ANTIOXIDANT ACTIVITY OF PHENOLIC COMPOUNDS IN Dioscorea alata L. (RAJA ALA) TUBER COOKING WATER

Nutritional compounds in yams may leach out to the cooking water under most traditional domestic cooking methods. Finding alternative uses of these waste waters without discarding, can maximize the usage and importance of these yams. This study aimed to quantify the bioactive compounds and determine the antioxidant activity in the cooking water collected after boiling of Dioscorea alata L. tubers under two domestic cooking methods. Raja ala yams were boiled in water using conventional boiling (CB) and pressure cooking (PC) methods. The cooking water of both methods were collected and concentrated to obtain the solid crude product. Aqueous solutions of the crude product of CB and PC samples were prepared and subjected to qualitative phytochemical analysis. Further, they were assayed for total phenolic content (TPC), total flavonoid content (TFC), and total anthocyanin content (TAC). Antioxidant activity of each crude product was determined and a correlation between the antioxidant activity and TPC, TFC and TAC of the samples was developed using the Pearson’s correlation method. Phytochemical screening of CB and PC samples showed the presence of alkaloids, flavonoids, phenols, saponin, tannins and coumarins and an absence of proteins. CB showed a significantly higher TPC than that of PC whereas the TFC of PC was higher than CB. Both methods however, showed no significant difference in TAC extraction. Antioxidant assays showed higher activity in CB over the PC sample. A strong correlation was observed between TPC versus DPPH activity (IC50 value) and TAA of the samples. It can thus be concluded that the wastewater of both cooking methods contain a significant amount of bioactive compounds, making it a nutritious source to be further investigated and to be made use for alternate purposes without discarding it.