THE INFLUENCE OF PHAGE-ASSISTED LYSIS OF LACTOCOCCUS-LACTIS SUBSP LACTIS ML8 ON CHEDDAR CHEESE RIPENING

Cheddar cheese was made with Lactococcus lactis subsp. lactis strain M L8 as starter and two levels of rennet and three levels of homologous phage. The use of the different phage levels in cheese milk resulted i n various degrees of starter lysis early in the ripening process, The levels of activity of two starter cytoplasmic enzymes, lysylaminopepti dase and FBP-aladlase, in the cheese matrix were used as a direct meas ure of lysis and increased with the level of phage added. Elevated sta rter lysis was associated with an increased rate of formation of amino acids and ammonia but the removal rate of lactose in the cheese was d ecreased. The relative levels of hydrophobic and hydrophilic peptides in aqueous cheese extracts were, also influenced by the extent of star ter lysis. Bitter flavour was prominent in cheese with high rennet con centration, but not when there was also high starter lysis. The result s suggest that a balance of lysed and intact cells is important for co ntrol of cheese ripening; enzymes released on cell lysis accelerate th e rate-limiting peptidolylic steps and removal of some bitter peptides , while intact cells are required for lactose removal. The consequence s of the relative levels of intact and lysed cells on substrate-enzyme interactions, enzyme stability and flavour profiles are discussed.