Abstract
Single and mixed starter cultures of lactic acid bacteria (LAB): Weissella confusa MNC20, Lactobacillus plantarum MNC21, Lactococcus lactis MNC24 and Lactobacillus fermentum MNC34 and yeasts: Issatchenkia orientalis MNC20Y and Saccharomyces cerevisiae MNC21Y were used to produce Obushera, a fermented sorghum beverage. Microbial counts, pH, sugars, organic acids, and volatile compounds in starter culture and spontaneous fermentations were monitored during 48 hrs. Maximum counts of LAB (8.4–9.4 log cfu g−1) and yeasts (7.5 ± 0.1 cfu g−1) starter cultures were attained in 6–48 hrs. Weissella confusa, Lc. lactis, and Lb. fermentum showed possible acid sensitivity while I. orientalis produced surface films. LAB starter cultures and their combinations with S. cerevisiae lowered pH from 5.83 to <4.5 (3.50–4.13) in a shorter time (12 hrs) than spontaneous fermentations (24 hrs). Lactococcus lactis and W. confusa metabolized glucose the fastest (p < .05) during the first 6 hrs. Lactobacillus fermentum, Lb. plantarum, and S. cerevisiae utilized glucose and maltose concurrently. Lactobacillus plantarum and S. cerevisiae additionally utilized fructose. S. cerevisiae metabolized sugars the fastest (p < .05) during the first 12–24 hrs. Lactobacillus plantarum and W. confusa produced the highest (p < .05) amounts of lactate (5.43 g kg−1) and diacetyl (9.5 mg kg−1), respectively. LAB also produced acetate, ethanol, acetaldehyde, acetone, and acetoin. Coculturing LAB with S. cerevisiae reduced (p < .05) lactate and diacetyl yield. Yeasts produced high amounts of acetaldehyde and methyl alcohols. Issatchenkia orientalis produced higher (p < .05) amounts of 2‐methy‐1‐propanol and 3‐methyl‐1‐butanol than S. cerevisiae. Combinations of LAB with S. cerevisiae produced a profile flavor compounds close to that of spontaneously fermented Obushera. These combinations can be adopted for controlled fermentation of Obushera and related fermented cereal products.
Highlights
Traditional fermented cereal products are important in nutrition as sources of carbohydrates, proteins, fiber, minerals, and vitamins (Nout, 2009)
Obushera fermented by the S. cerevisiae starter culture yielded less malty compounds after 48 hrs compared to the spontaneous fermentation
This study reveals that besides producing lactic acid, lactic acid bacteria (LAB) in cereal fermentations may contribute to production of other flavor compounds notably acetate, ethanol, acetaldehyde, diacetyl, acetone, and acetoin
Summary
Traditional fermented cereal products are important in nutrition as sources of carbohydrates, proteins, fiber, minerals, and vitamins (Nout, 2009). Others evaluated combinations of LAB and yeasts (Halm, Osei-Yaw, Hayford, Kpodo, & Amoa-Awua, 1996; Mugula et al, 2003; Omemu, Oyewole, & Bankole, 2007; Orji, Mbata, Aniche, & Ahonkhai, 2003). The flavor profile of cereal fermented products is composed of sugars, organic acids, aldehydes, ketones, alcohols, and esters (Mugula et al, 2003; Mukisa et al, 2012; Muyanja, Narvhus, & Langsrud, 2012). This study evaluated the individual and interactive effects of the dominant yeasts: S. cerevisiae and I. orientalis and the different LAB (Lb. plantarum, Lb. fermentum, W. confusa, Lc. lactis) on the flavor profile of traditional fermented cereals. Information generated from this study will enable the identification of potential starter cultures for traditional fermented cereal products
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