10 antioxidants generated in foods due to processing...
TRANSCRIPT
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10 ANTIOXIDANTS GENERATED IN FOODS DUE TO PROCESSING
María Dolores del Castillo, Elena Ibáñez, Miguel Herrero
CONTENTS
10.1 INTRODUCTION.
10.2 PROCESSING BY APPLICATION OF HEAT
10.2.1 Thermal processes for food preservation
10.2.2 Thermal processes for food transformation
10.2.3 Microwave heating
10.3 NON-THERMAL PROCESSING
10.3.1 Enzymatic treatments
10.3.2 Fermentation
10.3.3 Irradiation
10.3.4 High pressures
10.3.5 Others (separation, pulsed electric fields)
10.4. CONCLUSIONS
REFERENCES
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10.1 INTRODUCTION
In a recent review published by a group of experts from International Life Sciences
Institute, ILSI Europe, Process Related Compounds and Natural Toxins Task Force (van
Boekel et al., 2010), the beneficial aspects of food processing were identified and
widely discussed mainly to ensure the safety and food quality while guaranteeing
consumer acceptability.
Some of the beneficial aspects to consider include 1) food safety and food quality
improvement (by destruction or inactivation of unwanted compounds and
microorganisms such as pathogens, enzymes, etc.); 2) enhancement of nutritional value
(by improvement of digestibility and bioavailability); 3) improvement of sensory
quality (by releasing of flavor compounds or improving texture and taste); and 4)
formation of bioactives with associated health benefits: these compounds might be
either released or generated during food processing, mainly heat processing, and can
provide benefits for human health. Among the different compounds released or
generated during food processing, those with antioxidant activity will be reviewed and
discussed in the present chapter.
Food processes that can lead to the release or generation of health promoting
compounds can be either based on thermal and non-thermal processing. In both cases,
processes should be optimized in order to promote beneficial effects while avoiding
undesired side effects (losses of nutrients, formation of toxic compounds, formation of
artifacts affecting taste, flavor, etc.). Even considering that thermal processes are better
well known, including positive and negative effects, non-thermal processes are
receiving a lot of attention as alternative processes to minimize the negative effects of
heat processing. Non-thermal processes such as those based on fermentation, enzymatic
treatment, high-pressure, electric field, etc. may provide fewer risks and equal or better
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benefits than thermal processes and can also generate/release antioxidants with health-
related benefits. Those with some potential to be used at industrial scale are discussed in
the present chapter, mainly referring how they contribute to the generation of unique
antioxidants with new structures and health benefits.
10.2 PROCESSING BY APPLICATION OF HEAT
Traditionally, thermal processes have been used extensively in food technology with
two main goals: 1) to preserve foods and 2) to transform raw foods; the intensity of the
thermal processing conditions for either food preservation or transformation is very
different. Pasteurization and sterilization are two food preservation processes used to
ensure microbiological safety and to eliminate some enzymatic activity that might
reduce food shelf-life, while baking and roasting serve mainly to transform food by
obtaining particular sensory or texture features. The most popular thermal food
preservation processes can be classified according to the intensity of the heat treatment
as follows: pasteurization (70-80ºC), sterilization (110-120ºC) and UHT (140-160ºC).
Transformation processes such as roasting and baking are much more intense heat
treatments. On the other hand, microwave treatment is considered also a thermal food
process that can be used to achieve both goals: food preservation or transformation. As
mentioned, in the present chapter, we attempt to review the effects of all these processes
on the antioxidant profile of food.
It is well known that some reactions occur during food processing causing the formation
of both beneficial and harmful compounds. Although a lot of work has been performed
on the risks derived of thermal food processing, recently, there has been a lot of interest
in the enhancement of functional properties as key benefits derived of thermal
processing (Silván et al., 2006; van Boekel et al., 2010; Henle, 2005). Some of the
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beneficial properties of heated foods included increased antioxidants or antibacterial
effectiveness. The antioxidant power of the heated foods may be ascribed to both
natural antioxidants existing in the food and newly formed compounds generated during
food processing. Natural bioactives might be released to some extent during processing
by disruption of cell walls, breakdown of complex molecular structures, and
dissociation of molecular linkages between food components; these compounds can be
secondary plant metabolites such as carotenoids, glucosinolates and polyphenols. The
new bioactive compounds can derive from several chemical reactions undergoing
during food processing; for instance, Maillard reaction, which is the key chemical event
taking place during thermal food processing (Henle, 2005; Silván et al., 2006). In Figure
10.1, the chemical structure of some of the antioxidant compounds that might be formed
through Maillard reaction are shown.
PLACE FIGURE 10.1 NEAR HERE
The rate of release and/or formation of antioxidants along with its type depend on food
composition and on the intensity of the thermal food processing and, therefore, will be
different for preservation or transformation events. In agreement, in this section of the
book we will provide some examples on the effect of both types of thermal food
processing on the antioxidant profile (natural and newly formed antioxidants) of
processed foods. We will focus our discussion on highly consumed foods such as
coffee, bread, fruit and vegetables, with natural (polyphenols) and also newly formed
antioxidants, exposed to thermal conditions able to favour the simultaneous occurrence
of several chemical reactions, including Maillard reaction, and with epidemiological
evidences of health effects. The overall antioxidant activity (TAC) of some foods will
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be also discussed as affected by thermal processes since the TAC increase cannot be
merely attributed to release of antioxidants from plant matrix but also to other reactions
favored at higher temperature such as trans-cis isomerization of carotenoids,
intramolecular trans-esterification of polyphenols, etc. that may lead to the formation of
non-identified compounds with very high antioxidant power.
