engleski

Viability of brewer's yeast cells in aqueous suspension affected by ultrasonic treatment

The viability of brewer’s yeast (Saccharomyces uvarum) cell suspensions as a function of treatment time (1-10 min) was investigated during exposure to both standing (30 % to 60 % power) and pulsing (10 sec pulsation intervals) low frequency ultrasound wave fields (20 kHz). The concentration of yeast suspensions was 1 mg/mL (dry weight ; approximately 2 x 108 cells) and pH 5.0 ; 5.5 and 6.0. Changes in yeast cell morphology caused by the different mode of ultrasound treatment, pH value of yeast suspensions, and treatment time were observed by light microscopy (LM) (methylene blue staining) and recorded onto a PC. Aggregation of brewer’s yeast cells has been monitored and quantified. The aggregation effect was based on the acoustic radiation force, which may concentrate cells into “pearl chain”, clusters or large agglomerates. The obtained results show that exposure time and pulsing wave treatment obviously increased the degree of damaged cells and resulted in broadening the agglomerate size. Light microscopy confirmed the presence of large agglomerate regions in the ultrasonic field and evidenced that 75 % cells (suspension pH 5.5 ; exposure time 6 min) inside the cluster were damaged. The experimental set-up introduced here is a promising tool for future quantitative experiments on brewer’s yeast agglomeration capability.

aggregation; Saccharomyces uvarum; ultrasonic treatment

nije evidentirano