Dried Spent Yeast and Its Hydrolysate as Nitrogen Supplements for Single Batch and Repeated-Batch Ethanol Fermentation from Sweet Sorghum Juice

Abstract

Dried spent yeast (DSY) and its hydrolysate (DSYH) were used as low-cost nitrogen supplements to improve ethanol production from sweet sorghum juice by Saccharomyces cerevisiae NP01 under very high gravity (VHG) fermentation (280 g·L −1 of total sugar) conditions. The supplemented DSY and DSYH concentrations were 11, 16 and 21 g·L ). The use of DSYH at the same DSY concentration improved ethanol productivity (Q p ), but not P E and Y p/s . The ethanol production efficiencies of the juice under DSY and DSYH supplementations were markedly higher than those without nutrient supplementation. However, the P E and Q p values of the juice , respectively.

High Level Ethanol Production by Nitrogen and Osmoprotectant Supplementation under Very High Gravity Fermentation Conditions

“…The protein content of DSY in this study was about 8% higher than that (41.75%) reported by Suwanapong et al [19] indicating that the composition of the company-supplied DSY varied slightly from lot to lot. According to the protein content of yeast extract and DSY and data from many literature reports [5,6,13,19,25], the concentrations of yeast extract, DSY and glycine in the L 9 (3 4 ) orthogonal experiments for the ethanol fermentation were selected as previously mentioned.…”

“…The synthetic VHG medium modified from Melzock et al [24] [5,6,19] was used for control experiments. The medium was transferred into a 500-mL air-locked Erlenmeyer flask with a final working volume of 400 mL and autoclaved at 110 °C for 28 min [18].…”

“…Based on many literature reviews [5,6,13,19,25], the concentrations of yeast extract, DSY and glycine in the EP medium were varied as follows: yeast extract, 1 to 5 g·L ) on ethanol fermentation. All experimental runs were performed in duplicate.…”

“…Saccharomyces cerevisiae, the yeast commonly used for ethanol fermentations, can ferment increased amounts of sugars in the medium, when all required nutrients are provided in adequate amounts [13][14][15][16]. It was reported that under VHG conditions, yeast extract at 9 g·L −1 markedly stimulated the rates of fermentation and ethanol production [5,6,[17][18][19]. However, yeast extract is relatively expensive, which makes it unsuitable for routine use in the industrial manufacture of ethanol.…”

“…However, yeast extract is relatively expensive, which makes it unsuitable for routine use in the industrial manufacture of ethanol. Suwanapong et al [19] found that a low-cost by-product from brewer's industry, dried spent yeast (DSY) cells, could be used as a nitrogen source for VHG ethanol fermentation from sweet sorghum juice instead of yeast extract because it contained high nitrogen and many mineral salts. However, ethanol concentration and its productivity under DSY supplementation (21 g·L ).…”