A study has been conducted on the effect of two freezing conditions (slow and fast) and frozen storage of ewe's milk cheese (-20 °C for 4 months) on the viability and the proteolytic (cascinolytic and aminopeptidase) activity of Lactococcus lactis subsp. lactis and L. lactis subsp. cremoris used as starters in the manufacture of cheese. The study was carried out on the lactococci subjected to freezing and frozen storage, either in the cheeses or in curds simulating a model system. As well as other parameters used to quantity microbial activity, the total viable counts during the subsequent cheese ripening have been analysed in the frozen cheeses. Frozen storage of the investigated lactococci, either in the cheese or in model systems, gave rise to significant decreases in the caseinolytic and aminopeptidase activities greater than did freezing alone. No clear differences were found in enzymatic activity values when using slow or fast freezing conditions. Storage of the cheeses under frozen conditions also affected microbial viability and consequently caused a greater decrease of the viable flora during subsequent ripening of the frozen stored cheeses.

The authors wish to acknowledge the financial support for this study provided by the Comision Interministerial de Ciencia y Tecnologfa under project ALl 91-0387 and by the European Communities under project ECLAIR-AGRE-CT91-0064 (DTEE).

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