Proteolysis in raw milk in relation to microbiological indicators

Abstract

Proteolysis in raw milk is a crucial parameter indicating both cow's mastitis and the technological problems or spoilage risk of final products. However, a suitable analytical method for its early detection in practice is still missing. Thus, we proposed a spectrophotometric determination of milk proteolysis equivalent (MPE). We tested this method on 104 bovine raw milk samples in relation to their somatic cell count (SCC) as an indicator of native proteolysis, and the total count of mesophilic bacteria (TCMB) and the total count of psychrotrophic bacteria (TCPB) as indicators of microbial proteolysis. Correlation coefficients between log TCMB and MPE and log TCPB and MPE were 0.3651 and 0.4152, respectively (both P < 0.001). SCC was not correlated with MPE (P > 0.05). We estimated the MPE limit indicating an incipient risk of proteolysis in the range from 0.9366 to 1.02 mmol/l. The determination of MPE seems to be a promising method applicable in the control of raw milk.

Keywords

• primary amino groups
• proteolytic enzymes
• psychrotrophic microorganisms
• quality of bovine raw milk
• somatic cell count
• total count of microorganisms