Effects of using probiotic strains of Lactobacillus reuteri, Lactobacillus brevis and Lactobacillus delbrueckii subsp. bulgaricus on the microbial quality of farmed rainbow trout (Oncorhynchus mykiss) fillet

Probiotic strains of Lactobacillus can be used as food preservatives. The purpose of this study was to investigate the use of Lactobacillus delbrueckii subsp. bulgaricus (PTCC1737), L. reuteri (1655 PTCC), L. brevis CD0817 and the combination of Lactobacillus on microbial quality of rainbow trout fillet in refrigeration and freezing temperature. Treatments were immersing fillets in suspensions of L. reuteri, L. brevis, L. delbrueckii and the combination of Lactobacillus. The control treatments consisted of additive-free fillet and fillet processed with 2% solution of lactic acid. The control and test treatments were refrigerated (five days) and frozen (six months). Staphylococcus aureus and Escherichia coli were not observed in test and control treatments. L. delbrueckii subsp. bulgaricus was not observed in frozen storage. The number of Lactobacillus showed a decrease in combination treatments during freezing (1.34logCFU/g). In L. brevis, total saturated and unsaturated fatty acids were 23.91% and 77%, respectively. In L. reuteri, total saturated and unsaturated fatty acids were 27.12% and 72.88%, respectively (P<0.05). Significant increase in ratio of unsaturated to saturated fatty acids in L. brevis compared to L. reuteri and no significant difference in L. brevis number during storage at freezing temperature caused that L. brevis  is recommended for preserving farmed rainbow trout fillet under refrigeration and at freezing temperatures.