To facilitate the activation of these cultures, 0.05% (wt/vol) L-CysHCI was added to the milk in order to diminish the redox potential of the medium and thereby stimulate micro-organism growth. Glucose (2%; wt/vol) and yeast extract (1%; wt/vol) were also added to the mixture. The incubation was carried out under aerobic condition in the water bath (42 C; Julabo, Model Sw-21c or Haake Model SWD