Inhibition of rennet activity in cheese using equine blood serum

Abstract

The objective of this study was to inactivate chymosin in Cheddar-type cheese curd using equine blood serum. This blood serum was added (0.1–2%, v/v) to cheesemilk at 15 °C after completion of the first phase of renneting and before aggregation of the rennet-altered casein micelles, to inhibit the residual coagulant in Cheddar-type cheeses. Throughout ripening the level of pH 4.6-soluble nitrogen expressed as a percentage of total nitrogen was significantly higher in the control cheeses than in experimental cheeses and was about twice that of the experimental cheeses after ripening for 180 days. During ripening, there was almost no hydrolysis of αs1-casein in the cheeses made from milk containing 0.25–2% blood serum. Throughout ripening there were large quantitative differences between the peptide profiles of control and experimental cheeses. The results of this study suggest that the addition of equine blood serum to cheesemilk (0.25–2%) was very effective at inhibiting the residual chymosin activity in Cheddar-type cheeses during ripening; the activity of plasmin remained unaffected by the added blood serum. This study describes an easy and effective method for producing cheese curd free from residual coagulant activity, which will help to study the separate roles of the coagulant and other proteolytic enzymes in cheese ripening.