Abstract

Softening of dried Vangueria infausta using maltodextrin and sucrose was investigated experimentally. The pulp of V. infausta was dried in a convective dryer, the influence of drying temperature as well as relationship between water content and water activity were examined. In this study, 48 samples of V. infausta pulp, with and without maltodextrin or sucrose, were dried at air temperatures of 60 and 80°C, at a constant air velocity of 3 m/s, for 0-240 min, and until constant weight. The water content, water activity, hardness and toughness were evaluated throughout the drying process. Samples dried at 80°C exhibited shorter drying times than samples dried at 60°C. The water activity of fruit dried for 240 min at 80°C varied from 0.633 to 0.759, and the fruit was thus safe regarding microbiological spoilage. The hardness and toughness of the dried fruit pulp increased with the reduction in water content, and it was observed that samples of pure pulp became unacceptably hard and tough, when dried to the level needed to obtain microbiological stability. The addition of sucrose as well as maltodextrin has shown to be able to reduce the hardness as well as the toughness of the dried fruit pulp; which can be considered as a strategy to obtain dried fruit pulp with suitable consistency.

Key words: Vangueria infausta, drying, softener, sorption isotherm, hardness, toughness.

Abbreviation

a, Coeficient of equation of linear regression; b, coeficient of equation of linear regression; a_w, water activity; R², coefficient of determination; db, dry basis; Eq,equation; P_h, hardness (N); Md, maltodextrin; min, minutes; (%), percentage; P, pulp;Suc, sucrose; P_t, toughness (N.mm); X, water content (g/g dry basis); wt, wet basis; α,coefficient of GAB model; β, coefficient of GAB model; ϒ, coefficient of GAB model; Æ,standard error.