
E electric field strength (V/cm) P power intensity (W/m2) W width (m or mm)
λƒ wavelength (μm) frequency(Hz) L* lightness index P power (kW)
RH relative humidity (%) a* redness index Vs sample volume (m3)
Ea activation energy (kJ/mol) b* yellowness index v air velocity (m/s)
MC moisture content (g water/g dry solid) ΔE total color change h thickness (mm)
Va ambient air velocity (m/s)x cwe3 US ultrasound L length (mm)
AH absolute humidity (g/m3) BI brownness index RR rehydration ratio
Ta ambient temperature (°C) VC vitamin C T temperature (°C)
7

8. definition of Non-thermal hybrid drying
 Non-thermal processes, as the name suggest, are processes that do not involve the generation of
heat, but can cause a change in temperature inside a product.
 non-thermal techniques involves technologies that are effective at room or less intense
temperatures. They also stated that some of these technologies could result in the rise in
temperature during processing.
 Hybrid drying involves the combination of two or more different processing unit operation or
drying system either as a single unit or multistage arrangement. The combination of NT and CHAD
can improve and control the lethal influence of CHAD, minimize the severity of each technology
due to the synergetic effect, enhance the final quality of dried product, and higher overall drying
efficiency as compared with utilizing just CHAD.
8

9.  Application of non-thermal (NT) technologies which include ultrasound, pulsed electric
fields, and ultraviolet radiation may cause a change in the temperature inside a product,
but does not generate heat within the product. During non-thermal processing, the quality
of the food product is preserved due to the temperature difference inside the product
which is lower than the temperatures during thermal processing
 Additionally, non-thermal processing does not often rely on limiting heat transfer
coefficients and temperature boundary conditions. Other advantages of non-thermal
techniques include enhanced quality attributes, reduced drying time and increased
processing efficiency.
 The combination of NT and CHAD, otherwise known as non-thermal hybrid drying
provides the synergistic effect during the heat and mass transfer process within a product.
This effect leads to a better quality and stable dried product, increased energy saving,
reduced drying time, and increased drying efficiency
 Recently, several research involving combined non-thermal CHAD, also known as
hurdle technology (Cullen et al., 2012) have been carried out.
9

10. Non-thermal hybrid drying methods used in fruits and vegetables
1- Combined ultrasound and hot-air drying
 Mechanism of operation
 Effect of combined US and CHAD on the drying kinetics and product quality
 Effect of combined US and CHAD on energy consumption
 The advantages and Limitations of using combined US and CHAD in the drying fruits and vegetables
2- Combined pulse electric field (PEF) and hot-air drying
 Mechanism of operation
 Effect of combined PEF and CHAD on drying kinetics and energy consumption
 Effect of combined PEF and CHAD on product quality
 The advantages and Limitations of combined PEF and CHAD drying processes
3- Combined ultraviolet and hot-air drying
 Mechanism of operation
 Effect of combined UV and CHAD on drying kinetics.
 Effect of combined UV and CHAD on product quality
 The advantages and Limitations of combined UV and CHAD drying processes
10

11. 1- Combined ultrasound and hot-air drying
 Ultrasound (US) is a type of sound energy transmitted by waves in the form of pressure
at frequencies of 20 kHz and above .
 US can be categorized into high frequency (low energy, low intensity) at frequencies > 100 kHz,
and low frequency (high energy, high intensity) at frequencies range of 20–100 kHz .
 High frequency ultrasound technology is often applied as an analytical method for non-
destructive quality and process inspection, and control, such as to determine various
food properties, to check the quality of food product, to measure severity of spoilage, to
measure flow rate, and so on
 Low frequency also referred to as “power ultrasound,” produces variety of effects that
results in cavitation (swift development and implosion of gas bubbles), which can
regulate enzymes (activate or inactivate), and enhance the rate of heat and mass transfer
for different postharvest applications on agricultural crops, like drying, freezing and
osmotic dehydration .
11

12. Mechanism of operation
 US basic drying principle is based on mechanical mechanism and less on
heating mechanism, which leads to a reduced drying time without significantly
heating the product
 During US operation, the generated acoustic energy results in periodic
velocities and pulsation of the tissue particles at the interfaces during which the
water molecules bonding with the surface of the product may be broken. Cell
cavitation occurs, leading to diffusion from within the product to the boundary
layers
 added that the series of oscillation results in alternative compressions and
expansions of the product when ultrasonic waves travel through it.
 Combination of US and CHAD can be associated to sound transmission in the air,
liquid or solid.
 The combined US and CHAD technique with airborne transmission medium has
proven to be most likely applied in the drying of fruits and vegetables on a
continuous process in industrial scale, largely due to its positive effect on product
quality, and improved efficiency
12

