Abstract
This study aimed to investigate the effects of temperature and initial moisture content (M0) on the critical relative humidity (RHc) of whole-grain breakfast wheat biscuit, using the Dynamic Vapor Sorption (DVS) equilibrium and the Differential Scanning Calorimetry (DSC) methods. The effect of glass transition on physical quality of the product, as well as an optimal storage condition were also determined. The findings showed the RHc values of wheat biscuits measured by DVS were close to the relative humidity (RH) of onset glass transition temperature (Tg) measured by DSC. The RHc values indicated positive correlation with M0 and negative correlation with temperature. After the RHc values were defined, wheat biscuits (7% M0) were incubated at the conditions "below" (13.73 +/- 0.62% RH), "at" (37.79 +/- 0.46% RH) and "above" (54.66 +/- 0.68% RH) glass transition area at 20 degrees C for 15 weeks, during which texture and color of the wheat biscuits were determined. The results showed glass transition affected the biscuits predominantly on crispiness, but the effects were less pronounced on hardness and color. The findings suggested that at 20 degrees C, wheat biscuits with 7% moisture content are optimally stored at RH below 43.2% (water activity < 0.43).