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Lactobacillus delbrueckii ssp. bulgaricus, an important species of lactic acid bacteria, is widely used in the dairy industry, particularly in yogurt production. Commonly used in mixed cultures and especially with Streptococcus thermophilus, L. bulgaricus is mandatory for traditional yogurt and also confers several health benefits that meet the prerequisites for probiotic bacteria. The current standard medium, de Man, Rogosa and Sharpe (MRS), is unreliable as a selective method for isolating L. bulgarcius species from different sources including dairy products. MRS can also present a false positive for L. bulgaricus in some dairy products due to the presence of high background colonies of similar species. Consequently, there is a need for a better, more reliable medium for the differential enumeration of L. bulgaricus. The objective of this study was thus to formulate an agar medium that is effective for the differential isolation and enumeration of L. bulgaricus. A modified reinfor.
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One hundred samples of dairy products (25 each) of UHT milk, plain yoghurt, fruit yoghurt and white soft cheese samples were examined for total viable count, and the presence of foodborne pathogenic microorganisms. The results declared that the mean total bacterial counts/mL or gm were 2.9 x10 4 and 7.8 x10 4 in examined UHT milk and white soft cheese samples, respectively. Staphylococci, Enterococci, E. coli, and Clostridium perfringens were detected in (0.0, 28.0, 40.0 and 64.0 %) & (16.0, 20.0, 36.0 and 48.0 %) & (0.0, 20.0, 28.0 and 28.0 %) and (8.0, 0.0, 0.0 and 12.0 %) of examined samples, respectively. The mean values of isolated organisms/mL or gm were (0, 1.2 x10 3 , 1.3 x10 3 and 3.4 x10 3) & (1 x10 3 , 1.4 x10 3 , 1.98 x10 3 and 1.95 x10 3) & (0, 7.6 x10 2 , 2.2 x10 3 and 2.1 x10 3) and (0.9 x10 3 , 0, 0 and 3.3 x10 3), respectively. The predominant isolated bacterial stains were Staphylococcus aureus, Staphylococcus epidermidis, Enterococcus faecalis, Enterococcus faecium, Enterococcus durans, E. coli, and Clostridium perfringens by frequency distribution of (0.0, 21.7, 12.9 and 20.4 %) & (0.0, 26.2, 29.0 and 26.5 %) & (28.6, 21.7, 19.4 and 10.2 %) & (42.8, 8.7, 12.9 and 14.3 %) & (0.0, 0.0, 3.2 and 8.2 %) & (0.0, 21.7, 22.6 and 14.3 %) and (28.6, 0.0, 0.0 and 6.1 %) of total isolates, respectively. Meanwhile, Campylobacter jejuni and Salmonellae failed to be detected in all examined samples. The sanitary and public health importance of these organisms as well as control measures to improve the quality of dairy products and to safeguard the consumers from infection were discussed.
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Chocolate milk typically has higher microbiological counts than unflavored milk and is susceptible to off-flavor development before the end of targeted shelf life. It has been suggested that the addition of multiple ingredients (chocolate, sucrose, stabilizers, and vitamin A and D) contributes to expedited growth of spoilage organisms in chocolate milk. The objective of this study was to isolate and identify the organisms responsible for off-flavor development in nonfat chocolate milk. Nonfat chocolate milk was obtained from regional fluid milk processors (3 plants). At the end of shelf life (18 d) off-odors had developed and the milk was serial diluted and spread plated on standard and differential media including tryptic soy agar, De Man, Rogosa and Sharpe agar, skim milk agar, spirit blue agar, chocolate milk agar, and MacConkey agar. Isolates were streaked on chocolate milk agar (standard methods agar with 10% vol/vol chocolate milk). Five causative isolates were selected based .
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