Inhibition of Mesophilic Spoilage Aeromonas Spp. on Fish by Salt, Potassium Sorbate, Liquid Smoke, and Chilling

Abstract

The purpose of the present study has been to develop simple fish preservation techniques applicable at artisanal level in developing countries in the tropical zone. Mesophilic motile Aeromonas spp. which were classified as specific spoilage bacteria of Nile perch (Lates niloticus) from Lake Victoria stored at ambient temperature were inhibited in laboratory model systems using NaCl, potassium sorbate, and liquid smoke. Growth was not detected when the salt concentration exceeded 5% or the temperature was below 5°C. At 25–37°C growth occurred within 24 h when no preservation was applied, but a combination of 5% salt and 1000 ppm sorbate inhibited growth at 25–37°C. Liquid smoke inhibited growth at 37°C only when an initial low inoculum (102 CFU/ml) was used. Based on the model experiments, trials were carried out in Kenya and a lightly preserved fish product stable at ambient temperature was developed. The addition of 1.5% salt (w/w) and 1500 ppm sorbate (w/w) followed by 3 d of sun-drying resulted in a lightly brown, well preserved fish product which could be produced at artisanal level and was palatable to local consumers. Good agreement was seen between results from model experiments and trials with fish.