Characterization of pears during drying by conventional technique and portable non invasive NMR

Drying is an important process for the conservation and subsequent marketing of fruits due to their high water activity which makes them highly perishable. Dried products have to meet high quality standards, and one of the most important aspects in fruit drying is the need to obtain products with uniform organoleptic properties. Therefore, the knowledge and the optimization of drying process are very important in order to minimize thermal damage and quality loss. In the case of pears, sugar concentrations are relatively high (60–75 g/100 g dry basis) and greatly increase as water evaporates, offering, combined with fruit shrinkage, an additional resistance to moisture transfer from the fruit. In this study, the effect of drying on properties of pear samples (Pyrus Communis ‘Conference’) was analysed. In particular, the water transport mechanism was investigated in pear during drying process at 50 °C. The drying kinetics were obtained by standard weight measurements and the water loss in chosen sample sections (exterior, intermediate and central sections) was evaluated. The drying moisture profiles of samples were also investigated by portable NMR, a non-invasive and nondestructive technique. The water loss obtained by standard weight measurement and the extent of shrinkage obtained by means of a vernier calliper were found to be in a good agreement with the results obtained by portable NMR