Otimização do descascamento químico de raízes do yacon (Polymnia sonchifolia Poepp.) / Optimization of chemical peeling of yacon roots (Polymnia sonchifolia Poepp.)

Foi utilizado o delineamento fatorial completo 2³ para estudar o efeito das variáveis de processo no descascamento químico de raízes do yacon, cultivadas na região metropolitana de Curitiba, estado do Paraná. Foram realizados 11 experimentos, com três repetições no ponto central, nos quais foram avaliados em três níveis a concentração da solução de hidróxido de sódio, por cento (g/100 mL) [6, 10, 14], temperatura da solução de hidróxido de sódio, °C [70, 80, 90] e tempo de permanência na solução de hidróxido de sódio, minutos [2,4,6]. Todas as variáveis estudadas afetaram de forma significativa (p<0,05) o rendimento das raízes submetidas ao descascamento químico. A variável mais importante para o rendimento foi o tempo de permanência na solução de hidróxido de sódio. O modelo obtido para a resposta percentual de rendimento foi adequado, com R² aj = 0,8497 e com falta de ajuste não significativa (p = 0,9312), podendo ser utilizado para fins preditivos. No ponto central, foi obtido um rendimento satisfatório (84 por cento a 87 por cento) e elevado percentual de casca removida (96 por cento a 98 por cento), indicando que o tratamento com 10 por cento de solução de hidróxido de sódio a temperatura de 80º C por 4 minutos, pode ser empregado no descascamento químico das raízes do yacon.

A full factorial design 2³ was used to evaluate the effect of process variables in chemical peeling of yacon roots, cultivated in Curitiba, State of Paraná. Eleven treatments, with three central points, were done in which they had been evaluated at three different levels of sodium hydroxide solution, percent (g/100 mL) [6, 10, 14], temperature of the same solution, °C [70, 80, 90], and residence time in the sodium hydroxide solution, minutes [2, 4, 6]. All the studied variables had affected significantly (p<0.05) the yield of yacon roots subjected to chemical peeling. The variable that most affected the yield was the time of permanence in the sodium hydroxide solution. The mathematical model obtained for the yield ( percent) was good with R² aj = 0.8497, and non significant lack of fit (p=0.9312).Therefore, the model can be used for predictive purposes. In the central point a satisfactory yield (84 percent to 87 percent) with a high percentage of removed peel was obtained (96 percent to 98 percent) indicating that the treatment with 10 percent of sodium hydroxide solution, temperature of 80º C per 4 minutes can be used in the chemical peeling of yacon roots.

Relationships among the composition and physicochemical properties of starches with the characteristics of their films.

The physical, molecular, and functional properties of corn, cassava, and yam starches were related to the film properties of these starches. Corn, cassava, and yam starches contained 25%, 19%, and 30% amylose, respectively. Amylose from yam starch showed the smallest molecular weight among the starches and amylopectin from corn starch the smallest molecular weight. Cassava starch presented a higher amylopectin content, and its gels and films were less strong, more transparent, and more flexible than corn and yam films. Plasticized films of the three starches were more flexible, with a higher strain and lower stress at break when the glycerol content increased. Unplasticized films were brittle and had water vapor permeability values ranging from 6.75 x 10(-10) to 8.33 x 10(-10) g m(-1) s(-1) Pa(-1). These values decreased when the glycerol content reached 20 g/100 g of starch because a more compact structure was formed. Then, at a glycerol content of 40 g/100 g of starch, the WVP increased because the film matrixes became less dense.