10.2.1 Thermal processes for food preservation
At present there is a clear correlation between a diet high in fruits and vegetables and a
healthy life and prevention of chronic diseases. It is believed that there is a link between
antioxidant content and the health benefits of fruits and vegetables; antioxidants, mainly
phenols, are ubiquitous present in plant-based foods and, therefore, humans consume
them daily. These bioactive compounds have received a lot of attention (Robbins,
2003). However, few studies are available on the effects of thermal treatment on dietary
antioxidants, like phenolic compounds, as well as on their availability in heat processed
foods. Dietary antioxidants undergo several enzymatic and chemical reactions during
processing. Moreover, the consequences of food processing on natural antioxidants
behavior may dramatically differ depending on several variables such as: concentration,
chemical structure, oxidation state, localization in the cell, possible interaction with
other components and type and intensity of the thermal processing applied. Therefore,
food processing may cause decrease, increase or minor changes in content and
functionality of these natural dietary antioxidants (Patras et al, 2009; van Boekel et al.,
2010). On the other hand, there are some evidences about the generation or
improvement of antioxidant levels and total antioxidant capacity in processed foods.
Regular consumption of tomatoes and tomato-based products has been associated to
reduced incidence of some types of cancer and heart disease. These beneficial properties
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have been partially attributed to their content in various bioactive compounds, such as
carotenoids; among them, lycopene, which exhibits a high oxygen-radical scavenging
and quenching capacities, and β-carotene, which is the main carotenoid with provitamin
A activity. Studies on the changes of antioxidant profile during cold storage of tomato
juice stabilized by thermal or high intensity pulsed electric field treatments performed
by Odriozola-Serrano et al. (2008) indicated higher lycopene and lower vitamin C levels
in pasteurized tomato juices (90 °C for 1 min or 30 s), while no significant changes in
the total phenolic content and antioxidant capacity were detected between treated and
fresh juices just after processing. The influence of the food processing on the chemical
and physical properties of lycopene in tomatoes has been reviewed by Shi and Le
Maguer (2000). The main chemical reactions causing lycopene degradation during
processing are isomerization and oxidation. For instance, during heat processing, all-
trans-lycopene isomers are converted into cis-isomer, with higher bioavailability than
all-trans isomers. In Figure 10.2, the most important occurring lycopene cis-isomers are
shown. The analysis of lycopene isomerization has been proposed as a measure of the
health benefits of tomato based foods. According to Shi and Le Maguer (2000),
lycopene availability in processed tomato products is higher than in unprocessed fresh
tomatoes.
INSERT FIGURE 10.2 NEAR HERE
The consumption of citrus juices, especially orange juice, has been reported to be
beneficial for the prevention of several diseases. Citrus juices are very popular and daily
consumed and are considered a dietary source of provitamin A. Health benefits of citrus
could be attributed to the richness in various antioxidants, vitamin C, polyphenols,
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carotenoids, etc. (Dhuique-Mayer et al, 2007). Thermal treatments could cause
undesirable reactions such as non-enzymatic browning and nutrient losses. Vitamin C
(L-ascorbic acid) is a typical heat sensitive micronutrient, and its degradation plays a
major role in non-enzymatic browning reactions (Villamiel et al., 2012). The thermal
degradation kinetics of vitamin C, carotenoids (β-carotene and β-cryptoxanthin), and
hesperidin, as a function of temperature, has been determined for Citrus juice (Citrus
sinensis L.). The authors found that thermal treatments corresponding to classical
pasteurization conditions do not damage provitamin A carotenoids, polyphenols as
hesperidin, and vitamin C in citrus juice. Moreover, the model developed by them may
predict the optimal processing conditions to minimize degradation of vitamin C and
carotenoid in citrus juice. Authors also reported than xanthophyll carotenoids were
more heat sensitive than carotene and more likely to generate degradation products such
as furanoids and cis isomers. Violaxanthin was the most heat sensitive and its complete
conversion to auroxanthin results in a visually colorless juice. Further information
regarding the antioxidants' modification pathways during juice processing has been
described by Grajek and Olejnik (2010).
Fiore et al. assessed the antioxidant activity of pasteurized and sterilized commercial red
orange juice (Fiore et al., 2005) with the aim of finding out any relationship between the
antioxidant properties and the anthocyanin’s composition in juices submitted to
different thermal treatments. They concluded that the healthy antioxidant properties of
red orange juice associated to anthocyanins can be only attributed to short-shelf life
products containing 100% pure juice and submitted to mild thermal processing
conditions (pasteurization). Huge differences in antioxidant profile of short-shelf life
(mild pasteurized~ 80ºC) and long shelf-life sterilized juices were found and were
attributed to the intensity of the heat treatment. This is a common conclusion in most of
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the works done comparing low and high intensity thermal treatment processes;
evidences support that low intensity thermal treatment of food and vegetables provide
healthier foods due to the preservation of antioxidant bioactives and total antioxidant
capacity.
