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Frying Process: From Conventional to Air Frying Technology

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  • Universidade de Marília - Medicina

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Studies have shown that products resulting from oils heated for long periods under high temperatures contain polar compounds such as polymers, dimers, free fatty acids, and acrylamide, which lead to metabolic changes, malabsorption of essential fat, and development of cancer. The air frying process is capable of reaching the characteristic color and similar flavor obtained by deep fat frying, and reduces the amount of oil content and polar compounds. However, it has not been extensively studied and should receive a greater focus on the detailed evaluation of components and properties of foods and the effects on the human health.
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Food Reviews International
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Frying Process: From Conventional to Air Frying
Technology
Aline Nalon Zaghi, Sandra Maria Barbalho, Elen Landgraf Guiguer & Alda
Maria Otoboni
To cite this article: Aline Nalon Zaghi, Sandra Maria Barbalho, Elen Landgraf Guiguer & Alda
Maria Otoboni (2019) Frying Process: From Conventional to Air Frying Technology, Food Reviews
International, 35:8, 763-777, DOI: 10.1080/87559129.2019.1600541
To link to this article: https://doi.org/10.1080/87559129.2019.1600541
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Frying Process: From Conventional to Air Frying Technology
Aline Nalon Zaghi
a
, Sandra Maria Barbalho
a,b
, Elen Landgraf Guiguer
a,b
,
and Alda Maria Otoboni
a
a
Department of Food Technology, Food Technology School, São Paulo, Brazil;
b
Medical School of Marília,
UNIMAR, São Paulo, Brazil
ABSTRACT
Studies have shown that products resulting from oils heated for long
periods under high temperatures contain polar compounds such as
polymers, dimers, free fatty acids, and acrylamide, which lead to
metabolic changes, malabsorption of essential fat, and development
of cancer. The air frying process is capable of reaching the character-
istic color and similar avor obtained by deep fat frying, and reduces
the amount of oil content and polar compounds. However, it has not
been extensively studied and should receive a greater focus on the
detailed evaluation of components and properties of foods and the
eects on the human health.
KEYWORDS
Deep frying; air frying;
acrylamide
Introduction
Frying is one of the most common practices used in food preparation and employed in
restaurants, homes, and food industry. Fried food is based on dehydrating food that is
immersed in hot oil, a technique widely used all over the world. The rapidity and ease of
preparation, the relatively low price and the aggregation of desirable food properties, such as
color, texture, and taste, contribute to its overall use. These positive attributes are results of
physical and chemical changes during frying, including oxidation, hydrolysis, and polymer-
ization, which are related to chemical and physical modications in the food products.
[1,2]
Few studies have focused on the biological consequences of the consumption of oil-fried
foods for humans. However, it has been found that the content of the polar compounds in
frying is associated with endothelial dysfunction, hypertension, and may berelated to a higher
chance of developing chronic diseases, especially those of the cardiovascular system. Also,
people who eat fried foods are more likely to develop obesity and intestinal diseases.
[36]
Despite all the restrictions, fried products are trendy and highly consumed both inside and
outside homes and are typically found in fast food dishes and many other food services.
However, because of the risks of a high-fat diet, there is an increasing tendency for consumers
to seek more nutritious and safer food alternatives. Therefore, the reduction of the oil content
in fried foods has become a necessity. A series of alternatives have been proposed, with the
intention of replacing the traditional frying process with systems capable of providing proper-
ties similar to those of fried food while providing higher nutritional quality to the product as
well as ease of use.
[79]
CONTACT Sandra Maria Barbalho smbarbalho@gmail.com School of Medicine, University of Marília, Av. Higino
Muzzi Filho 1001, Marília 15525-902, SP, Brazil
Color versions of one or more of the gures in the article can be found online at www.tandfonline.com/lfri.
FOOD REVIEWS INTERNATIONAL
2019, VOL. 35, NO. 8, 763777
https://doi.org/10.1080/87559129.2019.1600541
© 2019 Taylor & Francis
Based on this idea, air frying technology has emerged in the market. The equipment uses hot
air in combination with high-speed air circulation. Foods are heated from all sides at once, and
there is no need to add oil to most of them. The proposal is to obtain fried food with small
amounts of fat. Its acceptability depends on, among other characteristics, the sensorial properties
of the nal product, which should approximate those present in the conventional frying
process.
[10]
Objective
This review intends to gather information about the physicochemical changes that occur
in food submitted to the conventional and air frying process and compare the advantages
and disadvantages of these processes.
Methods
Focused objective
The focused objective for this review is to compare the conventional frying process and
the air frying process.
Inclusion and exclusion criteria
Studies related to conventional frying process and air frying process published in
MEDLINEPubMed, Scielo and Google Scholar were included. Reviews and original
articles in English were selected. The exclusion criteria for this search were editorials,
case reports, poster presentations, and studies not in English or Portuguese.
Databases
For this review, we have searched Scielo, Google Scholar, and MEDLINEPubMed
(National Library of Medicine, National Institutes of Health) databases for appropriate
articles addressing the focused question. The combination of descriptors used for this
search was conventional frying and air frying;air frying and oxidation;air frying and
health.With the list of references for these combinations of the keywords, we have
selected articles to build the results and to perform the discussion.
We did not restrict a specic period to do this review since the technology of air frying
is recent, and there are not many studies relating this type of process to the frying usually
performed with oil heated to high temperatures and immersion of the food for the
cooking process. Each author checked the screening of the articles found in the above-
described databases, and the articles were only used after the agreement of all.
