Glass transition spray-dried lactose

The present study has shovm that spray-dried and freeze-dried lactose have different physical structures, thermal transitions, and time-dependent lactose crystallization behavior. Spray-dried lactose had round-shaped particles but freeze-dried lactose resembled broken glass or had a flakelike structure. Tg and Tq. of freeze-dried lactose were higher than those of... 

Glass-transition temperature (onset) for spray-dried and freeze-dried lactose as a function of water content, determined using DSC during heating at 5°C/min. 

The study of volatile diacetyl retention (BP 88°C) in various constituents of milk (lactose, fat, proteins) during spray-drying showed the importance of amorphous/crystalline ratio in lactose for aroma retention that is in tnm linked to glass transition phenomena, temperature, and water/RH. The presence of microcrystals in drops (concentration, fast drying) may be a barrier to diffusion of volatile molecnles, therefore increasing the retention in the final spray-dried powder. 

The retention or loss of aroma compounds is also influenced by the structure (amorphous or crystallized) of the dried product Structural changes can be used for spray drying encapsulation processes (Bhandari et al., 1992 Re, 1998). Crystallization tends to increase the loss of aroma, because it rejects impurities, including volatiles. Senoussi et al. (1995) measured the loss of diacetyl as a function of the rate of crystallization of lactose during storage. They found that when the lactose was stored at 20 °C above the glass transition temperature Tg, the amorphous product immediately crystallized and practically all diacetyl was lost after 6 days. Levi and Karel (1995) also found increased rates of loss of volatile (1-n-propanol) as a result of crystallization in an initially amorphous sucrose system. 

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