BACTERIOLOGY OF READY-TO-EAT VEGETABLE SALADS SOLD IN FASTFOOD RESTUARANTS IN BENIN CITY AND THE EFFECT OF CHLORINE WASH ON THEIR SHELF LIFE

Abstract

Ready-to-eat vegetable salads purchased from three fast food restaurants; Mr Biggs, Chicken Republic and Kada Fried in Benin City, Edo State, Nigeria, were analyzed for their bacteriological quality over a period of ten days of storage at 4 0C. Pour plate technique was used, enumeration and identification were done using cultural, morphological and biochemical methods. Mean bacterial counts on nutrient agar ranged from 1.10 ± 3.12 x 103 – 10.40 ± 1.61 x 103 cfu/g for Mr Biggs, 1.60 ± 1.00 x 103 - 11.0 ± 2.36 x 103 cfu/g for Chicken Republic and 2.40 ± 2.50 x 103 – 12.00 ± 1.76 x 103 cfu/g for Kada Fried. Mean coliform counts ranged from 4.20 ± 1.53 x 102 – 56.00 ± 2.18 x 102 cfu/g for Mr Biggs, 4.00 ± 2.29 x 102 – 63.00 ± 2.26 x102 cfu/g for Chicken Republic and 1.02 ± 1.16 x 103 – 7.60 ± 1.76 x 103 cfu/g for Kada Fried. The effect of chlorine wash on the shelf-life of self-made vegetable salad samples was also examined. There was reduction in the bacterial load of the salad samples with increasing sodium hypochlorite concentration, from 10-200ppm. Least bacterial counts were obtained on day 1 at 200ppm ( 1.10 ± 3.12 x 103 cfu/g) while the highest bacterial counts were obtained on day 10 at 10ppm (12.00 ± 1.76 x 103 cfu/g) concentration of sodium hypochlorite. Bacteria isolated from the stored salad samples were Serratia sp., Bacillus subtilis, Enterobacter aerogenes, Pseudomonas aeruginosa and Staphylococcus aureus. Results of this study reawakens the need to wash vegetables properly before consumption and shows that the efficacy of sodium hypochlorite in reducing bacterial load and in storing vegetable salads at low temperature of 40C, is concentration dependent.. Vegetable salads should be consumed immediately after preparation or not later than two days after storage in the refrigerator to avoid spoilage organisms that can cause food poisoning.Key words: salad, shelf-life, bacteria, Nigeria