THE ACCELERATING EFFECT OF A LACTOCOCCUS-LACTIS SUBSP LACTIS LACTOSE-UTILIZATION PROTEINASE-DEFICIENT STRAIN ON PROTEOLYSIS AND FLAVOR DEVELOPMENT/

This study describes the accelerating effect exerted on proteolysis an d flavour development in cheese-curd slurries by combined application of Lactococcus lactis subsp, lactis IFPL359 and high concentrations of its Lac(-) Prt(-) derivative, (i.e. that which has reduced capacity t o metabolize lactose and reduced proteolytic activity, strain T1). Cel ls of strain T1 partially lysed by either sonication or incubation wit h lysozyme, were also used to ascertain how proteolysis was affected b y release of intracellular enzymes in the initial stage of incubation of the strains in cheese-curd slurries. The presence of strain T1 prod uced higher levels of non-protein nitrogen (NPN) and amine nitrogen (A N) during the first weeks of incubation when partially lysed cells had been added. Addition of whole cells of strain T1 produced higher valu es of NPN and AN at the end of incubation of slurries, accelerating pr oteolysis by about 2 weeks with respect to the control, which only con tained the parental strain IFPL359. At the end of the experimental per iod higher amino acid levels were detected by HPLC in the slurry conta ining whole T1 cells. Volatile fractions of the different cheese-curd slurries were also analysed. The higher level of proteolysis produced by addition of high levels of strain T1 appeared to be related to rele ase of intracellular enzymes by this strain owing to its greater capac ity for autolysis.