Proteolytic activity of lactic acid bacteria in skim milk with special reference to the biodegradation of casein fractions
✍ Scribed by Hegazi, Fakhreya Z.
- Publisher
- John Wiley and Sons
- Year
- 1987
- Tongue
- English
- Weight
- 414 KB
- Volume
- 31
- Category
- Article
- ISSN
- 0027-769X
No coin nor oath required. For personal study only.
✦ Synopsis
Proteolytic activity of lactic acid bacteria in skim milk with special reference to the biodegradation of casein fractions FAKHREYA 2. HECAZI Streptococci and lactobacilli were assayed for their proteolytic activity in pasteurised (95 "C for 30 min) fresh Friesian cows' skim milk incubated at 30 "C for 48 h. Lactobacilli were more proteolytic than the streptococci except S. faecalis subsp. liquefaciens. S. faecalis and S. thermophilus followed S. lactis subsp. diacetylacfis in the proteolytic activity. Electrophoretic analysis of the precipitated casein revealed K-, pre-jand the small slow band of a,,-casein to be the most fractions and /?-casein the least fraction susceptable to the biodegradation. S. faecalir subsp. liquefaciens was the only organism able to degrade jcasein to 3 fractions within 48 h. S. lactir with its subsp. diacerylactk was characterized by its inability to degrade ycasein. Addition of 2.0 g glucose, 0.5 g yeast extract, 2.0 mmol M$+, 0.5 mmol Mn2+ and 0.1 mmol Fe2+/I of skim milk culture of each L. casei and L. planfarum increased acid formation but decreased proteolysis. 6 % NaCl was inhibitory to both. After 60 days at 18 "C, a fraction, probably derived from /?-casein, was noticeable. The large intense band of a,,-casein appears to be degraded gradually to only small peptides which in turn are transfered immediately into the cells. The hydrolysis of y-casein and /?casein also appears to be inhibited by exogenously supplied NaCl and nutrients, respectively.