Results
Recently, air frying technology has become a viable alternative to deep fat frying since it
advocates the use of technology with little or no oil, and this, at least in theory, would
764 A. N. ZAGHI ET AL.
bring benets to maintaining health. On the other hand, the sensory characteristics that
conventional frying provides attract consumers worldwide.
Before presenting the discussion of the articles that fullled the eligibility criteria for the
search, it was necessary to collect some aspects related to the importance of frying in the food
industry as well as its relation with the resulting products to the process and its health
implications. The results for oxidation products such as acrylamide and health implications
may be found in Table 1.
[1119]
We have found ve original articles that fullled the eligibility
criteria for this search (Fig. 1). These articles are found in Table 2.
[7,10,2022]
As may be
observed, only a few articles provide information about the air frying process.
Discussion
The importance of frying in the food industry
The frying process is an ecient and widely used method due to its rapidity and,
mainly, the supply of unique sensorial characteristics with much acceptance by the
population. The preservative eect is another secondary character that results from the
thermal destruction of microorganisms and enzymes, in addition to a reduction of
water activity on the food surface. The shelf life of fried foods is determined, above all,
bythemoisturecontentafterfrying.Thosethatsuer more dehydration through frying
(e.g., potato chips or corn chips), have a shelf life of up to twelve months at room
temperature.
[2225]
There are two main techniques of commercial frying that are distinguished by the
method of heat transfer: shallow frying and deep frying. Surface or contact frying consists
of heat transfer to the food mainly by conduction of the hot surface of the frying pan
through a thin layer of oil. This type of frying produces variable browning in the food,
preventing standardization of the product. In deep frying, the heat transfer is
a combination of convection in the hot oil and conduction into the food. All surfaces
receive similar heat treatment, producing uniform color and appearance.
[2527]
The frying process can be continuous, which is usually used by the industrial market for
frying extruded snacks, fried pasta, pre-fried and fried potatoes, or discontinuous, which is
used mainly by the institutional market that includes fast food chains, restaurants, and
pastries.
[28]
When the food is placed in hot oil, its surface temperature rises quickly, and
water evaporates. The surface then begins to dry. The evaporation plane moves into the
food, and a surface crust of porous structure is formed. Its rapid formation is benecial as
it maintains moisture in the food and restricts the rate of heat transfer to the interior. The
temperature used for frying is determined primarily by economic considerations and
product needs. At high temperatures (180200°C), processing times are reduced, and
production rates are increased.
[25,27]
Concern about harmful health eects due to the consumption of trans fatty acids has
led industries to substitute raw materials such as frying oils.
[2931]
Substitution of saturated
to unsaturated fats, which is nutritionally and functionally favorable, involves a large
number of disadvantages. The high degree of unsaturation makes them unstable at high
temperature and more susceptible to oxidation, resulting in faster rancidity and alteration
of taste, thus limiting the shelf life of the nal product. Also, the sensory characteristics of
some of these oils may interfere with the taste of the food or lead to loss of crispness,
palatability, and taste.
[3235]
FOOD REVIEWS INTERNATIONAL 765
During the heating of the oil, a number of reactions produce numerous degradation
compounds. With the continuity of the reactions, the functional, sensorial and nutritional
change leads to a low-quality product.
[36]
For these reasons frequent oil changes are necessary,
thus increasing costs. Also, there are amounts of degraded oil that are disposed of by users in
the environment. Furthermore, acrolein, a product of oil degradation characterized by the
formation of a bluish mist, is considered a source of air pollution.
[7,11,13,25,37]
Table 1. Eects of the acrylamide on the human organism.
Reference Eects on health Mechanisms of action
Lee et al.
[11]
Ataxia; skeletal muscle weakness; cognitive and
memory impairment; numbness of the
extremities; impaired hippocampal neurogenesis
and increased neural progenitor cell death;
mitochondrial dysfunction in primary neurons.
Since learning and memory are inuenced by
neural plasticity as well as by hippocampal
neurogenesis, acrylamide-mediated memory
complications may be associated with changes
in brain plasticity which, when aected, impair
the maturation of the primary neuron and the
proliferation of neuritis. Also, mitochondrial
dysfunction is related to oxidative stress by the
increase in the levels of reactive oxygen species.
Huang et al.
[12]
Augment in the incidence of thyroid follicular cell
tumors; scrotal sac mesotheliomas; mammary
gland broadenomas and lung adenomas.
Acrylamide may exert its genotoxicity via DNA
alkylation, resulting in mutagenicity.
Stošić, Matavulj,
Marković
[13]
Decrease in the corticosterone and testosterone
levels; decrease in serum insulin level.
Acrylamide interferes with the reasonable
balance of several hormones. Prolonged and
chronic exposure can reduce blood insulin level
caused by reduction of beta cells.
Kadawathagedara
et al.
[14]
Acrylamide is a neurotoxicant and can exert
reproductive and developmental toxicity eects;
prenatal acrylamide exposure is associated with
impaired fetal growth and a moderate increase in
the prevalence of children being overweight or
obese.
One possible biological mechanism between
acrylamide exposure and growth is through
oxidative stress and inammation. During
pregnancy, high acrylamide exposure can result
in increased oxidative stress through increased
expression of CYP2E1 leading to a heightened
perinatal inammatory status.
Pan et al.
[15]
Induces a high risk of neuropathic alteration Evidence strongly suggested that acrylamide-
induced neurotoxicity was possibly caused by
the imbalance of oxidation and antioxidant
function, resulting from the elevated levels of
intracellular reactive oxygen species (ROS) and
lipid peroxidation.
Liu et al.
