Effect of ripening time and type of rennet (farmhouse rennet from kid or commercial calf) on proteolysis during the ripening of Leon cow milk cheese

摘要

Classical nitrogen fractions, caseins and their degradation products, and free amino acids were determined during ripening of six batches of Leon raw cow milk cheese. Three batches were made using commercial calf rennet (average 1/8342 strength and 76% of chymosin) and three were made using farmhouse rennet obtained from kid abomasum (average 1/857 strength and 34% of chy-mosin). The pH 4.6-soluble nitrogen and the 12% TCA-soluble nitrogen contents increased moderately during ripening, reaching significantly (P<0.05) higher average final values in the cheeses made using commercial rennet (18.0 and 11.0% of TN, respectively) than in the cheeses made using farmhouse rennet (8.3 and 5.1% of TN, respectively). The greater extent and intensity of proteolysis registered in the cheeses made using commercial rennet, especially after 15 days of ripening, became clear again on quantifying the caseins and their degradation products. β-Casein did not undergo any appreciable degradation during ripening. In the cheeses made using commercial rennet, 20% of the txs-caseins were degraded during ripening, whilst in those made using farmhouse rennet only 10% of the αs-caseins were degraded. These results show that this cheese undergoes a slight proteolysis and that the rennet plays a preponderant role in protein degradation. The content of total free amino acids increases progressively during ripening. In the batches made using commercial rennet, the final values were double those found in the batches made using farmhouse rennet. In the mature cheeses, the major free amino acid was lysine, followed by leucine, glutamic acid, tryptophan, valine, and phenylalanine. The type of rennet used during manufacture made no difference to the free amino acid profile at maturity.