ANTIOXIDANT PROPERTIES AND MINERAL BIOACCESSIBILITY OF BASELLA RUBRA AFTER SIMULATED HUMAN GASTRO-INTESTINAL DIGESTION

Abstract

Previous studies have shown that Basella rubra is rich in minerals, vitamins and phytochemicals. This information does not automatically relate to the availability and bio-accessibility of these constituents when the vegetables are processed (blanched) and degraded by the enzymes and juices of the gastrointestinal tract. This investigation is therefore aimed at evaluating the mineral bio-accessibility of B. rubra after simulated human gastrointestinal digestion; and comparing the antioxidant activities of B. rubra at different stages of in vitro gastrointestinal digestion. Phytochemical examination of B. rubra revealed the presence of cardiac glycosides, flavonoids, alkaloids, tannins, terpenoids and steroids. Mineral content of Basella rubra at three phase of digestion (oral, oral-gastric and total gastrointestinal) were also assessed using flame photometry (sodium and Potassium), atomic absorption spectroscopy (Calcium, Manganese, Magnesium, Zinc, Iron, Copper and Lead) and Vanadomolybdate yellow method (Phosphorus). The following antioxidant assays were carried out on the digests: total phenolic content (TPC), total flavonoid content (TFC), Ferric reducing antioxidant potential (FRAP), hydroxyl (OH*), nitric oxide (NO*), DPPH, ABTS radical scavenging ability. The ability of the studied vegetable to inhibit lipid peroxidation in the brain and liver of adult albino rats were also carried out. HPLC-DAD qualitative estimation revealed the presence of gallic acid, catechin, chlorogenic acid, caffeic acid, ellagic acid, p-coumaric acid, quercetin and apigenin in the raw and blanched samples. Quantitative estimation revealed that p-coumaric acid and apigenin were the most abundant phenolic compounds while ellagic acid and quercetin were found in minute quantities in B. rubra. The mineral composition, phytochemical and anti-nutrient level of B. rubra reduced after blanching. Na, K and Ca were present in high concentrations after in vitro digestion, in both raw and blanched samples of the studied vegetable; Mg, Mn, Cu, P, Fe, Zn, and Pb on the other hand were present in minute quantities. Zn was not bioavailable in the presence of Phytate. The in vitro enzyme digested samples exhibited potent and appreciable antioxidant activities than its corresponding non-enzymic digest (control) samples as observed in the total phenolic content (TPC), total flavonoid content (TFC), ferric reducing antioxidant potential (FRAP), 2,2’- azinobis-(3-ethylbenzothiazoline-6-sulfonic (ABTS) and lipid peroxidation assays; reverse was the case with NO, OH and DPPH assays. Blanching led to a considerable loss of minerals, phenolic compounds and phytochemicals in the studied vegetable. High antioxidant activity demonstrated by the studied vegetables could be attributed to the presence of bioactive compounds highlighted in the study. The result also revealed that the bioactive components will be retained after the passage of the food along the gastrointestinal tracts. However, moderate heat processing should be adopted in order to prevent and/or reduce phytochemical loss. Therefore, this plant (if minimally processed) may be harnessed in preventive health care by manufacturers and researchers in the design of nutraceutical products.