Lactic acid fermentation of sour porridge and mahewu, a non-alcoholic fermented cereal beverage

Abstract

The microbiological and acidic changes during the natural fermentation of mahewu, a non-alcoholic cereal beverage, and sour porridge were investigated. The presence of pathogenic yeasts in both products was also investigated. The study was carried out over a period of six months in the year 2000. The pH and total acidity as well as microbiological analysis were carried out at intervals of time during the fermentation period. There was a sharp decrease in pH in the mahewu and sour porridge broths in the first 12 to 24 hours of fermentation. Very little titratable acids were produced in the first 6 to 12 hours which was followed by a steady increase during the rest of the fermentation period. Enteric bacteria increased slightly in the first 12 hours but decreased sharply afterwards and could not be detected when the pH was around 3.5 whereas lactic acid bacteria predominated during the fermentation period. Yeasts increased in numbers as the pH dropped and were detected in lower numbers than lactic acid bacteria throughout the fermentation period. The yeasts isolated in both mahewu and sour porridge broths were Saccharomyces cerevisiae, Candida species which included the pathogenic species, C.glabrata, C.kefyr, and Zygosaccharomyces species. The other pathogenic Candida species isolated in sour porridge broth only were C.inconspicua and C.guilliermondii. Klebsiella pneumoniae, Enterobacter species, Escherichia coli and Serratia ficaria were the enteric bacteria isolated in mahewu broth whereas Klebsiella and Enterobacter species were the enteric bacteria isolated in sour porridge. The lactic acid bacteria isolated in mahewu broth were Lactobacillus species, Pediococcus pentosaceus, Lactococcus lactis and Leuconostoc lactis whereas Lactobacillus coprophilus and Leuconostoc lactis were isolated in sour porridge broth.