Abstract
Micro- and nano-bubbles (MNB) have unique properties and have attracted great attention in the past 2 decades, offering prospective applications in various disciplines. The first objective of this study was to investigate whether venturi-style MNB generation is capable of producing sufficient bulk MNB. A nanoparticle tracking system was used to measure the bubble concentration and particle size of MNB-treated deionized water. The MNB-treated deionized water had a bubble concentration of 3.76 × 108 particles/mL (∼350 million bubbles/mL more compared with control) and a mean particle size of 249.8 nm. The second objective of this study was to investigate the effects of MNB treatment on the microstructure and functional properties of milk protein concentrate (MPC) dispersions. Reconstituted MPC dispersions (21%, wt/wt) without air injection were considered as control (C-MPC), and MPC dispersions passed through the MNB system were considered as MNB-treated (MNB-MPC) dispersions. Control and MNB-MPC dispersions were evaluated in terms of rheological behavior and microstructure. The microscopic observations of MNB-MPC dispersions showed less aggregated microstructures and greater structural differences compared with C-MPC dispersions, therefore lowering the viscosity. The viscosity of MNB-MPC at a shear rate of 100 s-1 significantly decreased to 57.58 mPa·s (C-MPC: 162.40 mPa·s), a net decrease in viscosity by ∼65% after MNB treatment. Additionally, MPC dispersions were spray dried after the MNB treatment, and the resultant MNB-MPC powders were characterized and compared with the control MPC in terms of rehydration characteristics and microstructure. Focused beam reflectance measurement of the MNB-MPC powders indicated lower counts of large particles (150-300 μm) during dissolution, signifying that MNB-MPC powders exhibited better rehydration properties than the C-MPC powders. This study, therefore, recommends the possibility of using MNB treatment for more efficient drying while improving the functional properties of the resultant MPC powders.
Highlights
Applications of micro- and nano-scaled materials are constantly evolving, and they have great potential to bring significant advantages in various manufacturing sectors
This study aims to (1) characterize the micro- and nano-bubbles (MNB) generated by the venturi-based air injection method in deionized (DI) water in terms of bubble concentration and mean diameter; (2) evaluate the effects of MNB on rheology and microstructure of milk protein concentrate (MPC) dispersions; and (3) investigate the rehydration and microstructure of MNB-treated MPC powders
The NanoSight showed a significant increase in particle concentration upon MNB treatment, suggesting that the venturi injector was efficient in generating MNB
Summary
Applications of micro- and nano-scaled materials are constantly evolving, and they have great potential to bring significant advantages in various manufacturing sectors. Nanostructured materials are defined to be of diameters in the range of 1 to 100 nm. Agarwal et al (2011) presented the name micro- and nano-bubbles (MNB), distinct categories for NB and MNB are still unclear. Tiny bubbles with diameters ranging from hundreds of nanometers to several tens of micrometers, MNB are gaining interest due to their wide range of applications in many fields of science and technology. The physical properties of MNB are different from those of milliscaled bubbles, and MNB are stable for considerably long periods, having shown stability for as long as 2 wk; clusters of NB could further increase their stability (Weijs et al, 2012; Azevedo et al, 2016). Amamcharla et al (2017) and Phan et al (2020) have outlined applications of MNB in various food and dairy processing applications
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