期刊
JOURNAL OF DAIRY SCIENCE
卷 92, 期 2, 页码 477-482出版社
ELSEVIER SCIENCE INC
DOI: 10.3168/jds.2008-1312
关键词
exopolysaccharide; yogurt; Streptococcus thermophilus
资金
- Fonds quebecois de la recherche sur la nature et les technologies
- Novalait Inc.
- Ministere de l'Agriculture, des Pecheries et de l'Alimentation du Quebec-Agriculture and AgriFood Canada
- Natural Sciences and Engineering Research Council (NSERC) of Canada
To prevent textural defects in low-fat and fat-free yogurts, fat substitutes are routinely added to milk. In situ production of exopolysaccharides (EPS) by starter cultures is an acknowledged alternative to the addition of biothickeners. With the aim of increasing in situ EPS production, a recombinant galactose-positive EPS+ Streptococcus thermophilus strain, RD-534-S1, was generated and compared with the parent galactose-negative EPS+ strain RD-534. The RD-534-S1 strain produced up to 84 mg/L of EPS during a single-strain milk fermentation process, which represented 1.3 times more than the EPS produced by strain RD-534. Under conditions that mimic industrial yogurt production, the starter culture consisting of RD-534-S1 and (EPS-) Lactobacillus bulgaricus L210R strain (RD-534-S1/L210R) led to an EPS production increase of 1.65-fold as compared with RD-534-S1 alone. However, the amount of EPS produced did not differ from that found in yogurts produced using an isogenic starter culture that included the parent S. thermophilus strain RD-534 and Lb. bulgaricus L210R (RD-534/L210R). Moreover, the gel characteristics of set-style yogurt and the rheological properties of stirred-style yogurt produced using RD-534-S1/L210R were similar to the values obtained for yogurts made with RD-534/L210R. In conclusion, it is possible to increase the production of EPS by ropy S. thermophilus strains through genetic engineering of galactose metabolism. However, when used in combination with Lb. bulgaricus for yogurt manufacture, the EPS overproduction of recombinant strain is not significant.
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