Retention of flavonols in onions after osmotic dehydration

The aim of the study was to examine mass transport, retention, and migration of polyphenols of selected onion varieties during osmotic dehydration. The varieties Alonso F1, Hystore F1, Hysky F1 and Red Lady F1 were treated with 40°Bx sucrose solution containing NaCl (5 g/100g) at 20 °C for 5 h. The greatest increase in the dry substance level occurred in the first hour - from approx. 12-13% to approx. 21–23%. Onions of the Hystore variety lost the most water, and Hysky the least. The sum of polyphenols in the raw material was from 711 mg/100g of d.m. (Hysky) up to 1228 mg/100g of d.m. (Hystore); it consisted of quercetin-3,4′-O-diglucoside, quercetin-4′-O-glucoside, quercetin-3-O-glucoside, quercetin-3-O-(6″-acetyl-glucoside) and quercetin. The retention of polyphenols after 1 h of dehydration was 73–85%, from 5 to 19% of these compounds went into the solution. After a different time, less than 10% polyphenols were degraded in Red Lady and Alonso varieties, and in Hystore and Hysky up to approx. 30%. The main polyphenols, quercetin-4′-O-glucoside and quercetin-3,4′-O-diglucoside, showed similar stability during dehydration. •Osmotic dehydration reduces the amount of polyphenols in onions.•Polyphenols are degraded, more of them is transferred to the hypertonic solution.•The major quercetin glucosides show similar stability during dehydration.