The cell survival and moisture content of spray dried WPI at three different inlet temperatures and two different flow rates are presented in Table 1 and the resulting cell survival ranged from 34.7% to 82.8% with corresponding moisture contents of 4.60–8.37%.
Inlet temperature significantly (p < 0.05) affected both cell survival and moisture content of the dried powder, whereas
flow rate only significantly (p < 0.05) influenced the moisture content of the powder.
In the literature, a variety of different critical moisture contents have been described for the storage stability of
dried powders.
Masters (1985) reported 4% (w/w) moisture content as a good quality parameter for spray dried dairy product. However,
Jouppila and Roos (1994) referred to a critical moisture content of dried milk powder of 7% for storage stability at 25 C, based on the calculated glass transition temperature value.
Zayed and Roos (2004) examined the effect of water content on the survival of bacteria in a mixture of skimmed milk, trehalose and sucrose, and reported enhanced survival during storage for moisture contents within the range of 2.8–5.6%.