[16]
Increased overall mortality and cancer in the
digestive tract in elderly; induce changes in the
redox state of cells, transcription, and expression
of genes, interfering in DNA repair and hormonal
balances; breast cancer.
Acrylamide can cause cancer through non-
genotoxic mechanisms such as oxidative stress
after glutathione depletion. It may also alter the
levels of steroid hormones and interact with
genes involved in the production of sex
hormones, with circulating estrogen inuencing
various factors and recognizing their
participation in the incidence of breast cancer.
Semla et al.
[17]
Production of free radicals, hydroperoxides and
lipid peroxidation.
Free radicals can damage mitochondria and
other cellular organelles. They induce apoptosis
and cause oxidation of DNA bases, fragmenting
the double strand leading to cell death or
neoplastic transformation.
Olesen et al.
[18]
Formation of adducts with proteins and DNA
bases.
Acrylamide is highly reactive and mutagenic
and can induce chromosomal breakage or
degradation.
Sickles et al.
[19]
Aneuploidy; generation of micronuclei with
kinetochores; dominant lethal eects; delays in
the cell cycle; blockages in mitosis and meiosis;
heritable translocations; chromosomal
aberrations.
Interaction of acrylamide with the proteins
involved in cell division, interfering in the
mitotic/meiotic spindle.
766 A. N. ZAGHI ET AL.
Degradation reactions in the frying process
During the frying process, oils and fats are exposed to the action of three agents that
contribute to decrease its quality and modify its structure. These agents include the
moisture from food (which is the cause of the hydrolytic alteration), the oxygen in the
air (which enters the oil through the surface of the cooking vessel, allowing the oxidative
change) and, the high temperature.
[38]
There are many changes in the properties of oils
and food, such as sensory (avor, aroma, texture, and color), nutritional, functional and
toxicity qualities.
[39]
The most frequently observed physical changes in oils are increased
viscosity, color change and foaming.
[40]
Fig. 2 shows the modications observed in the
frying process.
For foods subjected to such a process, the possible results may be both desirable and
undesirable. For example, the color presented by the potato after frying directly implies its
acceptance. This visual characteristic is mainly inuenced by the type of oil, the age and
thermal history of the oil, the interfacial tension between the oil and the product, the
temperature, the frying time and the sample size.
[10,39]
Duarte-Delgado et al.
[41]
showed
that the sugar content also inuences the color of the fried potatoes because the hydrolysis
of sucrose by the invertase enzyme is the primary source of glucose and fructose reducing
sugars, which are precursors of the Maillard reaction. This reaction produces dark
pigments and toxic products such as acrylamide during the non-enzymatic reaction
between free amino acids and reducing sugars at high temperatures. The high content
of reducing sugars in tubers causes a poor quality of potato chips.
The texture of fried foods is produced by changes in proteins, fats and polymeric
carbohydrates. Changes in protein quality occur as a result of the Maillard reaction with
the amino acids in the crust. The eect of frying on the nutritional value of food depends
on the type of the of the process. As the high temperatures of the oils produce a rapid
Figure 1. Flow diagram depicting the articles selected for this review.
FOOD REVIEWS INTERNATIONAL 767
Table 2. Air frying versus conventional frying.
Reference Objective Analysis Technique Results
Santos
et al.,
2017
[10]
To compare samples
of chips processed in
air fryers versus
traditional frying
method
Lipid composition;
indicators of
degradation;
tocopherols; total
ascorbic acid; β-
carotene; antioxidant
activity
Conventional
frying with
soy oil
Trans Fatty
Acids
Tocopherols Total ascorbic
acid
β-carotene Total phenolics Total
antioxidant
activity
0.026g/100g
potato
4.60mg/100g 0.88mg/100g 167μm/100g 20.46mg gallic acid/100g 9.06mg gallic
acid/100g
Air frying 0.004g/100g
potato
1.13mg/100g 1.44mg/100g 167.5μm/100g 27.21mg gallic acid/100g 7.27mg gallic
acid/100g
Giovanelli
et al.,
2017
[7]
Evaluation of the
characteristics of the
chips processed by
the primary kitchen
equipment.
Equipment
performance;
nutritional quality of
the samples;
acrylamide content
Conventional
frying with
soy oil
Lipids Acrylamide
content
Energy consumption
15.79g/100g 94.5 μg/kg Time of cooking Consumption
13 minutes 270.4 Wh
Air frying Equipment 1 9.25g/100g 209.5 μg/kg 20 minutes 233.0 Wh
Equipment 2 9.14g/100g 89 μg/kg 16 minutes 193.8 Wh
Teruel
et al.,
2015
[20]
Compare air frying
with conventional
deep fat frying and
products formed by
these processes
(color, texture,
calorimetric
properties, and
sensory characteristic)
Evaluation of oil and
moisture content,
color, texture, sensorial
analysis and
calorimetry.
Air and deep
frying
The deep frying process: products with higher content of fat; similar moisture and color, better surface crust,
higher extend of starch gelatinization, and less time for preparation.
768 A. N. ZAGHI ET AL.
Shaker,
2014
[21]
To investigate the
eect that the air
frying technology
exerts on the oil
content and sensorial
characteristics of the
potato, compared to
the traditional
process of frying.
