Lacticaseibacillus casei are commonly utilized as probiotic in a wide-range of fermented and unfe... more Lacticaseibacillus casei are commonly utilized as probiotic in a wide-range of fermented and unfermented dairy products. The stability of probiotics in fermented dairy products during shelf-life is of concern due to low pH and high level of organic acids. The objective of this study is to evaluate L. casei for their ability to survive in a model yogurt and fluid milk; additionally, their impact on the pH, organic acids, and sensory attributes of these products was examined. The strain-to-strain differences in cell densities in yogurt and milk inoculated at a therapeutic level at the end of shelf-life were 1.2 and 1.4 log CFU/ml, respectively. Five of the strains examined increased the pH of the yogurt, while two strains were observed to reduce the pH. In milk, one strain raised the pH, while eleven strains reduced the pH. The levels of lactate, acetate, and formate in both the yogurt and milk were altered in a strain-specific manner. The results suggested that the metabolism by thes...
This is an Open Access article distributed under the terms of the Creative Commons Attribution No... more This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License
Flavor development in ripening Cheddar cheese depends on complex microbial and biochemical proces... more Flavor development in ripening Cheddar cheese depends on complex microbial and biochemical processes that are difficult to study in natural cheese. Thus, our group has developed Cheddar cheese extract (CCE) as a model system to study these processes. In previous work, we found that CCE supported growth of Lactobacillus casei, one of the most prominent nonstarter lactic acid bacteria (NSLAB) species found in ripening Cheddar cheese, to a final cell density of 10(8) cfu/mL at 37°C. However, when similar growth experiments were performed at 8°C in CCE derived from 4-mo-old cheese (4mCCE), the final cell densities obtained were only about 10(6) cfu/mL, which is at the lower end of the range of the NSLAB population expected in ripening Cheddar cheese. Here, we report that addition of Tween 80 to CCE resulted in a significant increase in the final cell density of L. casei during growth at 8°C and produced concomitant changes in cytoplasmic membrane fatty acid (CMFA) composition. Although ...
Lactobacillus casei is remarkably adaptable to diverse habitats and widely used in the food indus... more Lactobacillus casei is remarkably adaptable to diverse habitats and widely used in the food industry. To reveal the genomic features that contribute to its broad ecological adaptability and examine the evolution of the species, the genome sequence of L. casei ATCC 334 is analyzed and compared with other sequenced lactobacilli. This analysis reveals that ATCC 334 contains a high number of coding sequences involved in carbohydrate utilization and transcriptional regulation, reflecting its requirement for dealing with diverse environmental conditions. A comparison of the genome sequences of ATCC 334 to L. casei BL23 reveals 12 and 19 genomic islands, respectively. For a broader assessment of the genetic variability within L. casei, gene content of 21 L. casei strains isolated from various habitats (cheeses, n = 7; plant materials, n = 8; and human sources, n = 6) was examined by comparative genome hybridization with an ATCC 334-based microarray. This analysis resulted in identification of 25 hypervariable regions. One of these regions contains an overrepresentation of genes involved in carbohydrate utilization and transcriptional regulation and was thus proposed as a lifestyle adaptation island. Differences in L. casei genome inventory reveal both gene gain and gene decay. Gene gain, via acquisition of genomic islands, likely confers a fitness benefit in specific habitats. Gene decay, that is, loss of unnecessary ancestral traits, is observed in the cheese isolates and likely results in enhanced fitness in the dairy niche. This study gives the first picture of the stable versus variable regions in L. casei and provides valuable insights into evolution, lifestyle adaptation, and metabolic diversity of L. casei.
Lacticaseibacillus casei are commonly utilized as probiotic in a wide-range of fermented and unfe... more Lacticaseibacillus casei are commonly utilized as probiotic in a wide-range of fermented and unfermented dairy products. The stability of probiotics in fermented dairy products during shelf-life is of concern due to low pH and high level of organic acids. The objective of this study is to evaluate L. casei for their ability to survive in a model yogurt and fluid milk; additionally, their impact on the pH, organic acids, and sensory attributes of these products was examined. The strain-to-strain differences in cell densities in yogurt and milk inoculated at a therapeutic level at the end of shelf-life were 1.2 and 1.4 log CFU/ml, respectively. Five of the strains examined increased the pH of the yogurt, while two strains were observed to reduce the pH. In milk, one strain raised the pH, while eleven strains reduced the pH. The levels of lactate, acetate, and formate in both the yogurt and milk were altered in a strain-specific manner. The results suggested that the metabolism by thes...
This is an Open Access article distributed under the terms of the Creative Commons Attribution No... more This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License
Flavor development in ripening Cheddar cheese depends on complex microbial and biochemical proces... more Flavor development in ripening Cheddar cheese depends on complex microbial and biochemical processes that are difficult to study in natural cheese. Thus, our group has developed Cheddar cheese extract (CCE) as a model system to study these processes. In previous work, we found that CCE supported growth of Lactobacillus casei, one of the most prominent nonstarter lactic acid bacteria (NSLAB) species found in ripening Cheddar cheese, to a final cell density of 10(8) cfu/mL at 37°C. However, when similar growth experiments were performed at 8°C in CCE derived from 4-mo-old cheese (4mCCE), the final cell densities obtained were only about 10(6) cfu/mL, which is at the lower end of the range of the NSLAB population expected in ripening Cheddar cheese. Here, we report that addition of Tween 80 to CCE resulted in a significant increase in the final cell density of L. casei during growth at 8°C and produced concomitant changes in cytoplasmic membrane fatty acid (CMFA) composition. Although ...
Lactobacillus casei is remarkably adaptable to diverse habitats and widely used in the food indus... more Lactobacillus casei is remarkably adaptable to diverse habitats and widely used in the food industry. To reveal the genomic features that contribute to its broad ecological adaptability and examine the evolution of the species, the genome sequence of L. casei ATCC 334 is analyzed and compared with other sequenced lactobacilli. This analysis reveals that ATCC 334 contains a high number of coding sequences involved in carbohydrate utilization and transcriptional regulation, reflecting its requirement for dealing with diverse environmental conditions. A comparison of the genome sequences of ATCC 334 to L. casei BL23 reveals 12 and 19 genomic islands, respectively. For a broader assessment of the genetic variability within L. casei, gene content of 21 L. casei strains isolated from various habitats (cheeses, n = 7; plant materials, n = 8; and human sources, n = 6) was examined by comparative genome hybridization with an ATCC 334-based microarray. This analysis resulted in identification of 25 hypervariable regions. One of these regions contains an overrepresentation of genes involved in carbohydrate utilization and transcriptional regulation and was thus proposed as a lifestyle adaptation island. Differences in L. casei genome inventory reveal both gene gain and gene decay. Gene gain, via acquisition of genomic islands, likely confers a fitness benefit in specific habitats. Gene decay, that is, loss of unnecessary ancestral traits, is observed in the cheese isolates and likely results in enhanced fitness in the dairy niche. This study gives the first picture of the stable versus variable regions in L. casei and provides valuable insights into evolution, lifestyle adaptation, and metabolic diversity of L. casei.
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