Application of Infrared Heating for Roasting Nuts

Abstract

Roasting is a key process in production of nuts. Improving the flavor and crispiness of texture in nuts is considered as a purpose of roasting, which increases the overall acceptance of the product. This review aims to introduce the infrared method as a new technique of roasting and evaluate the quality characteristics of some nuts after infrared roasting. Usually, the traditional roasting methods are time-consuming with high energy consumption and low production efficiency. One of the best ways to decrease roasting time and energy consumption is to provide heat by infrared (IR) radiation. However, the low penetration power of infrared radiation is one of the limitations of this method. The combination of infrared with other thermal methods can overcome this limitation. Studies have been done on roasting of nuts and other foods by different IR roasting methods such as IR, IR-hot air, and IR-microwave roasting methods. This paper reviews the effect of different IR roasting methods on the quality characteristics of roasted pistachio, peanut, hazelnut, almond, sunflower, soybean, and other food products. IR heating has been applied successfully to the roasting of some nuts. The use of infrared roasting has several advantages in comparison with traditional convective roasting methods. According to the results of most of these studies, the combination of infrared with other thermal methods to roast nuts has distinctly improved the potential of the technology as compared to the IR roasting alone.

Full text

Review Article
Application of Infrared Heating for Roasting Nuts
Hadi Bagheri
Faculty of Food Science & Technology, Gorgan University of Agricultural Sciences and Natural Resources, Gorgan, Iran
Correspondence should be addressed to Hadi Bagheri; bagherihadi51@yahoo.com
Received 3 June 2020; Revised 5 July 2020; Accepted 9 July 2020; Published 4 August 2020
Academic Editor: Francisca Hern´andez
Copyright ©2020 Hadi Bagheri. is is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Roasting is a key process in production of nuts. Improving the flavor and crispiness of texture in nuts is considered as a purpose of
roasting, which increases the overall acceptance of the product. is review aims to introduce the infrared method as a new
technique of roasting and evaluate the quality characteristics of some nuts after infrared roasting. Usually, the traditional roasting
methods are time-consuming with high energy consumption and low production efficiency. One of the best ways to decrease
roasting time and energy consumption is to provide heat by infrared (IR) radiation. However, the low penetration power of
infrared radiation is one of the limitations of this method. e combination of infrared with other thermal methods can overcome
this limitation. Studies have been done on roasting of nuts and other foods by different IR roasting methods such as IR, IR-hot air,
and IR-microwave roasting methods. is paper reviews the effect of different IR roasting methods on the quality characteristics of
roasted pistachio, peanut, hazelnut, almond, sunflower, soybean, and other food products. IR heating has been applied suc-
cessfully to the roasting of some nuts. e use of infrared roasting has several advantages in comparison with traditional
convective roasting methods. According to the results of most of these studies, the combination of infrared with other thermal
methods to roast nuts has distinctly improved the potential of the technology as compared to the IR roasting alone.
1. Introduction
Roasting is known as a thermal time-temperature-depen-
dent process at high temperatures (>150°C). It leads to the
production of high value-added products with better flavor
and crispier texture [1]. Along with salting and drying,
roasting is one of the main unit operations used for pro-
cessing nuts (Figure 1). is operation is aimed at improving
appeal and taste to consumers. Roasting through physico-
chemical reactions (nonenzymatic browning as Millard
reaction) and heat and mass transfer leads to an improve-
ment of color, flavor, and textural of nuts [1].
1.1. Purpose of Roasting. Improving taste, flavor, color, and
textural is the main objective of roasting. Furthermore,
removing unwanted volatile acids; lowing water content;
destroying troublesome microbes, toxicant material, and
food pollution; and inactivating detrimental enzymes (en-
zymes that cause nutrient loss) are other purposes of
roasting [2]. Moreover, some compounds such as fatty acids,
peptides, free amino acids, and vitamins are altered during
the roasting process [3, 4]. Starch gelatinization and protein
denaturation are the most critical changes in grains and
legumes during the roasting process [5].
