Use of a nisin-producing starter culture of Lactococcus lactis subsp, lactis to improve traditional fish fermentation in Senegal.

Lactococcus lactis subsp. lactis strain CWBI B1410, which produces various antibacterial compounds including organic acids and nisin, was used as a starter culture to improve the traditional Senegalese fish fermentation in which fish are mostly transformed to guedj by spontaneous fermentation for 24 to 48 h at ambient temperatures near 30 degrees C followed by salting (with NaCl) and sun drying. Assays were performed on lean fish (Podamasys jubelini) and fat fish (Arius heudelotii) purchased at a local market. The total viable microbial counts in raw fillets of P. jubelini and A. heudelotii were 5.78 and 5.39 log CFU/g, respectively. Populations of enteric bacteria (which can include pathogenic bacteria) in P. jubelini and A. heudelotii were 4.08 and 4.12 log CFU/g, respectively. Spontaneous fermentation of raw fillets at 30 degrees C led to the proliferation of enteric bacteria to 9 log CFU/g after 24 h in fermented P. jubelini and A. heudelotii fillets with pH values of 6.83 and 7.50, respectively. When raw fish fillets were supplemented with glucose (1%, wt/wt) and inoculated with Lactococcus lactis (10(7) CFU/g), the pH decreased to about 4.60 after 10 h at 30 degrees C, and nisin activity was detected in juice from the fillets. Traditionally fermented fillets of P. jubelini and A. heudelotii contained enteric bacteria at higher levels of 4 and 2 log CFU/g, respectively, than did fillets of the same fish supplemented with glucose and fermented with the starter culture. These data suggest that this new fish fermentation strategy combined with salting and drying can be used to enhance the safety of guedj.