Characterisation of soft cheese proteolysis by RP-HPLC analysis of its nitrogenous fractions: effect of ripening time and sampling zone

Abstract

Port Salut Argentino cheeses were studied at different ripening times (1, 6, 13, 27 and 56 days) and two sampling zones (central and external). Moisture content, salt concentration, water-insoluble fraction, water-soluble fraction, and free amino acids in the sulphosalicylic acid-soluble fraction were analysed. Moisture and salt contents at the beginning of ripening were higher in the external zone than in the central zone (51 and 46% w/w moisture, 0.95 and 0.25% w/w NaCl, respectively). Cheeses reached a uniform salt content but not a uniformm oisture content during the 56 days of ripening. The hydrolysis of as1-casein during cheese ripening was modelled using first-order kinetics. The kinetics constant of as1-casein degradation was 0.017 day–1. Most of the water soluble peptides increased during cheese ripening, particularly from day 13 of ripening. Free amino acids also increased from day 13 of ripening. Amino acids that characterised the ripening of Port Salut Argentino cheese were leucine, lysine, asparagine, phenylalanine, threonine, tyrosine, glutamine and valine. Proteolysis increased in both zones during ripening and there was no appreciable difference between zones using any of the methods used for investigating proteolysis.