title: Heterofermentative pattern and exopolysaccharide production by Lactobacillus helveticus ATCC 15807 in response to environmental pH.
abstract: OBJECTIVE
  The objective of this work was to evaluate the fermentation pattern of and the exopolysaccharide (EPS) production by Lactobacillus helveticus ATCC 15807 in milk batch cultures under controlled pH (4.5, 5.0 and 6.2).
  
  
  RESULTS
  EPS concentration was estimated by the phenol/sulphuric acid method and the chemical composition of purified EPS by HPLC. Fermentation products and residual sugars were determined by HPLC and enzymatic methods. The micro-organism shifted from a homofermentative to a heterofermentative pattern, producing acetate (9.5 and 5.8 mmol l(-1)) at pH 5.0 and 6.2, respectively, and acetate (7.1 mmol l(-1)) plus succinate (1.2 mmol l(-1)) at pH 4.5. At pH 5.0 and 6.2, acetate derived from citrate while at pH 4.5 it came from both citrate and pyruvate splitting. The EPS has a MW of 10(5)-10(6) and contains phosphate (81% in average), rhamnose (traces), and glucose and galactose in a ratio of 1 : 1 (pH 6.2) and 2 : 1 (pH 4.5 and 5.0). The highest production (549 mg l(-1)) corresponded to pH 5.0 and the lowest (49 mg l(-1)) to pH 6.2.
  
  
  CONCLUSIONS
  The heterofermentative pattern of Lact. helveticus ATCC 15807 was linked to alternative pyruvate pathways and/or citrate metabolism according to the environmental pH. The EPS production was improved under low environmental pH conditions.
  
  
  CONCLUSIONS
  This work provides relevant information of the effect of pH on the metabolism of citrate and EPS production by Lact. helveticus. It may contribute to improve technological aspects of ropy and citrate-utilizing lactic acid bacteria.
authors.affiliation: Centro de Referencia para Lactobacilos (CERELA, CONICET), Tucumán, Argentina.
authors.forename: M I
authors.initials: MI
authors.lastname: Torino
authors.forename: M P
authors.initials: MP
authors.lastname: Taranto
authors.forename: F
authors.initials: F
authors.lastname: Sesma
authors.forename: G F
authors.initials: GF
authors.lastname: de Valdez
mesh_terms: D000818:Animals; D019343:Citric Acid / Q000378:metabolism; D003470:Culture Media; D005285:Fermentation; D006863:Hydrogen-Ion Concentration; D007778:Lactobacillus / Q000254:growth & development* / Q000378:metabolism*; D008892:Milk / Q000378:metabolism; D011135:Polysaccharides, Bacterial / Q000096:biosynthesis*; D019289:Pyruvic Acid / Q000378:metabolism
chemical_list: D003470:Culture Media; D011135:Polysaccharides, Bacterial; D019343:Citric Acid; D019289:Pyruvic Acid