Ultrasonic Disruption Of Yeast Cells: Effects Of Processing Parameters

Recent trends in health and wellness have favored the application of non-thermal processing technologies,such as high-pressure,high-intensity ultrasound,or pulsed electric fields,to minimize losses in the nutrition and quality of products associated with conventional thermal processing.High-intensity ultrasound for non-thermal processing has been researched for many years,but its commercialization is lagged compared with other technologies because a good understanding of the microbial inactivation mechanism and its influencing factors is lacking.In this project,we have studied this topic and the application of research findings in the ultrasonic extraction of protein and polysaccharides.During the ultrasonic treatment of yeast cells,the damage to the cell walls and membranes was monitored by assessing the release of cell wall polysaccharides andintracellular proteins,respectively.At a low acoustic intensity(10 W/cm2),the polysaccharides were released faster than the proteins,whereas at higher acoustic intensities(24 and 39 W/cm2),this trend was reversed.At elevated temperatures,additional cell wall polysaccharides were released,whereas fewer intracellular proteins were released.Increasing processed volumes,initial cell concentrations,and salt concentrations led to the decrease of both fractions.However,the total releases per ultrasound treatment remained constant regardless of the processed volumes,and increased with the increase of initial cell concentrations.The results suggest the ultrasonic disruption of yeast cells begins with the breakdown of the cell wall before continuing to the cell membrane.On the basis of these findings,we compared the extraction selectivity of yeast polysaccharide and protein by using hot-water(H),alkali(A),sonication(S)and their combinations.Results revealed that polysaccharides were effectively extracted by all methods while proteins were effectively extracted by S,H + A,and H + A + S.Hot-water or alkali extraction showed higher selectivity toward the polysaccharide.Sonication alone exhibited poor extraction selectivity,which can however be improved by combining with hot-water or alkali.Moreover,the modulation of extraction selectivity by hot-water or alkali is probably caused by the thermal coagulation of intracellular protein with yeast cells at elevated temperature,or inhibition of cavitation activity in the presence of alkali salt.These findings may offer new avenues for exploring more efficient cell disruption,microbial inactivation or extraction processes by ultrasound.