Overview Of Abtioxidants: Flavonoids, Vitamin C, And Phytates

Flavonoids are polyphenols which have the C6–C3–C6 general structural backbone in which the two C6 units are of phenolic nature. They are present in high concentrations in the epidermis of leaves and fruits and have important and varied roles as secondary metabolites, being involved in processes like UV protection, pigmentation, stimulation of nitrogen-fixing nodules and disease resistance (Cartea et al. , 2010). Flavonoids occur widely in plants and are a biologically major and chemically diverse group of secondary metabolites that is divided into subgroups including anthocyanidins, flavonols, flavones, flavanols, flavanones, isoflavones, neoflavonoids, chalcones, dihydrochalcones and dihydroflavonols (Treutter, 2006; Tsao, 2010). They are classified basing on the number and arrangement of carbon atoms(Cartea et al. , 2010). Flavones, Flavonols, Flavanones and Flavanols are the most common in vegetables (Tsao, 2010). Anthocyanidins are the principal components of the red, blue and purple pigments of the majority of flower petals, fruits and vegetables (Tsao, 2010).

Flavonoids are beneficial for the plant itself as physiological active compounds, as stress protecting agents (Hou et al. , 2016; Khlestkina, 2013), as attractants or as feeding deterrents, and have a significant role in plant resistance. This explains why the level of flavonoids and other polyphenols increases during harsh conditions that is water stress, high temperature and infection by pathogens (Hou et al. , 2016; Khlestkina, 2013; H. G. Kim et al. , 2011; Park et al. , 2012; Rusjan, Halbwirth, Stich, Mikulič-Petkovšek, & Veberič, 2012)Vitamin CVitamin C is in the form of ascorbic acid and dehydroascorbic acid (Mohammed, Hamad, & Mohammed, 2009). Ascorbic acid and dehydroascorbic acid are widely found in many fruits and vegetables (S. K. Lee & Kader, 2000) and ascorbic acid has an antioxidant activity(Valko et al. , 2007) because it possesses a relatively high reducing power due to the hydrogen atoms on the hydroxyl groups (Rasanu, Magearu, Matei, & Soceanu, 2005), which dehydroascorbic acid does not have. Ascorbic acid can reversibly be oxidized to dehydroascorbic acid which is inactive in terms of antioxidant capacity. Ascorbic acid is a water-soluble antioxidant (Ogunlesi et al. , 2010), known to be important to health and for proper functioning of the human body.

As an anti-oxidant (Shetty, Magadum, & Managanvi, 2013), vitamin C protects against cancers, heart disease, stress, it is part of the cellular chemistry that provides energy, it is essential for sperm production, and for making the collagen protein involved in the building and health of cartilage, joints, ligaments, skin, gums and blood vessels (Johnston, Steinberg, & Rucker, 2007). Vitamin C helps in maintaining a healthy immune system, it aids in neutralizing pollutants, is needed for antibody production, acts to increase the absorption of nutrients (including iron) in the gut, and thus into the blood (Rasanu et al. , 2005). Ascorbic acid is a cofactor in numerous physiological reactions, including the post-translational hydroxylation of proline and lysine in collagen and other connective tissue proteins, collagen gene expression, synthesis of norepinephrine and adrenal hormones, activation of many peptide hormones, and synthesis of carnitine (Akanyijuka, 2017; Johnston et al. , 2007). The content of vitamin C in fruits and vegetables can be influenced by various factors such as genotypic differences, pre-harvest climatic conditions and cultural practices, maturity and harvesting methods, and postharvest handling procedures (S. K. Lee & Kader, 2000).

Ascorbic acid is readily oxidized (Mohammed et al. , 2009) and therefore should not be left exposed to oxygen or air (El-Ramady et al. , 2015). Temperature management after harvest is the most important factor to maintain vitamin C of fruits and vegetables; losses are accelerated at higher temperatures and with longer storage durations (S. K. Lee & Kader, 2000; Phillips et al. , 2010; Rickman, Barrett, & Bruhn, 2007). 2. 7. 4 PhytatesPhytates are the primary storage form of both phosphate and inositol in plants (Greiner, Konietzny, & Jany, 2006; Kumar, Sinha, Makkar, & Becker, 2010). It accounts for 60% - 90% of the seed phosphorus (Petry, Egli, Campion, Nielsen, & Hurrell, 2013). Phytate which is chemically known as myo-inositol(1,2,3,4,5,6) hexakisphosphate is a salt of phytic acid and it is a compound naturally formed during maturation and common constituent of plant derived food (Greiner et al. , 2006). Myo-inositol(1,2,3,4,5,6) hexakisphosphoric acid (phytic acid) salts are common in animals, plants and soil (Greiner et al. , 2006; J. Kim et al. , 2009; Schlemmer, Frølich, Prieto, & Grases, 2009). Phytic acid has a strong chelating characteristic. It chelates ions like Ca2+, Zn2+, Mg2+, Mn2+, Fe2+ and Fe3+ to form globoids (Petry et al. , 2013). Phytic acid is negatively charged at physiological pH approximately 1. 5 to 7 (Petry et al. , 2013) and for this reason phytates have ability to chelate mineral cations. In phytates the inositol ring is highly phosphorylated and the more phosphorylated the inositol rings, the stronger the interaction with cations and the lower solubility (Petry et al. , 2013)

This reduces the bioavailability of the ions thus highly decreases the absorption of non-haem iron and zinc ions in humans (Petry et al. , 2013) hence increasing zinc and iron deficiency causing anemia and rickets caused by calcium deficiency. Phytates form complexes with proteins at both low and high pH values and this changes the protein structure resulting in decrease in protein solubility, enzymatic activity and proteolytic digestibility (Kumar et al. , 2010). Phytic acid decreases energy digestibility by reducing the digestibility of energy generating molecules such as carbohydrates, lipids and protein (Woyengo & Nyachoti, 2013). Phytates reduce carbohydrate solubility by forming complexes with the carbohydrate, decreasing the digestibility and absorption of glucose (Kumar et al. , 2010) hence reducing the glycaemic index. However, phytates are reported to have anti-oxidant capacity and reported to protect against various cancers like colon cancer, prostate cancer, mammary carcinoma, pancreatic cancer (Kumar et al. , 2010).