Phenolic Metabolites in Red Pigmented Lettuce (Lactuca sativa). Changes with Minimal Processing and Cold Storage

Abstract

Minimally processed products are more perishable than unprocessed raw materials and readily deteriorate in quality, especially in color and texture. The effects of minimal processing on phenolic metabolites have been studied on red lettuce. Three different tissues of cv. Lollo Rosso were separated as white, green, and red and stored at 5 °C for 7−14 days. The phenolic acids caffeoyltartaric, chlorogenic, dicaffeoyltartaric, and dicaffeoylquinic, the flavonoids quercetin 3-glucuronide, quercetin 3-glucoside, quercetin 3-(6-malonylglucoside), and the new compound quercetin 3-(6-malonylglucoside) 7-glucoside, and the anthocyanin cyanidin 3-malonylglucoside were isolated and identified in lettuce extracts. Phenolic compound content was evaluated immediately after cutting and after storage of the minimally processed products at 5 °C. In midrib, wounding induced an increase in phenylpropanoids during storage, particularly phenolic acids and anthocyanins. On the contrary, wounding did not induce significant changes in the caffeic acid derivatives and flavonoids in green and red tissues. The anthocyanin content decreased in both green and red tissues during storage. Keywords: Lettuce; Lactuca sativa; Lollo Rosso; anthocyanins; phenolics; flavonoids; minimal processing; wound-induced changes; pigment stability; quality