P62: Effect of salt (NaCl) on the viability and acidification activity of cheese starter culture Lactococcus lactis subsp lactis and Lactococcus lactis subsp cremoris at 30°C in vitro

A blend of a freeze-dried strains ,Lactococcus lactis subsp lactis and Lactococcus lactis subsp cremoris  were exposed to different   concentrations of salt (NaCl)  ( 0%, 1%, 2%, 3%, 4%, 5% and 6% w/v ) for  monitoring their viability  and ability to  fermentation of milk, in addition  to determine the salt concentrations, which can be used in cheese manufacturing for keeping the quality and safety of cheese and the acidification activity of  culture .. The strains were grown in LM17 broth (M17 broth containing 5gL-1 lactose), LM17 agar (M17 agar containing 5gL-1 lactose) and reconstituted skim milk (RSM) (9.5% w/v) and incubated for 24, 48 and 24 h respectively in presence of   salt. Growth of culture was measured using optical density at 600nm, viable count (cfu / ml) and acidification activity (DpH) respectively. There was a highly significant difference (P < 0.05) in the optical density, viable count and acidification activity (Δ pH) at 5% and 6%. The relative decline in viable count was 69.34% and 93.7% and the relative increase in pH values of milk was 32.66% and 44.8% at 5% and 6% respectively.  Values of pH of milk was (4.01 ± 0.02) at 0% and (6.13± 0.02) at 6%,   ranging between (4.03 ±   0.01) at 1% and (4.55± 0.02) at 4%.   Direct vat set culture more resistant to salt than a bulk culture and more suitable for cheese manufacturing in presence of salt (NaCl) between 1% and 4%   in relation to the milk fermentation.