Bioaccessibility of Polyphenols from Onion (<i>Allium cepa</i>) as Influenced by Domestic Heat Processing and Food Acidulants

Abstract

Polyphenols are gaining importance in view of their health beneficial influences. Onion (<em>Allium cepa</em>) was analyzed for total polyphenol and flavonoid contents and their bioaccessibility as influenced by heat processing and food acidulants. Total polyphenols in raw onion (2.17 mg/g) were increased by 50% upon roasting. Total flavonoids in onion (0.27 mg/g) remained unchanged in heat processing. Bio accessible polyphenols and flavonoids from onion were 0.96 and 0.02 mg/g respectively and open-pan boiling increased the bio accessible polyphenols from onion. Addition of food acidulants to onion altered the composition and concentration of phenolic compounds. Total bio accessible polyphenols of onion decreased by 15% in presence of lime juice, while the same increased from microwave heated onions by 21% in presence of amchur. Presence of lime juice decreased bio accessible polyphenols in native and pressure-cooked onion, while the same increased by 37% in roasted onion in presence of amchur. Bioaccessibility of quercetin from onion increased 6-fold in presence of amchur, while a few polyphenols viz., protocatechuic acid, syringic acid, rutin and myricetin became bio accessible in presence of these food acidulants. Amchur enhanced the bio accessible polyphenols from onion more than lime juice. Concentration of bio accessible polyphenols was higher upon open-pan boiling of onion. There was a qualitative as well as quantitative change in the phenolic composition on addition of the food acidulants. Since amchur enhances the concentration of bio accessible polyphenols more than lime juice, its use in food preparations could be a strategy to maximize bioavailability of polyphenols, especially flavonoids from onion.