Application of a nisin Z-producing Lactococcus lactis subsp lactis KT2W2L isolated from brackish water for biopreservation in cooked, peeled and ionized tropical shrimps during storage at 8 A degrees C under modified atmosphere packaging

摘要

Lactococcus lactis subsp. lactis KT2W2L was used for biopreservation in cooked, peeled and ionized tropical shrimps (CPITS) during storage at 8 A degrees C under modified atmosphere packaging (MAP). The neutralized and filtered cell-free supernatant produced by this strain exhibited a broad spectrum of inhibition against 23 strains from 24 indicator strains of food-spoilage bacteria and food-borne pathogens by agar well diffusion assay. The growth of Brochothrix thermosphacta CD274, Carnobacterium maltaromaticum CD263 and Listeria innocua CIP 80.11T was inhibited by L. lactis subsp. lactis KT2W2L when co-cultivated at 25 A degrees C. However, only L. innocua CIP 80.11T was inhibited in a co-cultivation at 8 A degrees C. L. lactis subsp. lactis KT2W2L was then used for biopreservation in CPITS. Growth of bacteria group inoculated in CPITS was monitored at regular intervals during storage period under MAP at 8 A degrees C by microbial counts and the thermal temperature gradient gel electrophoresis (TTGE) technique. L. lactis subsp. lactis KT2W2L inhibited the growth of B. thermosphacta and L. innocua CIP 80.11T batches after 7 days of storage. However, it was inactive against C. maltaromaticum batch. The growth of L. lactis subsp. lactis KT2W2L alone or in the presence of indicators increased to reach about 8-9 log CFU/g within 7 days of storage and remained constant until the end of the experiment. In the batches without L. lactis subsp. lactis KT2W2L, all bacterial groups grew well on the cooked shrimp matrix, reaching their maximal levels after 2 weeks of storage. The pH of all homogenized suspensions of MAP-CPITS was quite stable at 6.0-6.7. The control batches were under the enumeration threshold ( 1.70 +/- A 0.00 log CFU/g) until 14 days of storage, and then, an increase in growth was detected on agar plates. In addition, TTGE revealed to be an excellent tool to monitor the change of the microbial ecosystem in this product.