Generation methods, stability, detection techniques, and applications of bulk nanobubbles in agro-food industries: a review and future perspective.

Nanobubble (NB) technologies have received considerable attention for various applications due to their low cost, eco-friendliness, scale-up potential, process control, and unique physical characteristics. NB stands for nanoscopic gaseous cavities, typically <1 µm in diameter. NBs can exist on surfaces (surface or interfacial NBs) and be dispersed in a bulk liquid phase (bulk NBs). Compared to the microbubbles, NBs exhibit high specific surface area, negative surface charge, and better adsorption. Bulk NBs can be generated by hydrodynamic/acoustic cavitation, electrolysis, water-solvent mixing, nano-membrane filtration, and so on. NBs exhibit extraordinary longevity compared to microbubbles, prompting the interest of the scientific community aiming for potential applications including medicine, agriculture, food, wastewater treatment, surface cleaning, and so on. Based on the limited amount of research work available regarding the influence of NBs on food matrices, further research, however, needs to be done to provide more insights into its applications in food industries. This review provides an overview of the generation methods for NBs, techniques to evaluate them, and a discussion of their stability and several applications in various fields of science were discussed. However, recent studies have revealed that, despite the many benefits of NB technologies, several NB generating approaches are still limited in their application in specific agro-food industries. Further study should focus on process optimization, integrating various NB generation techniques/combining with other emerging technologies in order to achieve rapid technical progress and industrialization of NB-based technologies.HighlightsNanobubbles (NBs) are stable spherical entities of gas within liquid and are operationally defined as having diameters less than 1 µm.Currently, various reported theories still lack the ability to explain the evidence and stability of NBs in water, numerous NB applications have emerged due to the unique properties of NBs.NB technologies can be applied to various food and dairy products (e.g. yogurt and ice cream) and other potential applications, including agriculture (e.g. seed germination and plant growth), wastewater treatment, surface cleaning, and so on.

A rapid method to quantify casein in fluid milk by front-face fluorescence spectroscopy combined with chemometrics.

Casein in fluid milk determines cheese yield and affects cheese quality. Traditional methods of measuring casein in milk involve lengthy sample preparations with labor-intensive nitrogen-based protein quantifications. The objective of this study was to quantify casein in fluid milk with different casein-to-crude-protein ratios using front-face fluorescence spectroscopy (FFFS) and chemometrics. We constructed calibration samples by mixing microfiltration and ultrafiltration retentate and permeate in different ratios to obtain different casein concentrations and casein-to-crude-protein ratios. We developed partial least squares regression and elastic net regression models for casein prediction in fluid milk using FFFS tryptophan emission spectra and reference casein contents. We used a set of 20 validation samples (including raw, skim, and ultrafiltered milk) to optimize and validate model performance. We externally tested another independent set of 20 test samples (including raw, skim, and ultrafiltered milk) by root mean square error of prediction (RMSEP), residual prediction deviation (RPD), and relative prediction error (RPE). The RMSEP for casein content quantification in raw, skim, and ultrafiltered milk ranged from 0.12 to 0.13%, and the RPD ranged from 3.2 to 3.4. The externally validated error of prediction was comparable to the existing rapid method and showed practical model performance for quality-control purposes. This FFFS-based method can be implemented as a routine quality-control tool in the dairy industry, providing rapid quantification of casein content in fluid milk intended for cheese manufacturing.

The Influence of Sodium Hexametaphosphate Chain Length on the Physicochemical Properties of High-Milk Protein Dispersions.