1.2. Conventional Roasting Methods. Commonly hot air, hot
pan, and oven are basic ways for roasting nuts. Usually, these
roasting methods are time-consuming and have high energy
consumption and low production efficiency [6]. Hot air
roasting is one of the simplest convective methods of heating
with low operating costs and is commonly applied for
roasting of nuts. However, this system requires high thermal
energy and extended time for roasting and results in adverse
changes in the final product, mainly due to the Maillard
reaction [4, 7].
In conventional roasting methods, the exterior surface of
the nut is overroasted, while the center of the nut is not
perfectly roasted. is can cause nonuniform roasting,
burned surfaces, and development of unpleasant aroma and
flavor and bitter burned taste. To overcome nonuniform
Hindawi
Journal of Food Quality
Volume 2020, Article ID 8813047, 10 pages
https://doi.org/10.1155/2020/8813047

roasting and its drawbacks, novel methods such as infrared
heating have the potential to improve roasting behavior.
Infrared radiation can significantly reduce the roasting time
of nuts by roasting the thin layer of substance [8].
Unfortunately, very few studies have been conducted on
the use of infrared for roasting nuts, and there are no review
articles about infrared roasting. us the main objectives of
this review were (1) to introduce the infrared heating as a
new method of roasting and (2) to evaluate the quality
characteristics of some nuts after IR roasting.
1.3. Infrared Radiation. Infrared (IR) roasting has gained
popularity as a promising alternative technique for roasting
of nuts and seeds because of its advantages like lower energy
cost, high heat efficiency, compact size of the equipment, and
high diffusion coefficient [9]. Infrared is energy in the range
of the electromagnetic spectrum between microwaves and
visible light. IR has frequencies from about 30 THz up to
about 430 THz and wavelengths of about 0.75 to 1000 μm
(Figure 2) subdivided into short-wave IR (0.75–2 μm near
infrared), medium-wave IR (2–4 μm mid-infrared), and
long-wave IR (4–1000 μm far infrared) [10, 11]. For pro-
cesses such as drying, roasting, thawing, baking, pasteuri-
zation, and cooking, FIR heat can be used, which has a
wavelength between 4 and 1000 μm [11].
Using IR heating in roasting is newly of special interest
due to the development in radiator construction. Effec-
tiveness is the capability of producing a desired result or the
ability to produce desired output. IR heating effectiveness is
between 80% and 90%, the emitted radiation is in narrow
wavelength range, and they are miniaturized [12].
1.4. Mode of Heating. IR roasting methods have some basic
differences in the mode of heating. In hot air roasting, heat
energy generated is transferred to the surface of the material
by convection which is then conveyed internally by thermal
conduction [13]. In IR roasting, the material is exposed to IR
radiation which interacts, penetrates, and transfers thermal
energy in the form of electromagnetic waves throughout the
material. Hence, heating occurs uniformly throughout the
food mass in IR roasting [9].
1.5. Advantages and Disadvantages of Infrared Rays.
Continuous and uniform distribution of IR energy and
direct transfer of radiation from IR emitters to the product
surface without the need for any physical environment cause
the production of high-quality food with minimal energy
consumption. ese are some advantages of infrared heat-
ing. Also, high degree of process control, an alternate source
of energy, possibility of selective heating close-packed
configurations and different types of IR emitters, and en-
vironment-friendly energy are other advantages of this
method (Figure 3) [13, 14]. e low penetration power of
infrared radiation is one of the limitations of this method.
Also, prolonged exposure may cause fracturing in biological
materials, and insensitivity to the reflective properties of the
coating is another limitation of this technology [15, 16].
In recent years, the use of infrared for roasting nuts and
beans has attracted the attention of researchers and has
become particularly popular [17]. Due to advances in the
construction of emitters, the use of IR heating for roasting
nuts has grown significantly [18]. Roasting of nuts and other
food products is done with IR roasters (Table 1). As shown in
Table 1, the different types of nuts and other foods roasted by
infrared heat and acceptable results have been reported by
researchers.
