Effects of Vacuum Impregnation with Various Substances in Combination with Pulsed Electric Field to Improve the Freezing Tolerance of Arugula Leaves

Abstract: As of 2020 an estimated number of 821 million people across the world are undernourished and that figure is expected to grow by 2 billion before the end of 2050 (United Nations Sustainable Development 2020). Despite this, every year over 1/3 of food produced globally is disposed of without consumption (Global Panel on Agriculture and Food Systems for Nutrition 2018), and the actual number might be much higher. The food is either lost (defined as being disposed of somewhere between production and delivery to market) or goes to waste (disposed of without consumption after being purchased). To help mitigate the issue of food loss, it is important to have adequate methods of preservation in place. Freezing is a widely used method of food preservation but applying it to sensitive plant tissue such as leaves often results in degradation of their flavor and texture. To reduce said effects, arugula leaves were subjected to a combination of two pre-treatment methods: Pulsed Electric Field treatment and Vacuum Impregnation with a cryoprotectant and secondary metabolites. Pulsed Electric Fields induced electroporation of the leaves’ cellular membranes, thereby allowing the solutions infused into extracellular spaces through Vacuum Impregnation to enter intracellular spaces as well, while introducing a cryoprotectant and vital secondary metabolites into the cells helps mitigate the damage from cell leaks that occur during freezing and thawing. The experiment was conducted on leaves imported from Italy, as well as leaves grown within the Lund university greenhouse. The leaves were first subjected to PEF treatment and then immediately to Vacuum Impregnation with cryoprotectant solutions of varying concentration. Along with the cryoprotectant, the solutions contained different amounts of different substances. This was done to determine the optimal concentrations for the survival of leaves. Following this, the leaves were rested, then frozen, thawed and observed to assess their survival. It was observed that groups of leaves processed using a higher concentration of cryoprotectant had a higher survival rate when compared to their counterparts processed with lower concentrations.