Food by-products, such as grape seed extracts, can be used as functional food
ingredients, mainly for their content in phenolic acids, flavan-3-ols (catechins and their
isomers) and proanthocyanidins. An important aspect to consider is the stability of the
functional food ingredient during food processing, in terms of composition and
bioavailability. Little work has been done so far regarding the effects of heat treatment
on potential functional food ingredients. Recently, new information has been provided
on the kinetics of thermal modifications in grape seed extracts. Mathematical models
have been proposed as the appropriate way to predict thermal stability and quantify
changes in individual antioxidant compounds, antioxidant capacity and browning
(Davidov-Pardo et al., 2011). In this work, grape seed extract were submitted to thermal
treatments of 60, 90 and 120ºC for 5, 10, 15, 30, 45 and 60 min; these heating
conditions simulated those commonly used in the food industry for food preservation.
Results showed that the individual antioxidants behave differently during heating: both
proanthocyanidins and gallic acid increased, while catechin and epicatechin decreased.
In addition, no statistical significant changes on total antioxidant capacity were
observed after thermal treatment. Authors concluded that during heating of grape seed
extract release of gallic acid units, epimerization and polymerization of catechins, and
darkening of the samples, occurred.
Several extraction methods have been suggested to obtain natural antioxidant extracts
from different natural sources such food by-products and algae. Obviously, the stability
of the natural antioxidants to extraction conditions is a critical issue since it will
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determine the extract composition and the bioavailability of the extract´s bioactive
components. Among the different methods available for natural antioxidants extraction,
green and safe processes, such as those based on the use of sub- and supercritical fluids,
are preferred by the consumers and producers. Although these processes provide with
important advantages compared to the traditional ones, they commonly imply the use of
thermal treatments of different intensity to improve extraction yields and selectivity. A
promising procedure to obtain natural extracts with important antioxidant activity in a
sustainable way is subcritical water extraction (SWE), which is based in the use of
water at high temperatures and pressure enough to be kept at liquid state. Very recently,
our research team probed the feasibility of this approach to obtain extracts with potent
antioxidant activity and provided novel information related to the chemical reactions
occurring during SWE, such as thermoxidation, caramelization and Maillard reactions
that overall contribute to the antioxidant character of the extracts (Plaza et al., 2010a;
Plaza et al., 2010b). Results showed that pressurized water extraction at mild thermal
conditions (50ºC for 20 min) seems to be adequate to achieve good antioxidant extracts
while avoiding further degradation of natural antioxidants and generation of other
undesirable substances. Heating to higher temperatures may generate new antioxidants
with different mechanism of action than those natural existing in the raw matrix.
Extraction conditions should be carefully optimized for any particular application
considering the different matrix composition and the stability of their components.
10.2.2 Thermal processes for food transformation
Most of the food products that have been identified as health-promoting are, for
instance, heat-processed foods such as coffee, cocoa, bread and barley, in which the
Maillard reaction played a very important role.
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Recent epidemiological studies on coffee effects provide evidence of its beneficial
effects on human health (van Boekel et al., 2010). The health promoting properties of
coffee brews are associated to its composition on antioxidant phenolic compounds. The
most prevalent phenolic compounds in foods are hydroxycinnamic acids, being the
major component of this class caffeic acid, which occurs in food mainly as ester, known
as chlorogenic acid. Coffee is the major source of chlorogenic acid in the human diet,
being the daily intake, in coffee drinkers, around 0.5-1 g.
During roasting, which is a typical food transformation thermal process, coffee beans
are heated to 200-250 °C during a given time (from 0.75 to 25 min), depending on the
degree of roasting required. Many complex physical and chemical changes take place
during this process, including the obvious change in color from green to brown. The
major compositional changes occurring are decreases in protein, amino acids,
arabinogalactan, reducing sugars, trigonelline, chlorogenic acid, sucrose, and water and
the formation of melanoidins. Many of these changes are related to the Maillard
reaction. Although compounds with antioxidant properties (mainly chlorogenic acid)
are lost during roasting, the overall antioxidant properties of coffee brews can be
maintained, or even enhanced, by the development of compounds possessing
antioxidant activity, including Maillard reaction products (MRP). Maillard reaction
products formed in foods under heating have been reported to possess antioxidant
activity and even pro-oxidant properties (Silván et al., 2006). Although a huge number
of studies have been carried out to achieve a better degree of understanding of the
effects of food transformation processes on the antioxidants profile and total antioxidant
capacity of coffee brews (Farah and Doanangelo, 2006: Alves et al., 2010; Renouf et al.,
2011), this information is still not complete. This fact might be due to the complex
network of reactions that may take place simultaneously during the roasting process.
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Figure 10.3 summarizes most of the reactions taking place during coffee roasting that
affect antioxidant properties of the coffee brews and antioxidants intake due to coffee
drinking.
