title: The potential of species-specific tagatose-6-phosphate (T6P) pathway in Lactobacillus casei group for galactose reduction in fermented dairy foods.
abstract: Residual lactose and galactose in fermented dairy foods leads to several industrial and health concerns. There is very little information pertaining to manufacture of fermented dairy foods that are low in lactose and galactose. In the present study, comparative genomic survey demonstrated the constant presence of chromosome-encoded tagatose-6-phosphate (T6P) pathway in Lactobacillus casei group. Lactose/galactose utilization tests and β-galactosidase assay suggest that PTSGalsystem, PTSLacsystem and T6P pathway are major contributors for lactose/galactose catabolism in this group of organisms. In addition, it was found than lactose catabolism by Lb. casei group accumulated very limited galactose in the MRS-lactose medium and in reconstituted skim milk, whereas Streptococcus thermophilus and Lb. delbrueckii subsp. bulgaricus (Lb. bulgaricus) strains secreted high amount of galactose extracellularly. Moreover, co-culturing Lb. casei group with Str. thermophilus showed significant reduction in galactose content, while co-culturing Lb. casei group with Lb. bulgaricus showed significant reduction in lactose content but significant increase in galactose content in milk. Overall, the present study highlighted the potential of Lb. casei group for reducing galactose accumulation in fermented milks due to its species-specific T6P pathway.
authors.affiliation: Food and Nutritional Science, School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong.
authors.forename: Qinglong
authors.initials: Q
authors.lastname: Wu
authors.affiliation: Food and Nutritional Science, School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong. Electronic address: npshah@hku.hk.
authors.forename: Nagendra P
authors.initials: NP
authors.lastname: Shah
mesh_terms: D000818:Animals; D043302:Cultured Milk Products / Q000032:analysis / Q000382:microbiology*; D005690:Galactose / Q000032:analysis / Q000096:biosynthesis / Q000378:metabolism*; D023281:Genomics; D006600:Hexosephosphates / Q000235:genetics / Q000378:metabolism*; D007780:Lacticaseibacillus casei / Q000201:enzymology / Q000378:metabolism*; D007785:Lactose / Q000032:analysis / Q000378:metabolism; D008892:Milk / Q000737:chemistry* / Q000382:microbiology; D013045:Species Specificity; D048249:Streptococcus thermophilus / Q000378:metabolism; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
chemical_list: D006600:Hexosephosphates; C026634:tagatose 6-phosphate; D001616:beta-Galactosidase; D007785:Lactose; D005690:Galactose
keywords: Comparative genomics; Galactose catabolism; Lactobacillus casei group; Phosphotransferase system; Tagatose-6-phosphate pathway