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Influence of fermentation time and an 'indigenous tenderiser' (Kanwa) on the microbial profile, chemical attributes and shelf-life of rice masa (a Nigerian fermented product)

Efiuvwevwere, B.J., Ezeama, C.F.
Journal of the science of food and agriculture 1996 v.71 no.4 pp. 442-448
fermented foods, shelf life, rice, fermentation, Saccharomyces, lactic acid bacteria, sodium carbonate, chemical composition, sensory evaluation, food spoilage, food acceptability, plate count, potassium sorbate, duration, Nigeria
Investigations on the influence of fermentation time, 'Kanwa' (an indigenous tenderiser and a flavouring agent) and potassium sorbate (0.5, 1.0 or 1.5 g kg-1) were conducted by examining the microbial profile, chemical attributes and shelf-life of rice 'Mesa' (a Nigerian fermented product). Various types of microorganisms occurred at the initial stages of rice slurry fermentation and these included fungi (Aspergillus spp, Penicillium spp, Saccharomyces spp, Rhizopus spp) and bacteria (Lactic acid bacteria, Bacillus spp, Enterobacter spp and Acetobacter spp). But beyond 8 h fermentation time, fewer types of microorganisms (Lactobacillus spp, Saccharomyces spp and Rhizopus spp) were isolated. Total aerobic counts increased significantly (P = 0.05) as fermentation progressed (0, 6 or 12 h), with lactic acid bacteria (LAB) and yeasts dominating and probably contributed to the sour-sweet spongy characteristic of the rice Masa. But after fermentation and baking process, the rice Masa became dominated and spoilt by Bacillus spp, Lactobacillus spp and Saccharomyces spp with storage time. Longer fermentation time resulted in a less acceptable product, being more acidic. Rice Masa produced from a 6 h fermentation showed better sensory qualities (aroma and visual appearance). Use of Kanwa (Na2CO3.NaHCO3.2H2O) improved aroma but was detrimental to visual appearance and spoilage was accelerated, probably due to higher pH. Potassium sorbate at higher concentrations (1.0 and 1.5 g kg-1) induced beneficial antimicrobial effects and reduced the microbial load thereby prolonging the shelf life of the rice Masa (treated with 1.5 g kg-1) by about 3 days.