RESEARCHES CONCERNING MICROBIOLOGICAL EVOLUTION OF LACTIC ACID BACTERIA TO YOGHURT STORAGE DURING SHELF-LIFE

Abstract

Lactic acid bacteria evolution ( Lactobacilus delbrueckii ssp bulgaricus and Streptococcus termophilus ) was followed in tree stages of storage: in first day of storage after processing; in the middle of storage during s helf-life; in the last day of storage during shelf-life. For yoghurt, the manufacture depends on a symbiotic relationship between two bacteria, Streptococcus thermophilus and Lactobacillus bulgaricus, where each species of bacterium stimulates the growth of the other. The a im of this study was to research in which way lactic acid bacteria evolved (concentrati on of viable cells) to storage during shelf-life. The method for determination of lactic acid bacter ia was conforming Romanian standard SR ISO 13437/1999 and was used enrich and isolation microbial mediums . Also, from the same samples was determined and total yeast and molds. 5 samples of yoghurt were taken in study and determination was made at s torage, during shelf-life. A decrease of concentration of lactic acid bacter ia was observed to storage, especially in the last decade of shelf-life to all samples taken in study. Concentration of lactic acid bacteria witch should be from 10 7 ufc/gram until the end of shelf-life is registered only in the first day of product storage ..The end of shelf-life the concentration was very low, by 10 4 ufc/gram (witch is consider inadequate). Also, in 15% from total samples taken in study, wer e observed that in the last decade of storage, lactic acid bacteria are inhibit ed by yeast and molds. The concentration continues to decrease until the end of shelf-life. This indicate a low stability of starter culture in fermented dairy, the viable germs being inhibited by the development of other microorganisms, primarily Enterobacteriaceae and then yeasts and molds.