PLACE FIGURE 10.3 NEAR HERE
This complexity has been illustrated analyzing Colombian Arabica coffee beans roasted
at three different levels. A progressive decrease in antioxidant activity (associated
mainly to a decrease in chlorogenic acids) was observed with the increasing degree of
roasting together with the simultaneous generation of high (HMM) and low molecular
mass (LMM) compounds, possessing antioxidant activity. The highest antioxidant
activity was observed in the medium-roasted coffee, being the contribution to the
overall antioxidant activity of the low molecular mass fraction greater than that of the
high molecular mass fraction (del Castillo et al. 2002).
Besides Maillard reaction, other chemical events could also take place during roasting,
such as pyrolysis. In fact, it has been observed an increase in the antioxidant activity of
pyrolysated chlorogenic and caffeic acids (11-fold and 460-fold, respectively) after a
heat treatment equivalent to roasting (Guillot et al., 1996). Tetraoxygenated 1,3-cis and
1,3-trans-phenyllindan isomers were identified as the main active components in the
caffeic acid pyrolysates.
Similar observations have been obtained from the roasting of small black soybeans;
Roasted soybeans (at 250 ºC for 30 min) showed significantly higher antioxidant
activity than unroasted small black soybeans in-vitro. This enhancement of antioxidant
properties of the roasted samples was ascribed to an increase in phenolic acid and MRPs
due to roast processing (Kim et al., 2011). Thus, roasting process under controlled
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conditions might be a feasible and helpful way to obtain food with optimal antioxidant
properties. However, further research to confirm this hypothesis has to be undertaken
considering also that the identity of some of the newly formed antioxidants is still
unknown.
Baking is another very common food transformation process. Baked products such as
bread are part of human daily diet worldwide. It has been observed that the baking
process can positively influence the overall antioxidant capacity of the obtained
products, mainly through Maillard reaction, of rye bread (Michalska et al., 2008).
Baking favored the formation of antioxidant compounds during the manufacture of rye
bread made of whole grains. The bread crust, where the heating is more intense, was the
portion of the bread where the main changes due to Maillard reaction were observed.
However, not all the MRPs provide the same antioxidant activity; for instance it was
demonstrated that advanced MRPs showed good scavenging of peroxyl and ABTS
radicals, whereas early MRPs did not seem to be linked to the overall antioxidant
capacity (Michalska et al., 2008).
10.2.3 Microwave heating
Microwave heating has been employed either to assist an extraction process or as an
alternative to traditional heating processes. Depending on the particular application, the
intensity of the treatment differs and, as a result, the concentrations of antioxidants and
the total antioxidant capacity of the treated foods also change. Microwaves have been
used in food processing to inactivate enzymes from vegetable products that otherwise
might induce sensory and chemical changes. It has been shown that, although the
treatment with microvawes was enough to inactivate enzymes from red peppers, the
amount of phenolic compounds was reduced approximately in a 20 %. Nevertheless,
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interestingly, the total antioxidant capacity of the samples was significantly enhanced
after the treatment. These results were associated to the emergence of new phenol
derivatives that increased the overall antioxidant capacity of the treated samples
(Dorantes-Alvarez et al., 2011).
Other investigations have revealed that a microwave treatment can also promote
changes on the chemical compositions of the food towards the release of free phenolic
acids, reducing the amount of bound phenolics and producing an increase on the overall
antioxidant capacity. This fact has been observed in mandarin pomace (Hayat et al.,
2010) where a correlation between the intensity of the microwaves treatment and the
stability of flavonol compounds was detected; whereas the amount of total flavonol
compounds increased with the treatment power, long irradiation times caused a
degradation of these components (Hayat et al., 2010). Therefore, it was concluded that
an efficient control of microwaves treatment might improve the composition and
antioxidant properties of mandarin pomace by increasing both the content and
bioavailability of the bioactive components present.
From the information provided in this section, it can be deduced that moderate heat
treatments might be considered as a useful tool to improve the health properties of some
vegetables, considering that increases in the amounts of phenolic compounds and total
antioxidant activities may be observed. Nevertheless, processing conditions should be
carefully optimized and the composition of the food has to be closely studied in order to
assure their safety and health promoting effects. In this sense, it is important to consider
the safety and health promoting properties of neoantioxidants generated during
processing, such as some MRPs like hydroxymethylfurfural (HMF). For instance, some
controversy exists in the literature about the positive effects and the safety issues related
to HMF consumption (Herrero et al., 2012; Zhao and Hall, 2008; Li et al., 2009).
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10.3 NON-THERMAL PROCESSING OF FOODS
Although, as mentioned in previous sections, some of the most-used processes in the
food industry for increasing shelf-life deal with the use of heat, it is also true that with
the increasing interest of the consumer in high-quality food, including preservation of
both sensory and nutritional parameters, new non-thermal processes are being further
developed. For instance, processes such as irradiation or application of high pressures
are gaining importance to inactivate microorganisms while preserving food quality
parameters. In this section, the main non-thermal processes used, or with potential to be
used, in the food industry are briefly described focusing on the formation of
antioxidants during their application. In this regard, some basic food treatments that do
not imply the use of heat including wet cleaning, sorting, knife peeling, size reduction,
mixing or separations will not be described considering their little, if not null, effect on
the generation of antioxidants.
