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Optimize microencapsulation of probiotic bacteria for stability.

Probiotics can be microencapsulated as a way to enhance their gastrointestinal transit and to prolong their shelf life in certain foods. Scientists in Australia have applied an extra coating of palm oil and poly-L-lysine (POPL) to alginate (ALG) microcapsules to enhance the survival of encapsulated probiotic bacteria. It appears that coating the microcapsules may improve the viability of probiotic organisms in functional foods.

The researchers encapsulated eight strains of probiotic bacteria, including Lactobacillus rhamnosus, Bifidobacterium longum, L. salivarius, L. plantarum, L. acidophilus, L. paracasei, B. lactis type Bl-04, and B. lactis type Bl-07 using alginate alone or alginate with POPL. To determine if adding POPL improved the viability of probiotic bacteria in acidic conditions, both ALG and POPL microcapsules were inoculated into pH 2.0 MRS broths. Their viability was assessed over a two-hour incubation period.

Two bile salts, including oxgall bile salt and taurocholic acid, were used to test the bile tolerance of probiotic bacteria entrapped in ALG and POPL microcapsules. To assess the porosity and the ability of the microcapsule to hold small molecules in an aqueous environment, a water-soluble fluorescent dye, 6-carboxyflourescin (6 FAM), was encapsulated. Its release was monitored with a UV spectrophotometer.

The researchers found that coating the microcapsules with POPL increased the overall size of the capsules by an average of 3 microns. However, the microcapsules with POPL had a much smoother surface texture. The results also indicated that adding POPL to microcapsules improved the average viability of the encapsulated probiotic bacteria by more than 1 log CFU per mL, compared with ALG microcapsules, after two hours of exposure to acidic conditions.

The investigators found similar plate counts between ALG and POPL microcapsules when they were exposed to bile salts. This suggests that an extra coating of POPL could be readily broken down by bile salts commonly found in the lower gastrointestinal tract. When the porosity of the microcapsules was tested, the scientists found that POPL microcapsules were less porous and held 52.2% more fluorescent dye over a six-week storage period. Future studies could explore how bile could help free encapsulated probiotic bacteria in the lower gastrointestinal tract.

Further information. Nagendra Shah, School of Molecular Sciences, Victoria University, Werribee Campus, P.O. Box 14428, Melbourne, Victoria 8001, Australia; phone: +61 3 9919 4000; fax: +61 3 9689 4069; email:
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Publication:Emerging Food R&D Report
Date:Jun 1, 2009
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