13.  this process can promote an enhanced drying process
 it is limited by decreased overall drying efficiency.
 On the other hand, the simultaneous and intermittent US and CHAD are often
carried out using the airborne ultrasound air as a means to transmit sound energy.
Fig. Ultrasound in air.
(Adapted from Kowalski & Pawlowski, 2015)
13

14. Fig. 2. Schematic of combined US and CHAD. 1. Fan;
2. Heating unit; 3. Anemometer; 4. Valve; 5. Thermocouple;
6. Sample loading chamber; 7. Coupling material;
8. Pneumatic system; 9. US transducer; 10. Vibrating
cylinder; 11. Drying trays; 12. Weigh balance;
13.Impedance matching unit; 14. Digital power meter; 15.
Power US generator; 16. PC.
 Fig. 2 shows a schematic of a typical US-CHAD combined dryer. It is good to note that
sequential US + CHAD can also be carried out using this set-up .
14

15. Several recent studies have shown that US and HA combined drying is applicable in the drying of fruits and vegetables
published data on combined ultrasound and hot-air drying of fruits and vegetables.
ReferencesSignificant findingsDrying process conditionsCombination modeFruits and vegetables
(Santacatalina
et al., 2016)
The higher the power
level, the shorter the
drying time.
h = 8.8 mm;
L = 8.8 mm;
v = 2 m/s;
RH = 15 ± 5%;
T = −10 °C–10 °C;
USP = 25–75 W
US-HADApples (Malus
domestica cv.
Grany Smith)
(Fernandes,
Rodrigues,
Cárcel,&García
-
Pérez, 2015a)
USP has more effect at lower
velocity and power; at 45 °C and
1 m/s, the D eff was 54% higher
than when drying using HAD
alone.
L = 8.5 mm;
W = 8.5 mm;
h = 8.5 mm;
v = 1–5 m/s;
T = 45–60 °C;
USP = 75 W at 21 kHz
US - HADApples (Malus
domestica L.var.
Royal
Gala)
(Garcia-Perez,
Ortuño, Puig,
Carcel,&Perez-
Munuera,2012)
Reduced drying time by 30–45%
when compared with HAD;
reduction in energy
consumption of about 12–20%
when compared with HAD
L = 80 ± 2.5 mm;
W = 40 ± 2.0 mm;
h = 5.9 ± 0.4 mm;
v = 1.0 m/s;
T = 40 °C;
R.H = 26.5 ± 0.9%
USP = 90 and 45 W
US – HADOranges
Citrussinensis
var.Navelina)

16. Seaweed
16

17. (Schössler et al.,2012)Drying time savings
of 18–23% for US-HAD when
compared
L = 1 cm;
W = 1 cm;
h = 0.5–1 cm;
US - HADPeppers (red bell)
(Kadam,Tiwari,&O'Don
ne-ll, 2015)
Retained the color properties of
seaweed
L = 2–3 cm;
v = 0.3 m/s; US
time = 10 min;
T = 50 °C
USI = 7–75.78 W c-
m −2
US + HADSeaweed
(A.nodosum)
(Liu et al., 2017)Effect of US on sample reduces as
MC decreases;
D ef =1.058×10 −1-
0−5.471×10−10 m 2 /s; better color
preservation and higher RR when
compared to results of HAD.
h = 5 mm;
d = 40 mm;
v = 1 m/s;
T = 40–70 °C;
USP = 30–60 W;
USI = 0.17–0.34 W/cm 2
US-HADSweet potato
(purple-fleshed)
(Fernandes,
Rodrigues, García-
Pérez,&Cárcel,2016)
Reduction in drying time up to 43%
and 65% at 60 °C and 45 °C,
respectively, as compared with
drying using HAD under same
conditions.
L = 15 mm;
W = 15 mm;
h = 10 mm;
v = 1–3 m/s;
T = 45–60 °C;
USP = 75 W;ƒ = 21 kHz
US-HADTomatoes (Solanum
lycopersicum
var.Cerasiforme)
17

18. Effect of combined US and CHAD on the drying kinetics
18
 The effective moisture diffusivity, which increased with increased temperature, were also
higher than that of CHAD alone. The higher reduction in the drying time at low
temperature, is due to the extra energy provided by US during the combined drying process,
which is less intense at higher temperatures than lower ones
 In addition, the reduction in the drying time ( up to 80.3%) also depends on the US power
applied, higher power level results in shorter drying time, The improvement in the drying
rate and time of fruits and vegetables using combined US and CHAD also depends on the
drying air velocity and the type material to be dried. This is evident in the case of combined
US and CHAD drying of lemon as reported by García-Pérez et al. (2007).

