INFLUÊNCIA DO TRATAMENTO TÉRMICO NAS CARACTERÍSTICAS FÍSICO-QUÍMICAS E REOLÓGICAS DE IOGURTES NATURAIS

Abstract

This paper aimed to evaluate the influence of thermal treatment on physicochemical and rheological characteristics of natural yoghurt, and also to evaluate the influence of the lyophilization process on natural yoghurt after its reconstitution. In the first experiment, three treatments of yoghurt were processed: (a) Treatment 1 - yogurt made from refrigerated raw milk; (b) Treatment 2 - yoghurt made from pasteurized and refrigerated milk; (c) Treatment 3 - yoghurt produced with Ultra High Temperature (UHT) milk; for all treatments, the analyzes of fat, protein, moisture, acidity, and pH were made. The shelf life of yoghurt was also evaluated at the 1st, 8th, 15th, 22nd , and 29th days of storage; analyzes of the pH, acidity, syneresis, viscosity, viable lactic acid bacteria, and total coliforms were made. In the second experiment, the yogurts were subjected to lyophilization process and then reconstituted and the physicochemical, rheological, and viable lactic acid bacteria characteristics were evaluated. Results of the first experiment showed that the thermal treatment was positive for viscosity, syneresis, and also to 20 lactic acid bacteria, which were viable until the 15 th day of storage only for yoghurts subjected to this treatment. In the second experiment, it was found that lyophilization process preserved the physicochemical characteristics of yogurts, and that the numbers of initial lactic acid bacteria were not kept and has also negatively affected the viscosity of yogurt.