Total protease activity in goat milk

Milk protein system exerts a crucial role from the point of view of both milk nutritional quality and technological properties. It is a dynamic system: milk caseins and whey proteins, which are synthesized by the mammary cells, undergo the action of proteolitic enzymes with important effects on milk composition and quality. Proteolysis of milk protein may be caused both by the native milk protease, either by proteases produced by psychrotrophic bacteria. These proteases cause beneficial or deleterious changes, depending on the specific dairy products to which milk is devoted. Milk protein enzymatic hydrolysis can favorably affect flavour development and texture changes during cheese ripening. However, unwished proteolysis can have a negative effect on both dairy product quality and shelf-life. A colorimetric method was used to quantify total protease activity in goat milk. The method is based on azocasein substrate which, under appropriate pH and temperature conditions, is degraded by milk proteolitic enzymes thus allowing quantification of milk total protease activity. The azocasein degradation releases the chromophore group, red when is covalently bound to the casein and colorless when it is free in solution. The method was developed for the analysis of bovine milk. The aim of the present study was to optimize and standardize this technique for quantifying goat milk total protease activity. Preliminary results on the variation of total protease activity in different goat milk samples are presented. The method applied is a cheap and easily applicable technique which can be used for routine milk tests on bulk and individual goat milk. Further studies need to be developed on the relations between total protease activity and the wide qualitative and quantitative genetic polymorphisms involving milk goat caseins