Quality of ready to eat swordfish fillets biopreserved by the probiotic Lactobacillus paracasei IMPC 2.1

The probiotic strain Lactobacillus paracasei IMPC 2.1 (LMG P22043) has been successfully used for the development of innovative probiotic ready to eat (PR-RTE) swordfish (Xiphias gladius) fillets. PR-RTE fillets have been demonstrated to be suitable for delivering viable bacterial cells that transiently colonize the human gut (Valerio et al., 2015) after an alternate-day diet supplementation. The aim of this study was to assess the effect of the probiotic inoculation on the biochemical and microbiological profile of the PR-RTE fillets. Marinated fillets, obtained after 2 days of mild fermentation in the presence of the probiotic strain (final concentration of about log 7 CFU/g of fillet), were seasoned, vacuum packed and analysed at 0, 7, 14, 30, 60, 90 days' storage (4°C). Experiments were performed 2 times with 3 replicates each (n=6). Lipid oxidation, assessed by malondialdehyde determination, resulted to increase over 3 times during storage in both control (C-RTE, fillets in chemically acidified marinade) and inoculated fillets, with significantly lower values in PR-RTE fillets. The probiotic inoculation decreased the mono-unsaturated and increased the poly-unsaturated fatty acids content. Biogenic amines showed no significant variations in their contents, as a consequence of treatment and duration of storage. During shelf-life, populations of the probiotic strain were always higher than log 7.0 CFU/g, representing the totality of LAB populations. L. monocytogenes and Salmonella spp were not detected during the entire shelf life in both PR- and C-RTE products; furthermore, Enterobacteriacee and Pseudomonadaceae were not found. Generally, the use of a reduced salt concentration for fish processing needs to be associated to other preservative methods to maintain physicochemical and microbiological quality of the product. L. paracasei IMPC 2.1 plays a double role of probiotic and bio-preserving culture preventing spoilage, thus reducing the need for chemical preservatives in low-salt products.