Development of Pre- and Postharvest Techniques to Produce Safe Baby Leaf Vegetables in a Plant Factory

Abstract

This study was conducted to develop preharvest techniques at each cultivation stage in a plant factory for improving the safety and yield of baby leaf vegetables and postharvest techniques for cleaning them. In the first chapter of this thesis, seeds of tat soi, romaine lettuce, and beet were sterilized with electrolyzed water (EW) and chlorine (CL) for 5 and 10 min. Microbial populations of the sterilized seeds decreased by sterilization treatments. E.coli and Salmonella spp. were not detected in any treatment. CL sterilization was most effective in reducing microbial populations. However, percentage of germination in all seeds was significantly decreased by CL treatments. When cultivation trays used in plant factory was irradiated with UVB for 20 min, the standard plate counts were less than 1 log CFU/g on cultivation tray. For improving the degree of safety and yield of baby leaf vegetables, the effects of different nutrient solutions on growth and quality of tat soi, romaine lettuce, and beet in a plant factory were examined. Fresh weights of tat soi and romaine lettuce increased the most when grown using nutrient solution of Yamazaki for lettuce (YMZK). Hunters a values of tat soi and romaine lettuce decreased when using Korea Wonshi (KRWS) and Japan Enshi (JPES) nutrient solutions and the leaves were greener. Hunters a values of beet increased when YMZK nutrient solution was used and the leaves were redder. Total phenolic contents of romaine lettuce were significantly increased in the treatment of KRWS. But, there was no significant difference in that of tat soi and beet. In the second chapter, the effects of surfactants and ultrasonic techniques for cleaning the harvested baby leaf vegetables were examined. Application of surfactants and ultrasonic treatment decreased the microbial population of tat soi to 1-2 log CFU/g. At the same time, rate of weight loss increased and visual index, and sogginess of tat soi decreased 9 days after storage. Hunters L and b values of tat soi treated with surfactants and ultrasound increased during storage. No significant changes in Hunters a value of tat soi was not found during storage. Results suggest that application of the pre- and postharvest techniques developed in the present study was effective for improving safety and yield of baby leaf vegetables.