Banana was used as the raw material for the preparation of fermentation media of Lactobacillus acidophilus, and cell immobilization was applied to improve the fermentation efficiency of L. acidophilus in banana media. Cell immobilization was performed using calcium alginate and ？e -carrageenan as the entrapping matrix, and gel beads of diameters around 2.6 mm for the former and 3.0 mm for the latter were obtained. Both green and ripe bananas were used for the preparation of banana media, and both free and immobilized cells were used to conduct the fermentation for 80 hours. The viable cell number in ripe banana media was found to be higher than that in green ones during both free cell and immobilized cell fermentation. During the fermentation of immobilized cell, cells would leak out from the gel beads and grew in the medium solution. In immobilized cell fermentation, the final viable cell number could reach 105 CFU/ml in medium suspension and that in gel beads could become over 108 CFU/ml gel. In free cell fermentation, the final viable cell number was around 106 CFU/ml. Immobilized cell could overcome the unfavorable conditions in green banana media and improved results could be obtained. During the fermentation, the variation of pH and titratable acidity showed obvious relationships with the growth of cells. Variation of fructooligosaccharides contents in ripe banana media was not remarkable in immobilized cell fermentation compared to free cell. Immobilized L. acidophilus fermented banana medium was able to be used as a synbiotic product by combining the probiotic effect of L. acidophilus and the prebiotic effect of banana. The effect of Ca-alginate immobilization was better than ？e -carrageenan. Based on the overall results of cost analysis, Ca-alginate immobilization was a better choice compared to ？e -carrageenan immobilization. On the other hand, L. acidophilus was immobilized using Ca-alginate and ？e -carrageenan, and protection effects of cell immobilization on the viability of the bacteria after freezing and freeze-drying were studied, and its influence on the storage stability of the freeze-dried cells at 5.degree. C, 25.degree. C, 45.degree. C, 60.degree. C, 70.degree. C was also investigated. Initial concentration of both free and immobilized cells used for experiments all reached the level of 1010 cells/ml. Results indicated that the immobilization in Ca-alginate gel beads and？e-carrageenan gel beads could provide effective protection to reduce the damage of bacteria under operations. High correlations were obtained between Log D values and storage temperatures for both free and immobilized cells under those various storage temperatures used. the z value which derived from the linear regression equation of Log D and storage temperature for free and immobilized cells were significantly different (p < 0.05). Cell immobilization could enhance temperature tolerance of the freeze-dried bacteria during storage and diminish the influence of temperature variation on the storage stability of freeze-dried cells.