Stability of the oil and
sensory evaluation of
French fries
Conventional
frying with
soy oil
Oil degradation (180°C) Amount of used oil Amount of
absorbed oil
Free fatty
acids
Oxidized fatty
acids
Polar content Peroxides
Initial
value = 0,09%
Initial
value = 0,002%
Initial
value = 0,08%
Initial
value = 0,75
meq.O
2
/kg oil
2kg for each 200g of
potato
14.81%
After frying
value = 0.22%
After frying
value = 0.11%
After frying
value = 0.71%
After frying
value = 2.75
meq.O
2
/kg
óleo
Air frying Initial
value = 0.09%
Initial
value = 0.002%
Initial
value = 0.08%
Initial
value = 0.75
meq.O
2
/kg
óleo
30g/kg potato 0.0025%
After frying
value = 0.12%
After frying
value = 0.06%
After frying
value = 0.34%
After frying
value = 1.22
meq.O
2
/kg
oil
Andres
et al.,
2012
[22]
Evaluation of volume
and inuence of pre-
treatment (blanching
and freezing).
Analysis of the kinetics
of mass transfer and
modications in
volume.
Air and deep
frying.
-The nal content of oil is much lower in air frying.
-The heat transfer coecient for air frying was lower.
-Frozen samples showed the highest content of fat in the deep frying.
-The evolution in the content of oil in the unpretreated and blanched samples was much higher in the deep
frying as well as the water loss, and the frozen samples showed the lowest rate of water loss.
FOOD REVIEWS INTERNATIONAL 769
formation of crust, it seals the surface of the food, reducing the range of changes in the
interior and, consequently, there is signicant retention of nutrients.
[25]
Neethu et al.
[42]
also attributed changes in fried food quality to starch gelatinization reactions, protein
denaturation, caramelization, enzyme inactivation and fat absorption.
The oxidation of fat-soluble vitamins in the oil results in loss of nutritional value.
Retinol, carotenoids, and tocopherols are destroyed, contributing to changes in the
taste and color of the oil. However, the preferential oxidation of tocopherols has an
antioxidant eect on the oil that is particularly important since most frying oils have
a vegetable origin and contain a substantial proportion of unsaturated fats that oxidize
quickly.
[25,43,44]
Due to the knowledge that the frying process alters the chemical nature of the heated
oil, generating toxic compounds, the safety of the consumer and possible consequences for
the human organism are a concern.
Oxidized compounds and their eects on health
The relevance of ingestion of vegetable oils in the human diet, especially those containing
essential fatty acids, primarily as energy-supplying food resources, is indisputable.
However, frying present limitations from the nutritional point of view and may pose
serious health risks.
[45,46]
Researchers have shown that products resulting from oils heated for long periods under
extremely high temperatures contain more than 50% polar compounds, which are the
products of the breakdown of triglycerides (polymers, dimers, free fatty acids and oxidized
fatty acids). These compounds lead to metabolic changes resulting in weight loss, suppres-
sion of growth, development of cancer, decrease in liver and kidney size, malabsorption of
Figure 2. Diagram of changes occurring during the frying process.
770 A. N. ZAGHI ET AL.
fat, decrease in the desaturation rate of linoleic and α-linolenic fatty acids, and reduced
fertility.
[12,14,15,40,47]
Another toxic contaminant in a plethora of heat-treated foods is acrylamide, a polar
organic substance, highly reactive, mainly generated through the Maillard reaction.
[17]
It is
commonly present in foods rich in carbohydrates that are processed at high temperatures
(>120°C).
[16]
This compound is considered genotoxic and neurotoxic and has been related
to the development of cancer.
[48]
There is an estimate that the dietary exposure for the
population to acrylamide is around 1 mg kg-1 per day indicating that this scenario is
a human health concern.
[37,49]
The metabolism of acrylamide follows two central paths: epoxidation and conjugation
with glutathione.
[18]
Once ingested, approximately 50% of the acrylamide is metabolized;
the biotransformation occurs in the cytochrome P450 by the action of the enzyme
CYP2E1 and, as a result, obtains its metabolite epoxy glycidamid.
[17,50]
During
the second phase of biotransformation, acrylamide and glycidamid are coupled to reduced
glutathione through glutathione S-transferase group enzymes, which constitute the glu-
tathione conjugation phase. As a result of this reaction, acrylamide and its derivatives lose
their toxic properties. Afterward, they are excreted as mercapturic acid derivatives by
urine, the main route of excretion of acrylamide metabolites in humans.
[16,18]
The half-life
of acrylamide in the body is 27 hours, which demonstrates a long time that this substance
takes to be removed from the body. It is still unclear whether the toxic eects of chronic
exposure to acrylamide may be cumulative in the organism in the long term.
[17]
Some
eects of acrylamide on health are described in Table 1.
Although there is awareness of the contraindications of the consumption of fried foods,
there are no signs that they suggest a withdrawal or change in the preparation or
consumption habits of these foods. However, current nutritional recommendations sug-
gest that fat intake should not exceed 3035% of total calories, with a maximum of 10%
for saturated fats.
[32]
In this context, new technologies need to be developed to obtain fried
products with sensorial properties similar to those of the conventional frying process,
which are much appreciated by consumers, but with reduced fat content.
[21]
Air frying technology
An alternative found for the disadvantages of conventional frying is the air frying
process, which is intended to produce a variety of fried products using mainly hot air
around the material instead of immersion in hot oil. This technique acts by direct
contact between a ne mist consisting of oil droplets in the hot air and the product
inside a chamber. The heat transfer is extremely high and evenly distributed in the
product, which minimizes variations in its quality. The product is dehydrated during
the process and a crust, typically associated with deep frying, appears gradually in the
food.
[20,21]
Table 2 shows some comparisons of the air frying process compared to the
conventional frying process.
