Study of the effect of vacuum impregnation with different substances on respiration and color of packed baby spinach leaves.

Abstract: In this study, vacuum impregnation (VI) was used to investigate the effect of different solutions: sucrose 21 % (w/v), calcium lactate 1 % (w/v), ascorbic acid 0.1 % (w/v), and GABA 0.075 % (w/v) on atmospheric composition, color, and shelf life of packed baby spinach leaves. VI was performed at two different temperatures: 21 C and 7.5 C. The packed, impregnated leaves were stored for 8 days at 21 C and 7.5 C. The efficiency of VI was evaluated by measuring the weight gained after impregnation, color changes of the leaves during the storage period, and the modification of the atmospheric composition in the packages. The influence of GABA impregnated into baby spinach leaves was studied further for 22 days at a storage temperature of 7.5 C, in order to study its effect on the shelf life of the spinach leaves. The metabolic activity of GABA impregnated leaves was measured for a short term (14 h) with isothermal calorimetry at 7.5 C, in order to evaluate the changes on the heat production created inside the packed leaves. Results show that respiration (O2 consumption and CO2 production) of baby spinach leaves increased after VI and this increase depends on the substance used for impregnation as well as the temperature. Sucrose played a major role at both the studied temperatures, by displaying the highest alteration of the atmosphere created inside the packed spinach during storage. Impregnation with ascorbic acid leads to faster deterioration of packed spinach leaves in comparison to the other substances used. Impregnation with GABA extended the shelf life of the packed baby spinach leaves at 7.5 C, till 22 days, while the control samples were discarded after 10 days. Measurement of the metabolic activity by isothermal calorimetry showed less heat production from the treated spinach with GABA comparing to the untreated control at 7.5 C. The calorimetry studies showed higher heat production of the unpacked spinach comparing to the packed leaves at the same storage temperature. The measurement of metabolic activity was in correspondence with the respiration measurements (O2 consumption and CO2 production) for short time scales, where the lower respiration in the GABA impregnated samples was followed by less heat production, regardless if the sample was packed or not.