Cinética de degradação térmica de folhas de mandioca (Manihot Esculeta Crantz) durante tratamentos de secagem em estufa e cocção

Abstract

Cassava leaves (Manihot esculenta Crantz), despite their use in animal feeding as silage, hay, or raw material, they are commonly used for human consumption in regional dishes in the North and Northeast of Brazil. Cassava presents cyanogenic glycosides in its composition linamarin and lotaustralin, which release hydrocyanic acid (HCN) after hydrolysis. The goal of this work was to study the effect of temperature and time of thermal processes application on the degradation of HCN from cassava leaves in order to establish processing conditions to obtain a safe product for human consumption. The cassava leaves were collected after six months of cultivation in a cassava farm from Salvaterra (Marajó-PA). Nine varieties of cassava leaves were characterized regarding their moisture, pH, total acidity, ashes, total lipids, crude protein, water activity, carbohydrates, total energetic value and HCN contents. Among the nine varieties, three of them were submitted to drying process at different temperatures and the thermal degradation of HCN was studied under drying and boiling conditions. The physicochemical characteristics of all studied cassava leaves were similar and total HCN content varied from 90.64- 560.88 mg HCN/kg leaves (total HCN, wet basis) and free HCN 16.65-59.24 mg HCN/kg leaves (free HCN, wet basis). Concerning the drying process, the increase in the temperature increased the effective diffusivity (Deff) of cassava leaves, which facilitates water loss; and temperatures above 50 °C are more effective. Thermal degradation studies of HCN showed that the drying and boiling processes were effective on total HCN removal after 180 minutes. Furthermore, a remarkable decrease in HCN contents was observed after 20 minutes of boiling, since the water facilitates HCN volatilization during the cooking process. Regarding free HCN, the drying method was more effective than cooking, showing high degradation percentages 74.07%- 92.19%).