Prevention of microbial deterioration in salted dried fish

The reduction of microbial deterioration in salted dried fish by application of the food preservatives, sodium sorbate, sodium benzoate, sodium propionate and sodium bisulphite was assessed using Aspergillus niger and A.penicillioides, Halobacterium salinarium and Staphylococcus sp as test organisms. The two bacteria were grown on complex halophilic medium (CHM) and salted dried fish homogenate (SDFH), whilst the moulds were grown in Czapek Yeast Medium/Malt Extract Medium and 10 % salt-Czapek Yeast Medium. Effectiveness of the food preservatives was' also tested on one or two-dimensional gradient diffusion systems and on salted dried fish samples. Sodium sorbate was most effective in controlling growth of A.niger. Growth on both 10 % salt-CYA and 10 % salt-CYB prevented growth at a level of 0.1 % (w/v). Visible growth of the mould was delayed for 3 days when 0.2 % sodium benzoate was combined with 10 % salt. Total dry weight increase was zero, when 10 % salt-CYB was supplemented with a concentration of 0.15 % sodium benzoate. Initiation of A.penicillioides grown on/in 10 % saltMEA or 10 % salt-CYB, was delayed by sodium bisulphite, sodium propionate and sodium benzoate at the highest levels tested (0.04 %, 0.3 %, and 0.2 % respectively). Growth was significantly inhibited using 0.1 % sodium propionate and 0.1 % sodium benzoate in these systems. Sodium sorbate at a level of 0.1 % prevented growth of A.penicillioides on 10 % salt-MEA and in 10 % salt-CYB. H.salinarium grown on CHM and SDFH was not sensitive to sodium propionate and sodium bisulphite at the highest levels tested 0.3 % and 0.03 %, respectively, but sodium benzoate at a a level of 0.10 % was lethal to the bacterium grown in the two media. The lag phase was extended for 7 days, in CHM but no growth was observed in SDFH. Salted dried fish previously dipped in a 1 % solution of either sodium benzoate or sodium sorbate showed no sign of spoilage by H.salinarium after 17 days incubation. Sodium sorbate was also effective against the bacterium grown on SDFH when growth remained in lag phase until the end of the incubation period of day 7. Growth of Staphylococcus sp was totally inhibited using either 0.05 % sodium sorbate, 0.03 % sodium bisulphite or 0.15 % sodium benzoate. At the highest level of 0.3 %, sodium propionate did not significantly inhibit growth of this bacterium.