2019 ASHS Annual Conference

Fresh-cut lettuce is widely used in packaged leafy vegetable salads. Most fresh-cut products involve harvesting whole mature heads of romaine or iceberg lettuce, cutting leaves to a specified size, and packing in modified atmosphere packaging (MAP). Despite MAP, fresh-cut lettuce has short shelf life and loss of nutrient content. Lettuce cultivars exhibited genetic variation for shelf life in MAP, but genetic variation for nutrient retention is not known. The objectives of this research were to determine if there is genetic variation among cultivars for retention of different nutrients and to determine the relationship between shelf life and nutrient retention. Fifty accessions were selected based on previously observed differences in shelf life and lettuce type. Accessions were planted in randomized complete block design in a field in Salinas, CA, with three replications. Mature lettuce heads were harvested, processed, and stored at 4°C. Vitamin C (ascorbic acid) was analyzed 1, 2 and 3 weeks after processing (WAP), vitamin A (carotenoids) and sugars (glucose, fructose) were evaluated at 1 and 3 WAP. Stored samples were visually evaluated for shelf-life using a 0 to 10 scale, where the rating corresponds to 1/10^th of the estimated percentage of deteriorated tissue. Variation in nutrient content among the accessions was observed 1 WAP. Lactuca serriola (wild species closely related to cultivated lettuce), UC96US23, had highest content of vitamin C and A and lowest content of sugars at the initial evaluations. Iceberg lettuce, ‘Salinas’ and ‘Salinas88’, had lowest content of vitamins, and romaine lettuce, ‘Triple Threat’, had highest content of sugars. Three WAP, different levels of tissue deterioration were observed among the accessions. Romaine cultivars Romanor and Balady Cairo had the slowest and the fastest rate of deterioration, respectively. There was a positive correlation between tissue deterioration and degradation of all nutrients with the Pearson correlation coefficients (r) of 0.69 for ascorbic acid, 0.51 for glucose, 0.46 for fructose, 0.44 for total sugar, and 0.18 for total beta carotene degradation. Variation was observed in nutrient retention among accessions within slow deterioration and fast deterioration groups, which indicates an independent genetic component responsible for nutrient retention. ‘Romanor’, ‘Salinas88’, ‘Darkland’, and ‘Green Forest’ are some of the accessions with good shelf life and high retention of all evaluated nutrients. Identification of material with extended shelf life and high nutrient retention in this study provides valuable information for the fresh-cut salad industry and has implications for other types of fresh-cut salads.