Otimização da desidratação osmo-convectiva de cubos de mandioca.

Abstract

The present work had as objective to study the hybrid process of osmotic dehydration and convective drying of cassava cubes (Manihot esculenta Crantz.). The osmotic dehydration process was studied through the Rotational Central Compound Design (DCCR) at different conditions of the temperature process (19-63°C), solute concentration (23-67% w/w), operating time (70- 190 min.) and NaCl concentration (0-20% w/w). The optimization process was verified through the fraction of minimum solids gain with the maximum moisture loss and the material water activity reduction. Convective drying was performed at different temperatures of the drying air (50 to 70°C), 1.35 m/s air velocity and 0,060 g water/g dry mass absolute humidity. The optimum condition chosen for osmotic dehydration of cassava cubes was: 52°C, 56% by weight solute, 10% by weight sodium chloride, 190 minutes and 180 stirring. The lower ranges of volume reduction and surface area of the osmotically dehydrated cassava cubes occurred at low operating temperatures (30°C) and NaCl concentrations (5%), and the maximum ranges of reduction of these parameters occurred at high operation temperatures (52°C) and NaCl concentration (15%). The cassava cubes reduction in the osmotic dehydration process presented anisotropic behavior. The average effective moisture and solids diffusivity for the osmotic dehydration of the cassava cubes in the optimized condition were in the order of 10-8 m2/s. The desorption isotherms to the cassava cube “in natura” and osmotically dehydrated has presented sigmoidal form II and the GAB model presented the best fit (R² > 98% and P% <10%) for the two types of samples analyzed. The connective drying of the cassava cubes dehydrated osmotically at different temperatures has produced products with low moisture value ( within 13% humidity base). Drying at 60°C were obtained products dehydrated osmotically and dry with lower color change and humidity accepted value ( from 10 to 11%). The effective diffusivity moisture obtained by the Fick model for the convective drying of the manioc cubes in natura and dehydrated osmotically to the 50°C to 70°C were in the order of 10-10 m2/s. The hybrid process at better operation conditions has generated a dry product with 10.2% humididy, 15.2% sucrose, 5.3% sodium choride and 44.94% starch. The obtained product from the cassava cubes hybrid process can be used in the food production at cassava base.