1.6. Heat Transfer during Infrared Roasting. IR heating has
demonstrated the advantage of efficient heat transfer to food
products with reduced processing time and energy costs.
Infrared (IR) radiation is energy in the form of electro-
magnetic wave and is more rapid in heat transfer than
convection and conduction mechanisms.
e infrared radiation heat transfer rate (1) between the
infrared emitter and the sample surface, q
0
, is given by [33]
q0�σT4
IF −T4
S
 􏼁
1−εIF/AIF εIF
 􏼁+AIFFs,IF +1/ 1/AIF FIF,w+1/ASFW,S
􏼐 􏼑􏼐 􏼑􏼐 􏼑􏼐 􏼑−1+1−εs/Asεs
 􏼁􏼒 􏼓.(1)
erefore, radiation heat transfer flux (2) between the
emitter and the sample is given by [34]
qf�q0
A0
,(2)
where ε
IF
is the infrared emitter emissivity, ε
s
is the emis-
sivity of the sample, T
IF
is the temperature of the emitter; T
s
is the temperature of the sample surface; σis Ste-
fan–Boltzmann radiation constant (5.67 ×10–8 W m
−2
K
−4
),
A
s
is the surface area of the sample, and A
IF
is the area of the
infrared emitter.
F
s,IF
is the fraction of energy between the IR emitter
surface and sample surface, F
IF,w
is the fraction of energy
between the emitter surface and the wall surface, and F
w,s
is
Salting
Drying
Roasting
Figure 1: Processing steps and preparation of roasted nuts (unit
operations).
2Journal of Food Quality

the fraction of energy between the sample surface and the
wall surface.
e heat transfer coefficient, h
r
(W/m
2
K), is calculated
using the following equation:
hr�q0
AIF TIF −Ts
 􏼁.(3)
2. Trends and State of the Art on Infrared
Roasting Technology
Since the penetrating power of infrared rays is limited to the
depth of nuts, the combination of infrared with other
thermal methods such as hot air, microwave, vacuum, and
other states of convection and conduction can overcome this
limitation. e capability of the combination of infrared rays
with other roasting methods is weighed as one of its
outstanding features. Reducing roasting time and in-
creasing roasting efficiency are advantages of combining
IR with another heating method. e combination of
infrared and hot air method has been extensively used for
drying and roasting agricultural products, including or-
ganic blackberry [16], potato chips [35], sponge gourd
slices [36], whole longans [37], pineapple rings [38], and
murta berries [39]. e combination of these thermal
methods intensifies the transfer of mass and heat, thus
reducing the roasting time and energy consumption and
increasing production efficiency [40, 41]. However, in-
frared roasting is recognized to be a talented novel method;
it is not suitable for roasting all nuts due to restriction of its
penetrating power [42], so combining infrared and other
roasting methods can be more efficient and helpful because
it provides synergistic results and is considered as a
currently known solution [43].
Advantages
of IR
heating
1
High-quality
food
High energy
efficiency
Compact
design
4
Environment
friendly
Precise
controlling
Short process
time
6
2
3
5
(a)
Limitations
of IR
heating
1
Low
penetration
power
Prolonged
exposure causes
fracturing
Not sensitive to
reflective
properties of
coating
3
2
(b)
Figure 3: Some advantages and limitations of IR heating used for roasting nuts and other foods.
Gamma rays
1019 1018 1017 1016 1015 1014 1013 1012 1011
10–5 10–4 10–3 10–2 10–1 1101102103104
Microwave
Frequency (Hz)
Wavelength (μm)
InfraredX-ray Ultraviolet
Visible
Figure 2: Electromagnetic radiation spectrum and wavelength range.