19. Figure. Button mushroom slices moisture ratio versus drying time at different pretreatment methods
investigated and fitted with logarithmic model. (a) FID, (b) HAD. Note: FID, far infrared
drying; HAD, hot air drying; CB, conventional blanching; UB,blanching and ultrasound; US1,
ultrasound for 3 min; US2,ultrasound for 10 min.

20.  They mentioned that US power affects the influence of air velocity on drying behavior of
lemon, by reducing the boundary layer thickness. They also observed that US-CHAD
improved drying rate at lower air velocity and reduces the drying rate with increase in air
velocity. This same finding was recently collaborated by Fernandes,., and García-Pérez
et al. (2015a, 2015b). They found that combined US and CHAD has more effect on the
drying rate and time at lower velocity than at high air velocity. A possible explanation for
this idea may be the disruption of ultrasonic field at high air velocities, preventing the
ultrasonic waves from effectively reaching the products.
 When compared to drying using CHAD alone, it was observed that the effective
moisture diffusivity was 54% higher than values of CHAD alone and a 35% reduction in
the drying time when compared to results of CHAD. Similar reduction in the drying time
during US-CHAD as a result of low temperature and air velocity was also observed by
Kowalski and Pawlowski (2015).
20

21. Effective water diffusivity for
a) Mango and b) Tamarillo slices in US air drying

22.  Generally, several authors have also observed the influence of air velocity during combined US and
CHAD on the drying rate and time of various fruits. Taylor et al. (2007) studied the US – CHAD
drying of persimmons. They showed a decrease in the influence of US on the drying kinetics at higher
velocity. García-Pérez et al. (2007) further showed that US-CHAD improved drying rate of
persimmons at lower air velocity. They highlighted two important aspect of US-CHAD drying as air
velocity and material characteristics.
 they further demonstrated that the effect of US power (low air velocity) exist only in low porous
product. Conversely, in highly porous product such as lemon peel and orange, the effect exists even at
high velocity especially when the acoustic energy is low.
 For vegetables, Similar to the effect on fruits as earlier discussed, the authors observed increased
drying rate when compared with CHAD alone. A 30% reduction in the total drying time was also
observed, In addition, US increased the effective moisture diffusivity by 40% when compared with
CHAD alone. The results of their study showed a decrease in the effect of US sonication at higher load
densities due to reduction in transfer area. Increase in the reduction of boundary layer thickness due to
US power and air velocity were also observed.
22

23.  In a more recent study, Liu et al. (2017) observed the effect of USCHAD on the drying of
sweet potato. They observed a reduction in drying time of about 31.5–47.7% at US power
range of 30–60 W, respectively, when compared with results of CHAD. More so, they
observed an increase in the drying rate by 50.8% and 100.8% at 30 W and 60 W, respectively,
compared to results of CHAD alone. They also found that the effect of US-CHAD on sample
decreases as moisture content (MC) reduces. The observed decrease in MC due to US-CHAD
could be attributed to the fact that although the increase of US power could enhance the
drying process, the strengthened effect of US is better when MC is high than at lower MC. At
high moisture content, the free water content in the material is high, aiding the easy
penetration and transmission of ultrasound wave into the material. This increases the pressure
inside the material and causes cavitation; it also causes mechanical effect which eventually
enhances internal mass transfer. Conversely, when the MC becomes low, the resulting
cavitation and mechanical effect of US become weaker, significantly reducing the
strengthening effects of US on moisture diffusion. Further application of US to the product
may result to the loss of products quality and structural matrix. Thus, the need to model and
optimize the US power during combined US and CHAD drying of vegetables.
 Other drying conditions that can affect the drying kinetics of vegetables include temperature,
and material characteristics. Fernandes et al. (2015a, 2015b) showed the effect of drying
temperature on the drying kinetics of tomatoes during combined US-CHAD. The results of
their study showed a reduced drying time up to 43% and 65%, at 60 °C and 45 °C,
respectively, as compared to CHAD under same conditions.
23

