Effect of Co-Inoculation with Saccharomyces cerevisiae and Lactic Acid Bacteria on the Content of Propan-2-ol, Acetaldehyde and Weak Acids in Fermented Distillery Mashes

Abstract

The qualitative and quantitative composition of volatile compounds in fermented distillery mash determines the quality of the obtained distillate of agricultural origin (i.e., raw spirit) and the effectiveness of further purification steps. Propan-2-ol (syn. isopropyl alcohol), due to its low boiling point, is difficult to remove by rectification. Therefore, its synthesis needs to be limited during fermentation by Saccharomyces cerevisiae yeast, while at the same time controlling the levels of acetaldehyde and acetic acid, which are likewise known to determine the quality of raw spirit. Lactic acid bacteria (LAB) are a common but undesirable contaminant in distillery mashes. They are responsible for the production of undesirable compounds, which can affect synthesis of propan-2-ol. Some bacteria strains are able to synthesize isopropyl alcohol. This study therefore set out to investigate whether LAB with S. cerevisiae yeast are responsible for conversion of acetone to propan-2-ol, as well as the effects of the amount of LAB inoculum and fermentation parameters (pH and temperature) on the content of isopropyl alcohol, acetaldehyde, lactic acid and acetic acid in fermented mashes. The results of NMR and comprehensive two-dimensional gas chromatography coupled with time of flight mass spectrometry (GC × GC-TOF MS) analysis confirmed the ability of the yeast and LAB strains to metabolize acetone via its reduction to isopropyl alcohol. Efficient fermentation of distillery mashes was observed in all tested mashes with an initial LAB count of 3.34–6.34 log cfu/mL, which had no significant effect on the ethanol content. However, changes were observed in the contents of by-products. Lowering the initial pH of the mashes to 4.5, without and with LAB (3.34–4.34 log cfu/mL), resulted in a decrease in propan-2-ol and a concomitant increase in acetaldehyde content, while a higher pH (5.0 and 5.5) increased the content of propan-2-ol and decreased acetaldehyde content. Higher temperature (35 °C) promoted propan-2-ol synthesis and also resulted in increased acetic acid content in the fermented mashes compared to the controls. Moreover, the acetic acid content rose with increases in the initial pH and the initial LAB count.

Recent advances in modified poly (lactic acid) as tissue engineering materials

“…Several microorganisms have been able to produce lactic acid and organic lactates, such as fungi [26,27], cereal [28], yeast [29][30][31], cyanobacteria [32][33][34][35], and even algae [36], despite the great variety of microorganisms that produce LA, bacteria have been the most commonly used for the biotechnological production of lactic acid due to the ease and versatility of the handling and processing of bacteria. One of the most important genera of bacteria for producing lactic acid is the genera Lactobacillus.…”

Value-Added Products from Ethanol Fermentation—A Review

“…The production of these organic acids could produce considerable additional value (Table 1), but a portion of the organic acids (e.g., acetic acid and lactic acid) seen in commercial ethanol beers are typically attributable to nuisance organisms present during bioethanol production. At modest concentrations, these organic acids can inhibit fermentation [5,97,98]. For example, acetic acid present in commercial Saccharomyces cerevisiae fermentations is undesirable, with concentrations > 0.4 g/L signifying bacterial contamination and concentrations > 0.6 g/L leading to impaired fermentations [95,99].…”

Identyfikacja chemicznych zanieczyszczeń etanolu uzyskanego z ziarna różnych odmian kukurydzy

“…Związki te tworzą się podczas procesów biochemicznych lub są wynikiem aktywności metabolicznej niepożądanej mikroflory. Wyróżnia się wśród nich: metanol, estry, aldehydy, wyższe alkohole oraz kwasy organiczne [3,7,11]. Poszczególne substancje należące do wymienionych grup zanieczyszczeń różnią się w sposób istotny progiem wyczuwalności sensorycznej.…”