Bifidobacterium longum KCTC 3128 and HLC 3742 were independently immobilized (entrapped) in calcium alginate beads containing 2, 3, and 4% sodium alginate. When the bifidobacteria entrapped in calcium alginate beads were exposed to simulated gastric juices and a bile salt solution, the death rate of the cells in the beads decreased proportionally with an increase in both the alginate gel concentration and bead size. The initial cell numbers in the beads affected the numbers of survivors after exposure to these solutions; however, the death rates of the viable cells were not affected. Accordingly, a mathematical model was formulated which expressed the influences of several parameters (gel concentration, bead size, and initial cell numbers) on the survival of entrapped bifidobacteria after sequential exposure to simulated gastric juices followed by a bile salt solution. The model proposed in this paper may be useful for estimating the survival of bifidobacteria in beads and establishing optimal entrapment conditions.It has been reported that the microencapsulation of bifidobacteria can ensure greater survival in gastric and intestinal environments (18). Immobilized cells exhibit many advantages over free cells, including the maintenance of stable and active biocatalysts, high volumetric productivity, improved process control, the protection of cells against damage, and reduced susceptibility to contamination (12,19). Recently, yogurt products containing encapsulated lactic acid bacteria have been distributed under the brand name Doctor-Capsule (Bingrae Co., Kyunggi-do, Korea) in Korea. Among the available techniques for immobilizing living cells, entrapment in Ca alginate beads has been frequently used for the immobilization of lactic acid bacteria (22). Alginate has the benefits of being nontoxic to the cells being immobilized, and it is an accepted food additive (17). This study used mathematical modelling to represent the influences of alginate concentration, bead size, and initial cell numbers on the survival rate of entrapped bifidobacteria against simulated gastric juices and bile salt solution.Entrapment of bifidobacteria. Bifidobacterium longum KCTC 3128 (ATCC 15707) was purchased in lyophilized form from the Korea Collection for Type Cultures (Genetic Resource Center, Taejon, Korea). B. longum HLC 3742 was screened from feces from a healthy Korean (14). These two types of bacteria were transferred twice in Trypticase-protease peptone-yeast extract (TPY) broth at 37°C. Cultivation was carried out in a 2.5-liter fermentor containing 1,000 ml of TPY broth. After cultivation for 20 h, cultures were collected by centrifugation (3,000 ϫ g, 10 min), washed, and resuspended in a 0.85% NaCl saline solution to approximately 10 9 cells/ml. Sodium alginate (medium viscosity) obtained from Sigma Chemical Co. was used in this study. Various amounts of sodium alginate (5, 7.5, and 10 g) were autoclaved at 121°C for 15 min in powder and then individually dissolved in 250-ml resuspended cell solutions in aseptic vinyl ba...

The effect of the binders, such as silica, alumina, and aluminum phosphate solution (APS), was studied on the acidity and catalytic performance of HZSM-5 zeolite (SiO 2 /Al 2 O 3 = 80) in methanol-to-propylene (MTP) process. The strong acidity of catalyst increased slightly with alumina binder but decreased with silica and APS binders. It is noted that the catalyst with APS binder showed the highest bulk crush strength. Catalytic performance of the alumina or silica bound catalyst was comparable to that of pure HZSM-5 catalyst while that of APS bound catalyst was completely different depending on the binder content. Low content (10 wt%) of APS resulted in a dramatically enhanced propylene selectivity ([40 C mol%) due to the decrease in strong acidity. On the other hand with high content ([20 wt%) of APS, methanol was mostly dehydrated into dimethylether without further transformation into hydrocarbons even if the mechanical strength was significantly improved. The binary binder system was proposed not only to improve the mechanical strength of catalyst with small amount of APS binder but also to keep a high propylene selectivity. The catalyst bound with APS-and-alumina or APS-and-silica showed a comparable propylene selectivity to that of HZSM-5 with the 10 wt% of APS single binder while demonstrated much higher bulk crush strengths.

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