Obtenção de amido de inhame e sua utilização no preparo de alimentos à base de leite.

Abstract

There is a great interest in new sources of starch, especially by the food processing industries. Due to its high starch content, the yam is a potential source for use to produce industrialized food. The starch from yam, associated with milk (goat and cattle) which has a high nutritional value, can be used to produce food that provides healthful body maintenance. The objective of this work was to get more information about some proprieties of the yam starch (Dioscorea alata L.) São Tomé variety and study the possibility to use it to prepare foods with milk from goat and cattle (porridges) The starch was extracted by a grinding process using NaOH 0,03N solution and a dry process by freeze-drying. It was investigated the kinetics of freezing of starch at -17 and -26 °C, the content of extraction of starch, physic-chemical and microbiological characteristics, the index of solubility in water and water absorption capacity, the isotherms of hygroscopic equilibrium at 25, 30, 35, 40 and 45 °C, the rheological behavior of the pastes of starch in concentrations of 4, 5 and 6% at 20, 30, 40 and 50 °C, and the sensory analysis of porridges with three different concentrations of starch (4, 5 and 6%). For the starch with water content of 45% (w.b.), and to the temperature of -17 °C, the average effective thermal diffusivity was 1.779 mm2.s-1, while at -26 °C the value was 2.196 mm2. s-1. The practical yield observed in the extraction of starch was 18.28%. In relation to its physicchemical characteristics the starch of yam showed pH equal to 6.50, with a water content of 5.81% (w.b.), ash equal to 0.14%, acid percentage of 0.98, fiber content of 0.18%, purity of 80.18%, protein of 1.24% and lipid content of 3.33%. Through the icrobiological analysis it was observed that there was not presence of any microorganisms investigated (Salmonella sp., Bacillus cereus and Coliforms at 45 °C). It was found values of 2.02% and 0.25 gram of water per gram of sample for the index of solubility in water and water absorption capacity, respectively. The behavior of the isotherms obtained for the starch was typical type II and Chung-Pfost model was the best one that adjusted to the experimental data and can be used satisfactorily in the prediction of isotherms of hygroscopic equilibrium of the yam starch. The paste with 4, 5 and 6% of starch showed non-Newtonian fluid behavior and that it depends on time, with predominance of thixotropic character and the Power Law model that best adjusted the experimental rheological data. By sensorial analysis was possible to verify that the porridges prepared with concentration of 6% of starch were the most accepted and porridges with 4% starch, the least accepted by the judges, independent of milk used to prepare it. The starch obtained from yam follow the standards established by Brazilian legislation and the ANVISA, respectively, and due to its pureness degree (80.18%), it can be considered that the method used in this work to extract it is efficient.