Air frying technology was initially introduced in some European markets and, due to
its remarkable acceptance in response, the product was launched throughout Europe. Over
time, it has spread on a global scale, becoming a great success worldwide. The patented
technology cooks products in a short time, keeping the taste pleasant and containing up to
80% less fat compared to frying by deep frying.
[51]
However, it is necessary to analyze
FOOD REVIEWS INTERNATIONAL 771
other possible advantages as well as disadvantages of this technology including modica-
tions in the properties of the food, besides making comparisons about the traditional
process of frying.
Comparison of air frying and deep fat frying Andrés et al.
[22]
, when comparing air
frying to deep frying, found that during the same frying time, the oil absorption in the
samples of French fries was about ten times greater for those submitted to hot oil. In
frozen potatoes subjected to deep frying, the oil content was substantially modied from
the original content. In the air frying process, a decrease of the concentration of the oil to
values of half the initial content was found. However, this reduction of oil content resulted
in the formation of a less consistent crust (leading to less resistance to water loss) and
interfered with the sensorial characteristic of the nal product. They also observed similar
moisture concentration when comparing to deep frying, but water and volume losses were
higher in air frying process. The loss of water is limited by the crust of the products, which
is formed rapidly in the deep frying process. Changes in oil content in both processes were
shown when samples of French fries were pretreated with blanching or freezing.
According to Teruel et al.
[20]
, the air frying process is capable of reaching the characteristic
color of frying by deep frying. The deep frying process results in products with lower content
of fat and similar moisture and color when compared to the air frying process. The authors
also observed interferences in color, texture, moisture, sensory characteristics, and starch
gelatinization. However, it requires a signicantly longer processing time (the use of air frying
requires more than twice the time of deep fat frying.), which is a relative disadvantage
considering that the current lifestyle (because people spend much of their time away from
home) requires agility and rapid preparation of meals. In general, the air frying process allows
the manufacture of a product that contains low fat content, although it exhibits dierent
sensory characteristics such as taste, color, odor, appearance, hardness, crispness, crispiness,
and oiliness. In contrast, for Shaker
[21]
, air frying technology did not show signicant
dierences in sensory attributes like taste, appearance, odor and overall acceptance when
compared to oil frying. In aspects such as crispness, hardness, oiliness, and color, air frying
was preferred. Nevertheless, potato strips prepared by air frying process showed superiority in
attributes such as hardness, crispness, and oiliness when compared to that traditional fried
potato. Thecharacteristics of better hardness and oiliness may be attributed to lower uptake of
oil compared to deep frying process.
Furthermore, studies using scanning electron microscopy (SEM) and dierential scan-
ning calorimetry(DSC)
[20]
show that the dierence between products submitted to air
frying and immersion frying is the greater extent of gelatinization of the starch that occurs
in traditional frying, which is observed visually as a dry and thick crust. This is the result
of high temperatures rapidly reaching the surface of the product, causing intense evapora-
tion of the local water and preventing gelatinization of the starch. In products subjected to
air frying, the water evaporates more slowly, the surface crust is thinner, homogeneous
and without irregularities, which gives a noticeable dierence in texture. However, in the
central region, the air frying samples presented higher hardness than the samples resulting
from immersion frying possibly related to a lower degree of gelatinization of the starch
associated with the low temperatures.
Tarmizi and Niranjan
[52]
studied the relationship of oil absorption in immersion frying,
and veried that it occurs predominantly at the end of the process, due to the condensa-
tion of water vapor inside the food caused by the temperature drop below the boiling
772 A. N. ZAGHI ET AL.
water, creating a water vapor pressure gradient between the surface and the inner
structure of the product. During frying, both water and water vapor are rst removed
from the large capillaries and replaced with hot oil.
Studies performed by Andres et al
[22]
show that the mass losses of the product in air
frying were higher than in immersion frying because the water lost during this process was
not compensated by any signicant oil absorption, in agreement with the results described
by Tamizi and Niranjan.
[52]
In addition to the dierence in mass presented by the products submitted to the two types
of frying, color is one of the most important quality attributes to inuence the consumers
food choices.
[53]
For example, the study by Pedreschi et al
[54]
reported that the frying process
in hot air requires a signicantly longer processing time to obtain the characteristic color of
potato chips in oil.
Budzaki and Seruga
[55]
, Farinu and Baik
[56]
, Mir-Bel et al.
[57]
, when measuring the
potatoes in the two frying conditions (oil and air), veried that the initial temperature
increased, almost linearly with time, until reaching the boiling point of the water, although
the deep frying reached the boiling point faster than frying in hot air. According to Teruel
[20]
,
the speed to reach the boiling point in oil frying is 3.7 times higher than in hot air. According
to the author, a constant temperature is observed in the frying process in the hot air when it
reaches the boiling point of the water until the end of the process, dierent from the
signicant increase of temperature above 100ºC, observed in the frying in oil.
Authors agree that the air frying technology presents a higher nutritional quality than
conventional frying, being a practical alternative for obtaining healthier fried foods due to the
possibility of fat reduction, lipid degradation, and oxidation. Moreover, it also has environ-
mental advantages such as reduced consumption of oil, and emission of euents that would be
discarded after frying
[10,21,22]
According to Giovanelli et al.
[7]
, the air frying equipment showed
more signicant energy savings compared to others, corresponding to a savings of 70%.
Conclusion
The current context of changing eating habits in which society is inserted deserves
attention and suggests constant monitoring, mainly by the food industry. Since there is
no evidence of stopping the use of frying to prepare meals, it is recommended to use air
frying technology, since it has a proven reduction in the oil content of the products, once
the addition of the same is dispensed in the preparation of most foods.
