Estudo da caseína como agente espumante na secagem de tomate pelo método foam-mat

Abstract

Fruit powders have great potential for application in healthy products, because they concentrate nutrients and vitamins essential for the functioning of the immune system. Fruit powders are obtained by various drying methods, one of them being the foam layer method, in which the material is subjected to air incorporation to form a foam. In preparing the foam, it is common to use ingredientes with foaming and emulsifying properties, which aid in both the formation and stability of the foam. The ingredient with foaming property in this study is casein, a natural protein obtained from the coagulation of skim milk, which adds nutritional value to the final product obtained. The casein extraction process was coagulation by adding microbial rennin. The casein is transformed into foam after the beating. Afterwards the tomato pulp is incorporated and subjected again to beating in a planetary mixer. The experiments were conducted based on a 2³ factorial experimental design. The foams were formed from tomato pulp (without cooking, with 10 and 20 minutes of cooking), with different proportions of pulp (50, 60 and 70%), and were submitted to drying in an air oven with controlled temperature (60, 70 and 80ºC) until reaching a constant weight. Drying curves were obtained, and an important period of constant rate was identified in all experiments. The experimental data were fitted to semiempirical and phenomenological mathematical models. The model that best represented the drying kinetics of the foams was the Midili model for presenting the best R² and the most negative Akaike test value. The powders obtained showed compatible humidity and water activity, with the highest value of 2.68% for humidity and 0.367 for water activity, being in favorable conditions for storage and preservation. However, the powders showed to be hygroscopic. A drying time sufficient for the powders to reach a humidity content of 0.04 g/g of solid, estimated by the Midilli model, was defined as the response variable of the experimental planning along with hygroscopicity. From the analysis of the experimental planning results, significant and predictive models were found to represent both response variables. Employing the desirability function and simultaneously analyzing the dependent variables of time to reach the humidity content of 0.04 g/g of solid and hygroscopicity, the optimal condition for minimizing the variables and obtaining the best results in a joint analysis occurs in the condition of cooking time 0 minutes (raw tomato pulp) with 50% pulp concentration and drying temperature of 65 °C.