New insights into the glass transition of dried fruits and vegetables and the effect of pulsed electric field treatment

Pulsed Electric Field (PEF) pre-treatment has been recently studied to be applied to fresh apple, carrot, and potato tissue as novel food technology to improve the drying performances and the quality of final products. Although the modification induced by PEF and the related reactions have been studied as a function of many parameters and related to several quality aspects, no relationship has been investigated with glass transition temperature (Tg) modification of solid products. This study aims to evaluate the effect of PEF treatment on the Tg of different vegetable tissues. Obtained thermograms revealed the existence of two Tg (TgI, and TgII), the first one mainly dependent from the presence of small molecules, such as sugars, organic acids and small amount of amino acids, while high molecular weight starch, fibers and small amount of proteins are associated to higher temperature values of TgII. PEF treated samples of dried apple, carrot, and potato compared to the untreated ones showed a TgII shift at 0.22 aw to a lower temperature, from 45.12 to 43.37, from 45.15 to 31.04 and from 90.23 to 85.81 °C for apple, carrot and potato respectively. The TgII shift confirmed the mobility raise of the system promoted by PEF treatment, creating a less stable matrix.