24. Figure : shows the moisture progress in drying assays for mango and tamarillo slices. For both
fruits, US application during 5 minutes each half hour, intermittently, at 50°C, presented the
highest reduction in drying time. showed reductions in drying time of 79% for raspberries.
Drying curves of
a) Mango slices b) Tamarillo slices

25. Effect of combined US and CHAD on energy consumption
 To really ascertain the overall drying efficiency of combined US and CHAD, another important
feature to be considered is its energy efficiency. Despite the additional power feed required by US
assisted systems such as combined US and CHAD, a reduced drying time due to accelerated heat
and mass transfer process may cause a corresponding reduction in the amount of energy required
in comparison to CHAD.
 According to García-Pérez et al. (2007), a reduced energy consumption of about 12–20% was
observed during the drying of orange, when compared with CHAD. In a similar study on
combined US-CHAD of oranges, Ortuno et al. (2010) found a reduction in the energy
consumption by 30% compared to CHAD, as a result of corresponding reduction in the drying
time. Sabarez et al. (2012) observed a 42–54% reduction in the energy consumption during
combined US-CHAD drying of apples when compared with results of CHAD. Similarly,
Rodríguez et al. (2014) demonstrated that a reduction in the drying time due to increased drying
rate resulted in a corresponding reduction in the energy consumption rate and increased efficiency
during combined US-CHAD.
 For vegetables, Puig et al. (2012) also observed a great decrease in the energy consumption
during combined US and CHAD of eggplant, as US power was raised due to shorten total drying
time, high rehydration capability and hence reduced energy consumption. In a different
combination approach, Kadam et al. (2015) studied the sequential combined US + CHA drying of
seaweed. They observed that increase in US intensity, led to the reduction in energy consumption
of seaweed when compared with results of CHAD. This can be attributed to the reduced drying
time. Further,
25

26.  Fig. shows the total electrical energy consumption
during drying of potato using different drying
methods (Kroehnke et al., 2014). Although the
ultrasound assisted drying process is more energy-
intensive per unit time (Bantle & Eikevik, 2014;
Kowalski et al., 2017), it requires lesser amount of
energy when compared to CHAD. Kowalski and
Mierzwa (2015) also demonstrated the energy savings
when using combined US-CHAD. They reported the
energy saved when using US-CHAD as compared to
CHAD alone was 5.39 kWh/kg and the energy
efficiency ratio was 10.08%. Although the values
obtained were lower than expected (perhaps due to
heat loss during the experiments and laboratory
apparatus limitations), the results showed that
appropriate application of US-CHAD can reduce
energy demand when compared to drying using
CHAD alone. However, it is not clear if the reduced
energy consumption due to shorter drying time will
results in a more cost-effective process, which is a
basis for further research.
Fig.. Comparison of electrical energy consumption
(Kroehnke, Musielak, & Boratynska, 2014)

27. Effect of combined US and CHAD on product quality
 The demand for mild drying technique have seen the increased interest in combined NT and
CHAD techniques, particularly due to their immense influence on the quality parameters of
fruits and vegetables. Several research and development, have shown that combined US and
CHAD can be used to obtain high-quality dried fruits and vegetables with improved functional
and nutritional properties. As a result, in recent years, combined US and CHAD has become
well established (Lebovka, Shynkaryk, & Vorobiev, 2007). Nonetheless, several changes occur
during the combined US and CHAD drying process of fruits and vegetables. These changes
could affect the quality attributes of the products. The most common quality parameters
associated with dried fruits and vegetables include colour, shape of product, texture, flavour,
microbial load, retention of nutrients, and rehydration properties (Ratti, 2005).
 Rodríguez et al. (2014) showed that the quality attribute of apple was enhanced during the
simultaneous combined US-CHAD. In the same manner, Fernandes et al. (2015a, 2015b)
observed an increase in the availability of Thiamine (B1), Riboflavin (B2), Niacin (B3),
pantothenic acid (B5) and Pyridoxine (B6), and improve vitamin E and carotenoid retention,
thus improve overall nutritional quality. Similar results on the improvement of the quality
attributes of apples using combined US-CHAD have been reported.
27

28.  Furthermore, Liu et al. (2017) observed that US-CHAD had pronounce effect on the
structural properties of the sample tissue, resulted in better colour preservation and higher
rehydration rate when compared to results of CHAD.
 Kadam et al. (2015) showed that US-CHAD led to great improvement in the color
properties of seaweed. Fernandes et al. (2015a, 2015b) also observed an increase in the
availability of B1–B6, increase in vitamin E and carotenoid retention, of tomato during
US-CHAD. Conversely,
 Kowalski et al. (2017) observed the overall color change of apple dried using combined
US-CHAD was slightly higher for than those dried using CHAD alone, but low value of
water activity further validate the use of combined US-CHAD in microbiological stability.
 Generally, at low temperature, combined US and CHAD has been shown to results in
better quality of final product. However, more studies need to be carried out to determine
the effect of drying conditions of physiochemical, nutritional and functional properties of
fruits and vegetables during combined US and CHAD.
28

