Antioxidant Activity and Fresh Goat Cheese
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Currently, the study of food goes beyond evaluating not only its nutritional quality but also its functionality. Most food products are known to contain substances that can improve the consumer’s health. Milk is an example of these products having not only nutritional importance but also functional activity. Milk, as raw material, has been shown to have antihypertensive, antioxidant, antibacterial, and immunomodulatory qualities. Transformation of milk into different products such as cheese could preserve this functionality.
Nevertheless, most of the dairy products present higher biological activities than milk. The objective of this chapter is to make a count of the studies that have demonstrated the presence of antioxidant compounds in fresh goat’s cheeses. This chapter starts with goat milk, its nutritional components, as well as its fucntional compounds. Then the chapter focuses on fresh cheeses, considering animal feeding, cheese coagulation system, and the starter and adjoint cultures.
KeywordsFresh goat cheese Antioxidant activity Bioactive peptides Goat milk Casein’s hydrolysis
The presence of reactive oxygen species in cells causes affectations in the organism that can lead to diseases such as cancer, obesity, insulin resistance, and other diseases that have become major epidemics in various areas of the planet . Many authors have recommended the prevention of these diseases by consuming more antioxidant products, which can be obtained from a wide variety of foods [2, 3]. Among them is milk, which naturally contains peptides that have antioxidant activity and can be found in derived products such as fresh and ripened cheese [4, 5].
Various studies have shown that the antioxidant capacity of goat’s milk, which has been widely reported, is increased by casein precipitation process by enzymatic hydrolysis during cheese making. Studies have shown that the formation of peptides in the production of cheese increases the antioxidant capacity of fresh cheeses, and this same quality increases during a ripening process .
2 Antioxidant Peptides and Their Importance in Health
In recent decades, the study of food has become a success due to its recognition as a major agent for prevention or cure in chronic diseases like cancer, cardiovascular diseases, insulin resistance, and obesity. This knowledge has made it possible the development of new aliments that, beyond a nutritional value, have components that provide health benefits to consumers, resulting in attractive and healthy foods called “functional food,” which are defined as those foods that can present one or more physiological benefits that reduce the risk of developing any disease . In this regard, milk and dairy products have attracted significant attention due to its content of multiple molecules with specific biological activity. Thus, the antioxidant potential of food has been associated with health benefits of the consumers, and the search for novel antioxidant sources has increased considerably in the last few decades.
The oxidative metabolism is crucial for the survival of human cells, though this metabolism produces free radicals and reactive oxygen species that cause oxidative changes. Cells maintain complex systems of multiple types of antioxidants such as glutathione, vitamin C, and vitamin E, as well as enzymes such as catalase, superoxide dismutase, and various peroxidases. However, when free radicals and reactive oxygen species are present in higher amounts than the endogenous antioxidant systems, an imbalance in the redox state of the cell is produced, causing toxic effects through the production of peroxide and free radicals start chain reactions. This oxidative stress is involved in many diseases like Parkinson’s disease, Alzheimer’s disease, or even cancer .
Antioxidants stop these chain reactions by removing free radical intermediates and inhibit other oxidation reactions through their oxidation. Compounds that can act as antioxidants can be found in foods and microorganisms that can produce them. It has been shown that peptides derived from certain foods such as milk, cereals, and fermented products possess some properties that favor the health of consumers. One of these biological properties is the antioxidant activity . At present, it has been determined that many foods contain compounds that have antioxidant activity. However, only few foods of animal origin have been studied. Several authors have mentioned that the matrix of foods of animal origin is very complex to determine the source of antioxidant activity. In this area, dairy products have been widely studied since the milk of different mammals has shown the presence of bioactivity [2, 4, 9, 10]. Many authors have determined the presence of various biological activities in the milk of various mammals such as cow, goat, buffalo, or camel. The biological activities include antihypertensive, immunomodulatory, antibacterial, and antioxidant effects [11, 12].
3 Goat Milk as a Source of Antioxidant Compounds
Milk contains several antioxidant factors like peptides, lactoferrin, conjugated linoleic acid, coenzyme Q10, vitamins (C, E, A, and D3), uric acid, carotenoids, enzymatic systems, mainly superoxide dismutase, catalase, and glutathione peroxidase . Also, some of the peptides released from the milk caseins have attracted special interest for their antioxidant capacity [13, 14, 15]. In this regard, cow’s milk has been shown to contain large amounts of biologically active peptides, as observed by Català-Clariana et al. . The latter observed antihypertensive, immunomodulatory, antithrombotic, and antioxidant activities in infant milk. Another example is that of sheep’s milk, which has also been shown to have an antioxidant activity after hydrolysis using microbial proteases .
