**6. Applications in food**

In recent years, many polyphenols have been used as natural antioxidants in oils and fats to prevent lipid oxidation, protect food and beverages from light exposure, to prolong shelf‐life of food, supplement for animal feeds to improve their health, to protect animal products, like antimicrobial agent in foodstuffs and health functional ingredient in foods and dietary supplements; these applications can be attributed mainly to antioxidant and antimicrobial activities [47, 67, 68]. The use of synthetic additives in the food industry has been declining in recent years; this is mainly because man seeks to reduce risk in suffering from diseases which have been associated with synthetic products consumption. Flavonoids are phytochemicals that cannot be synthesized by humans; however, these compounds may be used as food addi‐ tives to improve health‐beneficial effects and increase their amount in humans [69, 70].

Flavonoids are present in significant amounts in many fruits and vegetables; natural antioxi‐ dants and flavonoids have been reported as two of the most important micronutrients, which can be used in industry to reduce the use of synthetic compounds on foods and improve health in humans due their potential to decrease several diseases. These bioactive compounds can be used to prolong shelf‐life and preserve many foods due to their antimicrobial and antioxidant properties [44]. Moreover, in recent years interest in acquiring ever more natural products has grown; this has been caused by restriction over the use of synthetic antioxidants in food (such as BHA and BHT) and increase the use of natural compounds such as antioxi‐ dants or food components, which have relatively low toxicity compared to synthetic products [57, 65].

Flavonoids are suitable compounds that may be used as food preservative due to their benefi‐ cial effects that have been demonstrated before: prevention of fat and oils oxidation, supple‐ ment for animal feeds, protection of vitamins and enzymes, inhibition of microbial growth in foodstuffs and health functional ingredient in foods and dietary supplements [68]. The most studied applications of flavonoids in foods are in red meats and poultry to inhibit lipid oxida‐ tion, use of natural extracts in foods as functional ingredients and retard spoilage microor‐ ganism growth in meats. Some studies have indicated that these compounds have protective effect on meat quality and other products [67].

Recently, flavonoids have gained attention due their antioxidant properties, which can act against oxygen free radical and lipid peroxidation [71]. Many studies have mentioned that *in vitro* antioxidant activity of these compounds depends on the arrangement of functional groups on its structures; however, the mechanism of their antioxidant activity is substan‐ tially influenced by their configuration and total number of hydroxyl groups presents in the flavonoid molecule and the glycosylation of flavonoid molecule, but could be increased by polymerization of flavonoid monomers [58, 72, 73].

The protective effect of flavonoids in biological systems is attributed to their antioxidant activ‐ ity due to their capability to donate a hydrogen atom [58]. However, it is important to con‐ sider the antioxidant effect *in vivo*, which can be different comparing with *in vitro* assays: (i) low concentration on systemic circulation compared with endogenous and exogenous anti‐ oxidant compounds, (ii) high level of biotransformation that flavonoids suffer during their absorption and distribution in the body, which can decrease their antioxidant activity and (iii) large doses of flavonoids may decrease bioavailability of trace elements, such vitamins, folic acid or other antioxidants [4, 74].
