Selection and characterization of naturally occurring high acidification rate Streptococcus thermophilus strains (original) (raw)
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Annals of Microbiology, 2008
The aim of this study was to explore the potential of indigenous strains ofLactobacillus delbrueckii subsp,bulgaricus andStreptococcus thermophilus as yoghurt starter culture, for this purpose some important technological properties were studied. The strains ofLactobacillus delbrueckii subsp.bulgaricus Lb5, Lb7, andStreptococcus thermophilus St4 and St7, produced more than 0.7% acidity after 6h of incubation in skim milk media. The acetaldehyde was detected as major aroma compound produced by mixed culture M1 (Lb5∶St4) i.e., 19.95 ppm at 43°C. Yoghurt was prepared with different combinations of the culture and sensory analysis performed by a trained panel revealed that pleasant yoghurt was prepared with mixed culture ofLactobacillus delbrueckii subsp.bulgaricus Lb5 andS. thermophilus St4. The results suggested that these strains have potential to be used as starters for yoghurt production.
The Behaviour of Starter Cultures in Concentrated Yoghurt (Labneh) Produced by Different Techniques
LWT - Food Science and Technology, 1999
Concentrated yoghurts were produced by fermenting milks concentrated by ultra-xltration and reverse osmosis, and by removing whey from batches of natural yoghurt using the same techniques. The choice of procedure inyuenced the chemical composition of the end-products and also, as indicated by the titratable acidities and acetaldehyde contents of the labnehs, the metabolic activity of the starter culture. Although the behaviour of the cultures varied with the total solids in the milk, the total colony counts of Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus recorded after 24 h at 43C were similar in all samples. A taste panel assessment revealed a dexnite preference for labneh (230 g/kg total solids) produced at this concentration by ultra-xltration of natural yoghurt (160 g/kg total solids).
The industrial production of yoghurt is increasingly developed in the world. Yoghurt is a fermented milk product obtained from fermentation of Lactobacillus bulgaricus and Streptococcus thermophilus strains. In Turkey, yoghurt is produced by the two ways; one of them is a traditional method without using starter culture in small dairy plants and the second production method by using industrial starter culture in modern plants. In this study yoghurt samples were collected from the local markets which were produced traditional process and produced in modern plants by addition of starter cultures, their viable L. bulgaricus and S. thermophilus bacteria numbers, coliform, Escherichia coli, yeast and mould counts, pH values were determined and compared each others. Yoghurts have pH values between 3.95-4.23, viable S. thermophilus and L. bulgaricus numbers were determined between 10-10 cfu/g for yoghurts producing with starter culture, 10-10 7 8 5 6 cfu/g and 10-10 cfu/g for yoghurts producing with traditional methods, respectively. Coliforms, E. coli, yeast 6 7 and mould counts have at low numbers for all yoghurt samples. As the result, yoghurts which are produced by starter cultures have high numbers of yoghurt bacteria means that yoghurts produced by using starter cultures have higher therapeutic and/or antimicrobial properties beside of their organoleptic characteristics. Importance of yoghurt production by using starter cultures should be known and advantages of using starter cultures in fermentation products should be stated.
African Journal of …, 2011
Streptococcus thermophilus mutants as starter culture was investigated. The results of milk fermentations using L. bulgaricus and S. thermophilus mutant isolates when compared with their wildtype strains (control) indicated that the pH values of "kindirmo" produced at different incubation periods (h) and the mean percentage titratable acidity were not significantly different (p > 0.05) when compared with the control. The pH values of "kindirmo" produced using L. bulgaricus mutant isolates at different incubation periods (h) and the mean percentage titratable acidity were not significantly different (p > 0.05) when compared with the control. Also, these physicochemical properties of color [yellow (9/12) and white (3/12)], consistency [(thick and uniform (2/12), thick (6/12), not so thick (1/12), very thick (1/12), very thick and uniform (1/12)] and presence of water [trace amount of water (4/12), water present (4/12), water moderately present (2/12), water in large amount present (1/12)] were observed. The pH values of "kindirmo" produced by S. thermophilus mutant isolates at different incubation periods (h) and the mean percentage titratable acidity were not significantly different (p > 0.05) when compared with the control. Also, these physicochemical properties of color [yellow (5/6) and white (1/6)], consistency [(thick and uniform (1/6), thick (3/6), not so thick (2/6)] and presence of water [(water present (3/6), trace amount of water present (2/6), water moderately present (1/6)] were observed. It should be noted that, the "kindirmo" produced in this work was not from a mixed culture of L. bulgaricus and S. thermophilus mutant isolates when compared with the normal procedures known. It is possible that if these mutant isolates are to be used in dairy industry as a mixed culture, it will give better and high quality yoghurt.
Viability of yoghurt and probiotic bacteria in yoghurts made from commercial starter cultures
International Dairy Journal, 1997
Viability of yoghurt and probiotic bacteria was assessed during manufacture and 35 d storage in yoghurt made from four commercial starter cultures. The titratable acidity, pH and dissolved oxygen content showed similar patterns of increase or decrease during manufacture and storage of yoghurt, whereas concentration of hydrogen peroxide increased in the product prepared with cultures that contained L. delbrueckii ssp. bulgaricus. The increase in numbers of probiotic organisms during manufacture and the viability of these organisms during storage were dependent on the species and strain of associative yoghurt organisms. The viability of L. acidophilus was affected by the presence of L. delbrueckii ssp. bulgaricus, whereas bifidobacteria exhibited better stability in the yoghurt prepared from cultures that contained L. delbrueckii ssp. bulgaricus. The viability of both probiotic organisms was improved when the dissolved oxygen concentration was low in the product. The storage temperature of yoghurt affected the viability of bifidobacteria, but not L. acidophilus. The variations in titratable acidity, pH, dissolved oxygen and hydrogen peroxide were almost identical at storage temperatures of 4 and 10 °C. In one of the commercial cultures, 3 log cycles inhibition of bifidobacteria was observed from initial counts of >106 mL−1.
