Effects of ultrasonic interventions on lipid oxidation in whey

© 2013 Amirehsan TorkamaniThe main objective of this study was to investigate the effect of ultrasonication on lipid oxidation in whey and its shelf stability. Influence of frequencies (20-2000 kHz), specific energies (8-300 kJ/kg) and ultrasound (US) processing times (10 and 30 minutes) was studied in detail. Trials were carried out using a single transducer configuration in a 1 litter acoustic chamber. Treatments were performed at 20, 400, 1000 and 2000 kHz for 10 and 30 minutes at 37 ºC. Depending on the power delivered to the transducers and treatment times, specific energy uptake ranged between 8-390 kJ/kg. Headspace analysis, free fatty acid (FFA) determination, polar lipid quantification and free radical formation were key analytical measurements performed to characterise whey lipid composition and assess the oxidative damage. Generation of free radicals in purified water matrix media (Milli-Q grade) as a result of ultrasonication was highest between 400 and 1000 kHz. Oxidative volatile compounds were initially detected at low concentrations in raw liquid whey samples prior to pasteurisation/sonication treatment. Thermal processing resulted in a significant increase in the concentration of ketone and aldehyde volatiles (P0.05). Thermal and ultrasonic treatments applied did not significantly (P>0.05) affect the abundance of polar lipid (Posphatidyle ethanolamine, serine, inositol, choline and sphingomyelin species). Free fatty acids concentration in raw whey samples was initially low but increased significantly after thermal treatment and incubation for 10 and 30 minutes (P0.05) affect FFA concentration in comparison to control samples. A secondary objective of this work was to evaluate the potential of high frequency ultrasound to separate fat from whey. Fresh whey was treated at 400 and 1000 kHz at different power input and durations (50%-100%, 5-30 minutes) to evaluate US potential for fat separation and extending whey shelf life. US treatment at 1000 kHz was more efficient to enhance fat separation. The volatile compound concentration was significantly reduced after the ultrasound separation of fat. The current study suggested that ultrasonication at selected frequencies and selected specific energies did not enhance oxidative reactions in whey more than interventions caused by conventional thermal processing. In addition, high frequency ultrasound demonstrated to enhance fat separation from whey without having an impact on whey composition and stability