-Ultrasonic processing is an emerging technology in food processing. When ultrasound passes through a liquid, bubble nuclei present in the liquid grow by bubble coalescence and rectified diffusion. When these bubbles reach a critical size range, they collapse under nearadiabatic conditions generating extreme conditions within the bubbles and in the surrounding liquid that include intense shear forces, turbulence and microstreaming effects. These ultrasound-induced physical effects are finding increasing use in food and dairy processing, in applications such as the enhancement of whey ultrafiltration, extraction of functional foods, reduction of product viscosity, homogenization of milk fat globules, crystallization of ice and lactose and the cutting of cheese blocks. After a brief introduction to the ultrasonic processing of food systems in general, this review presents a critical discussion of applications in dairy processing, together with the findings of some recent research on the use of ultrasound to modify the functionality of dairy protein ingredients. ultrasonic processing / acoustic cavitation / whey protein / dairy product Article published by EDP Sciences l'industrie alimentaire et laitière, dans des applications telles que l'amélioration de l'ultrafiltration du lactosérum, l'extraction d'aliments fonctionnels, la réduction de la viscosité des produits, l'homogénéisation des globules gras du lait, la cristallisation de la glace et du lactose et le décou-page des blocs de fromage. Après une brève introduction sur le traitement par ultrasons des systèmes alimentaires en général, cette revue présente une discussion critique des applications en technologie laitière, ainsi que les résultats de certaines recherches récentes sur l'usage des ultrasons pour modifier les fonctionnalités des ingrédients protéiques laitiers.ultrason / cavitation acoustique / protéine de lactosérum / produit laitier

High intensity low frequency ultrasound was used to process dairy ingredients to improve functional properties. Based on a number of lab-scale experiments, several experimental parameters were optimised for processing large volumes of whey and casein-based dairy systems in pilot scale ultrasonic reactors. A continuous sonication process at 20 kHz capable of delivering up to 4 kW of power with a flow-through reactor design was used to treat dairy ingredients at flow rates ranging from 200 to 6000 mL/min. Dairy ingredients treated by ultrasound included reconstituted whey protein concentrate (WPC), whey protein and milk protein retentates and calcium caseinate. The sonication of solutions with a contact time of less than 1 min and up to 2.4 min led to a significant reduction in the viscosity of materials containing 18% to 54% (w/w) solids. The viscosity of aqueous dairy ingredients treated with ultrasound was reduced by between 6% and 50% depending greatly on the composition, processing history, acoustic power and contact time. A notable improvement in the gel strength of sonicated and heat coagulated dairy systems was also observed. When sonication was combined with a pre-heat treatment of 80 degrees C for 1 min or 85 degrees C for 30s, the heat stability of the dairy ingredients containing whey proteins was significantly improved. The effect of sonication was attributed mainly to physical forces generated through acoustic cavitation as supported by particle size reduction in response to sonication. As a result, the gelling properties and heat stability aspects of sonicated dairy ingredients were maintained after spray drying and reconstitution. Overall, the sonication procedure for processing dairy systems may be used to improve process efficiency, improve throughput and develop value added ingredients with the potential to deliver economical benefits to the dairy industry.

Ultrasonic processing in simple terms is the application of sound waves in the frequency range of 20 kHz-1 MHz which is above the range of human hearing. This review focuses on the applications of ultrasound to accelerate processes such as dehydration, drying, freezing and thawing, tenderization of meat, crystallization of lactose and fat and to improve processes such as cutting, extraction, emulsification, ageing of wines and esterification. The effect of ultrasound on physical properties such as viscosity, opacity, particle size and gel strength is also considered. We find that it is the physical effects of ultrasound that predominate in most applications considered to date. Ultrasound increases heat and mass transfer, disrupts aggregates and can break macromolecular chains.

Aqueous solutions of reconstituted whey protein- concentrate (WPC) & isolate (WPI) powders were sonicated at 20 kHz in a batch process for 1-60 min. Sonication at 20 kHz increased the clarity of WPC solutions largely due to the reduction in the size of the suspended insoluble aggregates. The gel strength of these solutions when heated at 80°C for 20 min also increased with sonication, while gelation time and gel syneresis were reduced. These improvements in gel strength were observed across a range of initial pH values, suggesting that the mechanism for gel promotion is different from the well known effects of pH. Examining the microstructure of the whey protein gels indicated a compact network of densely packed whey protein aggregates arising from ultrasound treatment. Comparable changes were not observed with whey protein isolate solutions, which may reflect the absence of larger aggregates in the initial solution or differences in composition.

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