Starter cultures for production of yoghurt from sheep’s milk with extended shelf life
Bulgarian Journal of Agricultural Science
Originally Bulgarian yoghurt was prepared from sheep’s milk, but the home-made product had only a few days of shelf life. Today under industrial conditions yoghurt with shelf life of 20 days is routinely produced. Nevertheless producers and exporters are still interested in sheep’s milk yoghurt with even longer storage period. In this study we produced yoghurt with three selected starters and followed up its quality during three months of storage at 5oC. All three starters had low post acidification in the products. The freshly produced yoghurt samples had a pH of 4,17-4,39 which decreased gradually, but after 90 days it was still in the range 4,12-4,30 which was within the acceptable range. Viable cells of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus remained above the critical threshold of 1E+08 and 1E+06 cfu.ml-1 respectively for the whole period of 90 days. With the selected starters the accumulation of products of proteolysis remained low with a slig...
African Journal of Food Science, 2011
Twenty two strains of lactic acid bacteria (LAB) were isolated from 30 samples of commercial Nigerian bottled yoghurt (produced on a small scale). Isolates were phenotypically characterized and their technological properties such as acidification, exopolysaccharides (EPS) production, enzymatic activities, biogenic amine production and bacteriocin production were studied following standard procedures. The population of LAB in the yoghurt samples varied between 0.00 and 6.63 log cfu ml-1. The pH and titratable acidity ranged from 3.80 to 4.48 and 0.73 to 1.78% lactic acid respectively. The isolated LAB strains belonged to Lactobacillus, Lactococcus, Leuconostoc, Streptococcus and Enterococcus genera. Thirteen strains showed proteolytic activity while four strains showed high lipolytic activity. The LAB strains exhibited medium to low acidification activities. About 77% of the LAB strains produced EPS. Six strains produced biogenic amines. Seven strains showed antagonistic properties due to organic acid against indicator organisms (Staphylococcus aureus, Klebsiella pneumoniae, Escherichia coli and Proteus vulgaris) while two strains (Enterococcus faecalis and Lactococcus cremoris) produced additional inhibitory substances against K. pneumoniae. The results revealed that the assayed commercial Nigerian bottled yoghurts contain several LAB species and genera different from Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus. The production of biogenic amine by some of the LAB strains is undesirable in yoghurt. The technological properties of the LAB associated with the fermented milk produced on a small scale will help in the selection and development of beneficial strains as starter or adjunct cultures.
International Journal of Food Microbiology, 2014
Proto-cooperation between Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus is one of the key factors that determine the fermentation process and final quality of yoghurt. In this study, the interaction between different proteolytic strains of S. thermophilus and L. delbrueckii subsp. bulgaricus was investigated in terms of microbial growth, acidification and changes in the biochemical composition of milk during set-yoghurt fermentation. A complementary metabolomics approach was applied for global characterization of volatile and non-volatile polar metabolite profiles of yoghurt associated with proteolytic activity of the individual strains in the starter cultures. The results demonstrated that only non-proteolytic S. thermophilus (Prt−) strain performed proto-cooperation with L. delbrueckii subsp. bulgaricus. The proto-cooperation resulted in significant higher populations of the two species, faster milk acidification, significant abundance of aroma volatiles and non-volatile metabolites desirable for a good organoleptic quality of yoghurt. Headspace SPME-GC/MS and 1 H NMR resulted in the identification of 35 volatiles and 43 non-volatile polar metabolites, respectively. Furthermore, multivariate statistical analysis allows discriminating set-yoghurts fermented by different types of starter cultures according to their metabolite profiles. Our finding underlines that selection of suitable strain combinations in yoghurt starters is important for achieving the best technological performance regarding the quality of product.
Mixed culture growth kinetics of Streptococcus thermophilus and Lactobacillus bulgaricus
Enzyme and microbial technology, 1990
The production of Nigerian indigenous yoghurt (kindirmo) using Lactobacillus bulgaricus and Streptococcus thermophilus mutants as starter culture was investigated. The results of milk fermentations using L. bulgaricus and S. thermophilus mutant isolates when compared with their wildtype strains (control) indicated that the pH values of "kindirmo" produced at different incubation periods (h) and the mean percentage titratable acidity were not significantly different (p > 0.05) when compared with the control. The pH values of "kindirmo" produced using L. bulgaricus mutant isolates at different incubation periods (h) and the mean percentage titratable acidity were not significantly different (p > 0.05) when compared with the control. Also, these physicochemical properties of color [yellow (9/12) and white (3/12)], consistency [(thick and uniform (2/12), thick (6/12), not so thick (1/12), very thick (1/12), very thick and uniform (1/12)] and presence of water [trace amount of water (4/12), water present (4/12), water moderately present (2/12), water in large amount present (1/12)] were observed. The pH values of "kindirmo" produced by S. thermophilus mutant isolates at different incubation periods (h) and the mean percentage titratable acidity were not significantly different (p > 0.05) when compared with the control. Also, these physicochemical properties of color [yellow (5/6) and white (1/6)], consistency [(thick and uniform (1/6), thick (3/6), not so thick (2/6)] and presence of water [(water present (3/6), trace amount of water present (2/6), water moderately present (1/6)] were observed. It should be noted that, the "kindirmo" produced in this work was not from a mixed culture of L. bulgaricus and S. thermophilus mutant isolates when compared with the normal procedures known. It is possible that if these mutant isolates are to be used in dairy industry as a mixed culture, it will give better and high quality yoghurt.