A preliminary study on using ultrasounds for the valorization of spent brewer’s yeast

Spent brewer’s yeast is a by-product rich in components with biological activity, being considered an innovative and economical viable solution for creating sustainable functional food systems. This work describes the use of ultrasound treatment, performed under various conditions, with the aim to facilitate the cell lysis and to further characterize the released cellular content of the spent brewer’s yeast. Solid residue content of the spent yeast suspensions was positively influenced by both the amplitude and the exposure time (p<0.05), reaching a maximum content (40.02±0.13 g/100 g dry yeast) at 70% amplitude, after 7.5 minutes of ultrasound treatment under pulsation mode, and the minimum after 2.5 minutes of exposure at 20% ultrasound amplitude under continuous mode (31.59±1.2 g/100 g dry yeast). The content of the soluble proteins released from the yeast cells during the ultrasound treatment under pulsation mode, reached a maximum increase at amplitude of 70%, after 7.5 minutes, being by 85% higher compared to the control represented by untreated yeast suspension. The disintegration index, Z, indicated that the maximum degree of yeast cells disintegration was obtained when applying the ultrasound treatment under pulsation mode for 5 minutes, at 50% amplitude. The antioxidant activity of the yeast extracts depended on the ultrasound conditions applied, the maximum antioxidant activity being measured in the sample exposed to ultrasound under pulsation mode for 5 minutes at 50% amplitude. In conclusion, ultrasound is a good approach to release the intracellular components from the spent brewer’s yeast. Further studies factoring ultrasounds power and frequency should be conducted, such to identify the optimum set of parameters which allow the highest release of the intracellular yeast compounds.