Protein-protein and protein-mineral interactions can result in defects, such as sedimentation and age gelation, during the storage of high-protein beverages. It is well known that age gelation can be delayed by adding cyclic polyphosphates such as sodium hexametaphosphate (SHMP). This study aims to assess the influence of different phosphate chain lengths of SHMP on the physicochemical properties of high-protein dispersions. The effect of adding different SHMP concentrations at 0%, 0.15%, and 0.25% (w/w) before and after heating of 6%, 8%, and 10% (w/w) milk protein concentrate dispersions was studied. The phosphate chain lengths of SHMPs used in this study were 16.47, 13.31, and 9.88, and they were classified as long-, medium-, and short-chain SHMPs, respectively. Apparent viscosity, particle size, heat coagulation time (HCT), color, and turbidity were evaluated. It was observed that the addition of SHMP (0.15% and 0.25%) increased the apparent viscosity of MPC dispersions. However, the chain length and the concentration of the added SHMP had no significant (p > 0.05) effect on the apparent viscosity after heating the dispersions. The HCT of a dispersion containing 6%, 8%, and 10% protein with no SHMP added was 15.28, 15.61, and 11.35 min, respectively. The addition of SHMP at both levels (0.15% and 0.25%) significantly increased the HCT. Protein dispersions (6%, 8%, and 10%) containing 0.25% short-chain SHMP had the highest HCT at 19.29, 19.61, and 16.09 min, respectively. Therefore, the chain length and concentration of added SHMP significantly affected the HCT of unheated protein dispersion (p < 0.05).

Influence of Bulk Nanobubbles Generated by Acoustic Cavitation on Powder Microstructure and Rehydration Characteristics of Spray-Dried Milk Protein Concentrate Powders.

Bulk nanobubbles (BNBs) have widespread applications in various fields of science due to numerous peculiar characteristics. Despite significant applications, only limited investigations are available on the application of BNBs in food processing. In the present study, a continuous acoustic cavitation technique was used to generate bulk nanobubbles (BNBs). The aim of this study was to evaluate the influence of BNB incorporation on the processability and spray drying of milk protein concentrate (MPC) dispersions. MPC powders were reconstituted to the desired total solids and incorporated with BNBs using acoustic cavitation as per the experimental design. The control MPC (C-MPC) and BNB-incorporated MPC (BNB-MPC) dispersions were analyzed for rheological, functional, and microstructural properties. The viscosity significantly decreased (p < 0.05) at all the amplitudes studied. The microscopic observations of BNB-MPC dispersions showed less aggregated microstructures and greater structural differences compared with C-MPC dispersions, therefore lowering the viscosity. The viscosity of BNB incorporated (90% amplitude) MPC dispersions at 19% total solids at a shear rate of 100 s-1 significantly decreased to 15.43 mPa·s (C-MPC: 201 mPa·s), a net decrease in viscosity by ~90% with the BNB treatment. The control and BNB incorporated MPC dispersions were spray-dried, and the resultant powders were characterized in terms of powder microstructure and rehydration characteristics. Focused beam reflectance measurement of the BNB-MPC powders indicated higher counts of fine particles (<10 µm) during dissolution, signifying that BNB-MPC powders exhibited better rehydration properties than the C-MPC powders. The enhanced powder rehydration with the BNB incorporation was attributed to the powder microstructure. Overall, reducing the viscosity of feed by BNB incorporation can enhance the performance of the evaporator. This study, therefore, recommends the possibility of using BNB treatment for more efficient drying while improving the functional properties of the resultant MPC powders.

Characterization of a Commercial Whey Protein Hydrolysate and Its Use as a Binding Agent in the Whey Protein Isolate Agglomeration Process.

The first objective of this study was to characterize the chemical properties of three lots of whey protein hydrolysate (WPH) obtained from a commercial manufacturer. The degree of hydrolysis (DH) of WPH was between 13.82 and 15.35%, and was not significantly (p > 0.05) different between the batches. From MALDI-TOF, 10 to 13 different peptides were observed in the range of 2.5−5 kDa and 5−8 kDa, respectively. The second objective of the study was to evaluate the effectiveness of WPH as a binder in whey protein isolate (WPI) wet agglomeration. For this purpose, a 3 × 3 × 2 factorial design was conducted with pre-wet mass (60, 100, and 140 g), WPH concentration (15, 20, and 25%), and flow rate (4.0 and 5.6 mL·min−1) as independent variables. WPI agglomeration was carried out in a top-spray fluid bed granulator (Midi-Glatt, Binzen, Germany). Agglomerated WPI samples were stored at 25 °C and analyzed for moisture content (MC), water activity, relative dissolution index (RDI), and emulsifying capacity. Pre-wet mass, flow rate, and the WPH concentration had a significant (p < 0.05) effect on the MC. Moreover, all interactions among the main effects had also a significant (p < 0.05) effect on MC. High MC and water activity were observed for the treatments with a higher pre-wet volume and higher flow rate, which also resulted in clumping of the powders. The treatment with the 60 g pre-wet mass, 20% WPH concentration, and 5.6 mL·min−1 flow rate combination had the highest RDI among all the samples. In conclusion, WPH can be used as a potential alternative to soy lecithin in WPI wet agglomeration.

