Desorption Isotherm of Mango Soy Fortified Yoghurt

Abstract

Desorption isotherms of three yoghurt samples viz. plain yoghurt, mango soy fortified yoghurt (MSFY) and MSFY containing 0.4 % gelatin stabilizer (MSFYG) were determined by gravimetric static method at 20, 30, 40 and 50 °C in the range of 0.11 – 0.81 water activity. It was found that desorption isotherm of yoghurt samples follow a typical type III sigmoid curve. Experimental data were fitted to five mathematical models i. e. modified Henderson, modified Chung Pfost, Oswin, Smith and Guggenheim-Anderson-deBoer (GAB). Equations were developed for the prediction of the GAB constants as a function of temperature and these equations were used during modeling. Standard error of estimate (SE), mean relative percentage error (P), percent root mean square (% RMS) and trend of residual plots were used to compare the goodness of fit. It was found that the GAB models were acceptable in describing equilibrium moisture content – water activity relationships for yoghurt samples over the entire experimental temperature range.