Generally beer contains number of antioxidants like phenolic compounds, Products of maillard reaction (melanoidins and reductones), sulfites, vitamins, chelating agents and carotenoids but among all of them phenolic compounds, melanoidins, sulfites are of major interest due to high activity of antioxidants as well as biological effects. The prime function of antioxidant in beer is to provide flavour stability as well as health benefits. So prime source of antioxidants in beer is barley (malt) and hops. Barley and hops: Barley and hops are good source of phytochemicals. Phytochemicals are non-nutrient component and present in free, conjugated or bound form and classified into major categories like phenolic acid, flavonoid, lignin, tocols and phytosterols. These phytochemicals shows strong antioxidant activity, antiproliferative and cholesterol lowering capacity that is definitely useful in curing certain diseases like cardiovascular, diabetes, cancer and also overcome obesity in fatty people. Beer generally contain two phenolic acid categories and i.e. Phenolic acids and flavonoids. a) Phenolic acids: They are major group of phytochemicals in barley that contribute crucial role as a antioxidant in beer and found in outer layer of kernel. Phenolic acid in malt is esterified with starch or other polysaccharides which can be released from malt by enzymatic hydrolysis that leads to bound phenolic acids as compare to free form during process of mashing. In bound form phenolic acids are found at higher concentration followed by conjugated and free form. It has been found that 68% of total phenolic acid is present in barley.
b) Flavonoids: Structurally flavonoids contains three carbon atoms attached with two aromatic rings. Flavonoids are known as a protector against UV radations in case of excess light stress. The main classes of flavonoids like flavanols, anthocyanins, Proanthocyanidins (polymers of Flavonoids) are present in beer that imparts color to beer. The concentration of flavonoids in barley is depend upon intensity of colour depth.
Melanoidin: Melanoidin is final brown colored, nitrogenous product of the maillard reactions between reducing sugars and proteins or amino acids, which are formed during malting, mashing and boiling that are hold at least partially up to the final beer. Melanoidin imparts organoleptic properties (color, aroma and flavor), helps in stabilization of the foam and effects the oxidation-reduction processes of beer due to their strong antioxidant properties and other biological effects.
Sulfites: Sulfites, a component of beer, that are by-products obtained after the synthesis of sulfur- containing amino acids by yeast during fermentation and retained into the finished beer. Apart from prevention of oxidative staling, sulfites contribute as a crucial mask agents for stale flavor by reacting with carbonyl staling compounds in beer to form bisulfite–carbonyl adducts, that are must for maintaining stability in beer. The variations in sulfite content in beer is depend upon brewer’s yeast strain and brewing process.
Wine is also a non distilled alcoholic beverage obtained after the fermentation of grape juice. The prime ingredients used for wine production are grapes (red and white) and yeast. On the type of grapes used, wine is categorized into red or white wine.
White and red wine production follows following steps such as grapes harvesting, juice processing, and then alcoholic fermentation and these steps can all effect the levels of antioxidants found in grape juice and wine. There are mainly two types antioxidants in wine named as phenolic compounds and glutathione.
In context to composition, the grape berry composed of skin, pulp, and seeds. Grape berry skin comprises of 6 to 10 cell wall layers. The major components of the skin are the colored compounds (red and yellow pigments), phenolics, and aromatic compounds, as well as potassium and other minerals. underneath the skin layer, pulp is found that makes up most of the berry volume. The pulp contains large vacuoles that comprises the grape juice, which gets released during crushing of the grapes when the grape skins and vacuoles are broken down. Grape juice consists of 70–80% water with many dissolved solids. The main solutes are sugars (mainly glucose and fructose) and organic acids, such as tartaric, malic, citric, and small amounts of amino acids. The seeds are located in the center of the flesh and contain mainly phenolics also commonly referred to as tannins. Sugars, organic acids and phenolics are the main constituents present in grapes.
Phenolics: phenolic are the major antioxidants present in wine. Phenolics provide colour, flavor as well as sensory characterstics to wine. The amount of phenols in wine depends upon the variety of grapes, viticultural practices, process of wine manufacturing, and transformations that can take place during wine ageing.