10.3.1 Enzymatic treatments
Enzymes are widely used in the food industry because of their broad applicability
(Fellows, 2000); the use of enzymes presents a series of advantages, such as reaction’s
specificity at mild conditions of temperature and pH. In addition, enzymes are active at
quite low concentrations. Besides the technological-related applications of these
compounds, such as texture improvement, viscosity reduction or flavor production,
enzymes used in different processes allow the formation of new antioxidant compounds,
not present before the treatment. Among the most-employed enzymes in the food
industry, α-amylases, invertases, cellulases and hemicellulases, lipases and some
proteases, including rennet, are pointed out.
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One of the main fields of generation of antioxidant compounds derived from the
enzymes’ application is the production of antioxidant peptides, mainly in dairy products
(Pihlanto, 2006). In fact, during cheese elaboration, different enzymes produce the
proteolysis of casein and other milk proteins and, as a result, different peptides might be
formed, depending on the type of milk, the enzymes added as well as on the particular
manufacturing process followed. It is also well known that new peptides can be also
formed during cheese ripening and that these bioactive peptides might differ depending
on the type of cheese (Sousa et al., 2011).
The formation of antioxidant peptides after the treatment with other enzymes has been
also assessed. For instance, a peptide composed of 11 amino acid residues was isolated
after the treatment of algae protein waste with pepsin, showing a potent antiradical
activity measured by using TEAC, ORAC, DPPH and radical oxygen assays (Sheih et
al., 2009). The use of this enzyme has been also widely explored for the generation of
active peptides from different protein sources, including chickpea proteins, milk casein
or fish proteins, among others.
The effect of the use of enzymes during processing on the formation of other
antioxidant compounds has been also studied. For instance, it has been shown that the
enzymatic treatment of the highly viscous puree resulting from the mechanical crushing
of carrots, allows a better recovery of the carrot juice, directly by pressing. In fact, it has
been observed that the treatment with cell wall degrading pectinases before pressing
enhanced the recovery of antioxidants in the juice, significantly improving the
bioactivity of the resulting product (Khandare et al., 2011). This strategy, based on the
treatment of vegetable products with pectinases, is potentially applicable to other
vegetable-derived products in which the recovery of antioxidants can be effectively
enhanced (Oszmianski et al., 2011).
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10.3.2 Fermentation
Fermentation can be classified as a non-thermal process usually employed in the food
industry to produce beneficial effects in food. During fermentation, different
microorganisms are utilized to induce a series of chemical changes that, at the end,
provide a food conservation method. After fermentation, the food products treated have
significantly changed, not only from a organoleptic point of view, but also from a
chemical perspective. In fact, the digestion of food components by microorganisms
(bacteria and yeast, most frequently) is responsible for the modification and formation
of new components derived of the action of the microorganisms’ enzymes. Beyond
shelf-life extension, fermentation produces other beneficial effects into foods, such as
the enrichment of the nutritional value, the elimination of antinutrients or the
improvement of the sensory properties of food. Besides, new compounds not formerly
present in the original food can be also formed, and among them, the formation of
antioxidants is a possibility.
Indeed, among the antioxidants formed from fermentation processes, antioxidant
peptides derived from food proteins are pointed out. Several antioxidative peptides have
been described in fermented foods, although their mechanism of action is still not fully
understood. Generally, these peptides possess from 2 to 10 amino acid residues and can
act through three different actions: as metal chelators, scavenging radicals or acting as
proton donors.
The generation of antioxidant peptides in different fermented foods has been assessed.
For instance, it was found that peptides derived from milk fermented by Lactobacillus
delbruekii spp. bulgaricus had a potential antioxidant activity, among other interesting
bioactivities (Qian et al., 2011). Similarly, other antioxidant peptides have been
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described from commercial fermented milk-based products (Hernandez-Ledesma et al.,
2005). Although dairy products are one of the most-studied food products regarding the
occurrence of bioactive peptides generated after fermentation processes, other examples
can also be found, as, for instance, fermented mussel (Mytilus edulis) sauce. An
interesting study performed using this product allowed the identification of a hepta-
peptide, which amino acid sequence was HFGBPFH (MW 962 kDa), that possessed a
good radical scavenging activity (Rajapakse et al., 2005). After the purification of this
peptide from the mussel sauce, its radical scavenging properties against superoxide and
hydroxyl radicals were assessed, showing an activity of about two-times higher than
that of α-tocopherol. Likewise, this peptide showed also metal ion chelation activities as
well as lipid peroxidation inhibition properties. In fact, as it can be observed in Figure
10.4, the isolated peptide derived from the fermentation process showed an inhibition of
the lipid peroxidation higher than α-tocopherol, which is a well-known lipid-soluble
antioxidant. The activity was attributed to the ability of the peptide to interfere in the
propagating cycle of lipid peroxidation, slowing radical-mediated linoleic oxidation; the
presence of several hydrophobic amino acids in its sequence would help to enhance the
solubility of the peptide in the lipid fraction facilitating its interaction with the radicals
(Rajapakse et al., 2005).
