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

English. 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.

English. Even though nowadays more food is produced in the world than ever before, global hunger remains a problem and the number of malnourished people keeps increasing. Could part of the solution be new techniques to help fruit and vegetables stay fresh all the way to our plates instead of ending their lives in the waste? The aim of this project was to improve the survival rate of arugula leaves during freezing and subsequent thawing, which is a common way of preserving food but can be difficult to apply to plants. Two methods were used together to achieve this goal: Vacuum Impregnation and Pulsed Electric Fields treatment. Vacuum Impregnation involves using a vacuum to expel gas from inside an object, creating free space which is then filled with a substance of our choice. This was used to fill the space between the cells of the leaves with substances that were thought to be helpful with surviving and recovering from freezing. Pulsed Electric Fields (PEF) treatment, meanwhile, is the process of applying short electrical shocks to organic tissue. This causes the formation of pores within the cells of said tissue. The pores then serve as an easy pathway between the inside and the outside of the cell. When used together these these two methods helped get the chosen substances into spaces directly within the cell. The combination of these two pre-treatment methods has been used to great effect to impregnate vegetable food products with cryoprotectants, which served to mitigate some of the more harmful effects of freezing and thawing. But using too much cryoprotectant can result in spoiling the taste of the product, while the application of pulsed electric fields and subsequent freezing/thawing causes stress to the cells of the organism, making it hard for them to recover. The introduction of certain substances into the solution which the leaves were impregnated with could help remedy this and increase the survival rate of the leaves. Results showed that increasing the concentration of the cryoprotectant to a certain threshold helped improve the survival rate of the leaves without affecting the taste and adding the additional substances in specific concentrations further improved the results.