Thermal behaviour and degradation kinetics of apple pomace flours

Abstract

Using differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) thermal characteristics and degradation kinetic parameters of apple pomace flours (APF1-5), obtained by dehydration of apple pomace (originating from single and mixed apple varieties, grown both organically and conventionally) and ground to particle size below of 300 mu m, were determined. Glass transition (T-g) close to common storage temperature (21 degrees C) was ascribed to commercial sample and T-g well above it (28-38 degrees C) to APF1-5. Both values of T-g and low water activity (0.2-0.4) prolong APF shelf-life. The kinetic parameters of the thermal degradation process: activation energy (E) in the range from 83 to118 kJ/mol, logarithmic value of pre-exponential factor (ln(A/min(-)1)) in the range from 20 to 28, and rate constant (k(200)) from 0.143 to 0.278 min(-1) were calculated. APF samples were grouped according to rate constant (k(200)) values of thermal degradation process at baking temperature (200 degrees C). Organic samples were found to have a higher thermal stability.