88D-8 |
Evaluation of culture mediums to enumerate Bifidobacterium lactis in yogurt |
C. R. F. GROSSO, Department of Food Planning and Nutrition, State University of Campinas (UNICAMP), Cidade Universitária Zeferino Vaz, Campinas-SP, 13083-970, Brazil and C. S. Fávaro-Trindade, Department of Food Technology, State University of Campinas (UNICAMP), Cidade Universitária Zeferino Vaz, Campinas-SP, 13083-970, Brazil. Foods containing probiotic microorganisms are traded in many countries, however, there have not been standardized methods to identify and enumerate such organisms. The aim of this study is to evaluate two culture mediums, being one selective and the other differential to count B. lactis in yogurt. The yogurt was produced with 2% of inoculum (Streptococcus salivarius subsp. thermophilus and Lactobacillus delbueckii subsp. bulgaricus) plus 1.5% of B. lactis and stored at 7oC/28 days. The enumeration was done in 0, 7, 14, 21 and 28 days. The B. lactis was counted by utilizing the spread-plate method, in the mediums: (selective) MRS supplemented with dicloxacilin, lithium chloride, aniline blue and cysteine and in the (differential) RCA with 0.03% of Prussian Blue. Lee's Agar medium was utilized to enumerate the S. thermophilus and L. bulgaricus when the B. lactis was counted in the selective medium. S. thermophilus and L bulgaricus and B. lactis were differentiated in RCA through the distinct morphology of their colonies. B. lactis formed blue colonies in MRS suplemented, the others did not grow. Both supplemented RCA and MRS were efficient to count B. lactis in yogurt while the cultures were equilibrated; when S. thermophilus and L. bulgaricus were predominant, the selective medium was more efficient. The disposability of B. lactis enumeration in fermented dairy products is essential in order to enable a reliable utilization of probiotic cultures.
Session 88D, Food Microbiology: General
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