Gyunghoon Hong (Mann Lab, Dept. Plant Sciences, University of California, Davis CA 95616), Leigh Schmidt (Mann Lab, Dept. Plant Sciences, University of California, Davis CA 95616), Henrik Ermen (Mann Lab, Dept. Plant Sciences, University of California, Davis CA 95616), and Marita Cantwell (Mann Lab, Dept. Plant Sciences, University of California, Davis CA 95616)
Modified atmosphere packaging is a key technology for maintaining lettuce salad quality, mainly by reducing cut edge discoloration. However, the use of MA may have detrimental consequences, and here we studied the impact of low O2 atmospheres (0.2 to 1%) alone or in combination with high CO2 atmospheres (3, 6, 9-10%) on Vitamin C concentrations. Romaine lettuce was trimmed, cut manually into 2 x 2 cm pieces, rinsed in chlorinated water (50 ppm sodium hypochlorite, pH 7, 20 seconds), spun in a manual spinner, and packaged in perforated plastic bags and stored in containers with flows of humidified air or modified atmospheres up to 12 days at 5 degrees C. Green leaf lettuce was prepared as whole washed leaves and stored under the same conditions. Pieces or leaves were evaluated for appearance (overall visual quality, discoloration and decay) and composition (sugars, chlorophyll, carotenoids, and phenolic compounds were determined by colorimetric methods, and Vitamin C by HPLC). Initial total Vitamin C varied from 25 to 50 mg/100g FW. The rate of Vitamin C loss varied, but in all experiments, total ascorbic acid concentrations decreased more rapidly in pieces or leaves stored in CO2-containing atmospheres than air, and before the loss of marketable quality. Low O2 alone helped retain Vitamin C concentrations. Of six enzymes in the Ascorbate-glutathione that were assayed, only ascorbate peroxidase activities were lower in a 10% CO2 atmosphere than in air-stored lettuce; reduced and total glutathione concentrations were also lower in the CO2-stored lettuce.