The ingestion of goat’s milk has also been shown to have positive effects on enzymatic oxidation processes, which lead to diseases if reactive oxygen species are present during oxidation. Díaz-Castro et al.  observed that the continuous consumption of goat milk could inhibit the production of superoxide dismutase, an important enzyme in the production of reactive oxygen species. These studies directly demonstrate the antioxidant capacity of goat’s milk. In this sense, milk has shown great antioxidant qualities in in vitro studies. Using DPPH radical scavenging test in goat and other ruminant milk, El-Fattah et al.  observed that the activity is strong in whole and raw milk. It was also shown that after the pasteurization process, the activity decreases but does not disappear, and finally it was determined that sterilization tends to increase the antioxidant capacity.
Most of the antioxidant compounds are directly derived from animal diet; thus, the origin of the milk is determinant in the antioxidant capacity . In this way, Alyaqoubi et al.  observed that the antioxidant activity is also widely related to the breed of the animal, observing that the milk of Jamnapari goats breed has a high antioxidant capacity.
The traditional goat farming using pastoral systems leads to uncontrolled consumption of natural browsing plants that could be carriers of several health-promoting compounds including antioxidants . Sanlidere Aloglu and Öner  measured and compared the antioxidant activity of traditional and commercial yogurt and found that the traditional product had the highest scavenging activity against the ABTS radical among all the tested samples. Ahmed et al.  determined antioxidant activity due to peptide release in both goats caseins and whey proteins. The antioxidant peptides are present after hydrolysis of caseins and generally remain after precipitation with pepsin in cheese production, finally, it was concluded that these peptides could be obtained in a better way from the production of goat cheese.
However, the composition of goat’s milk, including antioxidant compounds, varies, which depends on factors like breed, diet, stage of lactation, season, environment, and processing (i.e., mechanical, thermal, and fermentative) [15, 26, 27, 28]. In this regard, Alyaqoubi et al.  and Alyaqoubi et al.  studied the effect of the lactation period and pasteurization treatment on the antioxidant capacity of goat milk collected from different farms in Malaysia. The authors observed differences between farms, attributed to the type of breed. They also found that raw milk collected during the first lactation exhibited a higher total phenol content, ferric-reducing antioxidant content, and 2,2-diphenyl-1-picrylhydrazyl of antioxidant activity.
Grassland changes its chemical and nutritional composition seasonally (maybe due to variations in rainfall levels). When goats are feed with freerange grazing, pasture whith different nutritional properties, and flavors during the year-round season, the content on antioxidant compounds variates . Chávez-Servín et al.  compared the total phenolic compounds (TPC) present in raw and pasteurized milk from goats fed in free-range grazing against goats fed on permanent confinement, during the dry and rainy seasons. The authors found that the TPC was higher in raw milk from dry season than in pasteurized milk from the rainy season. Also, milk from goats fed on free-range grazing had a significantly higher concentration of phenolic compounds and higher antioxidant activity. Environmental factors had the same impact on the biological activity of milk by-products, where TPC and antioxidant capacity were higher in cheese than in milk and whey, highlighting the importance of the dairy matrix on the concentration of antioxidant compounds.
Antioxidant capacity in goats milk can be increased by including in the diet specific crops like Acacia farmesiana, a type of leguminous capable of providing nutrients to domestic herbivores . Delgadillo-Puga et al.  evaluated the effect of feeding supplementation with A. farmesiana pods on the antioxidant capacity and polyphenol content in goat milk and found that this crop increased the presence of phenolic acid and flavonoids (catechin) responsible of the antioxidant activity. These authors also confirmed previous findings of Chávez-Servín et al.  and concluded that grazing produces a healthier profile of bioactive compounds in milk and by-products than indoor feeding.
4 Antioxidant Capacity of Fresh Goats Cheeses
The antioxidant capacity of dairy products can be enhanced not only by phytochemical supplementation on the animal’s diet but also by the release of bioactive compounds through hydrolysis caused by commercial enzymes or during fermentation . Furthermore, some Lactobacillus strains have a direct contribution to the antioxidant activity of fermented products due to its high level of glutathione and its ability to express manganese superoxide dismutase (Mn-SOD) . The type of dairy matrix also regulates the total antioxidant capacity due to the difference in compound concentrations [9, 21].
Cheese is, without a doubt, the most known dairy product produced by the action of proteolytic and lipolytic enzymes on the dairy proteins. This biochemical process is influenced by the milk origin, manufacturing practices, starter, and nonstarter microorganisms, ripening time, etc., resulting in a unique peptide profile characteristic of each variety of cheese .
In the case of ripened cheese, there is secondary proteolysis by the action of bacterial proteinases and peptidases that generates small peptides and free amino acids . An example of enzymes that can lead to enzymatic hydrolysis is those reported by Awad et al. . They observed the hydrolysis process with chymosin and porcine pepsin on caseins from buffalo, cow, and goat milk, obtaining good results over β-casein in the presence of sodium chloride.
