Abstract
This study set out to assess the acetone content in rye sweet mashes prepared using the thermal-pressure method of starch liberation, and to investigate the formation of 2-propanol during the fermentation process. In the first set of experiments, we evaluated the correlation between the color and the content of acetone and furfural in industrially produced sweet mashes (n = 37). The L * value was negatively correlated with the content of both acetone and furfural, while chromatic parameters a * and b * and the yellowness index (YI) had strong positive correlations with acetone (r > 0.9) and furfural (r > 0.8 for a * and r > 0.9 for b * and YI). In the second set of experiments, we assessed the concentration of acetone and 2-propanol in distillery rye mashes, fermented by S. cerevisiae yeast and lactic acid bacteria. The influence of fermentation temperature on the formation of 2-propanol was also evaluated. The presence of 2-propanol in the post-fermentation media was confirmed, while a decrease in acetone content was observed. Fermentation temperature (27 °C or 35 °C) was found to have a significant effect on the concentration of 2-propanol in trials inoculated with lactic bacteria. The content of 2-propanol was more than 11 times higher in trials fermented at the higher temperature. In the case of yeast-fermented mashes, the temperature did not affect 2-propanol content. The acetone in the sweet mash was assumed to be a precursor of 2-propanol, which was found in the fermented mashes.
Highlights
Thermal-pressure processing is a common method in agricultural distilleries which use starchy raw materials
As the temperature in the fermentation tanks increased, the concentration of 2-propanol in the spirit rose in comparison to samples of spirits obtained from mashes fermented at lower temperatures
Mash samples prepared using the same method were found to differ significantly in color. This color variance was correlated to the concentration of acetone, which may be explained in part by the presence of furfural, an indicator of Maillard reactions
Summary
Thermal-pressure processing is a common method in agricultural distilleries which use starchy raw materials. High temperatures change the physical properties of starch, enabling more effective enzymatic hydrolysis. Heat treatment of starchy materials can lead to a number of chemical changes, involving. Molecules 2019, 24, 610 reducing sugars, amino acids, and peptides, which are abundant in cereal raw materials [2]. Reactions may occur between the carbonyl or hemiacetal groups in reducing sugars and the amino groups in amino acids and peptides. These can initiate a series of reactions, referred to collectively as Maillard reactions, which produce compounds with strong sensory properties
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