The incorporation of air frying equipment in snack factories, in commercial establish-
ments such as fast food chains, restaurants and even for domestic use may be an
investment trend for the coming years. Among the advantages are the reduction of
expenses with vegetable oils, reduction of emission of pollutants in the environment and
energy saving, as well as the attraction of consumers who seek a healthier diet, which will
undoubtedly add value to the company.
Although the air frying technology is a healthier frying alternative it has not been
extensively studied and should receive a greater focus on the detailed evaluation of its
mechanisms of action on the components and properties of foods and consequent eects
on the human health.
FOOD REVIEWS INTERNATIONAL 773
Practical applications
The concern over the increase in the incidence of chronic-degenerative diseases has increased the
search for a healthier diet. The substitution of food produced by deep fat frying is an increasingly
common reality since this type of processing carries with it the production of highly toxic
compounds in addition to being highly caloric. Air fryer technology may modify this scenario
since it does not produce toxic compounds and, on the other hand, preserves sensory characteristics
similar to deep fat frying.
Conicts of interest
We declare no conict of interests.
Notes on author contribution
ANZ, SMB, ELG and AMO designed, wrote and reviewed the manuscript. SMB submitted the
manuscript.
ORCID
Sandra Maria Barbalho http://orcid.org/0000-0002-5035-876X
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FOOD REVIEWS INTERNATIONAL 777
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Air-frying is an innovative technique for food frying that uses hot air circulation to prepare healthy products. The objectives of this study were to establish simplified models to reflect the efficacy of the air frying process at varying temperatures and times on the quality attributes of falafel, and to optimize the frying conditions for producing air-fried falafel. Moisture content, color, fat content, hardness, and sensory evaluation of the fried falafel were analyzed under varied temperatures (140 °C, 170 °C, and 200 °C) and time periods (5 min, 10 min, and 15 min). Statistical analysis was then applied to obtain the best fit model that can describe the properties of fried falafel. Results indicated that moisture content, fat content, and L*-value of air-fried falafel were adversely related to the frying temperature and time, but the hardness and ΔE of fried falafel were increased as the frying temperature and time increased. Moreover, an increase followed by a decrease was shown for the appearance, aroma, crispness, taste, and overall preference scores with the increase in frying temperature and time. The regression analysis showed that the proposed models could be properly used for predicting the properties of the fried falafel. In addition, the overlaid plots resulted in the optimum frying temperature of 178.8 °C and time of 11.1 min. Interestingly, the fat content of the air-fried falafel reduced by 45% at optimal frying conditions compared with that for the deep-fat fried one at 180 °C for 7 min (control). In comparison, the air-fried falafel was lower in fat content, higher in hardness with more acceptable appearance and crispness scores than deep-fat fried falafel. Such information could be beneficial to the manufacturers of the falafel to produce an optimal and healthy product.
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Background: Dyslipidemia during childhood has been associated with higher risk of atherosclerosis later in life. Information on the lipid profile of Ghanaian children is scarce. The aim of this study was to assess the lipid profiles of school children between the ages of 9-15 years, living in urban Ghana. Methods: A total of 802 randomly selected school-age children participated in the Ghana School Survey implemented in Kumasi and Accra, Ghana. A structured questionnaire was used to collect information on child and maternal socio-demographic characteristics (including age, education, and occupation), 7-day food frequency, home and school activity, as well as measurement of weight and standing height. Weight, height, and age data were converted into BMI-for-age indices to determine weight status. Finger-prick fasting blood samples were taken from the school-age children. Total cholesterol (TC), triglyceride (TG), high density lipoprotein (HDL-C) and low-density lipoprotein (LDL-C) cholesterol levels were determined using the CardioChek® PA Test System. Reference lipid levels based on the US National Cholesterol Education Program 2001 guidelines were used to determine the proportion of children with dyslipidemia. Results: The mean TC, LDL-C, HDL-C, and TG levels were 149.0 ± 57.0 mg/dl, 80.1 ± 38.6 mg/dl, 53.5 ± 19.4 mg/dl, and 71.4 ± 54.7 mg/dl, respectively. Mean TC/HDL-C ratio was 3.0 ± 1.0. The proportion of children with abnormal values were 12.1% for TC, 4.5% for TG, 28.4% for HDL-C, 9.2% for LDL-C, and 6.6% for TC/HDL-C ratio. The levels of dyslipidemia (HDL, LDL, and TC/HDL-C ratio) were higher among overweight/obese compared to normal-weight children. More frequent fruit consumption was also linked with lower LDL-C (p = 0.020) while watching television (TV) in the mornings was linked with both higher TC (p = 0.011) and TG (p = 0.006). Conclusions: Majority of urban-dwelling Ghanaian school children had normal lipid profiles. However, the higher levels of dyslipidemia observed among overweight and obese children suggest the need for population level physical activity and dietary interventions among children to reduce risk of cardiovascular diseases in adult life.
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In Northern Ghana, 33% of children are stunted due to economic disparities. Dietary fatty acids (FA) are critical for growth, but whether blood FA levels are adequate in Ghanaian children is unknown. The objective of this study was to determine the association between whole blood FAs and growth parameters in Northern Ghanaian children 2–6 years of age. A drop of blood was collected on an antioxidant treated card and analyzed for FA composition. Weight and height were measured and z-scores were calculated. Relationships between FAs and growth parameters were analyzed by Spearman correlations, linear regressions, and factor analysis. Of the 307 children who participated, 29.7% were stunted and 8% were essential FA deficient (triene/tetraene ratio>0.02). Essential FA did not differ between stunted and non-stunted children and was not associated with height-for-age z-score (HAZ) or weight-for-age z-score (WAZ). In hemoglobin adjusted regression models, both HAZ and WAZ were positively associated with arachidonic acid (p≤0.01), dihomo-gamma-linolenic acid (DGLA, p≤0.05), docosatetraenoic acid (p≤0.01) and the ratio of DGLA/linoleic acid (p≤0.01). These data add to the growing body of evidence indicating n-6 FAs are critical in childhood linear growth. Our findings provide new insights into the health status of an understudied Northern Ghanaian population.
