In this study, we developed and optimized a growth media by evaluating various nitrogen sources for the cultivation of Lactobacillus bulgaricus, a probiotic and an important dairy starter culture. We modified the composition of deMan, Rogosa and Sharpe (MRS) culture media and substituted the nitrogen content with alternative nitrogen sources X-Seed KAT, X-Seed Carbo Max and X-Seed Nucleo Max in various blends of 5 g/l and 10 g/l respectively. Results showed that bacterial growth was significantly higher when the nitrogen source blend KCMax (10/10) was used. The optical density (OD610 nm) of the Lactobacillus bulgaricus strains were higher (1.34 and 1.79) in the KCMax (10/10) medium than in the MRS medium (0.89 and 1.42) (P < 0.05). There was no significant difference in the bacterial counts for both the MRS medium and the KCMax (10/10) medium, and all bacterial counts were estimated at 8 log CFU/ml. The buffering capacity of KCMax (10/10) was also tested and supplemented with l-histidine and was significantly different (P < 0.05) than that of the MRS control medium. Calcium supplemented in the KCMax (10/10) also served as a cryoprotectant for the cells during freezing and freeze-drying. Bacterial counts of the recovered calcium-treated freeze-dried cells were statistically significant (P < 0.05). We hypothesized that alternative nitrogen sources such as selected yeast extracts from the X-Seed brand of complex nitrogen sources could efficiently support the viability of Lb. bulgaricus. Our results thus suggested the growth of Lb. bulgaricus was efficiently supported by the X-Seed KAT, X-Seed Nucleo Max and X-Seed Carbo Max nitrogen sources. Consequently, these alternative nitrogen sources could potentially be recommended for dairy starter culture fermentations.

Many psychrotrophic bacteria contaminating raw milk produce phospholipase that withstands pasteurization and UHT treatments. This enzyme acts on the milk fat globule membrane and exposes triacylglycerides to the action of lipase. Phospholipase production by various isolates of Pseudomonas was investigated. The isolates were cultured aerobically at 8 °C in nutrient broth, McKellar's minimal salts medium, Chrisope's medium, and skim milk. Each strain produced phospholipase during the 50 h incubation. Enzyme production varied significantly (P < 0·001) with strain and growth medium. Strains varied significantly (P < 0·001) in their enzyme production in each medium and during the incubation time as well. Strain, incubation time, and the growth medium significantly influenced (P < 0·001) heat stability of the enzyme activity. Pasteurization reduced the activity, but did not eliminate it in skim milk.