The phenolics present in grapes are well known and can be divided into two main classes: the flavonoids and non-flavonoids. The non-flavonoids comprises of the hydroxycinnamic (HCA) and benzoic acids (gallic acid). From the category of flavonoid compounds flavonols, anthocyanins, flavan-3-ols and their polymerized products are present in grapes and wine. Flavonols are the yellow pigments present in the skins of both white and red grapes, while anthocyanins are the red pigments present in red grape skins. Antioxidants in White Grape Juice During Processing identified are quercetin, isorhamnetin, kaempferol, and myricetin, and their glycosides. Anthocyanins are present in grapes and wine as monoglucosides and their acetylated esters with caftaric, p-coumaric, and acetic acid. Glutathione: it is an important sulfur-containing tripeptide, of glutamic acid, cysteine, and glycine are also produced during grape ripening.
Coffee is a well acceptable drink that is traditionally used to complement meals, as well as for hedonistic and stimulant purposes. It has been found that throughout the world, 80% of the adult population consume coffee.
From Centuries, coffee has been extensively used due to desirable aroma, flavor etc. Epidemiological studies suggested that various positive effects of regular coffee consumption on human health are because of its biochemical composition. Coffee is enriched with hidroxycinnamic acids family antioxidants (caffeic, chlorogenic, coumaric, ferulic, and sinapic) and some other biologically active compounds having antioxidant activity, such as caffeine, nicotinic acid, trigonelline, cafestol. Due to coffee’s well known antioxidant potential, it is source of two-thirds of the population consumption. During processing, the antioxidant concentration of coffee changes due to the degradation of native antioxidants and the formation of new ones. So it is estimated that antioxidant potential of coffee is related to the presence of both natural constituents and compounds formed during processing (roasting). PHENOLIC COMPOUNDS In the Western diet, Coffee is known for one of the richest sources of phenolics, contributing up to 350 mg per 7-oz cup (200 ml) (Higdon and Frei, 2006). In green coffee beans, the amount of polyphenolic antioxidants influenced by origin and species, while on other hand in coffee brews it depends procedure followed for brewing (Sanchez-Gonzalez et al., 2005). The major class of phenolic compounds in coffee are chlorogenic acids (CGAs) which may account for up to 12% of the dry matter of green coffee beans (Ky et al., 2001). As discussed earlier, antioxidant potential of coffee is influenced during processing, so during roasting (200–250°C, 1.5–6 min) both phenolic and non-phenolic coffee components are partially degraded and/or bound to polymer structures. During roasting of coffee results into degradation of phenolic compounds and the formation melanoidins (Maillard reaction products) (Farah et al., 2005). Non-roasted green coffee beans contains relatively higher antioxidant activity than the roasted ones.
Melanoidins are one of the prime component of coffee brews, accounting for up to 25% of dry matter. The melanoidin formation mechanism of is supposed to contains an early stage and an advanced stage. In the early stage, the aldehydic moiety of sugars and amino groups react to produce a component which has the partial structure of –CHOH-CO-CH2NHR, while in the advanced stage, various aldehydes, ketones, and furfurals are formed from the early-stage products, and these react with amino compounds to form high- molecular-weight melanoidins (Takenaka et al., 2005).The antioxidant potential of high molecular weight melanoidins is lower than low-molecular-weight melanoidins. High temperature possessed during roasting of coffee influence the native antioxidants and loss of (Chlorogenic acids) CGAs in the coffee bean, alongwith generation of melanoidins that ultimately effects the composition and antioxidant capacity of final products. (Delgado-Andrade and Morales, 2005).
Caffeine is an alkaloid found in considerable amounts in brewed coffees (Higdon and Frei, 2006),well known for its psychostimulant effects such as increased mental sharpness, faster attention, restlessness, reduction of fatigue, and decline in laziness. Caffeine is widely used in medication and beverages (Harland, 2000). Types of beans, brewing strength and processing method influence the amount of caffeine in coffee. Robusta brewed coffee contains more caffeine content (56 to 203 mg/100 ml) than Arabica brewed coffee beans between 36 and (112 mg caffeine/100 ml). (Oestreich-Janzen, 2010). Caffeine content of green coffee beans is within the range of 1–4% (on dry basis) (Mazzafera and Silvarolla, 2010), but after roasting caffeine content is reduced upto approximately 30%. Caffeine and its catabolic products theobromine and xanthine possess both antioxidant and pro-oxidant properties. So caffeine and its metabolites may responsible for overall antioxidant and chemopreventive properties of caffeine containing beverages (Azam et al., 2003).
