41-3 |
Influence of pH, temperature, nutrients and co-culturing with non-EPS starter on the production of exopolysaccharides by S. thermophilus 1275 |
B. ZISU, School of Life Sciences & Technology, Victoria Univ., PO Box 14428, Melbourne City Mail Centre, Melbourne, VIC, 8001, Australia and N. P. Shah, School of Molecular Sciences, Victoria University, Werribee Campus, PO Box 14428, Melbourne City Mail Centre, Melbourne, Victoria, 8001, Australia. Lactic acid bacteria that synthesise exopolysaccharides (EPS) are used increasingly in the dairy industry to improve rheological behaviour, mouthfeel and texture of fermented milks. EPS remain attached to the cell wall (capsular EPS) or excreted into the surrounding medium (ropy EPS). We have identified a strain of Streptococcus thermophilus 1275, which produces both capsular and ropy EPS. The objective of this study was to examine EPS production by S. thermophilus 1275 in skim milk under various pH and temperatures, supplementation with whey protein concentrate (WPC) and co-culturing with non-EPS S. thermophilus. S. thermophilus 1275 was grown in skim milk in a Biostat® B fermenter and sampled at 0, 6, 12, 18 and 24 h to determine the quantity of EPS, and levels of lactic acid, lactose, glucose and galactose. The bacterial population was determined and EPS was isolated by protein removal and precipitation with ethanol and quantified using the phenol-sulphuric method. Levels of lactic acid and lactose, glucose and galactose were determined using HPLC. S. thermophilus 1275 produced 406 mg/L of EPS at 37oC. High temperatures and low pH reduced the amount of EPS, which ultimately ceased at pH 4.5. Maximum growth occurred at conditions different to those for EPS production. The pH, temperature, WPC and co-culturing played an important role in the rate and the amount of EPS produced. EPS production peaked at pH 5.5 and 37-40oC reaching at 458mg/L and further stimulated by co-culturing with non-EPS S. thermophilus reaching at 832mg/L. EPS production reached the highest at 1029 mg/L with WPC supplementation at pH 5.5. EPS production can be increased by using WPC and co-culturing with non-EPS cultures. Non-EPS starters in particular can provide a cheap and alternative means of increasing EPS production, thereby improving textural and functional characteristics of dairy foods without the use of additives.
Session 41, Dairy Foods: Dairy microbiology
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