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School of Molecular Sciences, Victoria University, Werribee Campus, PO Box 14428, Melbourne City Mail Center, Victoria 8001, Australia
Corresponding Author: N. P. Shah; e-mail: Nagendra.Shah{at}vu.edu.au.
Effects of pH, temperature, supplementation with whey protein concentrate (WPC), and non-EPS culture on the exopolysaccharide (EPS) production by Streptococcus thermophilus 1275 were studied. The organism was grown in 10% reconstituted skim milk (RSM) in a Biostat B fermenter for 24 h at various pH (4.5, 5.5 and 6.5) and temperatures (30, 37, 40, and 42°C), and supplementation with WPC 392, and non-EPS producing S. thermophilus 1303 and the amount of EPS produced were determined. Bacterial counts were enumerated and the concentrations of lactic acid, lactose, glucose, and galactose were also determined. A maximum of 406 mg/L of EPS was produced in RSM at 37°C after 24 h of fermentation at pH 4.08 when the pH was not controlled. A pH of 5.5 and temperature of 40°C were found to be optimal for EPS production by S. thermophilus 1275, yielding 458 mg/L. The EPS production increased when RSM was supplemented with WPC 392. At optimum pH and at 37°C with WPC supplementation, the level of EPS increased to 1029 mg/L. Co-culturing S. thermophilus 1275 with non-EPS S. thermophilus 1303 increased EPS production at 37°C and pH 5.5 to 832 mg/L. High temperature (42°C) reduced the amount of EPS production, and EPS production ceased at pH 4.5 when maintained constantly at this pH. The level of lactose utilization and lactic acid production depended on growth conditions of the organism. No glucose was detected, while galactose was found to accumulate in the medium.
Key Words: exopolysaccharide • Streptococcus thermophilus 1275 • whey protein concentrate • adjunct culture
Abbreviation key: EPS = exopolysaccharides, LAB = lactic acid bacteria, RSM = reconstituted skim milk, SMP = skim milk powder, WPC = whey protein concentrate
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