The objective of this study was to determine the effect of encapsulation on survival of probiotic Lactobacillus acidophilus ATCC 4356 (4356) in yogurt and during gastric digestion. 4356 was added to yogurt in calcium-alginate microencapsulated or free form at a level of 8.26 and 9.47 log cfu/g respectively, and the influences of alginate micro- capsules (1.5 to 2.5 mm) on sensorial characteristics of yogurts were also investigated. Survival of 4356 in simulated gastric and bile juices included incubation in 0.08 N hydrochloric acid (pH 1.5) containing 0.2% NaCl and a simulated bile juice consisting of 1.2% bile salts in MRS broth. There were similar and statistically significant (P < 0.01) reductions (~1 log cfu/g) in both free and encapsulated 4356 during 4 wk refrigerated storage of yogurts. When incubated for 2h in gastric juice, the free 4356 did not survive (>7 log cfu/g reduction). There was, however, greater survival of encapsulated 4356 with only a 3 log cfu/g reduction occurred. Incubation in simulated bile juice (6h) did not significantly affect (P > 0.05) the viability of both free and encapsulated 4356 due to the natural bile resistance of the bacteria. The addition of probiotic cultures either in free or alginate encapsulated forms did not significantly (P > 0.05) affect appearance and color, flavor and odor of the yogurts. There were, however, significant deficiencies (P < 0.05) in body and texture (graininess) of encapsulated 4356 containing yogurts. It was concluded that incorporation of free and encapsulated probiotic bacteria do not substantially change the overall sensory properties of yogurts and alginate microencapsulation using extrusion method greatly enhanced the survival of probiotic bacteria against artificial human gastric digestive system.

Key Words: probiotic, microencapsulation, artificial gastric system