Effects of yeast and maltose concentration on ultrasonic velocity and attenuation coefficient and its application for process monitoring

Abstract

Monitoring substrate and cell concentration is important for controlling yeast propagation and fermentation processes. This usually requires two instruments, a density meter, and an optical turbidity meter. This paper presents a method for simultaneously determining yeast and maltose concentration with a single ultrasonic sensor. Ultrasonic velocity and attenuation were measured at varying maltose and yeast cell concentrations from 0 to 4 wt%. Ultrasonic velocity increased linearly with both yeast (R 2 = 0.999) and maltose concentration (R 2 = 0.996). In contrast, while attenuation coefficient depended linearly on yeast concentration (R 2 = 0.998), it did not significantly depend on maltose concentration (R 2 = 0.476). To draw conclusions about the main mechanisms of attenuation, the measured attenuation coefficients for yeast cells at 2 MHz were compared to predicted values. With a mean absolute percentage error of 0.25%, intrinsic absorption, thermal effects, and, to a lesser extent, viscous effects were identified as the main reason for damping. These results support the feasibility of combining ultrasonic velocity and attenuation measurements for estimating yeast cell and maltose concentration.

Assessment of avocado textural changes during ripening by using contactless air-coupled ultrasound

“…The absorption of ultrasonic energy in elastic materials gradually increases, as the material behaves as a more viscoelastic medium, due to the viscous attenuation. Viscous attenuation is based on the relative movement of the particle and the surrounding medium which causes dissipation of the acoustic energy due to shear friction (Geier et al, 2014). The use of efficient airborne transducers with multilayer matching materials (Gómez Álvarez-Arenas, 2004;Ginel and Gómez Álvarez-Arenas, 2019), like the ones used in the present study, makes the ultrasonic measurement in highly attenuating materials, such as avocado slices, feasible and may provide a more accurate assessment of the attenuation than conventional direct-contact ultrasonic techniques.…”

Noninvasive Determination of the Amount of Ethanol in Liquid Mixtures by Ultrasound Using Bilinear Interpolation Method

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