January 10th, 2018
Role of anti-oxidants in nutrition and health – sources of anti-oxidants
A number of studies have evaluated natural food sources of antioxidants. Ismail, Marjan and Foong (2004) for instance assessed the antioxidant contents in four types of vegetables – kale, spinach, cabbage, shallot and swamp cabbage. The study sought to find out “the total antioxidant activity and phenolic content” of these vegetables in their fresh and thermally-treated forms (Ismail, et al., 2004, p. 582). The study obtained the vegetables from various wet markets in Malaysia with these being randomly picked from the shelves (Ismail, et al., 2004). The vegetables were then prepared for extraction of compounds of interest with the samples for thermal evaluation being boiled in 500ml water for 1 minute (Ismail, et al., 2004, p.582). Repeated extraction was carried out using ethanol with the ethanol residues in the extract being removed under reduced pressure in a rotary evaporator at 40 oC (Ismail, et al., 2004, p. 582). The total antioxidant activity in all the extracts was measured to the extent of success in bleaching ß-carotene as evaluated by a formula relating initial absorbance for both control and test samples to the respective absorbance at time, t=120 minutes (Ismail, et al., 2004, p. 582). The Folin-Ciocalteu method was used for total phenolic content determination (Ismail, et al., 2004). The results of the study showed the antioxidant potency to differ among the studied vegetables with thermal treatment also having some effect on such antioxidant capacity. The antioxidant activity was for instance found to be highest in shallots with respective decreasing activity found in spinach, swamp cabbage, cabbage and kale (Ismail, et al., 2004). Thermal treatment also significantly reduced the antioxidant activity in all the vegetables except for shallots and also decreased the phenolic content in all the vegetables (Ismail, et al., 2004).
Similarly; Lako, Trenerry, Wahlqvist, Wattanapenpaiboon, Sotheeswaran and Premier (2007) evaluated the antioxidant properties and constituents of Fijian fruit, vegetables and other readily available foods. The study collected data in a random sampling process that ensured foods evaluated were representative of those consumed by Fiji population (Lako, et al., 2007). The samples were then prepared and ethanol extraction used to obtain the active ingredients for analysis (Lako, et al., 2007). Cintra 5 Spectrophotometer was used to assess the total antioxidant activity and Folin-Ciocalteu assay employed for the total polyphenol assay (Lako, et al., 2007). Anthocyanians in the foods were evaluated using a Cintra 5 UV–vis Spectrophotometer with varying pH being used for specific identification while carotenoids extraction was conducted in a dark room to avert their degradation by light (Lako, et al., 2007). Flavanols were also extracted using an antioxidant (terbutylhydroxyquinone) reinforced methanol solution to prevent their oxidation (degradation) before analysis (Lako, et al., 2007). The results of the study found highest antioxidant capacity in green leafy vegetables with fruits and root crops following in that order (Lako, et al., 2007). High antioxidant capacity was also observed in some herbs with a commonly used herb in Fiji – Zingiber zerumbet (wild ginger) – taken before meals being shown to be a rich source of a flavanol, kaemferol, that is suggested to have high antioxidant activity (Lako, et al., 2007). Among the vegetables, sweet potato leaves were notable for their high antioxidant activity, high polyphenol content, flavanol (quercetin), and ß-carotene (Lako, et al., 2007). Other food substances such as turmeric ginger, drumstick leaves, and wild ginger were also noted for their antioxidant capabilities (Lako, et al., 2007).
Other studies have suggested polyphenolic compounds (e.g. Catechins) found in tea to exhibit antioxidant activity (e.g. Tijburg, Wiseman, Meijer & Westrate, 1997; Riso, Erba, Criscuoli, & Testolin, 2002; Erba, Riso, Foti, Frigerio, Criscuoli & Testolin, 2003; reviewed under activity). Another study suggests that flavanoids (secondary metabolites) derived from honey could have protective functions against oxidative damage; as shown in the study using human red blood cells with oxidative damage being induced using radical species (Blasa, Candiracci, Accorsi, Piacentini & Piatti, 2007). In conclusion Bagchi and Puri (1998), provide a table (table 3) showing some of the natural sources (e.g. vegetables fruits and fish) of three compounds – Vitamin E, Vitamin C, and ß-carotene – widely suggested to exhibit antioxidants properties. Go to part 3 here.