Abstract

The effects of sugar component ratio, water fraction, and storage conditions on crystallisation and glass transition temperature (T-g) of three Chilean dried raisins were examined by using differential scanning calorimetry (DSC), polarised light microscopy and X-ray diffraction (XRD) techniques. Thompson, Flame and Golden raisins differed in fructose:glucose and glucose:water ratios, impacting on their measured T-gs (P < 0.05) and propensity of sugaring. The ratios of fructose:glucose (1:3, 1:2 and 1:1) and glucose:water (1.7, 1.9 and 2.1) also influenced the measured T-gs (P < 0.05) and sugaring of fructose-glucose-water model solutions. Measurement of T-gs in the raisins as a function of water activity (a(w) 0.11-0.74) showed that water acts as a strong plasticiser decreasing the T-gs ( -16.4 to - 61.6 degrees C). XRD results revealed that sugaring in Thompson raisins was delayed at low temperatures (5 & 15 degrees C) compared to that stored at 25 degrees C. The refrigeration may be a simple approach to delay the sugaring in raisins.