Bulb size influences the quality and bioactive compound contents in cold-stored onion (Allium cepa L.) peels

Abstract

This study evaluated the effects of bulb size on fresh weight, peel color attributes, and bioactive compounds in cold-stored onion peel tissues of onion (Allium cepa L.). Since cold storage is a crucial post-harvest step, understanding the impact of bulb size on bioactive compound retention is essential for maintaining onion peel quality. Onion bulbs were cultivated and stored in a temperature- and humidity-controlled system for five months, with evaluations conducted at monthly intervals. The results showed that onion peel lightness (L∗) and hue angle (h^o) were lower in large-sized bulbs compared to small-sized bulbs but peel chroma (C∗) was higher in large-sized bulbs. Onion peel color and hue angles were lower in the extra-large bulb than in the small bulb. The larger bulb was found to have lower levels of these compounds retained in them as compared to small bulbs. The contents of the bioactive compounds (protocatechuic acid, spiraeoside, and quercetin) in the peel tissues were generally lower in large bulbs compared to small bulbs during cold storage. Specifically, quercetin content was 1.52 mg/g DW in small bulbs but only 0.84 mg/g DW in large bulbs, while spiraeoside content decreased from 0.75 mg/g DW to 0.41 mg/g DW. Bulb fresh weight was negatively correlated with spiraeoside and quercetin contents. The findings of this study serve as a basis for quality control and the preservation of bioactive compounds in onion peel tissuees during cold storage. These insights can help the food industry and storage management optimize strategies to retain bioactive compounds in onion peels.