Journal of Food Quality 3

2.1. IR-Microwave. One of the problems associated with
microwave roasting is that the surface temperature is higher
than the inner parts of the food, which results in over- or
under-roasted food [44]. erefore, combining this method
with other roasting methods such as infrared can be useful
(Figure 4). Uysal et al. [23] studied the application of mi-
crowave-infrared method for roasting hazelnut. eir results
showed that the roasting time of the hazelnuts in micro-
wave-infrared method was deficient compared to the con-
ventional method. e quality of roasted hazelnuts at the
optimal point in terms of color, texture, moisture content,
and composition of fatty acids was similar to the quality of
roasted samples by conventional methods.
2.2. IR-Hot Air. e lack of uniform distribution of tem-
perature in the product is one of the main problems of hot
air thermal processes. e combination of hot air and in-
frared heating for roasting is much more efficient than using
either of these methods alone (Figure 5). A combination of
IR with hot air provides the synergistic effect, resulting in an
efficient roasting process [13, 45]. Bagheri et al. [20] com-
bined hot air and infrared heating for roasting peanut
kernels. ese researchers showed that when infrared and
hot air were combined for roasting peanut kernels, the
energy consumption was reduced with good quality of
peanut. e use of hybrid infrared radiation and hot air
decreases the energy requirement by 31% compared to hot
air alone.
Yang et al. [6] developed two new roasting methods for
almonds: infrared roasting; sequential infrared and hot air
roasting (SIRHA). Compared to traditional hot air roasting,
SIRHA heating can produce roasted almonds, with up to
30–70% reduction in processing time, and meet pasteuri-
zation requirements for producing medium degree roasted
almonds at 130, 140, and 150°C. In this study no significant
difference (P>0.05) was observed in sensory quality of
medium roasted almonds processed with different roasting
methods. ey pointed out that the SIRHA roasting is a
promising new method for the production of dry-roasted
pasteurized almonds.
3. Roasting of Some Nuts
3.1. Pistachio. Pistachio is one of the most popular edible
nuts in the world, which has valuable chemical and anti-
oxidant compounds. Pistachio has high contents of nutri-
tional compounds such as monounsaturated fatty acids,
vitamins, minerals, sterols, and polyphenols [46–49]. In
addition to having a pleasant taste, pistachio kernels as a
functional food have been welcomed by consumers due to
their significant effects on health, especially the human
cardiovascular system [34].
A large percentage of pistachios are consumed as salted
and roasted snacks and confections. Roasting is one of the
essential processing methods which is widely used in the nut
industry to improve the flavor, color, texture, and overall
acceptability [1]. Four Iranian commercial pistachio kernels
were roasted by Morshedi et al. [19] using an infrared
roasting method. e roasting process was optimized by
response surface methodology. e responses were chosen
based on different aspects of quality factors: texture, color,
taste, and time of roasting. e sample’s first fracture point
was in the range 20–40/5 N, second fracture point 37–55 N,
Table 1: Application of different IR roasting methods for roasting nuts and other food products.
