Starter Culture Characterization by Conductance Methods

¹ Swedish Dairies' Association, Ideon ß3, S-223 70 Lund, Sweden

Activity tests using conductance methodologies have been developed for three important bacterial groups in mixed-strain DL-lactococcal starter culture. When cultures are grown in reconstituted skim milk and measured with the Malthus® instrument, the change in conductance was due to the growth of Lactococcus lactis ssp. lactis with Lactococcus lactis ssp. cremoris. Lactococcus lactis ssp. lactis biovar. diacetylactis gave a similar signal but normally is much less prevalent in the culture than the L. lactis ssp. cremoris and L. lactis ssp. lactis. In reconstituted skim milk containing .15% yeast extract and .14 g/ L of MnSO₄, the growth of Leuconostoc mesenteroides ssp. cremoris was stimulated. In the same substrate supplemented with 200 µg/ml of vancomycin, the growth of L. lactis ssp. lactis, L. lactis ssp. cremoris, and L. lactis ssp. lactis biovar. diacetylactis was totally inhibited, but the growth of Leuconostoc was unaffected. The capacity of the cultures to produce CO₂ was analyzed in reconstituted skim milk containing .15% yeast extract, .14 g/L MnSO₄, and .5% sodium citrate by an indirect conductance method using a Rabit® instrument. In this substrate, the change in conductance was due to the growth of L. lactis ssp. lactis biovar. diacetylactis.

Key Words: starter culture activity • conductance • indirect conductance method

Submitted on March 10, 1994
Accepted on July 26, 1994