The use of probiotic bacteria in fish feed is of increasing interest and microencapsulation technology can be used to maintain the viability of probiotic bacteria during processing and storage.
In this study oat β-glucan (70%) was used for co-encapsulating probiotic Bacillus subtilis on the alginate matrix. The spray drying technique was used to produce the microcapsules.
Simulated gastric fluids (SGF) of Nile tilapia were prepared using saline solution, adjusted pH to 1.5, using HCl solution. Exactly 0.5 g of B. subtilis microcapsules and 0.5
mL of free B. subtilis were placed into separated test tubes containing 4.5 mL of SGF. One mL of each sample was taken after incubation at 25 °C in a water bath for 0, 1, 2, and 3 h and enumerated for the cell counts on LB agar using a pour- plate method (Figure 1) . For bile tolerance determination, 0.5 g of B. subtilis microcapsules and 0.5 mL of B. subtilis free cells were added into 4.5 mL of SGF at pH 1.5 and incubated at 25 °C for 1 h. After the incubation, the samples were then centrifuged . Then, SGF was removed and replaced with 4.5 mL of tilapia bile salt (10%). One mL of each sample was taken after further incubations of 1, 2, and 3 h at 25 °C and enumerated on LB agar using a pour-plate method to determine for the number of viable cells (Figure 2 ). Results were subjected to ANOVA and Tukey’s test (p<0.05).
The combination of β-glucan with sodium alginate improved viability of Bacillus subtilis under simulated tilapia gastrointestinal conditions. The spray dried B. subtilis with β-glucan could be incorporated into the feed ingredients to be pelleted or after feed pellet grading through a coating process, providing valuable effects to the fish.