Changes in physico-chemical properties and flavour compounds during fermentation of different Obushera (Sorghum and Millet) Beverages

摘要

Four types of Obushera, a fermented millet or sorghum beverage:Ekitiribita Obuteire, Obutoko and Enturire were analyzed for their physico-chemical properties, sugars, organic acids and volatile compounds during fermentation. Standard chemical methods were used to determine the physico-chemical properties of Obushera. The organic acids, carbohydrates, glucose, fructose and maltose were analyzed by high-performance liquid chromatography. The pH of all Obushera varied between 4.00±0.10 and 4.42±0.11 after 4 days of fermentation. The pH of Obuteire, Obutoko and Enturire dropped below 4.5 within one day of fermentation. Acidity ranged between 0.13% (Ekitiribita) to 1.33% (Enturire) after 4 days of fermentation. Dry matter decreased and varied between 5.4 and 22% after 4 days of fermentation. Fermentation resulted into a 20–40% reduction of dry matter in Obutoko, Obuteire and Enturire. Enturire had the highest dry matter content and decreased from 22% to 13%. Fermentation resulted in an apparent increase in protein concentration (5.7–12.3%). Flavour compounds identified included sugars, organic acids, aldehydes, ketones, alcohols and esters. Enturire contained the highest (p < 0.05) concentrations of most flavor compounds. Sugars (maltose, glucose and fructose) were reduced during fermentation. The predominant organic acids detected were lactate, acetate and succinate and increased with fermentation time. Alcohols identified in Obushera were ethanol, 3-methyl-1-butanol, 2-methyl-1-propanol and 2-methyl-1-butanol and increased during fermentation. Ethanol was the predominating alcohol reaching a maximum of 0.8–1.0% (Obuteire and Obutoko) and 4.5% in Enturire during fermentation. The aldehydes detected in Obushera were acetaldehyde, 2-methyl-1-propanal, 2-methyl-1-butanal and 3-methyl-1-butanal and varied from 0.1 mg kg-1 to 6.8 ± 1.2 mg kg-1. Diacetyl, acetoin and 2,3 pentanedione were the ketones identified in Obushera. Esters detected in Obushera included ethyl lactate, ethyl acetate, ethyl butyrate and isobutyl acetate. Significantly higher (p <0.05) amounts of esters were detected in Enturire than in the other types of Obushera. Principal Component analysis, grouped Obushera into three categories (Ekitiribita, Obuteire/Obutoko and Enturire) based on flavour profile differences. Keywords: Fermentation, Obushera, Millet, Sorghum, VolatilesAfrican Journal of Food, Agriculture, Nutrition and Development, Volume 12 No. 6.