Abstract
Five brands yoghurts designated A, B, C, D and E were obtained and used for assessing their microbial quality. A ten-fold serial dilution was carried out and appropriate dilution used to inoculate duplicate plates of SDA, Eosin methylene blue, MacConkey and Nutreint agars. Discrete colonies that developed were purified and stored on agar slant at 4 o C. The pH of the samples ranged from 5.6 to 6.0. In the total coliform count, sample A recorded no count while others had count from 2.0 to 5.0 x 10 2 cfu/ml. The total viable bacterial and fungal counts were 6.0 to 18.0 x 10 4 and 1.0 to 6.0 x 10 3 cfc/ml, respectively. Five fungal genera were obtained as Aspergillus, Penicillium, Fusarium, Mucor, Geotricum, Neurospora and Absidia. Mucor species occurred in all the samples while Fusarium species occurred only in sample B. Among the samples, yoghurt sample B harbored a greater percentage of the fungal isolates. Samples C and D had the least number of fungal of three (3) each. The bacterial isolates obtained include species of Staphylococcus, Lactobacillus, Escherichia, Bacillus, Pseudomonas and Klebsiella. Sample B also recorded the highest number of bacterial isolates. The genera Bacillus occurred in all the yoghurt samples whereas Lactobacillus and E.coli occurred only in two yoghurt samples each.
Highlights
Yoghurt is a cultured dairy product produced by the lactic acid fermentation of milk using a combination of bacteria such as Lactobacillus delbruekii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus in the ratio of 1:1 [1]
The results of the microbial count and pH determination of the yoghurt samples are shown in Table 1.The total aerobic count ranges from 1.0 x to 18.0 x CFU/ml
Samples C and D had the same number of bacterial isolates
Summary
Yoghurt is a cultured dairy product produced by the lactic acid fermentation of milk using a combination of bacteria such as Lactobacillus delbruekii subsp. bulgaricus and Streptococcus salivarius subsp. thermophilus in the ratio of 1:1 [1]. Yoghurt is a cultured dairy product produced by the lactic acid fermentation of milk using a combination of bacteria such as Lactobacillus delbruekii subsp. The milk used in yoghurt production is homogenized, heated to a temperature of between 85-100oC and cooled to 41-45oC. The special starter cultures, Streptococcus salivarius subsp.thermophilus and Lactobacillus delbruekii subsp.bulgaricus are added [4]. The relationship between the two starter organisms is known as proto-cooperation, that is, they have a mutually favorable interaction but are not completely interdependent. Both grow in milk on their own, but they grow and produce acidity faster when there is availability of peptide and free amino acids [5]. The acids produced as well as acetaldehyde and diacetyl give the product its unique smooth texture, tart flavor and aroma [6]
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