Development of starter culture for the fermentation of dehulled maize into nsiho (white kenkey)

Abstract

Nsiho kenkey is a bland tasting stiff porridge produced from dehulled maize grains and consumed mainly in some parts of Southern and Eastern Regions of Ghana. This study was carried out to identify the microorganisms responsible for nsiho fermentation and to develop a starter culture for its controlled fermentation in order to improve the safety and quality of the product. A brief field study was carried out in two districts in the Eastern Region of Ghana to observe the processing operations in nsiho production and obtain samples for laboratory analysis. The population of aerobic mesophiles, lactic acid bacteria (LAB) and yeasts were enumerated on Plate Count Agar, de Man Rogosa Sharpe Agar and Oxytetracycline Glucose Yeast Extract Agar respectively. The species of the LAB and yeasts were tentatively identified by phenotypic characterization based mainly on their pattern of carbohydrate assimilation and fermentation. Lactic acid bacterria isolates were screened for rate of acidification, production of exopolysaccharides (EPS), amylase and protease activity as well as antimicrobial activity against some common enteric pathogens using the Agar Well Diffusion Assay. Starter culture was developed through combination of dominant strain of lactic acid bacteria and yeasts in production trails. Survival of four enteric pathogens (Salmonella typhimurium, NCTC 12023, Staphylococcus aureus, NCTC 657, Vibrio cholerae NCTC 11348 and Escherichia coli. NCTC 9001) were also studied during steeping enriched with the starter cultures. Mean pH values decreased from 5.99-3.58 units whilst Titratable acidity increased from 0.03-0.30 % during 48 h steeping of dehulled maize grains in nsiho prodcution. Similarly, pH values decreased from 5.94-3.50 units and Titratable acidity increased from 0.27-0.36 % of 12 h of subsequent dough fermentation. Lactic acid bacteria population increased from a concentration of 104 to108 cfu/ml during steeping and from 105 to108 cfu/g during the dough fermentation. Yeasts counts increased from 102 to 106 cfu/ml during steeping and from 103 to107 cfu/g during dough fermentation. The lactic acid bacteria responsible for nsiho fermentation were identified to be Lactobacillus fermentum, 47.1%, Lactobacillus brevis, 25%, Lactobacillus plantarum, 14.42%, Pediococcus pentosaceus, 8.65% and Pediococcus acidilactici, 4.8%. The dominant yeasts species were Saccharyomyces cerevisiae, 47.6%, Candida krusei, 29.1%, Debaryomyces spp., 15% and Trichosporon spp., 8.3%. Isolates of Lactobacillus fermentum exhibited a faster rate of acidification than the other LAB isolates tested. Most of the LAB isolates screened produced EPS, a few showed amylolytic activity whilst none exhibited protease activity. There was no interaction between the LAB isolates; however, a few of the LAB inhibited the growth of yeasts. The use of starter culture involving combination of LAB and yeasts isolates decreased the steeping time of the dehulled maize grains from 48 h to 24 h. The use of various combinations of LAB and yeasts as inoculum enrichment during fermentation trials produced kenkey acceptable to the taste panel, however, no significant differences (p<0.05) were recorded in taste, texture and odour when compared to the spontaneous fermented nsiho. In challenge testing during steeping of maize grains Vibrio cholerae could not be detected after 48 h whilst counts for Salmonella typhimurium, Staphylococcus aureus and Escherichia coli were reduced by 3 log cycles. Based on antimicrobial activity and technological properties exhibited by the isolates and the sensory quality of nsiho, the best starter organisms selected for nsiho production consisted of mixed cultures of Lactobacillus fermentum, Lactobacillus brevis and Saccharomyces cerevisiae