Effect of microencapsulation using extrusion technique on viability of bacterial cells during spray drying of sweetened yoghurt

An improved extrusion spraying technique was employed for encapsulation of mixed bacteria culture of Streptococcus thermophilus and Lactobacillus bulgaricus using sodium alginate as the coating material for the purpose of better survival during spray drying of sweetened yoghurt. The effects of nozzle air pressure (200, 300, 400 and 500 kPa), sodium alginate concentration (1%, 1.5%, 2%, 2.5% and 3% w/v), calcium chloride concentration (0.1, 0.2, 1 M) and hardening time (15, 30, 45 and 60 min) on the viability of encapsulated bacteria were investigated. Alginate concentration increased the microcapsule size whereas, nozzle air pressure decreased the size. The encapsulation efficiency increased with the size of microcapsules. Hardening time exhibited a positive effect up to 30 min then the effect was non-significant. Increased level of sodium alginate significantly increased the survival ratio of encapsulated bacteria cells. The survival ratio of bacteria cells during spray drying of sweetened yoghurt were 2.48 × 10−1 and 2.36 × 10−3 for encapsulated and free cells of S. thermophilus, respectively and 7.26 × 10−1 and 8.27 × 10−3 for L. bulgaricus. This study demonstrated that microencapsulation of yoghurt culture in sodium alginate is an effective technique of protecting bacterial cells against extreme drying conditions.