Organic Acids and Volatile Organic Compounds Produced During Traditional and Starter Culture Fermentation of Bushera, a Ugandan Fermented Cereal Beverage

Starter cultures of lactic acid bacteria (Lactobacillus fermentum MINF99, Weissella confusa MINF8, Lactobacillus plantarum MINF277, Lactobacillus brevis MINF226, and Lactobacillus paracasei subsp paracasei MINF98) were used to ferment Bushera during fermentation (96 h). Organic acids and volatile compounds produced during starter and natural fermentation were investigated. Microbial counts, pH, and sugars were also determined. LAB counts increased from 5.87 +/- 0.00 to 8.32 +/- 0.02 log cfu mL(-1) while yeasts increased from 4.39 +/- 0.02 to 7.10 +/- 0.04 log cfu mL(-1) during natural fermentation. The pH decreased from 6.5 to 3.55-4.0. W. confusa MINF8 attained similar final pH (3.55) as naturally fermented Bushera. Lactate was the dominant acid and varied between 0.34% and 0.66%. W. confusa MINF8 produced the highest amounts of lactate (0.66%). Lactate content in naturally fermented Bushera was 0.89%, 96 h. Glucose and maltose decreased from 8.64-9.27 g kg(-1) to 0.13-2.11 g kg(-1) and 7.95-8.42 g kg(-1) to 0.06-2.66 g kg(-1), respectively, in all starter fermented Bushera within 24 h. Glucose and maltose increased during the first 24 h of natural fermentation and then decreased. No citrate was detectable after 24 h. Succinate, pyruvate, and pyro-glutamate were detected and varied between 1.44 and 1495.93 mg kg(-1). Methyl alcohols increased with fermentation time and ranged between 0.02 and 0.53 mg kg(-1). Methyl alcohols concentration of naturally fermented Bushera were significantly higher (P < 0.05) than those of starters after 24 h. Acetaldehyde levels detected in starter fermented bushera was below 5 mg kg(-1) compared to 17.6 mg kg(-1) of naturally fermented Bushera. All starters except L. paracasei subsp. paracasei MINF98 reduced the methyl aldehydes within 12 h to levels ranging between 0.01 and 0.06 mg kg(-1). Ethyl alcohol was the predominant volatile compound and ranged from 2.16 to 1406 mg kg(-1). W. confusa MINF8 produced the highest amounts of ethyl alcohol (1406 g kg(-1)). Maximum ethyl alcohol amount detected in naturally fermented Bushera was 10.4 g kg(-1). Other volatiles detected were butanone, 2, 3-pentanone, diacetyl and ethyl acetate. The study has shown that all starters have ability to singly ferment Bushera. The varying amounts of the volatile compounds observed may influence the sensory properties of Bushera and may be the basis for selecting suitable starters for commercial production.