Study of the relation between the formation of glass transition zones and betalain loss during convective drying of beetroot

Abstract

The high perishability of vegetables causes large losses of them along the production chain. Thus, processes that ensure better utilization and longer shelf life become essential. Among the various processes, drying has been widely used in the conservation of fruits and vegetables. Due to exposure of food to high temperature for a long time, nutrients susceptible to heat, light, and oxygen are degraded throughout the process. Therefore, studies are required to understand the mechanisms involved in the degradation of nutritive compounds. The role of water in the kinetic of food degradation has been the subject of intense discussion and several hypotheses on how moisture content and molecular mobility affect chemical reactions. During the drying process, different phenomena occur simultaneously, such as: reduction of moisture content, promoted by diffusion and subsequent loss of moisture to the air drying; product heating by hot air air; glass transition; and loss of thermolabile nutrients. Although these phenomena have been widely studied, there is little information about a correlation between them throughout the drying process and how the glass transition zones within the product is related to nutrient loss. The elucidation of such relations becomes indispensable for a better comprehension of the mechanisms of compounds degradation during the drying process. Therefore, the present work aims to evaluate the formation of glass transition zones during beetroot drying, verifying its relation with local nutrient losses. Initially, the glass transition temperatures of beetroot containing different moisture content will be determined. Samples with cylindrical geometry will be subjected to the convective drying process at different temperatures (40°C, 50°C, and 60°C). During drying, the moisture content and total betalain profiles will be determined within the product by hyperspectral imaging, as well as the temperature profile by thermal imaging. From the moisture content and temperature profiles, the formation of glass transition zones will be mapped inside the product during drying. Also, the relation between glass transition to the local betalain loss during drying will be verified. The results of this work intend to better understand the occurrence of glass transition and its role in product quality during the food drying. (AU)