Research On Shelf-life Extension Of Shipboard Pakchoi Based On Combined Treatment Of High-voltage Electrostatic Field/LED Irradiation And Modified Atmosphere Packaging

Rich in vitamins,minerals and proteins,pakchoi（Brassica Chinensis L.）is a characteristic raw food commonly found in traditional Chinese dietary culture and is considered an important source of nutrients for voyageur crews.However,high water content,brittle stalks,large leaf area and vigorous post-harvest respiratory metabolism make it exceptionally difficult to achieve long-term preservation of pakchoi.The long voyage period（>50 days）and the large number of crew members make it imperative to extend the freshness period of shipboard pakchoi in order to protect the physical and mental health of the crew.Modified atmosphere packaging（MAP）is an effective and easy-to-operate land-based preservation method,which has been gradually tried in large ships.Light-emitting diode（LED）irradiation and high-voltage electrostatic field（HVEF）,as non-thermal,efficient and easily regulated emerging preservation technologies,can regulate the sensory quality and physiological characteristics of post-harvest fruits and vegetables by affecting enzyme activity,phytochemical accumulation,respiration rate and other factors,providing more possibilities for post-harvest preservation.Therefore,this study investigates the effect of LED irradiation combined with HVEF treatment on the quality and the mechanism of shelf-life extension of modified atmosphere-packed pakchoi with MAP as the basic preservation method and the purpose of extending the shelf-life of shipboard pakchoi,and also conducts shipboard simulation storage experiments to verify the scalability and implementability of the technology and provide a technical basis for the long-term preservation of shipboard pakchoi.Finally,accelerated shelf-life experiments were conducted to establish shelf-life prediction models for shipboard simulated storage of pakchoi with different combined treatments to provide technical references for quality control,remote transportation and life monitoring of shipboard pakchoi.The main study contents and findings are as follows.（1）Firstly,the effect of red and white LED irradiation treatment on the shelf-life extension of packaged pakchoi was investigated.Gas ratio optimization experiments determined the optimal storage gas atmosphere for pakchoi to be 5%oxygen（O₂）,5%carbon dioxide（CO₂）,and 90%nitrogen（N₂）.The combined experiments showed that the combined treatment of 30μmol·m^-2·s^-1 LED irradiation and MAP effectively maintained the chlorophyll,ascorbic acid and thioglucoside contents of pakchoi,and maintained the photosynthetic capacity at the early stage of storage;significantly enhanced the activity of various antioxidant enzymes and controlled the respiration rate.However,the treated pakchoi showed higher weight loss and browning,no significant inhibition of polyphenol oxidase（PPO）activity,and accelerated textural softening by water mist condensation on the package interior.The comprehensive sensory evaluation determined that the freshness of pakchoi was extended to 35 days.30μmol·m^-2·s^-1 red and white LED irradiation combined with MAP was feasible for maintaining the quality of pakchoi,but did not extend the freshness period to the established requirements.（2）Secondly,the effect of intermittent HVEF treatment on the shelf-life extension of modified atmosphere packaged pakchoi was investigated.The frequency optimization experiment of electric field treatment determined the most efficient treatment frequency of once every 5 days.The combined experiments revealed that a high voltage electrostatic force of 4 k V/cm resulted in the best maintenance of textural and cellular structure and the highest inhibition of respiration rate of the modified atmosphere packaged pakchoi.The treatment reduced the water free degree in the pakchoi cells,reduced water loss,and effectively inhibited PPO activity by changing the enzyme structure.The small amount of ozone（O₃）and ionic mist generated by the electrostatic force effectively inhibited microbial reproduction and odor production.However,the treatment was unable to maintain the apparent color,nutrient content and superoxide dismutase（SOD）activity of pakchoi.The comprehensive sensory evaluation determined that the 4 k V/cm intermittent HVEF combined with MAP treatment extended the shelf life of pakchoi to 45 days,which was still less than 50 days and did not meet the established requirements.（3）The effect of intermittent HVEF treatment combined with red and white LED irradiation on the prolongation of freshness of packaged pakchoi was investigated.It was found that the combination of the three preservation methods could maintain the color,odor,texture,antioxidant properties and nutritional value of pakchoi;effectively inhibit the leaf stomatal opening,reduce the electrical conductivity and water dissipation,and delay the microbial reproduction and the increase of nitrite content.The comprehensive sensory evaluation determined that the 4 k V/cm intermittent HVEF combined with red and white LED irradiation treatment extended the shelf life of the modified atmosphere packaged pakchoi to more than 50 days,meeting the established requirements.（4）Finally,the effects of LED irradiation combined with MAP,HVEF combined with MAP,and the combination treatment of three preservation methods on the shelf-life extension of pakchoi at different temperatures（4°C,10°C,and 25°C）during simulated shipping storage were investigated,and the corresponding shelf-life prediction models were established.It was found that pakchoi stored in simulated storage at 4°C had the best preservation effect after the combined treatment of the three preservation methods,which effectively maintained chlorophyll content,thioglucoside content,stalk hardness and 1,1-Diphenyl-2-trinitrophenylhydrazine（DPPH）radical scavenging activity,and PPO activity was inhibited.The comprehensive sensory evaluation determined that the composite treatment of the three preservation methods extended the measured shelf life of the modified atmosphere packed ship-simulated storage of pakchoi to 55 days,demonstrating the high practicality and usability of the technology.The zero-level kinetic models established with sensory evaluation,hardness,and thioglucoside content as characteristic indicators can well predict the shelf life of ship-simulated stored pakchoi after treatment with LED irradiation combined with MAP,HVEF combined with MAP,and a combination of three preservation methods.The coefficients of determination R² of all nine prediction models were higher than 0.97,and the relative errors between the predicted and measured values of shelf life of freshness preservation were small,which can provide accurate technical references for quality control,remote transportation,and life monitoring of shipboard pakchoi.