Onion flower stalks: Its physicochemical, bioactive, and antioxidant characteristics as affected by thermal processing

Consuming vegetables is linked to health benefits. Onion flower stalk (OFS) is a green vegetable with a mild onion flavor and is widely consumed in South Asia. The objectives of this study were to evaluate and understand the effect of boiling time (5, 10, 15, and 20 min at 100 °C) on physicochemical, bioactive compounds, and antioxidant activity of OFS. After boiling, moisture content and pH increased, whereas total soluble solids, water activity, titratable acidity, and ascorbic acid content decreased with increasing boiling time. The ascorbic acid content of fresh OFS was 20.59 mg/100 g fresh weight (FW), which decreased by 71.45 % after 20 min of boiling. The total phenolics, flavonoids, and tannin content in fresh OFS were 517.16 mg GAE/kg FW, 341.55 mg QE/kg FW and 517.28 mg TAE/kg FW, respectively. However, prolonged boiling caused a damaging effect on these bioactive compounds. It was observed that 20 min of boiling caused about 55.50 % loss in total phenolic, 58.44 % loss in total flavonoids, and 55.88 % loss in total tannin. The decrease in antioxidant capability was associated with the depletion of phytochemicals. The results also demonstrated that the ethanolic extract of OFS was effective in DPPH free radical scavenging activity. For extended boiling, the IC50 values rose gradually, indicating a decrease in antioxidant activity. Kinetic modeling showed that a first order model could more accurately anticipate changes in ascorbic acid and bioactive components with a higher R2. Findings from this research would be useful in designing thermal processing equipment for fruits and vegetables.