THE EFFECT OF THERMAL TREATMENT ON ANTIOXIDANT AND PHYSICOCHEMICAL PROPERTIES OF BLACK SHALLOT (ALLIUM ASCALONICUM)

Black shallot is a newly developed food product from shallot (Allium ascalonicum), which is characterized by dark brown color, sweet taste and jelly texture. However, the effect of thermal treatment on physicochemical properties, bioactive compounds, antioxidant activity has not been assessed yet. In this study, we determined the changes of some physicochemical properties (reducing sugar, pH and acidity), polyphenols, and its antioxidant activity (via DPPH radical scavenging assay) during aging process at three different temperatures (60, 70, 80oC) with sampling intervals 3 days for a 21-day period. All thermal treatment conditions gradually reduced water content and pH versus increased the acidity, reducing sugar, total polyphenol content, and antioxidant activity. The optimal conditions to produce the antioxidant and polyphenols -enriched black shallot were 70oC for 18 days (63.95 & PLUSMN; 1.24 % and 52.86 & PLUSMN; 2.02 mg of GAE/g DW, respectively). These findings not only gives the basis for the optimization of processing for improvement food quality with desired attributes but also suggests black shallot as the promising source to extract bioactive compounds for application in pharmaceutical and food industry.