29. Table . Effects of different pretreatment methods on texture,shrinkage, and rehydration of dried
button mushroom slices.
Texture
Drying methods Hardness (g) Crispness (g)
Shrinkage (cm3/100
cm3)
FID
Untreated 457.47 ± 41.98b 276.67 ± 27.61b 91 ± 1.05b
CB 599.47 ± 39.95a 379.33 ± 50.12a 93 ± 2.15a,b
UB 523.73 ± 51.38b 371.13 ± 45.54a 94 ± 2a
US1 375.47 ± 34.46c 154.53 ± 34.39c 85 ± 2.1c
US2 HAD 331.33 ± 55.68c 145.53 ± 31.48c 86 ± 1.5c
Untreated 482.67 ± 51.3c 298.53 ± 22.77c 90 ± 0.96b
CB 608.13 ± 28.96b 404.8 ± 74.5a 92 ± 1.15a
UB 579.87 ± 59.46a 402.8 ± 70.46a 92 ± 2.07a,b
US1 480.53 ± 32.33c 240.4 ± 33.43c 84 ± 3.06c
US2 477.33 ± 64.73b 225.07 ± 21.28c 84 ± 2.06c
Means within columns with different letters are significantly different (p < 0.05).FID, far infrared drying; CB,
conventional blanching; UB, blanching and ultrasound; US1, ultrasound for 3 min; US2, ultrasound for 10 min;
HAD, hot air drying.
29

30. Figure 3. Microphotographs (500×) of the button mushroom slices. (A) FID and (B) HAD.
Note: a, untreated; b, CB; c, UB; d, US2; FID, far infrared drying; HAD, hot air drying; CB,
conventional blanching; UB, blanching and ultrasound; US2, ultrasound for 10 min.
30

31. The advantages of using combined US and CHAD in the
drying fruits and vegetables
 Significant reduction in the total drying time
 Increase in drying rate especially during the initial drying period
 Enhanced diffusion of heat and mass transfer
 Effective at low air velocity, low temperature, low US power and high
MC of the product.
 Better product quality and reduced energy savings.
31

32. Limitations of Combined US and CHAD
 For an industrial application, US is better applied during the initial drying period (where the
drying rate is high), further application of US could result in wastage of energy as sonic waves.
 Inadequate medium of transmission for power ultrasound • High US frequencies (over 16 kHz)
can cause hearing loss in operators if safety precautions are not taken.
 The US intensity required to achieve significant mass transfer enhancement can lead to the
formation of free radicals • High capital cost of design
 Practical difficulties for industrial-scale requirement
 Process conditions and complexity with equipment design.
Although the above limitations, combined US and CHAD could still be commercially viable
particularly for food industries that require short drying time, better product quality and higher
product throughput, notwithstanding the high cost of equipment design and installation.
32

33. 2-Combined pulse electric field (PEF) and hot-air drying
 Pulse electric field (PEF) comprises the use of very short pulses (μs) of high voltage
(kV/cm) to agricultural food materials kept between electrodes.
 PEF is a non-thermal technology since heating is not the main mechanism of operation.
 In the application of PEF to agricultural crops, the electrical properties must be
determined because PEF is often applied on materials with low electrical conductivity,
high electrical resistivity, and those free of bubbles, although it can also be efficiently
applied on materials with high conductivity only for a short period (micro-pulses).
 In parallel to thermal drying, the combined effects of PEF and CHAD may results in
enhancement of the drying kinetics due to the synergistic effect.
33
Schematic diagram of
a pulsed electric fields operation

34. Mechanism of operation different mechanism for PEF application on food.
 Zimmermann (1986) argued that during PEF treatment,
compounds of opposite charges in the food tissue is
accumulated due to increase in the trans-membrane potential
of cells. A continues increase in the cells trans-membrane
increases the pressure on the cell, decreasing the membrane
thickness and eventually results in pore formation.
 On the other hand, Tsong (1991) suggested the osmotic
swelling of cell results in the weakening of the membrane
until it burst. This process is due to electroporation in the
protein channels and lipid domains
 Although the mechanism of PEF on food is not well
understood, generally the mechanism could be called an
electroporation or electro Permeabilization.
 While there is no well-defined explanation in scientific
literature linking PEF treatment mechanism to the drying of
agricultural food product, PEF process have been used to
enhance the drying of fruits and vegetables.
34

35. 35
 The combination of PEF and CHAD can be based on Poration theory., during electro
Poration of the product tissue, increase in the formation of pores occurs.
 This reduces internal cell resistance and increases the heat and mass transfer process on
the application of hot-air (HA).
Fig.
(a)A schematic set-up of sequential PEF + CHAD (b) Scheme of the PEF + HAD chamber.

