Use of Nisaplin™ to Inhibit Spoilage Bacteria in Buttermilk Ranch Dressing†

Abstract

Nine commercial salad dressings (spoonable and pourable) were sampled for microbial flora, pH, and total acidity. Bacterial populations ranged from 102 to 104 CFU/g in the salad dressings, but yeasts and molds were largely undetected (<1 × 102 CFU/g). The range of pH (3.3 to 4.1) and titratable acidities (0.63 to 1.34% as acetic acid) indicates that such differences in formulation may lead to varying shelf lives among the dressings, especially in regard to aciduric microorganisms. Nisaplin™, a commercial antimicrobial food additive and shelf-life extender, inhibited 27 of 30 bacterial isolates obtained from 6 salad dressings. Nisaplin (200 ppm) was used as a preservative in a shelf-life study with a spoonable buttermilk ranch dressing at pH 3.8, 4.0, and 4.2, challenged with Lactobacillus brevis subsp. lindneri, a ranch dressing spoilage isolate, and maintained at 26°C. In control samples at pH 4.2, both the added Lactobacillus and the indigenous flora increased starting at day 6 to a maximum at 30 days. However, in buttermilk ranch dressing (pH 4.2) containing Nisaplin, initial levels of added inoculum were quickly reduced and no significant growth occurred during the 90-day shelf-life period. The data indicate that the natural preservative Nisaplin may be an effective spoilage inhibitor for spoilage-sensitive refrigerated salad dressings.