Purpose: We examined the ability of GRAS (generally recognized as safe) products to inhibit growth of pure cultures of Lm and Lm on refrigerated raw salmon fillets.
Methods: Two GRAS products (2% and 4% DV™ [vinegar-based] and 1% ProTek™ [NaCl:acetate:diacetate]) were evaluated using Bioscreen C (TSB + 0.1% yeast extract, 30°C, 18h) for effectiveness against pure cultures of Lm (strains 424, 427, 2307, 3371, 3382; 5 log CFU/ml). Subsequently, 25-g portions of raw salmon (3-6 replicates) were surface-inoculated with Lm strain 3382 at 4 log CFU/g and treated with sterile deionized water (DI, control) and 15% vinegar-based solution (≤ 2% pick-up) using a prototype sprayer. Lm counts were determined by spread-plating pulsified fillets on R&F chromogenic agar (30°C, 24-72h) immediately following treatment and at weekly intervals during cold storage (4°C, 4 weeks).
Results: With Bioscreen C, the greatest reduction in Lm growth (turbidity), 82-88%, was produced by 4% vinegar-based; growth was reduced 34-41% by 2% vinegar-based and 20-29% by 1% NaCl: acetate:diacetate. On raw salmon, vinegar-based prevented Lm growth for one week at 4°C; Lm numbers increased by 0.5 log CFU with DI treatment. Lm increased by 0.7 and 1.6 log CFU on vinegar-based- and DI-treated salmon, respectively, after two weeks at 4°C. Lm numbers were 1 log10CFU less on vinegar-based-treated salmon vs. control samples after four weeks at 4°C (P< 0.05).
Significance: These findings suggest that vinegar-based could be used as a listeristatic (<1 log increase) control measure during processing to reduce contamination of refrigerated raw salmon.