Nuts IR
type Aims References
Pistachio kernel IR Studying roasting optimum conditions of four Iranian commercial pistachio
kernels Morshedi et al. [19]
Peanut kernel
IR Studying optimum conditions roasting
Bagheri et al. [20, 21]IR-
HA Studying quality properties and energy consumption
Hazelnut
IR Monitoring quality properties of roasted hazelnuts during storage Belviso et al. [22]
IR-
MV Optimizing microwave-infrared roasting Uysal et al. [23]
Almond IR Infrared heating for dry-roasting and pasteurization of almonds Yang et al. [6]
Wild almond IR Evaluating physicochemical characterization Mokhtari & Ziaiifar [24]
Groundnuts IR Evaluating groundnuts quality Kumar et al. [25]
Soybean snack
IR Modeling infrared roasting using artificial neural network (ANN) Bagheri & Kashaninejad
[26, 27]
IR-
HA Investigating the kinetic modeling of mass transfer during roasting
Sunflower
kernels IR Evaluating quality characteristics and engineering of infrared-roasted sunflower
seed kernels by RSM Mosayebi et al. [28]
Rice IR Designing a roasting machine using infrared rays and evaluating roasted rice
qualities
Laohavanich & Yangyuen
[29]
Cocoa IR Evaluating physicochemical characterization Rojas et al. [30]
Sesame IR Evaluating formation of sesamol and quality of defatted flours Kumar et al. [31]
Buckwheat IR Evaluating antioxidant activity, phenolic composition, and Maillard reaction
products Bhinder et al. [9]
Black cumin
seed IR Assessing the impact of infrared roasting on the oxidative stability and other
chemical properties Suri et al. [32]
4Journal of Food Quality

browning index 38–41, roasting taste score 4–9/12, and
roasting time 127–746 S, in the optimum points. A full
quadratic model was fitted for responses by considering trial
and error. At last, results showed that optimized points were
different for every cultivar. e fitted model and experi-
mental interventions had a good correlation (P≤0.05).
Considering final product quality, it seems that IR roasting
can be a useful method for pistachio nut kernel and can
reduce the processing time by at least 50%.
3.2. Peanut Kernel. Peanut (Arachis hypogaea L.) is a nu-
tritious grain that is high in protein and fat (containing
47–50% fat, 25–30% protein) and is considered an important
nutrient source for humans. It belongs to the Leguminosae
family [50], and it is the second harvested legume after
soybeans [51]. Commonly, peanuts are known as nuts, al-
though peanuts are legumes. Also, the peanut is known as
the groundnut [50]. In addition to using peanuts for making
oil, peanuts as a cheap protein source have become a snack
due to their unique taste and numerous nutrients [51].
Roasting can change low-value raw materials to expensive
products, and roasted peanuts are one of the valuable snack
foods whose quality is directly affected by roasting [52].
Roasting peanut kernel under infrared and infrared-hot air
system was studied by Bagheri et al. [20, 21]. eir study
showed that, with increasing temperature, power, and time,
the moisture content, solid soluble content, pH, compressive
energy, and hardness decreased and browning index, total
phenolic compounds, and total acceptance of peanuts ker-
nels increased during the roasting. After the roasting pro-
cess, the hardness reduced from 91.31 N to 33.86 N; also, the
total color difference rose from 2.87 to 19.33. e highest
value of specific energy consumed in the roasting process
was related to roasting process at 120°C and 130 W for
30 min, and roasting at 100°C and 200 W for 10 min had the
lowest value of compressive specific energy. A combination
of infrared and hot-air-produced high-quality roasted
peanuts, compared to conventional methods, had lower
energy cost and shorter roasting time; therefore, it could be
considered as a novel method for the peanut roasting
industry.
Pulsed infrared roasting of groundnuts and its quality
were studied by Kumar et al. [25]. Infrared roasting sig-
nificantly reduced the roasting time as compared to other
roasting methods (33% and 60% less compared to sand and
drum roasting, respectively). In terms of color parameters,
FFA, and texture, roasting at 178–188°C for 6.8–9.2 min
constitutes the best conditions for roasting groundnuts. Still,
in terms of sensory characteristics, the best conditions for
roasting were 180°C and 8 min. Infrared can be used to roast
groundnuts, and pulsed infrared could be considered as a
promising technique for roasting of groundnuts.
3.3. Hazelnuts. High nutritional value and bioactive com-
pounds in hazelnut make it a valuable nutrient.
Hazelnuts are usually consumed both in a raw and
roasted form and have unique taste, aroma, and crunchy
texture; they are getting much attention [22]. Hazelnuts with
a unique and pleasant taste are used as an ingredient in
confectionery and bakery products [23]. Roasting causes
Infrared
Microwave
1-Reduced roasting time
2-Similar quality with sample roasted by the conventional
method
3-Desired color in roasting
4-New promising technology
5-Effective alternative method
6-Recommended technology for roasting
Figure 4: Combination of IR heating and microwave (IR-microwave) and its advantages.
