Protein degradation in bovine milk caused by Streptococcus agalactiae

• Published in: Journal of dairy research 2012-08, Vol.79 (3), p.297-303
• Main Authors: Åkerstedt, Maria, Wredle, Ewa, Lam, Vo, Johansson, Monika
• Format: Article
• Language: English
• Subjects: Agricultural Science; Animal productions; Animals; Annan veterinärmedicin; Bacteria; beta -lactoglobulin; Biodegradation; Biological and medical sciences; Casein; Caseins - metabolism; Cattle; Cheese; cheeses; Cow's milk; Economic importance; economic valuation; Economics; Female; Food industries; Fundamental and applied biological sciences. Psychology; High temperature; in vitro studies; Jordbruksvetenskap; lactalbumin; Lactalbumin - metabolism; Lactoglobulins - metabolism; Mastitis; Mastitis, Bovine - microbiology; Milk; Milk - microbiology; Milk and cheese industries. Ice creams; Milk Proteins - metabolism; milk quality; Optimal yield; Other Veterinary Science; Peptide Hydrolases - metabolism; Protein composition; protein degradation; Proteinase; proteinases; Streptococcus agalactiae; Streptococcus agalactiae - enzymology; Streptococcus agalactiae - growth & development; Terrestrial animal productions; texture; Udder; udders; UHT treatment; Ultrahigh temperature; Vertebrates; whey protein; yogurt
• ISSN: 1469-7629; 0022-0299; 1469-7629
• DOI: 10.1017/S0022029912000301

Streptococcus (Str.) agalactiae is a contagious mastitis bacterium, often associated with cases of subclinical mastitis. Different mastitis bacteria have been evaluated previously from a diagnostic point of view, but there is a lack of knowledge concerning their effect on milk composition. Protein composition is important in achieving optimal yield and texture when milk is processed to fermented products, such as cheese and yoghurt, and is thus of great economic value. The aim of this in vitro study was to evaluate protein degradation mainly caused by exogenous proteases originating from naturally occurring Str. agalactiae. The samples were incubated at 37°C to imitate degradation caused by the bacteria in the udder. Protein degradation caused by different strains of Str. agalactiae was also investigated. Protein degradation was observed to occur when Str. agalactiae was added to milk, but there were variations between strains of the bacteria. Caseins, the most economically important proteins in milk, were degraded up to 75% in milk inoculated with Str. agalactiae in relation to sterile ultra-high temperature (UHT) milk, used as control milk. The major whey proteins, α-lactalbumin and β-lactoglobulin, were degraded up to 21% in relation to the sterile control milk. These results suggest that different mastitis bacteria but also different strains of mastitis bacteria should be evaluated from a milk quality perspective to gain knowledge about their ability to degrade the economically important proteins in milk.