Growth and morphology of thermophilic dairy starters in alginate beads

[摘要] The aim of this research was to produce concentrated biomasses of thermophilic lactic starters using immobilized cell technology (ICT). Fermentations were carried out in milk using pH control with cells microentrapped in alginate beads. In the ICT fermentations, beads represented 17% of the weight. Some assays were carried out with free cells without pH control, in order to compare the ICT populations with those of classical starters. With Streptococcus thermophilus, overall populations in the fermentor were similar, but maximum bead population for (8.2×109 cfu/g beads) was 13 times higher than that obtained in a traditional starter (4.9×108 cfu/ml). For both Lactobacillus helveticus strains studied, immobilized-cell populations were about 3×109 cfu/g beads. Production of immobilized Lb. bulgaricus 210R strain was not possible, since no increases in viable counts occurred in beads. Therefore, production of concentrated cell suspension in alginate beads was more effective for S. thermophilus. Photomicrographs of cells in alginate beads demonstrated that, while the morphology of S. thermophilus remained unchanged during the ICT fermentation, immobilized cells of Lb. helveticus appeared wider. In addition, cells of Lb. bulgaricus were curved and elongated. These morphological changes would also impair the growth of immobilized lactobacilli.

[学科分类] 微生物学和免疫学

[关键词] cell immobilization;cell morphology;Lactobacillus bulgaricus;Lactobacillus helveticus;Streptococcus thermophilus