Infrared
radiation
Hot air
1-Reduced roasting time
2-Production of high quality product
3-Low energy consumption
4-Novel promising technology
5-Effective alternative method
6-Suitable for industrial-scale application
Figure 5: Combination of IR heating and hot air (IR-HA) and its
advantages.
Journal of Food Quality 5

positive changes in the organoleptic properties of hazelnuts.
e use of roasted hazelnuts improves the taste of sweets,
confectionery, chocolate, and biscuits [53]. Roasting also
removes the hazelnut skin, reduces the moisture, and de-
velops the desired appearance of hazelnuts [53, 54]. Also,
roasting is often used to increase the shelf life of the nuts. e
case occurs through the deactivation of oxidative enzymes
and the formation of antioxidant products during the
roasting process [55, 56].
e possibility of using hybridized microwave-infrared
method for roasting of hazelnut was surveyed by Uysal et al.
[23]. Optimal conditions for roasting hazelnuts in this
system were determined as 613.8 W of microwave power,
900 W of upper halogen lamp power, and 300 W of lower
halogen lamp power for 2.5 min. Hazelnuts roasted at op-
timum conditions had comparable quality with conven-
tionally roasted ones in terms of color, moisture content,
texture, and fatty acid composition. Besides, the roasting
time of the hazelnuts was significantly reduced by about
87.5%. erefore, hybridized microwave-infrared method
can be considered as a promising technique for roasting of
hazelnut and other nuts.
3.4. Almond Kernel. Almond (Prunus amygdalus) is a
member of the Rose family and is considered a popular tree
nut with essential nutrients like vitamins, minerals, and
protein. Also, almonds contain relatively high levels of vi-
tamin E that is beneficial for human health and nutrition
[57]. Roasting is an important step in nuts processing and
one of the ways to improve the color, flavor, and unique
aroma and taste. e use of infrared heating in combination
with hot air for roasting and safety of almonds was inves-
tigated by Yang et al. [6]. e result showed that sequential
infrared and hot air (SIRHA) roasting is preferable to in-
frared and hot air roasting methods. is advantage of
SIRHA was due to reduced roasting time and pasteurization
of almond kernels. erefore, SIRHA roasting is an excellent
method for the production of dry-roasted pasteurized
almonds.
3.5. Sunflower Seeds. e sunflower seed is the fruit of the
sunflower (Helianthus annuus L.) [58]. Sunflower seeds
contain several nutrients such as unsaturated fatty acids,
proteins, fiber, vitamins, and minerals. e use of sunflower
seeds for snack food is important for nutritional reasons, and
it is used in combination with other nuts or alone [59].
Roasting is the typical shape of sunflower seed processing,
and the purpose is to increase the total acceptability of the
product [28]. e effect of infrared (IR) power (400–600 W)
and roasting time (4–10 min) on energy consumption, color
parameters (L∗,a∗, and b∗values, ΔE, BI, SI, WI, h°), texture,
moisture content, and sensory properties of sunflower
kernel was investigated by Mosayebi et al. [28]. Also, the
regression models for the responses were obtained, and the
proper roasting conditions were determined using response
surface methodology (RSM). A quadratic model was pro-
posed for color change (L∗,a∗,ΔE, h°, WI) and linear re-
lation for texture, BI, and moisture content and 2FI for
energy consumption. Roasting at 492.5 W IR power for
9.1min was found to be suitable for proper roasting con-
ditions. Also, roasted kernels had acceptable quality in terms
of sensory properties compared to the conventional method
(hot air).
3.6. Wild Almond Kernel. Wild almond kernel (Amygdalus
Dulcis) could be used as edible nutritive oil and kernel [44].
