Caracterização e modificação do amido de Taro Roxo (Colocasia esculenta B. Tini) por ultrassom e congelamento e descongelamento

Abstract

The purple taro starch (Colocasia esculenta B. Tini) was isolated, characterized and submitted to physical modifications by the ultrasound technique (amplitudes of 40, 50 and 60%) and three freezing and thawing cycles with temperature at -18°C. The root presented higher moisture content (71.66%) and carbohydrates (21.61 %), the native starch showed lower lipid content (0.13%) and crude fiber (0.82%) and amylose content of 26.45% after proximal analysis. Three main events of mass losses were detected by thermogravimetry (TG/DTG) for all samples. A high range of thermal stability (152.6 - 267.0 °C) was achieved for modified starch using 50% amplitude. The lowest initial degradation temperature (398.3 °C) and the highest mass loss (Δm = 11.25%) were detected in native starch. Changes in parameters L*, a* and b* were observed between the native samples and modified by ultrasound. A decrease in the initial and peak temperature was observed during the gelatinization process for sonicated samples. Relative crystallinity was lower for ultrasound modified starches. An increase in the peak and final viscosities was observed for sonicated samples, accompanied by a decrease in the paste temperature. No agglomerations was observed after ultrasound. The freezing and thawing cycles were responsible for promoting differences in the initial (To), peak (Tp) and completion (Tc) temperatures in the gelatinization process among frozen samples of native starch. The use of ultrasound before freeze-thaw treatment decreased the initial (To) temperature of the samples, between the native starch sample and 60% modified starch there was a difference of approximately 1 °C regarding the gelatinization parameters. An increase in thermal stability was observed between previously modified samples with ultrasound before the freezing and thawing cycles, the highest final temperature (Tf) among frozen samples was 510.9 °C. The three cycles caused slight ruptures and formation of pores for the frozen native starches, with agglomeration and deformations due to the formation of ice crystals only in the ultrasound modified sample resulting in a significant decrease of the relative crystallinity of the samples. The oil adsorption capacity of the starch samples increased after freezing and thawing, with a further increase for the starches previously treated with ultrasound.