Influence of Vacuum Impregnation with Different Substances on the Metabolic Heat Production and Sugar Metabolism of Spinach Leaves

Noor Liyana Yusof,Lars Wadsö,Federico Gómez Galindo,Allan G Rasmusson

doi:10.1007/s11947-017-1959-3

Noor Liyana Yusof, Lars Wadsö + Show 2 more

Open Access

https://doi.org/10.1007/s11947-017-1959-3

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Abstract

Vacuum impregnation (VI) has been widely used as pre-treatment prior to, e.g., minimal processing, freezing, or drying of fruit and vegetables. Most of the investigations have focused on the applicability of VI to modify physicochemical, sensory, and nutritive characteristics. However, little attention has been paid to the metabolic consequences of impregnating different substances into the plant tissue. This study explores short- and long-term metabolic responses of baby spinach leaves at 5 °C after impregnation with several substances that are commonly used in food industry, e.g., sucrose, calcium lactate, citric acid, and ascorbic acid. Short-term metabolic response of impregnated spinach leaves was measured with isothermal calorimetry for 7 h. Results demonstrated that leaves impregnated with calcium lactate and sucrose showed a drastic increase in metabolic heat production, but no change was recorded in leaves impregnated with solutions of ascorbic acid or citric acid. Long-term metabolic responses were evaluated by measuring sugars and starch. The different impregnation solutes provoked specific changes in the carbohydrate composition during cold storage and the concentrations at each time point are likely to be the result of mobilization of starch, which sharply decreased during storage, and solute-specific differences in metabolization and interconversion of sugars.

Highlights

Vacuum impregnation (VI) is a unit operation that allows the introduction of solutions into the porous structures of fruit and vegetables
Metabolic effects might be true for the impregnation of other substances such as ascorbic acid, as suggested by the results reported by Rocculi et al (2007) where simple immersion of potato slices in this compound provoked an increase in their gross metabolic activity and depletion of reducing sugars
A transient change on thermal power shorter than 2 h cannot be excluded, a doubling of the thermal power was observed when the leaves were impregnated with calcium lactate solution; an increase in thermal power was seen for the sucrose solution

Summary

Introduction

Vacuum impregnation (VI) is a unit operation that allows the introduction of solutions into the porous structures of fruit and vegetables. It has been widely studied as a pre-treatment method prior to, e.g., minimal processing, freezing, or drying of fruit and vegetables (Chiralt et al 1999). The first step occurs when vacuum is applied to the solid-liquid system, the gas inside the pores expands, and the native liquid flows out until mechanical equilibrium is achieved. The second step occurs when the atmospheric pressure is restored, the residual gas in the pores is compressed, and the external liquid flows into the pores, replacing the air (Tylewicz et al 2013). VI is a controlled way to access the intercellular space and introduce different compounds that modify the structural, functional, or nutritional properties of plant tissues, depending on the type of molecules impregnated (Chiralt et al 1999)

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