Abstract:
The objective of this research was to study the optimum ratio of milk non fat (MNF) to sucrose or lactose for the production of probiotic bacteria powder using spray drying method. From the growth study of Lactobacillus gasseri, L. johnsonii, and L. salivarius, it was found that L. gasseri had the highest growth in coconut medium when incubated at 37℃ and was chosen for the following experiment. L. gasseri was spray-dried at an inlet temperature of 160℃ and 34 mL/min feed rate. 5%, 10%, 20%, and 30% (w/v) MNF solution was used as cell protectant. It was found that the product of 5% MNF as protectant had the highest cell survival of 97.55±1.76%, but the highest reduction of viable cell was found when stored at 30℃ for 60 days. Therefore, the 10% MNF protectant was selected for further study. To find the proper condition of spray drying, the inlet air temperature was varied at 160℃ and 180℃ and the feed rate was varied at 16 and 34 mL/min. Spray-drying at inlet air temperature of 160℃ and feed rate of 16 mL/min was the most suitable condition, which produced powder probiotic bacteria that contained 2.22±0.14% moisture content, and was selected for subsequent experiments. To improve the survival rate of L. gasseri by spray-drying, MNF was substituted with sucrose and lactose at the MNF:sugar ratio of 9:1, 7:3, and 5:5. The total concentration of cell protectant was kept at 10%. It was found that 97.05±0.31% cell survival rate resulted when MNF: sucrose equals to 7:3 was applied. As the powder probiotic bacteria was kept in a vacuum laminated bag (PP/PE/Alu/PE/LL) and stored at 30℃ for 8 and 16 weeks, the total viable cells was reduced to 9.66±0.05 and 9.42±0.03 log (CFU/g), respectively. This was higher than that with 10% MNF alone which had total viable cells of 6.40±0 log (CFU/g) when kept 8 weeks. Therefore, the condition for spray-drying L. gasseri in 10% cell protectant comprising 7:3 MNF:sucrose was at the inlet air temperature of 160℃ and feed rate of 16 mL/min.