INSERT FIGURE 10.4 NEAR HERE
Other fermented food-derived peptides have been also described to possess antioxidant
properties against a wide range of radicals. An example is the isolation of antioxidant
peptides from a fermented mushroom, Ganoderma lucidum (Sun et al., 2004).
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10.3.3 Irradiation
Irradiation is a non-thermal food processing technique involving the exposure of food
products to ionizing or non-ionizing radiation; and enabling processing at or nearly
ambient temperatures. The use of ionizing radiation, mainly through the application of
gamma-irradiation, improves the hygienic quality of food products without having a
critical impact on the sensory characteristics of the treated products. Besides,
considering that packaged food can be also treated, recontamination during food
production and consumption chains are low. On the other hand, the non-ionizing
radiation employed is electromagnetic radiation that does not possess energy enough to
ionize atoms or molecules, being ultraviolet rays (UV-A, UV-B, UV-C) the most
frequently used. During the irradiation process, reactive ions are produced which
destroy or damage microorganisms in a quite fast way by changing cell membranes’
structure and affecting the metabolic enzymes activity. The safety of food irradiation at
10 kGy and above has been assured (Alothman et al., 2009).
It has been observed that the irradiation of several foods and food products can have a
different effect on the antioxidants naturally present on the treated matrix. In this sense,
it has been commonly assessed that the antioxidant capacities of the irradiated products
and/or their antioxidant contents raised compared to non-irradiated counterparts. The
effect of radiation on the antioxidants has been shown to be dependent on the dose,
exposure time as well as on the matrix being irradiated itself. Table 10.1, presents a
summary of some of the most recently published reports in which positive effects have
been observed. In general, the increase of antioxidants after irradiation has been related
to an enhancement on the enzyme activity or to an improvement of extractability from
the tissues in which they are contained. For instance, the increasing synthesis of
phenolic compounds observed during storage of different vegetables after irradiation,
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was suggested as responsible for the enhancement on the antioxidant capacity and total
phenolic contents observed in those vegetables after ionizing radiation treatments, even
at doses below 1 kGy (Fan, 2005).
PLACE TABLE 10.1 NEAR HERE.
These observations allow to conclude that irradiation treatments can be a useful tool not
only to assure the microbiological safety of food products, but also to increase their
quality. This fact can be also applicable to non-ionizing radiation. In this sense, UV-C
has been proposed as a useful tool to improve the post-harvest quality of fruits. In a
recent work, authors demonstrated that a UV-C irradiation treatment of mango fruit, at
levels between 2.46 and 4.93 kJm-2, produced a significant increase on the total phenols
and total flavonoids content of the fruits during the storage following the irradiation
treatment, whereas fungi infections were reduced (Gonzalez-Aguilar et al., 2007).
Results suggested a response to the stress generated by UV radiation in plants that may
act by inducing enzymes related to scavenging radical oxygen species as well as to the
synthesis of flavonoids and phenolic compounds. Thus, UV-C was proposed as a useful
alternative to maintain the postharvest quality of the mango fruit (Gonzalez-Aguilar et
al., 2007).
It is also important to remark that the enhancement or decrease of antioxidants present
on the samples might happen as a result not only of the type of treatment (type of
radiation, intensity, and time, among others) but also on the solvents used for the
extraction. For instance, it was observed that the scavenging activity after irradiation
treatments at dose levels from 2 to 16 kGy of Nigella sativa seeds (black cumin), a spice
employed in a wide variety of food products, significantly varied among three different
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tested extraction solvents (i.e., water, methanol and acetone) (Khattak and Simpson,
2008). The free-radical scavenging activity of the methanol and acetone extracts was
enhanced after the treatment with gamma-radiation, as well as the total phenolic
contents.
Other antioxidants can also be formed after treatment with gamma-radiation as, for
instance, neoantioxidants derived from the Maillard reaction after irradiation. The
formation of this kind of compounds from cheese whey has been confirmed (Chawla et
al., 2009). The presence of reducing sugars and proteins in this important food by-
product allows the occurrence of Maillard reaction under certain conditions. Different
irradiation intensities, using gamma-radiation, were tested and a dose dependent
increase in browning and fluorescence, as well as a decrease on free amino groups, were
observed. Based on these results, the occurrence of Maillard reaction could be
confirmed after irradiation. Besides, it was clearly observed that the antioxidant
capacity of the products after irradiation, using different in-vitro assays, was
significantly higher. Thus, it could be concluded that an irradiation treatment, under
certain conditions, of cheese whey, can have a positive effect not only on the
microbiological safety of the product but also on the final antioxidant profile since it
was able to produce new antioxidants related to Maillard reaction, which could
potentially increase the interest on the final product (Chawla et al., 2009).