Almonds can be used as a snack food and as an ingredient in
a wide range of processed foods, especially in bakery and
confectionery [60, 61]. Besides, almonds have application in
the antidiabetic, anti-inflammation, antibacterial, and lax-
ative agent [62]. Roasting is one of the critical processing
methods widely used in the nut industry to improve the
flavor, color, texture, and overall acceptability. e infrared
roasting was applied to roast wild almond kernels by
Mokhtari and Ziaiifar [24]. Effect of processing conditions
including infrared power (200 W, 300 W) during roasting
(15, 25, and 35min) on moisture content, chemical prop-
erties, color, and sensory properties was investigated. e
results showed that increasing the infrared power and
roasting time decreased pH and moisture content. Finally,
infrared with power of 200 W for 15 min was the recom-
mendable processes for wild almond roasting.
3.7. Soybean. Soybean is recognized as a healthy food be-
cause it is an excellent source of essential nutrients, in-
cluding proteins, fat, and some active compounds, and is
obtaining increased notice due to its low cost and high
nutritious value [63]. Although soybean has been used for
human consumption in some countries in Asia, there is a
limitation to its use in other parts of the world. Raw soybeans
have a beany, bitter, and astringent flavor, which has been
the most significant factor limiting the utilization of this
product. Hence to raise its consumption, the specific flavor
of raw soybean must be eliminated. Roasting is one of the
methods for this purpose [26]. Roasting creates a pleasant
flavor without any beany odor or bitter taste [27] and sig-
nificantly enhances the flavor, color, texture, and appearance
of the beans and nuts [64]. e roasted product is delicate,
uniquely nutty, and widely enjoyed as compared to the raw
bean. Roasting also removes the bitter taste of soybean,
inactivates the enzymes, and destroys unwelcome micro-
organisms and food pollution [26]; therefore, roasted soy-
bean has the potential to be used as snacks. Bagheri and
Kashaninejad [27] developed new roasting methods for
roasting of soybeans. In this research, the kinetics and
modeling of soybean roasting using combined infrared-hot
air system and consumption of energy were investigated. e
results showed that the effect of hot air temperature, infrared
power, and combined hot air temperature and IR power on
the roasting rate of soybean was statistically significant and
the roasting process occurred within the falling rate period.
Among the five thin-layer roasting models fitted to the
experimental data, the page model was the best to describe
the roasting behavior. Comparison of roasting methods
showed that minimum energy was consumed in the infrared
process (0.0905 kWh) and maximum energy was recorded
6Journal of Food Quality

for hot air roasting (1.752 kWh); thus, infrared heating could
be considered proper technique for roasting of soybeans for
removing bitter taste of soybean and increasing its accep-
tance rate.
4. Roasting Other Food Products
4.1. Cocoa. Cocoa beans contain many more polyphenolic
compounds (flavonoids). Using this crop improves car-
diovascular health and helps balance cholesterol in the body
[64]. Antiallergic, anti-inflammatory, antiviral, and anti-
carcinogenic properties are other flavonoid advantages
[65, 66]. e most critical operation for processing cocoa
beans is roasting, and the amount of chemical changes
depends on the temperature and time applied during the
process. Roasting modifies the precursor compounds of
flavor and aromas of origin, those formed during fermen-
tation and drying (postharvest treatment). Also, during
roasting, unwanted volatile acids are removed, desired flavor
components are assembled by Maillard reaction, water
content of cocoa is reduced, and color of cocoa darkens [2].
Also, the heat treatment caused the generation of pyrazines,
which gives it a sweet taste and a chocolate aroma.
Physicochemical characterization of cocoa (eobroma
cacao L.) during infrared roasting was studied by Rojas et al.
[30]. e heating process caused a decrease in the surface area,
as well as the pore radius due to the melting and movement of
fats inside of structure resulting in a more compact material in
roasted cocoa. Heat treatment caused the generation of
pyrazines, which gives it a sweet taste and a chocolate aroma.
