Valentino, Marika (2022) Biopolymer active coating to extend the shelf life of minimally processed fruits and vegetables. [Tesi di dottorato]

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Abstract

The aim of PhD thesis work was to study the impact of biopolymer active coatings on the alteration kinetics of fresh and minimally processed fruits and vegetables. Moreover, the possibility to use plasma activated water (PAW) to produce the edible coating has been studied. Three study cases have been studied and results are reported below: A.1 Case study: fennel An active coating based on sodium caseinate and propyl gallate preserved the nutritional quality of fennels, by reducing the decrement of antioxidant capacity of about 30%, of vitamin C of about 35%, and of TPC of about 10% comparing with control samples. Moreover, the storage temperature affected the efficacy of the coating that showed better efficacy at 4°C and 10°C. The physical and nutritional quality indices critical for the product shelf life were the total color change (ΔE), the firmness, the total antioxidant capacity and the vitamin C content. The quality change over time were well described by using a kinetic approach. Pseudo zero order and first order kinetic model were able to describe the change of firmness and total polyphenols content and ΔE, antioxidant capacity and vitamin C, respectively. The effect of storage temperature was well described by using an Arrhenius type models. A.2 Case study: pear Firmness, vitamin C content, antioxidant capacity and total polyphenol content were selected as critical quality indices for the product shelf life. An active coating based on sodium caseinate, beeswax, guar gum and antioxidant compound (propyl gallate) was able to preserve the quality of the pear by reducing the decrement of firmness of about 70% and of nutritional properties of about 50% respect to control pears. The quality change over time were well described by using a kinetic approach. Pseudo first order kinetic model were able to describe the change physical and nutritional properties of products. A.3 Case study: apple PAW was a good solvent for cricket protein in 1 and 2%, whereas chitosan was not soluble in PAW at any concentration. The optimal coating composition was a blend of 2 % of protein dissolved in PAW and 2% chitosan dissolved in 1% acetic solution (ratio 1:1). The coating was applied on minimally processed apples and the kinetics of alteration process has been studied. The pseudo first order kinetic model well described the browning index, the antioxidant activity, the total polyphenols content and the vitamin C content, whereas the change of hardness was well described by a pseudo zero order kinetic model. Coatings were not able preserve browning index during storage, but they slowed down firmness degradation of about 10%, antioxidant capacity and vitamin C content of about 20%, and total polyphenol content of about 30% compared to the control samples.

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