Measurement of thermal characteristics of spray-dried milk and juice blend

Blended concentrated grape/peach (G/P) juice 60% total soluble solids (TSS) with condensed whole cow milk 40% TSS (1.5:8.5) was spray dried using a pilot-scale spray drier FT 80 at feeding pressure 7,000 Pa, at chamber temperature 180 degrees C and at chamber pressure -110 Pa. The glass transition state of blended G/P juice-milk powder, three pure sugars (glucose, sucrose and lactose) and casein were studied using differential scanning calorimetry. The calorimetry showed that G/P juice-milk powder is a glassy material. The glass transition temperature of blended G/P juice-milk powder at 0.248 water activity was 42 degrees C, compared with commercial full milk powder (control) of 29 degrees C at 0.334 at water activity (a(w)).