Tetramethyl pyrazine is the most relevant, which presents its
highest concentration when roasted at 150°C; that is, if 200°C
is used, it is probably volatilizing with higher speed due to the
high temperature; therefore, when analyzing the material,
roasted solid was found in a smaller amount.
4.2. Buckwheat. Buckwheat belongs to the Polygonaceae
family, and it is a drought-tolerant crop. Buckwheat is a
pseudocereal crop that is gaining amicability due to its
unique nutritional properties [67]. Buckwheat has numerous
nutritional benefits (high flavonoid content). Still, its crop
contains potential allergens like protein inhibitors and
toxins, such as fagopyrin, that are harmful to human health
[9]. Roasting can potentially reduce these harmful compo-
nents. In addition, roasting enhances the flavor, shelf life,
and crispness as compared to its raw sample. Effect of in-
frared roasting on the physicochemical properties of
buckwheat varieties was investigated by Bhinder et al. [9].
Roasting is a good method to improve flavor and inactivate
antinutritional components present in buckwheat. e
optimization of roasting time and temperature combination
helps to increase the consumption of this crop. e best
condition for roasting buckwheat was 130°C for 10 min due
to the high amount of preserved nutrients.
4.3. Chili Pepper. Chili pepper (Capsicum annuum L.) is one
of the most widely cultivated peppers in the world. Chili red
pepper is an excellent source of vitamins A and C and is rich in
beta-carotene and minerals such as potassium [68]. Commonly
electrically heated mechanical roasters are used for roasting
chili pepper. e effect of roasting with far-infrared heating on
quality of chili was studied by Fernando et al. [69]. e results
showed that FIR radiation could be used to roast chili peppers.
Also, the results indicated that processing time was significantly
reduced. About 25 minutes is needed to roast chili with the
drum roaster, but roasting chili with similar color and moisture
content using infrared with a radiation intensity of 7188 W/m
2
takes about 60 seconds. erefore, FIR radiation can be used to
roast chili with acceptable quality characteristics.
4.4. Roasted Rice. Roasted rice is simply white rice that has
been dry-roasted until the grains turn a rich brown color.
Roasted rice is a product made from rice or sticky rice. To
produce roasted rice, first, the rice grain is washed and
soaked in water for several hours. en the soaked rice is
roasted in a hot pan until it is crunchy. Roasted rice is the
primary material for preparing Larb Gai (spicy ground
chicken), a delicious dish served throughout ailand, and is
becoming very popular in ai restaurants around the
world. e effect of infrared roasting machine at 750–800°C
and drum speed of 5–7 rpm on rice quality was examined by
Laohavanich & Yangyuen [29]. Roasting at 800°C for
9.1min, drum speed of 6 rpm, and roasting time of 40
minutes were found to be suitable roasting conditions. Also,
it had acceptable quality in terms of sensory properties
compared to other roasted rice in the market.
5. Conclusion and Future Prospective of
IR Roasting
Roasting is an essential process that improves the taste,
color, texture, and appearance of products. Based on studies
done, infrared can be introduced as a replacement of the
conventional methods for roasting nuts and other foods.
Compared with other common roasting methods, IR
roasting offers many advantages such as high-quality
product, greater energy saving and efficiency, and higher
heat transfer rate and heat flux, which results in decreased
drying time and higher roasting rate. IR effectiveness is
between 80% and 90%, the produced radiation is in narrow
wavelength range, and they are miniaturized. e effect of IR
roasting on physicochemical properties, sensory properties,
and nutritional values of nuts as well as the interaction of
components under IR radiation may further justify the use of
IR radiation as a future novel roasting option. e inter-
action between processes and products needs coherent ex-
periments in order to gain more knowledge.
Data Availability
e data used to support the findings of this study are
available from the author upon request.
Conflicts of Interest
e author declares that there are no conflicts of interest
regarding the publication of this paper.
Journal of Food Quality 7

Acknowledgments
e author would like to thank the Gorgan University of
Agricultural Sciences and Natural Resources.
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