Functionalised dairy streams: Tailoring protein functionality using sonication and heating.

Ultrasound can be used to modify the functional interactions between casein and whey proteins in dairy systems. This study reports on ongoing developments in understanding the effect of ultrasound and heating on milk proteins in systems with modified casein-whey protein ratios (97:3, 80:20 and 50:50), prepared from milk protein concentrates that were fractionated by microfiltration, based on protein size. Heating of concentrated casein streams (9% w/w) at 80.0 °C for up to 9 min resulted in reduced gelation functionality and increased viscosity, even in the absence of added whey proteins. 20 kHz ultrasonication at 20.8 W calorimetric power for 1 min was able to break protein aggregates formed during heating, resulting in improved gelation and reduced viscosity. Interestingly, when heated whey protein was recombined with unheated casein the gelation properties were similar to unheated controls. In contrast, when heat treated casein streams were recombined with unheated whey protein, the gel forming functionality was reduced. This study therefore shows that using specific combinations of heat and/or ultrasound, fractionated dairy streams can be tailored for specific functional outcomes.

The inhibitory roles of native whey protein on the rennet gelation of bovine milk.

Rennet gelation is used to produce many types of cheese. The effect of native whey protein on rennet gelation kinetics was investigated. Milks with a wide range of whey protein:casein (WP:CN) ratios (with standardised casein concentrations) were made from powders produced by microfiltration. Measurements of casein macro peptide release showed that native whey protein inhibited the enzymatic action of chymosin, which delayed the onset and reduced the subsequent rate of gelation. Experiments in which increased chymosin concentrations compensated for the inhibition, demonstrated that other factors also contributed to the reduced gelation rate. Neither an increase in viscosity nor a reduction in soluble calcium was responsible, leading to the conclusion that in addition to inhibiting chymosin, native whey proteins present a physical barrier to para-casein aggregation. This study demonstrates and explains how casein-enriched retentates from microfiltration gel faster than regular cheese milk that contains higher amounts of native whey protein.

A study of the effectiveness and energy efficiency of ultrasonic emulsification.

Three essential experimental parameters in the ultrasonic emulsification process, namely sonication time, acoustic amplitude and processing volume, were individually investigated, theoretically and experimentally, and correlated to the emulsion droplet sizes produced. The results showed that with a decrease in droplet size, two kinetic regions can be separately correlated prior to reaching a steady state droplet size: a fast size reduction region and a steady state transition region. In the fast size reduction region, the power input and sonication time could be correlated to the volume-mean diameter by a power-law relationship, with separate power-law indices of -1.4 and -1.1, respectively. A proportional relationship was found between droplet size and processing volume. The effectiveness and energy efficiency of droplet size reduction was compared between ultrasound and high-pressure homogenisation (HPH) based on both the effective power delivered to the emulsion and the total electric power consumed. Sonication could produce emulsions across a broad range of sizes, while high-pressure homogenisation was able to produce emulsions at the smaller end of the range. For ultrasonication, the energy efficiency was higher at increased power inputs due to more effective droplet breakage at high ultrasound intensities. For HPH the consumed energy efficiency was improved by operating at higher pressures for fewer passes. At the laboratory scale, the ultrasound system required less electrical power than HPH to produce an emulsion of comparable droplet size. The energy efficiency of HPH is greatly improved at large scale, which may also be true for larger scale ultrasonic reactors.

Ultrasonic encapsulation - A review.

Encapsulation of materials in particles dispersed in water has many applications in nutritional foods, imaging, energy production and therapeutic/diagnostic medicine. Ultrasonic technology has been proven effective at creating encapsulating particles and droplets with specific physical and functional properties. Examples include highly stable emulsions, functional polymeric particles with environmental sensitivity, and microspheres for encapsulating drugs for targeted delivery. This article provides an overview of the primary mechanisms arising from ultrasonics responsible for the formation of these materials, highlighting examples that show promise particularly in the development of foods and bioproducts.