Despite the type of cheese, the main objective of proteolysis is the degradation of complex proteins into smaller peptides and amino acids, where some of these peptides have antioxidant properties [14, 25, 39]. These peptides have a length of 5–11 amino acids with hydrophobic properties and aromatic residues. The presence of proline, phenylalanine, histidine, tyrosine, and tryptophan has been correlated with the antioxidant capacity .
There are only a few works that focused on the evaluation of functional properties fresh goat cheeses since most of the goat cheeses produced in the world have a ripening step. This ripening process could take some days to some weeks. Hernández-Galán et al.  evaluated the antioxidant activity in fresh goat cheese fabricated without starters and with raw and pasteurized milk from different seasons. These authors compared antioxidant activity in nonprotein nitrogen (NPN) and soluble in acid (ASN) protein fractions. The NPN fraction exhibited significantly higher antioxidant activity than ASN, probably due to the smaller size of the peptides in the NPN fraction. However, the authors did not find significant differences between cheeses due to heat treatment or milk season.
Starter and adjoint cultures have an important role in the production of antioxidant compounds in fresh and ripened cheeses. Kocak et al.  reported antioxidant activities (DPPH method) of about 30% on day 1 for brined ripened goat cheeses added with different adjoint cultures. Revilla et al.  reported important antioxidant activity from month 0 in ripened cheeses (>5500 μmol of Trolox/mg of cheese) made with summer and winter goats milk.
On the other hand, important antioxidant activity has also been observed for goat cheeses with a short ripening time. Sulejmani et al.  reported important antioxidant activity in traditional goats cooked paste cheeses ripened in brine for two months with or without the addition of herbs. Barać et al.  analyzed the antioxidant capacity of water-soluble and water-insoluble protein fractions from white-brined cheese prepared with overheated goat milk and ripened for 50 days. These authors attributed the antioxidant activity in the water-soluble fraction (WSF) of fresh cheese (day 0) to the peptides that originated from weakly bound whey proteins and products of thermolysis and primary proteolysis. The water-soluble fraction of fresh cheese had almost three times more total antioxidant capacity than the water-insoluble fraction.
Meanwhile, the antioxidant capacity of the water-insoluble fraction was related to the proteins incorporated into the gel matrix. The antioxidant activity of both fractions increased during ripening. For the water-soluble protein fraction, the increase in antioxidant capacity was positively correlated with the content of water-soluble nitrogen, meaning that low molecular weight nitrogen compounds, a product of the secondary proteolysis, are significant contributors of the antioxidant capacity of this fraction. Barać et al.  probed that in vitro digestion of the water-insoluble protein fraction of goat cheese can significantly improve antioxidant activity.
Even though the antioxidant activity observed in fresh goat cheeses is attributed to the peptides released during clotting and storage, there are other compounds present in minor concentrations that come from the milk [21, 28, 32]. Delgadillo-Puga et al.  reported that milk from grazing goats showed a higher polyphenol content (mg of gallic acid equivalents/L of milk) than the milk from indoor goats fed with a conventional diet. However, this concentration increased when Acacia farnesiana (AF) pods were added to the conventional diet. Nevertheless, DPPH assay showed that antioxidant activity remained significantly higher in gazing goats’ milk despite the AF proportion in animal diet. On the other hand, oxygen radical absorbance capacity (ORAC) assay showed similar antioxidant capacity for milk obtained from gazing goats fed with 30% AF. Cuchillo Hilario et al.  evaluated the antioxidant capacity of polyphenol extracts from fresh soft goat cheeses made with grazing goats’ milk and indoor goats’ milk. These authors found significant differences in the antioxidant capacity between cheese extracts; cheeses from grazing goat’s milk showed higher antioxidant capacity and a higher concentration of total polyphenols. Both works conclude that antioxidant capacity in the milk as well as in the cheese could be increased by modifying the animal feeding system.
Fresh goat cheeses are an important product for human nutrition, not only due to the nutritional facts but also because of the functional activity they show. Most of the fresh goat cheeses are produced in small quantities, but they have a regional impact. Antioxidant activity, associated with health benefits, is present in fresh goat cheeses, despite the lower extent of proteolysis in this kind of cheeses.
Fresh goat cheeses contain a wide range of bioactive peptides and polyphenols responsible for the antioxidant capacity. Even if fresh cheeses show lower activities than ripened cheeses, the activity is significant to obtain health benefits.
The second author, Vazquez-Garcia, R gratefully acknowledges Consejo Nacional de Ciencia y Tecnología (CONACyT) for granting scholarship (No. 260794).
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