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Background The high amount of saturated fatty acids (SFA) coupled with the rising availability and consumption of palm oil have lead to the assumption that palm oil contributes to the increased prevalence of cardiovascular diseases worldwide. We aimed at systematically synthesising the association of palm oil consumption with cardiovascular disease risk and cardiovascular disease-specific mortality. Methods We systematically searched Central, Medline and Embase databases up to June 2017 without restriction on setting or language. We performed separate searches based on the outcomes: coronary heart disease and stroke, using keywords related to these outcomes and palm oil. We searched for published interventional and observational studies in adults (Age: >18 years old). Two investigators extracted data and a consensus was reached with involvement of a third. Only narrative synthesis was performed for all of the studies, as the data could not be pooled. Results Our search retrieved 2,738 citations for stroke with one included study and 1,777 citations for coronary heart disease (CHD) with four included studies. Palmitic acid was reported to be associated with risk of myocardial infarction (MI) (OR 2.76; 95%CI = 1.39–5.47). Total SFA intake was reported to be not significant for risk of MI. Varying intake of fried foods, highest contributor to total SFA with 36% of households using palm oil for frying, showed no significant associations to risk of MI. Odds of developing first non-fatal acute MI was higher in palm oil compared to soybean oil with 5% trans-fat (OR = 1.33; 95%CI = 1.09–1.62) than palm oil compared to soybean oil with 22% trans-fat (OR = 1.16; 95%CI = 0.86–1.56). Nevertheless, these risk estimates were non-significant and imprecise. The trend amongst those taking staple pattern diet (characterised by higher palm oil, red meat and added sugar consumption) was inconsistent across the factor score quintiles. During the years of 1980 and 1997, for every additional kilogram of palm oil consumed per-capita annually, CHD mortality risk was 68 deaths per 100,000 (95% CI = 21–115) in developing countries and 17 deaths per 100,000 (95%CI = 5.3–29) in high-income countries, whereas stroke was associated with 19 deaths per 100,000 (95%CI = -12–49) and 5.1 deaths per 100,000 (95% CI: -1.2–11) respectively. The evidence for the outcomes of this review were all graded as very low. The findings of this review should be interpreted with some caution, owing to the lack of a pooled effect estimate of the association, significant bias in selection criteria and confounding factors, inclusion of other food items together with palm oil, and the possible out-dated trend in the ecological study. Conclusion In view of the abundance of palm oil in the market, quantifying its true association with CVD outcomes is challenging. The present review could not establish strong evidence for or against palm oil consumption relating to cardiovascular disease risk and cardiovascular disease-specific mortality. Further studies are needed to establish the association of palm oil with CVD. A healthy overall diet should still be prioritised for good cardiometabolic health.
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Soybean oil contains approximately 20% oleic acid and 63% polyunsaturated fatty acids, which limits its uses in food products and industrial applications because of its poor oxidative stability. Increasing the oleic acid content in soybean seeds provides improved oxidative stability and is also beneficial to human health. Endoplasmic reticulum-associated delta-12 fatty acid desaturase 2 (FAD2) is the key enzyme responsible for converting oleic acid (18:1) precursors to linoleic acid (18:2) in the lipid biosynthetic pathway. In this study, a 390-bp conserved sequence of GmFAD2-1B was used to trigger a fragment of RNAi-mediated gene knockdown, and a seed-specific promoter of the β-conglycinin alpha subunit gene was employed to downregulate the expression of this gene in soybean seeds to increase the oleic acid content. PCR and Southern blot analysis showed that the T-DNA had inserted into the soybean genome and was stably inherited by the progeny. In addition, the expression analysis indicated that GmFAD2-1B was significantly downregulated in the seeds by RNAi-mediated post-transcription gene knockdown driven by the seed-specific promoter. The oleic acid content significantly increased from 20 to ~ 80% in the transgenic seeds, and the linoleic and linolenic acid content decreased concomitantly in the transgenic lines compared with that in the wild types. The fatty acid profiles also exhibited steady changes in three consecutive generations. However, the total protein and oil contents and agronomic traits of the transgenic lines did not show a significant difference compared with the wild types.
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Acrylamide (AA), a probable human carcinogen, is a widely-used industrial chemical but is also present in tobacco smoke and carbohydrate-rich foods processed at high temperatures. AA is metabolized to glycidamide (GA) to cause the formation of DNA adducts. N7-(2-carbamoyl-2-hydroxyethyl) guanine (N7-GAG), the most abundant DNA adduct induced by GA, was recently detected in urine of smokers and non-smokers. In this study, we assessed the variability of AA exposure and biomarkers of AA exposure in urine samples repeatedly collected from AA-exposed workers and explored the half-life of N7-GAG. A total of 8 AA-exposed workers and 36 non-exposed workers were recruited. Pre-shift and post-shift urine samples were collected from the exposed group in parallel with personal sampling for eight consecutive days and from the control group on day 1 of the study. Urinary N7-GAG and the mercapturic acids of AA and GA, namely N-acetyl-S-(2-carbamoylethyl)-L-cysteine (AAMA) and N-(R,S)-acetyl-S-(1-carbamoyl-2-hydroxyethyl)-l-cysteine (GAMA) were analyzed using on-line solid phase extraction-liquid chromatography-electrospray ionization/tandem mass spectrometry methods. We found that N7-GAG levels in urine were significantly higher in exposed workers than in controls and that N7-GAG level correlated positively with AAMA and GAMA levels. Results from this study showed that AAMA and GAMA possibly remain the more preferred biomarkers of AA exposure and that N7-GAG levels could be elevated by occupational exposures to AA and serve as a biomarker of AA-induced genotoxicity for epidemiological studies.
