title: Influence of casein hydrolysates on exopolysaccharide synthesis by Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus.
abstract: BACKGROUND
  A lot of interesting research has been undertaken to enhance the yield of exopolysaccharides (EPS) produced by lactic acid bacteria (LAB). The objective of this study was to determine the influence of casein hydrolysates (CH) with molecular weight less than 3 kDa on cell viability, EPS synthesis and the enzyme activity involved in EPS synthesis during the co-culturing of Streptococcus thermophilus and Lactobacillus delbrueckii ssp. bulgaricus in MRS broth for 72 h at 37 ± 0.1 °C.
  
  
  RESULTS
  The highest EPS yield (150.1 mg L⁻¹) was obtained on CH prepared with papain (CHP) at 48 h. At 24 h, EPS were composed of galactose, glucose and rhamnose in a molar ratio of 1.0:2.4:1.5. The monosaccharide composition changed with extension of the fermentation time. The activities of α-phosphoglucomutase, uridine 5'-diphosphate (UDP)-glucose pyrophosphorylase and UDP-galactose 4-epimerase were associated with EPS synthesis. Moreover, the activities of β-phosphoglucomutase and deoxythymadine 5'-diphosphate (dTDP)-glucose pyrophosphorylase involved in rhamnose synthesis were very low at the exponential growth phase and could not be detected during other given periods.
  
  
  CONCLUSIONS
  The influence of different CH (<3 kDa) on LAB viability, EPS production, EPS monomeric composition and activity levels of key metabolic enzymes was distinct. Besides, their influence was related to the distribution of amino acids.
authors.affiliation: College of Light Industry and Food Sciences, South China University of Technology, Guangzhou, 510640, China; Department of Animal and Food Science, Texas Tech University, Lubbock, TX, 79409, USA.
authors.forename: Qingli
authors.initials: Q
authors.lastname: Zhang
authors.forename: Bao
authors.initials: B
authors.lastname: Yang
authors.forename: Mindy M
authors.initials: MM
authors.lastname: Brashears
authors.forename: Zhimin
authors.initials: Z
authors.lastname: Yu
authors.forename: Mouming
authors.initials: M
authors.lastname: Zhao
authors.forename: Ning
authors.initials: N
authors.lastname: Liu
authors.forename: Yinjuan
authors.initials: Y
authors.lastname: Li
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000378:metabolism; D019149:Bioreactors; D002364:Caseins / Q000378:metabolism*; D002417:Cattle; D010450:Endopeptidases / Q000378:metabolism; D005285:Fermentation; D005503:Food Additives / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism*; D005690:Galactose / Q000032:analysis / Q000378:metabolism; D005947:Glucose / Q000032:analysis / Q000378:metabolism; D048668:Lactobacillus delbrueckii / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D050296:Microbial Viability; D010733:Phosphoglucomutase / Q000378:metabolism; D011135:Polysaccharides, Bacterial / Q000819:agonists / Q000096:biosynthesis* / Q000737:chemistry / Q000302:isolation & purification; D011492:Protein Hydrolysates / Q000378:metabolism*; D012210:Rhamnose / Q000032:analysis / Q000378:metabolism; D048249:Streptococcus thermophilus / Q000201:enzymology / Q000254:growth & development / Q000378:metabolism*; D014534:UDPglucose 4-Epimerase / Q000378:metabolism; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D002364:Caseins; D005503:Food Additives; D011135:Polysaccharides, Bacterial; D011492:Protein Hydrolysates; C098632:exopolysaccharide, Streptococcus; C475729:casein hydrolysate; D005957:UTP-Glucose-1-Phosphate Uridylyltransferase; D010450:Endopeptidases; D014534:UDPglucose 4-Epimerase; C020551:galactose epimerase; D010733:Phosphoglucomutase; D005947:Glucose; D012210:Rhamnose; D005690:Galactose
keywords: EPS biosynthesis; casein hydrolysates; enzyme activity; exopolysaccharides; lactic acid bacteria