Sound Stimulation Can Affect Saccharomyces cerevisiae Growth and Production of Volatile Metabolites in Liquid Medium

Abstract

The biological effect of sound on microorganisms has been a field of interest for many years, with studies mostly focusing on ultrasonic and infrasonic vibrations. In the audible range (20 Hz to 20 kHz), sound has been shown to both increase colony formation and disrupt microbial growth, depending upon the organism and frequency of sound used. In the brewer’s yeast Saccharomyces cerevisiae, sound has been shown to significantly alter growth, increase alcohol production, and affect the metabolite profile. In this study, S. cerevisiae was exposed to a continuous 90 dB @ 20 μPa tone at different frequencies (0.1 kHz, 10 kHz, and silence). Fermentation characteristics were monitored over a 50-h fermentation in liquid malt extract, with a focus on growth rate and biomass yield. The profile of volatile metabolites at the subsequent stationary phase of the ferment was characterised by headspace gas chromatography–mass spectrometry. Sound treatments resulted in a 23% increase in growth rate compared to that of silence. Subsequent analysis showed significant differences in the volatilomes between all experimental conditions. Specifically, aroma compounds associated with citrus notes were upregulated with the application of sound. Furthermore, there was a pronounced difference in the metabolites produced in high- versus low-frequency sounds. This suggests industrial processes, such as beer brewing, could be modulated by the application of audible sound at specific frequencies during growth.

The Effect of Sound Frequency and Intensity on Yeast Growth, Fermentation Performance and Volatile Composition of Beer

“…The application of various sound intensities and frequencies has previously been shown to enhance the growth rates of S . cerevisiae [ 3 , 4 , 5 , 6 , 9 ], bacterial species [ 5 , 8 , 10 , 11 , 12 , 13 ], algae species [ 14 , 15 ], and plant species [ 16 , 17 , 18 ] compared to control experiments. However, in the current study, the growth rate was not calculated, and rather the number of yeast cells in suspension was reported.…”

“…However, it has also been reported that hydrostatic pressure, and the amount of nitrogen and glucose in wort can alter ester synthesis [ 30 , 31 ]. The application of high (10 kHz, 90 dB @ 20 µPa) and low (100 Hz, 90 dB @ 20 µPa) audible sound to yeast significantly decreased the production of ethyl octanoate compared to the silence control [ 6 ]. Therefore, it is also possible that the changes in cell numbers in suspension and/or glucose utilization may underlie the differences in the observed levels of esters in our ferments.…”

“…Citronellol ( Figure 6 ) increased over time in all treatment samples, likely due to yeast biotransformation reactions, as previously reported [ 32 , 33 ], as did 1,2-dihydrolinalool ( Table A1 ). It has previously been reported that higher audible sound (10 kHz, 90 dB @ 20 µPa) enhanced (by 7.8-fold) the production of limonene by yeast compared to the silence control [ 6 ]. In contrast, the abundance of 2-methylbutyl isobutyrate, linalool, and geraniol decreased as fermentation progressed in this study.…”

“…Subjecting S. cerevisiae-170 to the Hindustani classical music Ahir Bhairav raga (172-581 Hz, 70-90 dB @ 20 µPa) and Pilu raga (86-839 Hz, 85-110 dB @ 20 µPa) increased the yeast biomass concentration compared to a silence control [5]. A more recent study showed that audible sound stimulated the yeast growth rate by 23% compared to that of a silence control [6].…”

“…From this prior research, it could be expected that applying sound to beer fermentation is likely to enhance yeast growth, thereby reducing fermentation and maturation time [ 3 , 6 ]. However, despite anecdotal accounts of the effect of sound on beer fermentation, research of this kind has not previously been reported.…”