Heterofermentative Pattern and Exopolysaccharide Production by Lactobacillus helveticus ATCC 15807 in Response to Environmental pH

TORINO, MARÍA INÉS; TARANTO, MARÍA PÍA; SESMA, FERNANDO; FONT DE VALDEZ, GRACIELA

JOURNAL OF APPLIED MICROBIOLOGY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2001 vol. 91 p. 846 - 852

1364-5072

Aims: The objective of this work was to evaluate the fermentation pattern of and theexopolysaccharide (EPS) production by Lactobacillus helveticus ATCC 15807 in milk batchcultures under controlled pH (4.5, 5.0 and 6.2).Methods and Results: EPS concentration was estimated by the phenol/sulphuric acidmethod and the chemical composition of puri®ed EPS by HPLC. Fermentation products andresidual 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 fromcitrate while at pH 4á5 it came from both citrate and pyruvate splitting. The EPS has a MW of105±106 and contains phosphate (81% in average), rhamnose (traces), and glucose and galactosein 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 toalternative pyruvate pathways and/or citrate metabolism according to the environmental pH.The EPS production was improved under low environmental pH conditions.Significance and Impact of the Study: This work provides relevant information of theeffect of pH on the metabolism of citrate and EPS production by Lact. helveticus. It maycontribute to improve technological aspects of ropy and citrate-utilizing lactic acid bacteria.