Impact of power ultrasound on the quality of fruits and vegetables during dehydration

Abstract

To date, most of dehydrated vegetables and fruits are obtained by convection preceded or not by a pre-treatment. In general, their quality is low due to the physical modi- fications, loss of vitamins, polyphenols and carbohydrates and Maillard reaction (MR). MR can originate a remarkable loss of nutritional value due to the involvement of lysine. To improve the final quality of these products, one of the alternatives is the application of power ultrasound (US). US produces mechanical effects, such as cavitation, microstream and formation of microscopic channels which facilitate the mass transport and so, the removal of water from the food. The synergistic effect of US and temperature allows carrying out dehydration at low temperatures and short times. In the present work, the influence of power US on the quality of fruits and vegetables during the pre-treatment and drying was evaluated. Chemical indicators such as pectinmethyl esterase and peroxidase enzymes, vitamin C, carbohydrates, proteins, polyphenols and 2-furoylmethylamino acids was studied. In addition, rehydration capacity, leaching losses, shrinkage and organoleptic characteristics of the final product was assessed. During blanching, similar leaching losses and enzyme inactivation were found in low temperature and prolonged conventional treatments and in US processes, but with a significant reduction in the time for the latter. Application of US in the drying of carrots and strawberries provided high-quality end-products. The quality was better as compared to marketed products and superior or equivalent to samples obtained in a convective dryer, and, in some indicators, similar to that of freeze-dried samples.