Production of organic flavor compounds by dominant lactic acid bacteria and yeasts from <i>Obushera,</i> a traditional sorghum malt fermented beverage

Abstract

Single and mixed starter cultures of lactic acid bacteria (LAB): <i>Weissella confusa</i> MNC20, <i>Lactobacillus plantarum</i> MNC21, <i>Lactococcus lactis</i> MNC24 and <i>Lactobacillus fermentum</i> MNC34 and yeasts: <i>Issatchenkia orientalis</i> MNC20Y and <i>Saccharomyces cerevisiae</i> MNC21Y were used to produce <i>Obushera</i>, 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. <i>Weissella confusa</i>, <i>Lc. lactis</i>, and <i>Lb. fermentum</i> showed possible acid sensitivity while <i>I. orientalis</i> produced surface films. LAB starter cultures and their combinations with <i>S. cerevisiae</i> lowered pH from 5.83 to <4.5 (3.50-4.13) in a shorter time (12 hrs) than spontaneous fermentations (24 hrs). <i>Lactococcus lactis</i> and <i>W. confusa</i> metabolized glucose the fastest (<i>p</i> < .05) during the first 6 hrs. <i>Lactobacillus fermentum, Lb. plantarum</i>, and <i>S. cerevisiae</i> utilized glucose and maltose concurrently. <i>Lactobacillus plantarum</i> and <i>S. cerevisiae</i> additionally utilized fructose. <i>S. cerevisiae</i> metabolized sugars the fastest (<i>p</i> < .05) during the first 12-24 hrs. <i>Lactobacillus plantarum</i> and <i>W. confusa</i> produced the highest (<i>p</i> < .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 <i>S. cerevisiae</i> reduced (<i>p</i> < .05) lactate and diacetyl yield. Yeasts produced high amounts of acetaldehyde and methyl alcohols. <i>Issatchenkia orientalis</i> produced higher (<i>p</i> < .05) amounts of 2-methy-1-propanol and 3-methyl-1-butanol than <i>S. cerevisiae</i>. Combinations of LAB with <i>S. cerevisiae</i> produced a profile flavor compounds close to that of spontaneously fermented <i>Obushera</i>. These combinations can be adopted for controlled fermentation of <i>Obushera</i> and related fermented cereal products.