EXPERIMENTAL VACUUM SPRAY DRYING OF PROBIOTIC FOODS INCLUDED WITH LACTIC ACID BACTERIA

ABSTRACT This research aims to develop a vacuum spray dryer (VSD) that performs spray drying in a vacuumed drying tower at a lower temperature than the conventional spray drying. The VSD operational drying temperatures for the probiotic foods containing lactic acid bacteria were determined by the relationships between the temperature and the vapor pressure, and were correlated by Clapeyron's equation. The drying of the fermented milk starter at 35C drying tower was experimentally possible; however, powder from the lactic fermenting beverage was not obtained even at 50C, which resulted from the lower glass transition temperature of the material. Compared with ATP concentration of the fermented milk starter before and after the VSD drying, the lower the drying temperature, the higher the microbial activity is retained. The ATP ratio as 30% of the raw materials shows the high feasibility of VSD for dairy processing. PRACTICAL APPLICATIONS During the spray drying of liquid or slurry food, the heat-sensitive functional ingredients such as vitamin, enzyme or bacteria are usually degraded or lost because of the contact with hot air between 120 and 180C. Markets need food powder that involves a lot of functional materials and a long shelf life for the expansion of healthy food. The experimental vacuum spray dryer (VSD) showed a potential to dry probiotic foods involving lactic acid bacteria without their inactivation. Although the lactic acid bacteria contained in the powder at 35C–VSD was 30% of the raw material, it is more economical than using the liquid type fermented milk starter. With some mechanical or operational modifications for the high moisture content and low recovery ratio of the powder, VSD is applicable for dairy processing factories.