Effects of nisin, EDTA and salts of organic acids on Listeria monocytogenes, Salmonella and native microflora on fresh vacuum packaged shrimps stored at 4 °C

Abstract

Nisin (500 IU ml⁻¹), EDTA (0.02 M), potassium sorbate (PS) (3%, w/v), sodium benzoate (SB) (3%, w/v) or sodium diacetate (SD) (3%, w/v); alone or in combination were used to dip uninoculated shrimps and shrimps inoculated with Listeria monocytogenes or Salmonella (∼4.0-5.0 log CFU g⁻¹). Shrimps were then drip-dried, vacuum packaged and stored at 4 °C for 7 days. Untreated shrimps were used as a control. Numbers of L. monocytogenes, Salmonella and native background microflora were determined on uninoculated and inoculated shrimps on days 0, 3 and 7. Nisin-EDTA-PS and nisin-EDTA-SD significantly reduced (p < 0.05) L. monocytogenes numbers by 1.07-1.27 and 1.32-1.36 log CFU g⁻¹, respectively, on day 0 and 3. However, all treatments failed to significantly reduce (p > 0.05) Salmonella counts on shrimps throughout storage. On day 7, numbers of aerobic bacteria, psychrotrophic bacteria and Pseudomonas on combined nisin-EDTA-salt of organic acids treated shrimps were significantly lower (p < 0.05) by 4.40-4.60, 3.50-4.01, and 3.84-3.99 log CFU g⁻¹ respectively, as compared to the control. Dipping in organic acids solutions followed by vacuum packaging and chilled storage can help reduce L. monocytogenes and native microflora, but not Salmonella, on fresh shrimps.