Moisture Desorption Isotherms of African Arrowroot Lily (Tacca involucrata) Tuber Mash as Influenced by Blanching and Natural Fermentation
The moisture desorption isotherms of the African arrowroot lily (Tacca involucrata S) tuber mash as influenced by blanching and natural fermentation were investigated using gravimetric method. Equilibrium Moisture Contents (EMCs) of four products comprising Non Blanched Non Fermented Mash (NBNFM), Non Blanched Fermented Mash (NBFM), Blanched Non Fermented Mash (BNFM) and Blanched and Fermented Mash (BFM) were obtained at 10-30°C and water activity (aw) of 0.08-0.95. Percent Root Mean Square of error (RMS%) was used to evaluated goodness of fit of common moisture sorption models to experimental data while isosteric heats of desorption were calculated using the Clausius-Clapeyron equation. The isotherms were sigmoid in shape (type II) with the EMCs being lowest for the blanched and fermented mash. The GAB, Halsey and Oswin equations in that order provided good fit to experimental data (<10% RMS). BET monolayer moisture contents were lower for pretreated samples and ranged from 10.6-16.3 g H2O/100 g solids for the Native Mash (NBNFM) and 6.04-8.9 g H2O/100 g solids for the BFM, surface areas for monolayer desorption ranged from 370.6-572.9 m2 g-1 solid for NBNFM and 212.2-312.9 m2 g-1 solid for BFM. Net isosteric heats of desorption significantly (p<0.05) decreased with increase in moisture content with maximum values varying from 6.6 kJ mol-1 for the native mash to 27.6 kJ mol-1 for the BFM.