Survival and growth of foodborne bacterial pathogens in fermenting dough of wadi, a legume-based indigenous food

Abstract

Wadi is a hollow, brittle, ball- or cone-shaped popular traditional legume-based product of many countries in the Indian Subcontinent. To prepare wadi, blackgram (Phaseolus mungo L.) dhal (dehusked split seeds) was soaked, ground to a soft dough, fermented for 10 h in a closed container, moulded into balls or cones and dried for ~60 h (repeating a cycle of 8 h sun-drying at 29–33 °C and then 16 h shade-drying at 28–30 °C). This study aims at understanding the fate of some selected foodborne bacterial pathogens during a chance contamination of blackgram dough at the time of preparing wadi. Uninoculated dough, during the course of its processing to wadi, remained free from Staphylococcus aureus and Escherichia coli, but got contained by Bacillus cereus during the first 10 h of fermentation and also the next 24 h of drying wadi. B. cereus, when spiked into freshly prepared dough at a load of 5.2 log cfu/g, also diminished after 24 h of drying (detection limit (DL), 100 cfu/g). S. aureus (DL, 100 cfu/g) and E. coli (DL, 10 cfu/g) reached below the DL after 36 h of drying. After 10 h of fermentation and 36 h of drying, the moisture content decreased from initial 61.9 to 33.5%, and the pH declined from 6.0 to 4.8.