Optimization of Innovative Non-Thermal Technologies for Fruit and Vegetables Processing

Pulsed electric fields, ultrasound, osmotic dehydration and high pressure homogenization are innovative non-thermal technologies which are attracting a growing interest in the fruit and vegetables sector because they allow processing of foodstuff with minimal drawbacks on their quality. In the present PhD thesis, these technologies were investigated from microstructural and metabolic point of view to provide evidence of the induced changes which could lead to potential benefits or disadvantages for different industrial purposes. Novel methods were developed and tested to assess the impact of the technologies on plant tissue and to provide tools for the optimization of the relevant parameters on industrial scale. Microstructural modifications produced by ultrasound and pulsed electric fields treatments were studied by observing the subcellular water redistribution which was found to be correlated with mass transfer kinetics. Both reversible and irreversible electroporation upon high electric fields enhanced the water and solute migrations when combined with osmotic dehydration in apple and strawberry tissues. Similarly, the addition of calcium and ascorbic salts to a sucrose osmotic solution led to the alteration of the membranes permeability with the consequent increase of water removal and solutes entrance in the plant tissue. The metabolic response induced by non-thermal technologies was evaluated in terms of cell viability, metabolic heat production and respiration rate while a metabolomic approach was adopted to finely explore their impact on specific metabolic pathways. High concentrations of ascorbic acid or high voltages applied to apple tissue markedly dropped the cell viability. Moreover, high electric field strengths affected both the anaerobic respiration pathways and the gamma-aminobutyric acid metabolism. High pressure homogenization, applied to a mandarin juice, influenced the microbial degradation pathways as a function of the applied pressure level.