Influence of cheese weight and type of rennet of composition and proteolysis of Canestrato Pugliese cheese II. Chromatographic characterization of soluble nitrogen

A chromatographic study, based on reversed-phase, size exclusion and hydrophobic interaction chromatography, was performed to evaluate the influence of weight of the cheese and type of rennet used on the evolution of soluble nitrogen in "Canestrato Pugliese", a Protected Designation of Origin (PDO) hard cheese produced in Southern Italy from sheep milk. The weight of the cheese had only a quantitative influence, with higher amounts of soluble nitrogen in the smaller cheeses. The influence of the rennet was both quantitative and qualitative, probably due to the different chymosin/pepsin ratios. More soluble nitrogen was found in cheeses obtained with lamb rennet and significant differences were observed among the chromatographic profiles. Size exclusion chromatography revealed a significant accumulation of medium- molecular-weight peptides during ripening in the lamb rennet cheeses, whereas a faster formation of low-molecular-weight peptides was found in those produced with bovine rennet. The most distinctive peptide fraction (about 4 KD), recovered and analysed by hydrophobic interaction chromatography, revealed the presence of further qualitative differences, which were confirmed by reversed phase chromatography and free amino acid analysis. Such findings indicate a different evolution of secondary proteolysis among the cheeses. Further study is needed to better understand the mechanism of pepsin retention in the curd and its residual activity during ripening