The effect of ultrasound on casein micelle integrity

Abstract

Samples of fresh skim milk, reconstituted micellar casein, and casein powder were sonicated at 20 kHz to investigate the effect of ultrasonication. For fresh skim milk, the average size of the remaining fat globules was reduced by approximately 10 nm after 60 min of sonication; however, the size of the casein micelles was determined to be unchanged. A small increase in soluble whey protein and a corresponding decrease in viscosity also occurred within the first few minutes of sonication, which could be attributed to the breakup of casein-whey protein aggregates. No measurable changes in free casein content could be detected in ultracentrifuged skim milk samples sonicated for up to 60 min. A small, temporary decrease in pH resulted from sonication; however, no measurable change in soluble calcium concentration was observed. Therefore, casein micelles in fresh skim milk were stable during the exposure to ultrasonication. Similar results were obtained for reconstituted micellar casein, whereas larger viscosity changes were observed as whey protein content was increased. Controlled application of ultrasound can be usefully applied to reverse process-induced protein aggregation without affecting the native state of casein micelles.

Inactivation of Staphylococcus aureus and Escherichia coli in milk by different processing sequences of ultrasound and heat

“…Table plotted the initial pH value of milk was 6.62 ± 0.00, and significant decrease of pH values ( p < .05) were seen in most treatment groups. According to some reports, the reaction between nitrogen and oxygen within the hot zone of the cavitation bubbles generated small amounts of nitric acid, which was able to alter the solution pH value (Chandrapala, Martin, Zisu, Kentish, & Ashokkumar, ). In addition, the pH of milk is also sensitive to temperature.…”

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“…Furthermore, ultrasound could cause some qualitative changes in the fat globule membrane, which would modify the ability of fat globules to interact with themselves and/or casein micelles, thereby improving the gelling properties. However, direct effects of ultrasound on casein micelles or individual caseins cannot be ruled out completely, although negligible effects were found on the individual caseins/casein micelles [31]. This may be because big multimeric protein complexes are more sensitive to the shearing forces created by micro-streaming and bubble implosion than single dissolved monomeric proteins.…”

“…A recent study by Chandrapala et al [31] showed that sonication did not appear to affect casein micelle size or composition or permanently affect the mineral balance in fresh skim milk. Sonication did, however, reduces the size of the already small fat globules remaining in skim milk, appeared to break up whey protein aggregates, and assist in breaking apart casein micelle, non-micellar casein and whey protein aggregates present in reconstituted casein powder systems.…”

Effect of high‐energy emulsification on properties of commercial low‐temperature pasteurised milk

“…Chandrapala et al . () reported that casein micelles are incorporated into milk fat globules during microfluidisation and that ultrasonication forms similar MFGM structures to those in milk treated by microfluidisation. MFGMs have a role in protecting fat globules from aggregation and degradation by enzymes, such as lipase (Garcia‐Amezquita et al .…”