Chemical composition and in vitro antioxidant properties of water-soluble extracts obtained from Bangladesh vegetables

The aim of this study was to evaluate the nutritional value and antioxidant properties of aqueous extracts of some Bangladesh vegetables using fruits of ash gourd, bitter gourd, brinjal, okra, ridge gourd, snake gourd, and leaves of Indian spinach, kangkong, and stem amaranth. Proximate composition showed that the dried extracts were composed mainly of crude protein (14.6%-46.7%) and non-fibre carbohydrates (26.4%-53.5%). With the exception of stem amaranth, all the extracts had >40% DPPH radical scavenging ability at 0.5 mg/ml. In contrast metal chelation was lower, except in Indian spinach with ~46%. The ferric reducing antioxidant power (FRAP) was highest for the kangkong (10.9 mM Fe³⁺ reduced), which is similar to the 9.9 mM for butylated hydroxytoluene (BHT). All the extracts suppressed linoleic acid oxidation better than BHT within the first 5 days of the incubation period. We conclude that the Indian spinach, kangkong, and okra could be considered as the most promising sources of antioxidant compounds. PRACTICAL APPLICATIONS: Vegetables are commonly consumed as part of a regular diet but the high water and fiber contents usually mean that large quantities are required to provide long-term health benefits. Therefore, in this work, aqueous extracts of nine Bangladesh vegetables were prepared to provide a more concentrated form of nutrients and bioactive compounds. The extracts had strong nutritional value based on the high contents of crude protein, potassium, iron, and non-fibre carbohydrates. The high content of polyphenolic compounds in the extracts can also provide health benefits, which was demonstrated through strong free radical scavenging, metal chelation, ferric iron reduction, and inhibition of linoleic acid oxidation. These vegetable extracts have the potential to be used as sources of bioactive compounds to prevent or treat non-communicable diseases that are associated with high oxidative stress.

Keywords: Bangladesh vegetables; amino acid composition; antioxidant; polyphenols; proximate composition.