Impact of potential fermentation inhibitors present in sweet sorghum sugar solutions

Authors: Klasson, Kjell

Submitted to: Sugar Tech
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2016
Publication Date: 1/16/2017
Publication URL: http://handle.nal.usda.gov/10113/5642511
Citation: Klasson, K.T. 2017. Impact of potential fermentation inhibitors present in sweet sorghum sugar solutions. Sugar Tech. 19(1):95-101.

Interpretive Summary: In this work, the fermentation of the sweet sorghum sugars to ethanol was studied in the presence of chemicals, which are present in the juice or produced by microorganisms during prolonged storage of harvested materials or juice. An industrial strain of distiller’s yeast was used to produce ethanol from sugars. The fermentation time ranged from 12 to 140 hours, with the long fermentation time corresponding to clear inhibition of yeast growth and production in the presence of the chemical acetic acid. Among the acids, only acetic acid showed a negative impact on the fermentation rates. All levels of the chemicals lactic and aconitic acid either showed an improvement in fermentation rates or in final ethanol concentration.

Technical Abstract: In this work, the fermentation of the sweet sorghum sugars sucrose, glucose, and fructose to ethanol was studied in the presence of acetic, lactic and aconitic acid, which are present in the juice or produced by microorganisms during prolonged storage of harvested materials or juice. An industrial strain of distiller’s yeast was used to produce ethanol from 100 g/L (83 g/L after inoculum) of total sugars. The fermentation time ranged from 12 to 140 h, with the long fermentation time corresponding to clear inhibition of yeast growth and production in the presence of 8 g/L of acetic acid. Among the acids, only acetic acid showed a negative impact on the fermentation rates and only at levels greater than 2 g/L. Lower levels of acetic acid and all levels of lactic and aconitic acid (1-5 g/L) either showed an improvement in fermentation rates or in final ethanol concentration. The acidity was not controlled during the fermentation but was initially adjusted and it is presumed that the pH buffering effect on the organic acids contributed to the higher fermentation rates and prevented the pH from naturally dropping as the fermentation progressed.