Effects of Vacuum Impregnation with Various Substances in Combination with Pulsed Electric Fields Treatment on Improving the Freezing Tolerance of Arugula Leaves

Author: George Lukhava
Keywords: Pulsed electric fields, PEF, Vacuum Impregnation, VI, Arugula, Folic Acid, Vitamin B1, Cryoprotectants, Glycerol
Annotation:

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. The aim of the study was to reduce said effects on arugula leaves, which are rich in vitamin C and Potassium and are used mostly as fresh ingredients in food. In countries with a colder climate, such as Sweden, arugula is typically imported from warmer regions. The import of arugula from a foreign country takes time, which shortens its shelf life, thus extending the shelf life of the leaves becomes a necessity. To reduce the negative effects of freezing and thawing, arugula leaves were subjected to a combination of two pre-treatment methods: 1. Pulsed Electric Fields (PEF) treatment; 2. Vacuum Impregnation (VI) with cryoprotectants and secondary metabolites. The first method induces electroporation in the cellular membranes of the leaves, while the second method (VI) allows the impregnation of the solution made up of a cryoprotectant and secondary metabolites into extracellular spaces, following which they penetrate intracellular spaces as well, due to the electroporation. It had already been shown that the combination of VI and PEF could improve the survival rate of arugula leaves as well as spinach leaves, however only cryoprotectants were used in these studies. In the study I conducted glycerol served as the cryoprotectant, while secondary metabolites: folic acid and vitamib B1 were added to the solution. It was hypothesized that the addition of secondary metabolites would help the leaves recover from the metabolic stresss induced by PEF. To determine the optimal solution, two concentrations (40 μM and 400 μM) and three types of metabolites (folic acid, vitamin B1, a combination of both) were tested along with four different concentrations of glycerol (9%; 11% 18%; 28%). Control groups consisted of a group treated only with PEF, groups which were treated by VI without PEF and groups which were treated with both VI and PEF but with a solution only containing glycerol without the addition of secondary metabolites. ANOVA was used for the statistical analysis of results of the study. It was determined that the survival rate of leaves increased along with the concentration of cryoprotectant in the solution. The survival rate of leaves was also far greater among groups impregnated with solutions containing secondary metabolites than the ones containing glycerol alone. Among the metabolites, vitamin B1 was the least effective at increasing the survival rate of the leaves, while folic acid was the most effective.

Lecture files:

რუკოლას ფოთლების ყინვაგამძლეობის გაუმჯობესება სხვადასხვა ნივთიერებებით ვაკუუმ გაჟღენთვითა და იმპულსური ელექტრული ველის გამოყენებით (ანოტაცია) [ka]