Vl. Crow et al., THE INFLUENCE OF PHAGE-ASSISTED LYSIS OF LACTOCOCCUS-LACTIS SUBSP LACTIS ML8 ON CHEDDAR CHEESE RIPENING, International dairy journal, 5(5), 1995, pp. 451-472
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.