Effect of acute ingestion of fresh and stored lettuce ( Lactuca sativa ) on plasma total antioxidant capacity and antioxidant levels in human subjects

Abstract

The present study investigated whether storage under modified-atmosphere packaging (MAP) affected the antioxidant properties of fresh lettuce ( Lactuca sativa ). Eleven healthy volunteers (six men, five women) consumed 250 g fresh lettuce, and blood was sampled before (0 h) and 2, 3 and 6 h after consumption. The protocol was repeated 3 d later with the same lettuce stored at 5°C under MAP conditions (O 2 –N 2 (5:95, v/v)). Results showed that after ingestion of fresh lettuce, plasma total radical-trapping antioxidant potential (TRAP), measured as area under the curve, was significantly higher (1·3 (SEM 0·3) MMOL/L PER 6 H; P <0·05) THAN THE VALUE OBTAINED WITH MAP-STORED LETTUCE (0·1 (sem 0·2) mmol/l per 6 h). Plasma TRAP, quercetin and p -coumaric acid were significantly different from baseline values ( P ≤0·05) 2 and 3 h after fresh lettuce ingestion. Caffeic acid increased significantly at 3 h ( P <0·05). Plasma β-carotene levels increased significantly at 6 h ( P <0·05). Vitamin C concentrations (mg/l) rose from 10·9 (sem 2·0) to 12·7 (sem 3·0) ( P <0·001), 12·7 (sem 2·0) ( P <0·01) and 12·9 (sem 3·0) ( P <0·05) at 0, 2, 3 and 6 h respectively. No changes were observed after ingestion of MAP-stored lettuce for all the measured markers. Our present results showed that ingestion of MAP-stored lettuce does not modify plasma redox status in healthy subjects. Further research is needed to develop post-harvesting techniques able to preserve the bioactive molecule content of plant food.