Microbiology and biochemistry of gorgonzola cheese during ripening

Abstract

A microbiological and biochemical characterization of Gorgonzola cheese during ripening is reported. Analyses were conducted on the core and under the rind of the cheese. In 86 day-old cheese there were high numbers of Streptococcus thermophilus, Penicillium roqueforti , lactococci and surface growth of micrococci, yeasts and moulds. A salt-in-moisture gradient from the surface to the core persisted until about 63 days. The increase in pH was initially higher in the cheese surface; the final value was ca. 6.80 in both cheese layers. After 86 days of ripening, the concentration of the water-soluble N in the core was more than 50% of the total N but was markedly less in the external region. The 12% TCA-soluble N was the only N fraction which increased markedly during late ripening. Proteolytic (peptidases and proteinase) activity strongly depended on the growth and enzyme activity of P. roqueforti . The proteolytic activity decreased from the centre to the surface of the cheese. Enzymes from the mould veins showed a very limited diffusion in the outer layer, giving zonal variations in the cheese. Electrophoresis showed extensive hydrolysis of α s 1 - and β-caseins, with the fastest degradation in the core. Electrophoresis of the pH 4.6-soluble fraction and RP-HPLC of pH 4.6-soluble, ethanol-soluble and -insoluble fractions showed a complex production of various sized peptides which were, in part, degraded subsequently. Limited differences were observed in the level of lipolysis and the two cheese layers had about the same final value of free fatty acids. The surface microflora contributed markedly to lipolysis, which depended less on the activity of P. roqueforti .