10.3.4 High pressures
At present, the use of high pressures in food processing is an interesting alternative for
the non-thermal inactivation of microorganisms and pathogens in general. Nevertheless,
its use is not widely distributed, mainly due to the expensive equipment required to
apply this treatment to food products. When high pressures, typically up to 1000 MPa
21
are applied to packaged food immersed in a liquid, this pressure is uniformly and
instantly distributed throughout the food causing the destruction of the microorganisms
present. Considering that pressure transmission is not time-dependent, times required to
apply these treatments are very short; under these conditions, the break of covalent
bonds does not occur, helping to maintain the sensory properties and nutritional value of
the foods. Instead, high hydrostatic pressure (HHP) produces changes in membrane
structures resulting in bacterial inactivation as well as on the structure of
macromolecules, such as enzymes, fostering their inactivation.
Due to these intrinsic characteristics, HHP will not generally produce significant
changes on the nutritional compositions of the treated foods. Nevertheless, some
changes have been reported in several applications. For instance, it has been shown how
the content of naringenin and hesperitin present in orange juices could be increased after
treatment at 400 MPa (Sanchez-Moreno et al., 2005). A similar effect was detected in
cashew apple juice when it was pressurized between 250 and 400 MPa. Under these
conditions, the juice presented higher content of soluble polyphenols, demonstrating
that HHP treatments could be potentially employed in the food industry to obtain
products with higher nutritional quality (Queiroz et al., 2010). The treatment of onions
with high pressures improved the extractability of glycoside flavonoids and aglycones,
when compared to untreated samples.
On the other hand, even if high pressure treatments could not increase the antioxidant
content in the treated foods, the changes promoted by high pressures in the food
structures might derive on a better accessibility and availability of important food
components such as antioxidants and minerals. This has been demonstrated with apples
treated with 500 MPa during 10 min, which showed, in comparison with untreated
samples, higher antioxidant capacities, minerals and starch contents. Consequently, the
22
consumption of this kind of fruits could provide with a further potential health
promoting effects than their corresponding untreated counterparts (Briones-Labarca et
al., 2011). The same has been observed for other kind of food components, such as
carotenoids; HHP treatments have shown to have a positive effect on the availability of
carotenoids present in some vegetables (McInerney et al., 2007).
10.3.5 Others (separation, pulsed electric fields)
Other non-thermal processes that may affect the antioxidants profile of food products
are, for example, pulsed electric fields and pulsed light.
The application of pulsed electric fields has raised some attention for the possibility to
obtain microbial inactivation in extremely short times. This technique is based on the
application of a pulsed high voltage field (usually between 20 and 80 kVcm-1) to food
products during times generally shorter than 1 s and by applying short duration pulses
(less than 5 µs each). The effects on the microorganisms include electrical breakdown
as well as electroporation, inducing the rupture of the cells by changing the structure of
the membrane. Figure 10.5 illustrates the effects of pulsed electric fields on the
membrane of Saccharomyces cerevisiae cells.
PLACE FIGURE 10.5 NEAR HERE
Although, obviously, heat is produced as a result of the application of high voltage, this
heat is controlled and the sample is never heated. Besides, the effects observed on the
microorganisms are due to the electric field and not to any thermal effect. During these
extremely short treatment times, the food properties are mainly unchanged, minimizing
the chance to find undesirable side-effects on the nutritional or sensory properties. Even
23
if these changes are minimal, some effects on the antioxidant composition of foods
treated with pulsed electric fields have been reported. This is the case when this
technique is applied as a pretreatment during juice production; the application of pulsed
electric fields before pressing allows the attainment of apple juices with increased
content on polyphenols and a higher antioxidant capacity (Grimi et al., 2011) (see
Figure 10.3 for examples). Other researchers have found that carrot juices stabilized by
using pulsed electric fields (35 kV cm-1 for 1500 µs using 6 µs pulses at 200 Hz) had
higher β-carotene content than untreated juices (Quitao-Teizeira et al., 2009). Besides,
the treatment using this technique allowed a better retention of the quality parameters
than using heat treatments. The same observations were obtained for other juices as well
(Odriozola-Serrano et al., 2008). The effect of this treatment on the vegetable matrix
could be also useful for the subsequent extraction of bioactive interesting compounds,
as anthocyanins. A fast pulsed electric field treatment (2.5 kV cm-1, 15 µs pulse width
and 50 pulses) allowed the improvement of more than 2-fold the extraction of
anthocyanins from red cabbage (Gachovska et al., 2010).
Pulsed light processing is being explored as non-thermal technique and is based on the
ability of pulsed light to treat food surfaces, eliminating the microorganisms present.
The light employed in this technique is broad spectrum white light, basically similar to
that of sunlight, but including also some UV wavelengths. The light is applied in single
or short series of short pulses (ms) with an intensity between 20000 and 90000 times
higher than that of the sunlight. The mechanisms employed would include
photochemical effects and DNA damage as well as short-term thin-layer photothermal
effects. The influence on the natural antioxidants present in foods as well as on the
generation of new components is still scarcely studied. Nevertheless, it has been
24
observed that these treatments would not imply a destruction of the nutritional quality of
different products (Caminiti et al., 2011; Muñoz et al., 2011).