Application of Micro- and Nano-Bubbles as a Tool to Improve the Rheological and Microstructural Properties of Formulated Greek-Style Yogurts.

The objective of this study was to develop an alternative novel process technology for enhancing the rheological and functional properties of Greek-style yogurt (GSY). The GSY was formulated and prepared in the lab using micellar casein concentrate as a source of protein to achieve a protein content of 10% (w/w). The changes in physicochemical, microstructural, rheological, and functional properties of control (C-GSY) and micro- and nano-bubbles-treated GSY (MNB-GSY) were studied and compared before and after storage for 1, 2, 3, and 4 weeks. Before storage, the apparent viscosity at 100 s-1 (η100) was 1.09 Pa·s for C-GSY and 0.71 Pa·s for MNB-GSY. Incorporation of MNBs into GSY significantly (p < 0.05) decreased the η100 by 30% on 1 week of storage. Additionally, the η100 of MNB-GSY was lesser than C-GSY on week 2, 3, and 4 of storage. Notable microstructural changes and significant rheological differences were observed between the C-GSY and MNB-GSY samples. Differences were also noticed in syneresis, which was lower for the MNB-GSY compared with the control. Overall, the incorporation of MNBs into GSY showed considerable improvements in rheological and functional properties. Additionally, it's a simple, cost-effective process to implement in existing GSY production plants.

Dietary Zinc-Amino Acid Complex Does Not Affect Markers of Mammary Epithelial Integrity or Heat Stability of Milk in Mid-Lactating Cows.

Supplying dietary zinc in excess of traditional requirements has clear impacts on the gut epithelium, but little research has explored whether similar impacts on the mammary epithelium may occur. Our objective was to determine the effects of supplemental Zn sources, in excess of minimal requirements, on markers of mammary epithelial integrity in blood and in milk as well as the heat stability of milk in mid-lactation cows. Twelve multiparous Holstein cows (132 ± 21 days in milk and 51 ± 3 kg/day milk) were blocked according to milk yield and enrolled in a replicated 3 × 3 Latin square experiment. Experimental periods were 21 days, with 17 days allowed for diet adaptation and 4 days for sampling. Treatment sequences were randomly assigned to animals and treatments were as follows: (1) 0.97 g Zn/day provided as ZnSO4 (34.5 mg supplemental Zn/kg diet DM; 30-ZS), (2) 1.64 g Zn/day provided as ZnSO4 (56.5 mg supplemental Zn/kg diet DM; 60-ZS), and (3) 0.55 g Zn/day provided as ZnSO4 plus 1.13 g Zn/day provided as a zinc-methionine complex (58.2 mg supplemental Zn/kg diet DM; 60-ZM). Treatments were administered once daily as an oral bolus containing all supplemental trace minerals. Rumen-bypass methionine was also included in the 30-ZS and 60-ZS boluses to provide metabolizable methionine equivalent to that provided in 60-ZM rations. Milk samples were assessed for electrolytes, somatic cell transcript abundance of genes related to zinc metabolism, and heat coagulation time. Whole blood samples were analyzed for Na and K concentrations, and plasma samples were analyzed for lactose concentration. Cows fed 60-ZS or 60-ZM had greater zinc intake compared to 30-ZS. Dry matter intake and milk fat content tended to be greater in 60-ZS and 60-ZM cows compared to 30-ZS. Somatic cell linear score was similar among treatments. Treatments neither affected markers of mammary epithelial integrity in blood nor in milk of cows, including plasma concentration of lactose, milk concentrations of Na+ and K+, and SLC30A2 and CLU transcript abundance. Treatments had no effect on milk N fractions or heat coagulation time. This study provided no evidence that supplemental Zn above the established requirements can improve blood-milk epithelial barrier or heat stability of milk in healthy mid-lactation dairy cows.