Growth characteristics of Lactobacillus delbrueckii subsp. bulgaricus ATCC 11842 as affected by different neutralisers

Abstract

Sodium, potassium or ammonium hydroxide were used to control pH during the cultivation of Lactabacillus delbrueckii subsp. bulgaricus ATCC 11842 (Lb11842) in skim milk at a constant pH of 5.6 at 43°C for 10 h for production of the crude cellular extract as a source of β-D-galactosidase. Cell growth, lactic acid production, β-D-galactosidase and proteolytic activities were monitored. The addition of NaOH or KOH resulted in slight but insignificant (p>0.05) differences on all parameters, while all parameters were significantly (p<0.05) affected by the addition of NH4OH. The proteolytic activity of Lb11842 was significantly lower (p<0.05) in the presence of ammonium hydroxide. The exopolysaccharides (EPS) production was also significantly higher (p<0.05) in the presence of NH4OH. The higher EPS content significantly (p<0.05) affected the apparent viscosity of the concentrated, cell-free fermentation medium resulting in pseudo-plastic behavior.