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Purpose: The association between dietary acrylamide intake and estrogen receptor-positive (ER+) breast cancer risk in epidemiological studies is inconsistent. By analyzing gene-acrylamide interactions for ER+ breast cancer risk, we aimed to clarify the role of acrylamide intake in ER+ breast cancer etiology. Methods: The prospective Netherlands Cohort Study on diet and cancer includes 62,573 women, aged 55-69 years. At baseline, a random subcohort of 2589 women was sampled from the total cohort for a case-cohort analysis approach. Dietary acrylamide intake of subcohort members (n = 1449) and ER+ breast cancer cases (n = 844) was assessed with a food frequency questionnaire. We genotyped single nucleotide polymorphisms (SNPs) in genes in acrylamide metabolism, sex steroid systems, oxidative stress and DNA repair. Multiplicative interaction between acrylamide intake and SNPs was assessed with Cox proportional hazards analysis, based on 20.3 years of follow-up. Results: Unexpectedly, there was a statistically non-significant inverse association between acrylamide and ER+ breast cancer risk among all women but with no clear dose-response relationship, and no association among never smokers. Among the results for 57 SNPs and 2 gene deletions, rs1056827 in CYP1B1, rs2959008 and rs7173655 in CYP11A1, the GSTT1 gene deletion, and rs1052133 in hOGG1 showed a statistically significant interaction with acrylamide intake for ER+ breast cancer risk. Conclusions: This study did not provide evidence for a positive association between acrylamide intake and ER+ breast cancer risk. If anything, acrylamide was associated with a decreased ER+ breast cancer risk. The interaction with SNPs in CYP1B1 and CYP11A1 suggests that acrylamide may influence ER+ breast cancer risk through sex hormone pathways.
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Edible oil adulteration has been a considerable problem worldwide, and rapid detection methods should be established. In this study, a validation method for edible oil adulterated with used frying oil (UFO) was introduced through Fourier transform infrared (FTIR) spectroscopy. The spectral region of 6000–400 cm⁻¹ was determined through FTIR by using a disposable polyethylene film, and absorption profiles at 1550–650 cm⁻¹ region could be used for detection analysis. A qualitative analysis model was established through discriminant analysis, and edible oil adulteration with more than 1% content of UFO could be qualitatively analyzed. A quantitative analysis model was also created through partial least squares regression. When the actual value was more than 1.5%, the predicted and actual values showed good linear correlation. FTIR coupled with chemometric analysis is a useful tool to detect edible oil adulteration.
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Objectives: To assess the level of awareness in population about cardiac diseases prevention and suggestion of recommendations. Study design: Descriptive cross-sectional survey was carried out in Rawalpindi Cantonment in Oct 2016. Methods: 100 respondents were selected through convenience sampling. Data was collected through questionnaire. Results: Results indicated low levels of awareness as only 30% of the population knew that cardiac diseases can be prevented to certain extent by lifestyle changes. 46% population knew about importance of physical activity and 34% knew that excess of fried and salty food can cause cardiac diseases. Only 22% population knew that red meat use in excess can cause cardiac diseases. 20% population were aware that lack of sleep can cause cardiac disease. 13% (for sodas), 15% (for sweets) 13% (for consuming egg yolk daily) and 28% (for stress) were the statistics for remaining modifiable risk factors. 80% of the population was aware of smoking hazards which shows the success of anti-smoking campaigns. Conclusion: These levels of awareness indicate that there is dire need of policy making for health education to make people aware of lifestyle modifications necessary to prevent cardiac diseases.
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Acrylamide (ACR) is a neurotoxin known to produce neurotoxicity characterized by ataxia, skeletal muscle weakness, cognitive impairment, and numbness of the extremities. Previously, investigators reported that high-dose (50 mg/kg) ACR impaired hippocampal neurogenesis and increased neural progenitor cell death; however, the influence of subchronic environmentally relevant low dose-(2, 20, or 200 μg/kg) ACRs have not been examined in adult neurogenesis or cognitive function in mice. Accordingly, the aim of the present study was to investigate whether low-dose ACR adversely affected mouse hippocampal neurogenesis and neurocognitive functions. Male C57BL/6 mice were orally administered vehicle or ACR at 2, 20, or 200 μg/kg/day for 4 weeks. ACR did not significantly alter the number of newly generated cells or produce neuroinflammation or neuronal loss in hippocampi. However, behavioral studies revealed that 200 μg/kg ACR produced learning and memory impairment. Furthermore, incubation of ACR with primary cultured neurons during the developmental stage was found to delay neuronal maturation without affecting cell viability indicating the presence of developmental neurotoxicity. These findings indicate that although exposure to in vivo low-dose ACR daily for 4 weeks exerted no apparent marked effect on hippocampal neurogenesis, in vitro observations in primary cultured neurons noted adverse effects on learning and memory impairment suggestive of neurotoxic actions.