La conservazione iperbarica come tecnologia innovativa per estendere la stabilità e migliorare la funzionalità degli alimenti

This Ph.D Thesis consisted of a multi-aspect investigation on hyperbaric storage, focusing the attention on: (i) the identification of packaging solutions feasible for pressurized storage applications; (ii) the capability of hyperbaric storage to obtain microbiological, enzymatic and chemical stabilization of food; (iii) the modification of the structure of proteins to improve the technological functionality of food. Firstly, a preliminary investigation was carried out to explore the effects of hyperbaric storage on food packaging materials. The objective was to identify plastic films that were adequate for packaging of food intended for hyperbaric storage. To this aim, single and multilayer packaging materials, derived from petroleum or renewable sources, were tested. Among these materials, petroleum-based multi-layer solutions (poly-amide/poly-ethylene, poly-propylene/ethylene-vinyl-alcohol/poly-ethylene) were identified as appropriate for pressurized storage purposes, and were thus used in the subsequent experimental work. Following, the capability of hyperbaric storage to guarantee microbiological, enzymatic and chemical stability of food was assessed. The attention was focused on the possibility to obtain: (i) pasteurization of raw skim milk; (ii) polyphenoloxidase inactivation in model systems and apple juice; (iii) inhibition of non-enzymatic browning in sugar-aminoacid solutions. Hyperbaric storage was shown to irreversibly inactivate 5 log units of inoculated E. coli and S. aureus in milk and to control the native milk microflora, demonstrating its suitability for pasteurization. Application of hyperbaric storage also allowed to irreversibly inactivate polyphenoloxidase in aqueous model systems and to inhibit enzymatic browning in apple juice. The rate of Maillard reaction in glucose-glycine model systems was significantly inhibited by pressure with kinetic parameters affected by solution pH and storage temperature. In this framework, a model based on the combination of Arrhenius and Eyring equations was developed to accurately predict reaction rate in different pressure and temperature conditions. In the last part of the Thesis, the capability of hyperbaric storage to modify protein structure was further investigated with the aim of improving techno-functional properties in protein-rich food. Milk, egg white and egg yolk were considered based on the different native structure of their proteins. The effects of hyperbaric storage were found to depend on protein structure: (i) globular proteins either unfolded or underwent changes in particle size and electrostatic behavior, leading to an increase in foaming properties; (ii) casein micelles progressively destabilized, resulting in coagulation; (iii) pressure-modified micelles were more prone to enzymatic hydrolysis mediated by endogenous proteases, resulting in the production of highly foaming peptides; (iv) differently organized proteins, concomitantly occurring in the food systems, easily interacted further modifying their structure; (v) proteins in protein-lipid complexes underwent sever unfolding, leading to the complete gelation. The results achieved in this Thesis demonstrate the multi-tasking character of hyperbaric storage, which is concomitantly capable to stabilize and improve techno-functionality of food. The technology has thus the potential to evolve from storage technology solely, to non-conventional treatment to improve food quality in a number of different ways. However, several development gaps need to be filled in order to make hyperbaric storage viable for the industrial context, with particular reference to the development of economically sustainable working units. Overcoming these gaps would allow to fully exploit the wide potential of hyperbaric storage.