36. Published data on PEF combined hot-air drying of fruits and vegetables
Vegetables and Fruits Combination mode Drying process conditions Significant findings
Apples
(Malusdomestica
‘ Idared’ )
PEF + HAD
h = 5 mm; d = 35 mm; v = 2 m/s; T =
70 °C; E = 18.75 kV/cm; n = 5; Pt =
1 s
Reduction in the drying time by 12% and
increase in Deff by 20% when compared to
HAD alone
Beetroots (red)
PEF + HAD
h = 5 mm; d = 24 mm; T = 30– 100
°C; E = 200– 1000 V/cm; n = 5– 500
An increase in the moisture diffusivity;
also, colour quality was also preserved;
Higher tissue shrinkage, as well as in longer
time of rehydration
Carrot (cv.Baltimore)
PEF + HAD
hc = 5 ± 0.7 mm; d = 30 ± 0.5 mm; v
= 2 m/s; Pt = 2 s; T = 70 °C; E = 5
kV/cm
The shortest drying time was at n = 10
;decrease in the L* value of up to 25.3%.
Potatoes (Agata)
PEF + HAD
d = 40 mm;h c = 10 mm; v = 6 m3
/h; T = 30– 70 °C; E = 500 V/cm;
n = 1– 30,000
Deff increases with increase degree of PEF
36

37. Effect of combined PEF and CHAD on drying kinetics
and energy consumption
 In spite of the limited study on PEF assisted CHAD of fruits and vegetables in recent years, some
study have shown promising results as can be seen in last Table investigated the combined PEF +
CHAD drying of potato tissue.
 The results of their study showed that PEF + CHAD enhanced drying rate. The contact between the
PEF electrode and the sample tissue reduces the effectiveness of the process. The effective moisture
diffusivity increases with increased degree of PEF.
 They also observed that drying at low temperature resulted in improved drying rate when compared
with drying at high temperature.
 It was noticed that the increased rate of diffusion depends on the drying conditions used (PEF process
parameters) and the type of agricultural crop to be dried.
 Wiktor et al. (2013) observed that PEF + CHAD enhanced drying process when compared with drying
using CHAD alone. A reduction in the drying time by 12%, increase in effective moisture diffusivity
by 20% and reduction in the overall energy consumption were observed when compared to CHAD
alone.
37

38. 38
Energy required for cell disintegration
with different techniques for Potato tissue

39.  Wiktor et al. (2015) observed a reduced process time by 6.2–8.2% compared with CHAD alone,
during the PEF + CHAD of carrot. The shortest drying time occurred at pulse number of 10, which is
not the highest number of pulse time, suggesting that there are optimal parameters for the application
of PEF + CHAD for every fruits and vegetables
 Shynkaryk et al. (2008) studied the effect of combined PEF + CHAD of red beetroot tissue different
drying temperatures (30–100 °C). They observed that combined PEF + CHAD allowed reduction of
drying time and the drying temperature by 20–25 °C.
 There are limitation in the application of combined PEF and CHAD for drying fruits and vegetables.
In terms of energy efficiency, Raso and Barbosa-Cánovas (2003) reported the energy requirement for
water evaporation of food during PEF assisted CHAD, which depends on temperature and pressure is
between 2.5 and 2.7 MJ/kg, whereas the total energy input required for CHAD alone is between 4
and 6 MJ/kg of removed water. This further proves that combined PEF and CHAD has the potential
of reducing the total energy required for drying fruits and vegetables, due to increased mass transfer
rates and reduction in drying time.
39

