The use of live probiotic bacteria as food supplement has become popular. Capability of probiotic bacteria to be kept at room temperature becomes necessary for customer's convenience and manufacturer's cost reduction. Hence, production of dried form of probiotic bacteria is important. Two common drying methods commonly used for microencapsulation are freeze drying and spray drying. In spite of their benefits, both methods have adverse effects on cell membrane integrity and protein structures resulting in decrease in bacterial viability. Microencapsulation of probiotic bacteria has been a promising technology to ensure bacterial stability during the drying process and to preserve their viability during storage without significantly losing their functional properties such acid tolerance, bile tolerance, surface hydrophobicity, and enzyme activities. Storage at room temperatures instead of freezing or low temperature storage is preferable for minimizing costs of handling, transportation, and storage. Concepts of water activity and glass transition become important in terms of determination of bacterial survival during the storage. The effectiveness of microencapsulation is also affected by microcapsule materials. Carbohydrate- and protein-based microencapsulants and their combination are discussed in terms of their protecting effect on probiotic bacteria during dehydration, during exposure to harsh gastrointestinal transit and small intestine transit and during storage.

The aims of this study were to evaluate the effect of types of protein-based microcapsules and storage at various ambient temperatures on the survival of Lactobacillus acidophilus during exposure to simulated gastrointestinal tract and on the change in thermo-tolerance during heating treatment. The encapsulating materials were prepared using emulsions of protein (sodium caseinate, soy protein isolate, or pea protein), vegetable oil, and glucose, with maltodextrin was used as a wall material. The formulations were heated at 90 °C for 30 min to develop Maillard substances prior to being incorporated with L. acidophilus. The mixtures were then spray dried. The microspheres were stored at 25, 30, and 35 °C for 8 wk and examined every 4 wk. The addition of proteins as encapsulating materials demonstrated a significant protective effect (P < 0.05) as compared to the control sample. Sodium caseinate and soy protein isolate appeared more effective than pea protein in protecting the bacteria after spray drying and during the storage at different room temperatures. Storage at 35 °C resulted in a significant decrease in survival at end of storage period regardless the type of encapsulating materials. The addition of protein-based materials also enhanced the survival of L. acidophilus during exposure to simulated gastrointestinal condition as compared to the control. After spray drying and after 0th wk storage, casein, soy protein isolate, and pea protein-based formulations protected the bacteria during heat treatment. In fact, a significant decrease in thermal tolerance was inevitable after 2 wk of storage at 25 °C.

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Survival, acid and bile tolerance, and surface hydrophobicity of microencapsulated Bifidobacterium animalis ssp. lactis Bb12 were studied during storage at room temperature (25 °C) at low water activity (0.07, 0.1, and 0.2). Two types of alginate-based systems were prepared with and without mannitol as microencapsulant of B. animalis ssp. lactis Bb12. Formation of gel beads containing cells was achieved by dropping each emulsion into CaCl(2) solution; then, the beads were freeze dried. Survival, acid tolerance during 2-h exposure in de Man, Rogosa, Sharpe (MRS) broth at pH 2.0, bile tolerance during 8-h exposure in MRS broth containing taurocholic acid at pH 5.8, and retention of surface hydrophobicity were determined after freeze drying and during storage. The result showed that neither alginate nor alginate-mannitol formulation was effective in protecting B. animalis ssp. lactis Bb12 during freezing and freeze drying. The viability in alginate-mannitol and alginate formulations after freeze drying was 6.61 and 6.34 log CFU/g, respectively. Storage at low a(w) improved survival, acid tolerance, bile tolerance, and surface hydrophobicity retention of microencapsulated B. animalis ssp. lactis Bb12 when compared with controlled storage in an aluminum foil (with a(w) of 0.38 and 0.40 for alginate-mannitol and alginate formulations, respectively). Alginate mannitol was more effective than the alginate system during a short period of storage, but its effectiveness decreased during a long period of storage (80% survival at 10 wk). Nevertheless, storage of microencapsulated B. animalis ssp. lactis Bb12 in an aluminum foil without a(w) adjustment during 10 wk at room temperature was not effective (survival was 64% to 65%).

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