Trigonelline (1-methylpyridinium-3-carboxylate) is also a major constituent of coffee beans (Mazzafera, 1991). The bitter taste of coffee brew is due to this component. Trigonelline is heat liable and while roasting it is converted to nicotinic acid and other nitrogenous compounds that provide flavor (Mazzafera, 1991). A restricted amount of trigonelline is catabolized and used as a substrate for the synthesis of nitrogen containing compounds during germination of coffee seeds (Shimizu and Mazzafera, 2000). Roasting of coffee beans at high temperature influences the content of trigonelline depending on the variety of coffee beans. (Casal et al. (2000) found that trigonelline degradation increased after treatment at 200°C and only 5% of this compound remained in Arabica and 15% in Robusta coffee at 240°C. In contrast, nicotinic acid content increased ≥ 500% in both brews. Proportionally to higher roasting temperature, the conversion to nicotinic acid is greater (Stadler et al., 2002). Decomposition of trigonelline can be characterized by the content ratio of trigonelline to nicotinic acid for any roasted sample, because the nicotinic acid found in roasted coffee was essentially derived from the trigonelline in the green coffee (Minamisawa et al., 2004).
Tocopherols are association of four lipid-soluble amphipathic molecules (α-, β-, γ-, δ-) that are completely formed by photosynthetic organisms. Tocopherols are an chief component of vitamin E (Gilliland et al., 2006), that are natural lipid-soluble antioxidant, provide protect cell membranes from peroxyl radicals and mutagenic nitrogen oxide species (Gliszczyńka-Świgło and Sikorska, 2004). Two main tocopherols (α- and β-) are found in Arabica and Robusta coffee beans, both green and roasted (Alves et al., 2010). The amount of α-tocopherol roasted coffees ranged between 7.55 μg/g and 33.54 μg/g, on other hand in green coffees it was between 2.02 μg/g and 16.76 μg/g. while content of β- and γ-tocopherols in roasted coffees is more rather than green coffees.
Heterocyclic compounds produced by maillard reaction
Some volatile heterocyclic compounds chracterized in brewed coffee extracts (pyrroles, furans, thiophenes, and thiazoles) shows certain levels of antioxidant capacity (Fuster et al., 2000), but antioxidant capacity is not as strong as that of the synthetic antioxidant butylated hydroxytoluene (BHT).
Antioxidants in tea
The tea plant also known as (Camellia sinensis) is originated in china and grown in more than 30 countries. Tea is the most commonly consumed in the form of prepared beverage worldwide. Among the major tea varieties, green tea is minimally processed, as compared to black tea, so as to preserve its high content of monomeric catechins. The health benefits of green tea are mainly because of the antioxidant and anti-inflammatory activities of its catechins that effectively control oxidative stress responses that leads to chronic disease. Specifically antioxidant activity of tea covers the framework of chronic disorders, like obesity, cardiovascular disease (CVD), and nonalcoholic fatty liver disease (NAFLD), that are characterized by a pathogenesis of significant oxidative stress.
Antioxidants in tea
Among the other tea products, the tea leaves used for green tea are harvested, immediately withered, and steamed or pan fried so as to inactivate polyphenol oxidase and preserve its fresh character and monomeric polyphenol profile (Frei and Higdon, 2003). So timely post-harvest processes maintains the amount ofcatechins that would have been oxidized otherwise. Catechins accounts approximately one-third of the dry weight of the tea leaves, alongwith the eight prime green tea catechins namely epigallocatechin gallate (EGCG), gallocatechin gallate (GCG), epicatechin gallate (ECG), catechin gallate (CG), epigallocatechin (EGC), gallocatechin (GC), epicatechin (EC) and catechein (C) (Neilson and Ferruzzi, 2011). EGCG is the most abundant representing near about 50% of the total catechin content and shows the greatest antioxidant activity. Meanwhile, partially fermented oolong tea and fully fermented black tea contains high levels of theaflavins and thearubigins, but a total catechin content that can be more than 50% lower than that of green tea. Apart from the catechin quantity and distribution, green, black, and oolong teas contains similar caffeine content with 40–50 mg of caffeine per freshly brewed cup of tea.
All tea beverages are rich in flavonoids, particularly catechins and flavonols, which scavenge ROS and free radicals. Tea beverages are prime contributors of daily flavonoids intake and accounts for health benefits. The antioxidant activity of flavonoids may be an major attribute of their proposed beneficial health properties. Green tea and its catechins possess anti-obesity properties by reducing intestinal lipid absorption that leads to weight loss, and provide protection against disorders. It is estimated that a beverage containing tea catechins, caffeine, and calcium increased 24 h energy expenditure (Rudelle et al., 2007).