Effect of temperature on the moisture sorption isotherm of a biscuit containing processed mango (Mangifera indica) kernel flour

Proximate composition and moisture adsorption isotherm of a biscuit (PMKWB) prepared from equal amounts of wheat and processed mango (Mangifera indica) kernel flours of less than or equal to 0.6 mm granulation were analysed. The sorption study was conducted at 14, 31 and 58 +/- 2 degreesC, with the application of Brunauer-Emmett-Teller (BET), Henderson, and Clausius-Clapeyron equations. Results showed that the flour characteristics influenced the creaming requirement as well as the final product composition. The PMKWB had 5.0, 29.5, 0.01, and < 0.01% (w/w) (dry weight basis) of moisture, fat, crude fibre and ash contents, respectively. The isotherms at the temperatures studied exhibited sigmoidal shape. Equilibrium moisture content (EMC) increased with decrease in storage temperature at any given water activity (a(w)) The calculated monolayer moisture content of PMKWB, using the BET equation, was 6.1 +/- 0.4% (S.D.) and was independent of the storage temperatures. With the Henderson equation, a critical change in the water binding capacity of PMKWB was noted at EMC of 13.1% (fat-free dry matter basis.) The corresponding net isosteric heat of sorption was 18.2 +/- 1.6 kJ/mol. Storage temperatures not exceeding 31<degrees>C were recommended to achieve prolonged shelf-stability of the PMKWB. The Henderson equation predicted the isotherms better than BET with mean relative deviations %E less than or equal to 5.0.% (C) 2001 Elsevier Science Ltd. All rights reserved.