40. Effect of combined PEF and CHAD on product quality
 only a few studies on the effect of combined PEF and CHAD on quality parameters of fruits and
vegetables have been reported in the literature in the past 9 year, thus a basis for future research.
A very important quality selection criteria is the colour of a product (Barbosa de Lima, da Silva,
Pereira, dos Santos, & Barbosa de Lima, 2015). Wiktor et al. (2015) demonstrated a decrease in
the lightness (L*) value of carrot up to 25.3%, when compare to results of CHAD, due to
electroporation phenomenon.
 In contrast, Shynkaryk et al. (2008) further demonstrated that PEF + CHAD results in
improved colour attributes of beetroots when compared to the results of CHAD.
 Another relevant quality factors are the shrinkage effect and rehydration compliance. A
technology that will reduce the shrinkage of fruits and vegetables during drying is
indispensable. The shrinkage effect and rehydration capability can be also used as a quality
indicator during the drying of fruits and vegetables, Shynkaryk et al. (2008) reported that
combined PEF + HAD resulted in greater degree of tissue shrinkage and hence increase in
rehydration time.
 All the above observations are useful for future research.
40

41. some of the advantages of combined PEF and CHAD drying processes
 Combined PEF and CHAD drying improves the colour of fruits and vegetables.
 Combined PEF and CHAD causes uniform rise in product temperature.
 Works better for thermal sensitive products at moderate temperatures.
This method is promising in the food and agricultural processing
industries to the following reasons:
 The potential for saving energy and minimising product quality damage. For example, in
the bakery industry, the energy of consumption in the production of crackers and cookies
can greatly be reduced and the final product quality enhanced.
 higher quality of products, in terms of microorganism inactivation, nutritional and
functional properties. This is also very useful in the industrial production of premium foods.
 The uniform moisture distribution experienced when using this novel non-thermal method
is particularly important for industries requiring uniform drying.
 This technology can also result in minimal alteration in product taste. This also useful in the
industrial production of premium snacks and cookies.
41

42. Limitations of Combined PEF and CHAD
 Inadequate proper processing conditions
 Complex equipment design and installation
 Suitability and electrical properties of fruits and vegetables
 Increased product damage electrically, with increased resistance of smaller cells.
42

43. 3-Combined ultraviolet and hot-air drying
 Ultraviolet (UV) radiation falls in the electromagnetic spectrum with
wavelengths between 100 and 400 nm.
 UV technology is a non-thermal technology that is free of chemicals and
waste discharges, making it a very ecological friendly energy source.
 In the last decade, UV light radiation has been used in pharmaceutical,
electronics and aquaculture industries as a medium of disinfection,
inactivation of microorganisms in liquid food, and as post-harvest
treatment of fruits and vegetables .
 , there are no much reports on the application of UV in the convective
drying of fruits and vegetables.
43

44. Mechanism of operation
 UV-C (254 nm) light has been reported to be the best in the treatment of food materials,
because the peak germicidal effect occurs at wavelength 254 nm.
 UV-C assisted CHAD, Phimphilai et al. (2014) observed that UV-C assisted hot-air drying
was able to lower microbial load thereby assisting the drying process,
 The scanning electron microscope results of their research further revealed that samples
dried using UV-C combined CHAD showed deeper shell layers which caused higher rate of
moisture evaporation as compared to drying using CHAD.
 Generally, during UV-C treatment process, microorganisms that are exposed to the
UV-C light are affected at the DNA, thereby inhabiting microbial growth. The formation of
pyrimidine dimers changes the structure of DNA helix and block microbial cell replication.
Thus, the injured reproductive systems of cells, which become unable to repair, leads to the
death of cells. This process could eventually result in increased pore formation, thereby
increasing the rate of moisture transfer on the application of other sources of heat.
44

45. Effect of combined UV and CHAD on drying kinetics
 The application of combined UV and CHAD to fruits and vegetables has not been widely investigated (see
Table) despite the numerous advantages in UV treatment of fruits and vegetables.
 Kose and Erenturk (2010) further observed a decreased drying time by up to 38% when compared to results of
CHAD alone.
 Phimphilai et al. (2014) demonstrated that the sequential UV and CHAD (UV + CHAD) had significant
influence on the drying rate of long an at a high temperature (75 °C). They noticed a significant reduction of the
total drying time when compared to drying using CHAD alone. This may be due to the deeper shell layers
caused by the UV light on long an tissue leading to higher evaporation of moisture, shorter drying time and
reduction in the energy consumption.
45