10.4 CONCLUSIONS
Food processing seems to generate some controversy in terms of risks and benefits
associated to its use. Although some risks have been stressed during the last years and a
lot of research has been concentrated in order to minimize them (for instance,
production of acrylamide or heterocyclic amines, losses of essential nutrients, formation
of artifacts), it is clear that food processing is a need in terms of food safety
requirements. Moreover, the new trends are focused on the possibility of using
controlled food processes to improve the health benefits of certain foods, that is, food
processing understood beyond its own basic function. Food processes susceptible to be
fine-tuned to generate beneficial compounds are based on thermal and non-thermal
treatments and are discussed in the present book chapter based on their ability to
produce antioxidant compounds or to improve the overall antioxidant activity of the
food commodity. Although it is true that evidences have been presented widely that
demonstrated the in-vitro effects of antioxidants either released or generated in foods
during processing, a lot of research is still needed to provide with scientific evidences of
the real effect of such compounds in the human health. Therefore, in the future more
research will be needed in order to decipher the molecular mechanisms of such products
in the human body and new approaches, such as those based on –omics technologies,
will be required. In this sense, the development of Foodomics together with
metabolomics, proteomics and transcriptomics, can be the key for a holistic approach on
the real effect of antioxidants generated during food processing as functional food
ingredients. More research will be also needed in terms of systematic studies on food
25
processing conditions (thermal and non-thermal) and on their effects on different types
of foods, and also on the development of industrial applications of new technologies
(for instance, non-thermal) able to minimize the risks and maximize the benefits of the
food processing. By building all this new knowledge, the possibility of “producing”
new compounds with antioxidant activity able to provide a health benefit might be a
reality.
To conclude, only research carried out considering multidisciplinary teams (chemists,
biochemists, food technologists, nutritionists, medical doctors, etc.) can warranty the
real effects of such antioxidant compounds, generated during food processing, as
relevant for human health.
ACKNOWLEDGEMENTS
Authors want to thank Projects AGL2011-29857-C03-01, AGL2010-17779
(NATURAGE), CONSOLIDER INGENIO 2010 CSD2007-00063 FUN-C-FOOD
(Ministerio de Educación y Ciencia) and ALIBIRD, project S-505/AGR-0153,
(Comunidad Autónoma de Madrid) for economical support. M.H. would like to thank
MICINN for a “Ramon y Cajal” research contract.
26
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FIGURE LEGENDS.
FIGURE 10.1 Maillard reaction products with known structure and antioxidant
properties. Reproduced with permission from Silván et al. (2006).
FIGURE 10.2 Chemical structures of cis-isomers of lycopene.
FIGURE 10.3 Chemical and enzymatic reactions affecting chlorogenic acid during
processing. LMW: low molecular weight compounds, HMW: high molecular weight
compounds.
FIGURE 10.4 Lipid peroxidation inhibitory activity of the peptide (54 µM) isolated
from fermented mussel sauce (MRSP). The activity was measured in a linoleic acid
oxidation system for 8 days using butylated hydroxytoluene (BHT) and α-tocopherol as
positive controls at the same concentrations. Reproduced with permission from
Rajapakse et al. (2005).
FIGURE 10.5 Transmission electron microscopy of A) untreated cells of
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for 600 µs at 35 kV/cm. Reproduced with permission from Martín-Belloso et al. (2011).
35
TABLE 10.1 Some recently published works in which a positive effect on the antioxidants has been observed after an irradiation treatment of food products.
Product Antioxidants Irradiation type Observations Reference
Romaine lettuce, Iceberg lettuce, endive
Phenolic compounds γ-radiation (up to 2 kGy) Increased antioxidant capacity and total phenolic content after irradiation
Fan, 2005
Mushrooms (Agaricus blazei) Phenolic compounds γ-radiation (from 2.5 to 20 kGy) Antioxidant capacity of extracts increased Huang et al., 2006
Mango (fresh-cut) Phenolics, flavonoids UV-C Total phenolics and flavonoids accumulation during storage
Gonzalez-Aguilar et al., 2007
Carrot juice Phenolic compounds γ-radiation (10 kGy) Total phenolics and antioxidant capacity increased
Song et al., 2006
Almond skin Phenolic compounds γ-radiation (0-16 kGy) Increased antioxidant capacity and total phenolic content after irradiation
Harrison et al., 2007
Apple Anthocyanins, flavonols, quercetin glycosides, phenolic
compounds
UV-B Antioxidant activity increased Hagen et al., 2007
Rosemary Phenolic compounds γ-radiation (30 kGy) Antioxidant capacity and total phenolic contents increased in extracts
Perez et al., 2007
Broccoli Phenolic compounds, ascorbic acid
UV-C (8kJm-2) Increased phenolics and ascorbic acid contents as well as antioxidant capacity
Lemoine et al., 2007
Nigella sativa seeds Phenolic compounds γ-radiation (2-16 kGy) Antioxidant capacity and total phenols content increased depending on solvent
Khattak et al., 2008
Strawberries Anthocyanins UV-C Increased antioxidant capacity and Erkan et al., 2008
36
anthocyanins content
Soybean Phenolic compounds UV-C Increased flavonoids content Winter et al., 2008
Hizikia fusiformis alga Polyphenolic compounds γ-radiation (1 kGy) Antioxidant activity increased Choi et al., 2010
Beet (fresh-cut) γ-radiation (1-2 kGy) Antioxidant activity increased Latorre et al., 2010