Fate of Salmonella typhimurium DT 104 during the Fermentation of ‘Siljo’, a Traditional Ethiopian Fermented Legume Condiment, and during Product Storage at Ambient and Refrigeration Temperatures

Abstract

The survival of Salmonella spp. in fermenting foods and their elimination during prolonged fermentation is documented. This prompted the study to evaluate the fate of Salmonella typhimurium DT 104 during the fermentation of ‘Siljo’, a traditional fermented legume condiment, and during the storage of the fermented product at ambient and cold temperatures. ‘Siljo‘ was made to ferment naturally and the count of lactic acid bacteria reached 9.9 log c.f.u./ml on day 5. The pH dropped from an initial value of 5.8–4.65 during this time. The lactic acid flora was dominated by Leuconostoc spp. At ambient temperature storage (18–22 °C), the product spoiled on day 16. The spoilage was caused by Bacillus spp. At refrigerated storage (4 °C), however, the count of Bacillus spp. was below detectable limits (<1 log c.f.u./ml) until the end of experiment on day 16. When Salmonella typhimurium DT 104 was inoculated into the fermenting gruel at low initial levels (2.8 log c.f.u./ml), the count decreased steadily and the test strain was not detected by enrichment on day 5. At higher initial inoculum level (5.5 log c.f.u./ml), complete elimination was observed on day 7. In a non-fermenting control gruel, count of the test strain increased by about 3 log units on day 7. In another experiment, the fermented product was inoculated with Salmonella typhimurium DT 104 at low or high inoculum levels and stored at ambient and refrigeration temperatures. Under ambient temperature storage, the test strain was not detectable by enrichment on days 3 and 6 at low and high initial inoculum levels, respectively. The count of the test strain did not decrease markedly under refrigerated storage. The results indicated that, at normal contamination levels in the kitchen environment, fermentation for five days would completely eliminate Salmonella typhimurium DT 104 from the fermenting gruel; ambient temperature storage of the product would completely eliminate the pathogen after three days; and its survival is markedly prolonged by cold storage.