LAB viability in alginate films used to wrap salmon inoculated with L. monocytogenes
Both LAB strains presented stationary growth pattern in the alginate films used to wrap the salmon (Fig. 3). Previous work in D-MRS broth had shown that the BLS production of both lactic strains occurred during the stationary growth phase at 4 _C (unpublished data). The LAB strain viability and growth within the film matrix was improved with the nutrient diffusion from the salmon. The water activity of the film (Aw 0.91 after drying) also
contributed to maintaining cell viability, as a slight increase in Aw of the alginate film was observed at the time of contact with the salmon (Aw 0.92). According to Paludan-Muller, Dalgaard, Huss, and Gram (1998), when the Aw of smoked salmon is in the range 0.91e0.96, the film used should have a similar Aw to prevent drying of the salmon surface. Thus, thewater activity of the film used in the present study did not significantly influence the organoleptic properties of the salmon. Romero-Bastida and Bello-Pérez (2006), found that films containing starch absorbwater fromfoods, an effect thatwasminor in this case. Such water absorption may affect the salmon texture, thus producing loss of firmness, that alter the organoleptic properties. No negative effect of nisin was observed on LAB in films used to
cover salmon, indicating that conditions were suitable for LAB viability in the film interior.
The pH of the film increased significantly (P <0.05) from 4.4 to pH 5.6 after the salmonwas wrapped for 24 h in the film and stored at 4 _C due to diffusion and buffering capacity of the salmon juice, since the meat has an initial pH close to 6.0 (Brillet et al., 2004). The
pH of the film did not change significantly during storage and after 14 days a pH of 5.5 was recorded. This condition also favoured the viability of the LAB in the films and the BLS production. The results demonstrate that it is possible to maintain LAB-A and LAB-B strains under stationary growth conditions and produce BLS in the alginate films during 28 days at 4 _C. Cold-smoked salmon covered with a film containing strains LAB-A and LAB-B plus nisin before packaging had a bacteriostatic effect on the development of L. monocytogenes.
Industrial application of this type of wrapping is a feasible alternative, providing the consumer with a product of good quality owing to the use of non-toxic compounds without contaminating chemicals that might be harmful to human health and the environment.
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