Impact of various vacuum degrees during grinding and on the quality characteristics of the onion: Color, antioxidant activities, quercetin, and quercetin glucoside compounds

Abstract

This study examines the effects of grinding under various absolute pressures (2.67, 6.67, 13.33, 19.99, and 101.33 kPa) on the quality characteristics of onion. Grinding under atmospheric and vacuum conditions showed no significant difference in mean particle size (p < 0.05), with values ranging from 201.5 to 205.3 μm. Grinding and storing onion under atmospheric conditions (control, 101.33 kPa, 0% vacuum) increased enzymatic browning and b value and decreased L value and antioxidant activity. However, under vacuum conditions (2.67 kPa, 97.4% vacuum), no significant differences (p > 0.05) in color value, browning, and antioxidant activities were observed. The individual contents of quercetin and quercetin glucosides decreased within 6 h of storage under atmospheric conditions. In contrast, at a vacuum level of 2.67 kPa (97.4% vacuum), the levels of quercetin-7,4′-O diglucoside, quercetin 3,4-diglucoside, rutin, isoquercitrin, quercetin 4′-glucoside, quercetin, and kaempferol were 1.2, 32, 2, 2.7, 3.2, 3, and 4.7 times higher, respectively, than under atmospheric conditions after 12 h of storage. Model fitting indicated that even minimal oxygen exposure considerably influenced the antioxidant activities of onions. Our results indicate that grinding in low-oxygen environments effectively prevents the oxidation of antioxidants and preserves quercetin, quercetin glucoside components, color, and the overall quality onion puree products. © 2024 Elsevier Ltd