46. Published data on UV combined hot-air drying of fruits and vegetables
Significant findingsDrying process conditionsCombination modeVegetables and Fruits
UV had effect on the drying rate at higher
temperatures (75 °C)
T = 60– 75 °C; UVP = 60 W;λ= 254
nm; duv = 2.5 cm; UVet = 70 min
UV + HADLongan (cv.Daw)
Decreased drying time by up to 38%
when compared to results of HAD alone
v = 0.5– 1.5 m/s; T = 60– 80 °C; UVP
= 15 W; duv = 15 cm
UV– HAD
Mistletoe
46
Fig. schematic of UV and HA combined dryer

47. Effect of combined UV and CHAD on product quality
 In the case of UV assisted CHAD of fruits and vegetables, only 2 articles were reviewed.
Nevertheless, Kose and Erenturk (2010) was able to demonstrated that combined UV – CHAD
can results in lower a*/b* values and higher L* values of Mistletoe. The quality of dried products
when using this technology may effectively depend on the dosage (intensity x drying time) of UV
radiation been supplied. Again, more study on the use of combined UV and CHAD is required.
47

48.  This technology, when fully developed, has the potential to become an environmental friendly, easy
to operate, cost and energy effective drying technology. Other advantages of using combined UV
and CHAD technology in the drying of fruits and vegetables include:
 Higher drying rate
 Reduction in drying time
 Reduction in energy consumption
 Easy and affordable to design and install
 Better product colour when compared with drying using CHAD
Limitations of Combined UV and CHAD:
 Drying mechanism is not yet understood
 No specified process conditions for achieving optimum result
 Still in the early stages and needs further research before acceptability
48

49. Current status and challenges of combined NT and CHAD
 One common drawback associated with the application of all the combined non-thermal and convective
hot-air drying technology reviewed is the non-standardized reporting of methodology and drying
parameters. This is largely because current investigations are still at the experimental stages, carried out at
laboratory scale.
 is for future research and development. In terms of the adoption of combined PEF and CHAD, and UV and
CHAD for fruits and vegetables, the efficiency and adaptability of the technology is currently being
investigated as most of the study are in the experimental stages. In view of this, more research and
development activities are required to understand, optimize, and apply this complex drying technique to its
full potential. Aside understanding the drying mechanism of combined PEF and CHAD of fruits and
vegetables (e.g. effect of electroporation) (Wiktor et al., 2015),
 another challenge to the development of this technology is the cost of operation due to limited amount of
product to be dried at a time. Also, the effect of this drying method (PEF and UV assisted CHAD) on
quality attributes of fruits and vegetables need to be studied and validated to gain popularity and broaden
the category of non-thermal assisted processed commercial products.
49

50.  there are some drawback that must be addressed before it can widely be developed and deployed
industrially. As earlier discussed, one of the major drawback is the medium of energy transmission
 Although , more study need to be done to enlarge the penetration depth of cavitation, and automate
the process so as to further enhance its efficiency and adaptability.
 Additional challenges for industrial combined US and CHAD are the developments of the
heterogeneous moisture profiles in sequential drying and the high US extra energy in the system.
 On the other hand, the effect of drying conditions of the drying kinetics of fruits and vegetables has
shown that the air velocity, temperature, power, intensity, and material structure largely affect the
rate and efficiency of drying. For an improved efficiency, modelling and optimization is required.
 Considering the design and set-up of combined US-CHAD, the modelling process is a complex
phenomenon consisting of the cavitation phenomenon, medium of transmission, temperature
profile of the product, shrinkage phenomenon, correlation between the different drying conditions
(air velocity, temperature, power, and material structure) and type of combination mode. Thus, the
application of this technology is still limited by inadequate modelling information and data, which
can be a basis for future research and development.
50

51. Conclusion
 Recent advances of drying technologies in agricultural, process and food engineering research
and development for preserving fruits and vegetables has gained increased interest as a
potential method to replace, at least partly, the conventional preservation methods. The recent
application of non-thermal assisted technologies (ultrasound, pulse electric field and
ultraviolet technologies) with hot-air drying of fruits and vegetables are presented in this
paper. The findings of this study have demonstrated that these techniques provide great
potential in the development of an environmental friendly drying technology.
 The application of the combined non-thermal and convective hot-air drying produced better
quality of dried products, with great retention of colour and nutritional attributes. In addition,
combined non-thermal ,and convective hot-air drying are cost effective alternate systems to
drying systems with single mode. Therefore, an optimal drying system for preserving fruits
and vegetables is a system the reduced the drying time and energy consumption, lower
operating cost, and with minimum reduction in the final quality of dried products. In this case,
both the combined ultrasound and convective hot-air drying, and combined pulse electric field
and convective hot-air drying are therefore ideal optimum advanced drying systems.
51

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55. Thanks