Gaulin homogenization: A mechanistic study

Free radical-based oxidation has been detected in the normal operating regi me of the Gaulin homogenizer, demonstrating that cavitation occurs in this important industrial bioprocessing equipment. Free radical generation is su ppressed by imposition of back pressure, proving that such cavitation occur s in the impingement section. The calculated value of the cavitation number is consistent with submerged jet cavitation, wherein a high-speed jet exit ing from the valve gap accelerates fluid in the impingement region, creatin g the vacuum conditions for cavitation. Using polysaccharides as a model sh ear-sensitive compound, their breakage pattern in the homogenizer was chara cterized by molecular size and polydispersity and compared to those of flui d shear flows in capillary tubes and cavitating flow from a sonic horn. The results indicate that breakage occurs primarily by fluid shear, although a contribution by cavitation is also apparent when back pressure is applied. Because biological molecules can readily react with free radicals and the alterations caused thereby are subtle in nature, a thorough evaluation of t he impact of free radicals in upstream homogenization is warranted.