Air-water interfacial and foaming properties of nanoparticles based on commercial and lab-scale isolated maize (Zea mays L.) zein

Maize zein based nanoparticles (ZNPs) can have applications as food dispersion stabilizers. It has not been documented to what extent the used zein isolation method and conditions thereof impact the structure and functionality of nanoparticles (NPs) based thereupon. Here, zein extracted from maize flour on lab scale (LS-zein) was compared with a commercial zein powder (CS-zein). On a dry matter basis, CS-zein contained 96.5% protein, while LS-zein contained 74.5% protein, 12.7% lipid, 2.9% ash, and a residual fraction, likely starch remnants. SE-HPLC analysis showed that 27.8% of CS-zein protein occurred in an aggregated and insoluble form, while LS-zein mainly contained mono-/dimeric proteins but also approximately 30% hydrophilic peptides. These differences resulted in notably different behavior in the functionality of ZNPs based on CS- and LS-zein (CS-ZNPs and LS-ZNPs, respectively) produced via liquid antisolvent precipitation. CS-ZNPs had poor foaming properties regardless of the pH, in line with their low interfacial dilatational moduli (12.9-15.0 mN/m). The foaming properties of LS-ZNPs were notably better. The high LS-ZNP foam stability (FS) at pH 8.0 and 10.0 was attributed to electrostatic repulsive effects between interfaces of adjacent air bubbles due to the adsorption of peptides and to synergistic protein-lipid interaction effects at the air-water interface. The LS-ZNP FS at pH 4.0 was low despite a high interfacial dilatational modulus (52.6 mN/m). It is hypothesized that intact LS-ZNPs in the liquid thin films between gas bubbles negatively affect FS by a bridging de-wetting effect. Overall, it can be concluded that the (partial) co-isolation of lipids with zein may positively influence foaming properties of NPs based thereupon, while extensive zein purification as applied in industrial zein isolation leads to (partial) zein aggregation and overall low foaming capacity of the obtained CS-ZNPs.

Classification of surfactants and admixtures for producing stable aqueous foam

Surfactants and foam have captured the interest of researchers worldwide due to their unique behavior of surface activity, the dynamic nature of foam formation, and simultaneous destruction. The present review focuses on the surfactants' classification, surfactant-solvent interaction, foam formation, characteristics, and a range of admixtures to enhance the foam performance. Although surfactants have been researched and developed for decades, recently, their sustainability has been given special attention. One such aspect is the development of green foaming agents from natural and renewable sources and assessing their suitability for different applications. Further, widely researched parameters are the type of surfactant, surfactant concentration, surfactant-solvent interaction, and foam production method on the foamability of a surfactant solution and related foam characteristics, including stability and texture. However, still, there is no rule to predict the best foam. Another vital concern is the non-standardization of foam assessment methods across industries and regions. Recently, research has progressed in identifying suitable admixtures for foam performance enhancement and utilizing them to produce stable foams for application in enhanced oil recovery, drug delivery, and manufacturing of aerated food products and foamed concrete. Although foam stabilization using various admixtures has been recognized well in the literature, the underlying mechanism requires further research. The interaction of surfactant and admixtures in solution is complicated and requires more research.

Understanding the effects of ultrasound processng on texture and rheological properties of food

The demand for the production of high quality and safe food products has been ever increasing. Consequently, the industry is looking for novel technologies in food processing operations that are cost-effective, rapid and have a better efficiency over traditional methods. Ultrasound is well-known technology to enhance the rate of heat and mass transfer providing a high end-product quality, at just a fraction of time and energy normally required for conventional methods. The irradiation of foods with ultrasound creates acoustic cavitation that has been used to cause desirable changes in the treated products. The technology is being successfully used in various unit operations such as sterilization, pasteurization, extraction, drying, emulsification, degassing, enhancing oxidation, thawing, freezing and crystallization, brining, pickling, foaming and rehydration, and so forth. However, the high pressure and temperature associated with the cavitation process is expected to induce some changes in the textural and rheological properties of foods which form an important aspect of product quality in terms of consumer acceptability. The present review is aimed to focus on the effects of ultrasound processing on the textural and rheological properties of food products and how these properties are influenced by the process variables.

Adsorption and foaming properties of edible egg yolk peptide nanoparticles: Effect of particle aggregation

The adsorption and foaming properties of an edible colloidal nanoparticle (EYPNs), self-assembled from the food-derived, amphiphilic egg yolk peptides, were investigated, with the aim of evaluating their potential as efficient particulate stabilizers for development of aqueous food foams. The influence of particle aggregation induced by the changes of environmental conditions (mainly the pH) on these properties of EYPN systems was determined. Our results showed that the EYPNs are a highly pH-responsive system, showing the pH-dependent particle aggregation behavior, which is found to strongly affect the interfacial adsorption and macroscopic foaming behaviors of systems. Compared to high pH (6.0–9.0), the EYPNs at low pH (2.0–5.0) showed higher surface activity with a lower equilibrated surface tension as well as a higher packing density of particles and particle aggregates at the interface, probably due to the reduced electrostatic adsorption barrier. Accordingly, the EYPNs at these low pH values exhibited significantly higher foamability and foam stability. The presence of large particle clusters and/or aggregates formed at low pH in the continuous phase may contribute to the foam stability of EYPNs. These results indicate that our edible peptide-based nanoparticle EYPNs can be used as a new class of Pickering-type foam stabilizer for the design of food foams with controlled material properties, which may have sustainable applications in foods, cosmetics, and personal care products.

•

Edible nanoparticle EYPNs are efficient particulate stabilizers for making food foams.

•

EYPNs have a pH-dependent particle aggregation behavior in aqueous solutions.

•

The particle aggregation strongly affects the adsorption and foaming properties.

•

The presence of particle aggregates contributes to the foam stability of EYPNs.

•

The particle aggregates show higher surface activity and interfacial packing density.

Effects of ionic strength on removal of toxic pollutants from aqueous media with multifarious adsorbents: A review

Adsorption is one of the most widely used and effective wastewater treatment methods. The role of ionic strength (IS) in shaping the adsorption performances is much necessary due to the ubiquity of electrolyte ions in water body and industrial effluents. The influences of IS on adsorption are rather complex, because electrolyte ions affect both adsorption kinetics and thermodynamics by changing the basic characteristics of adsorbents and adsorbates. For a given adsorption system, multiple or even contradictory effects of IS may coexist under identical experimental conditions, rendering the dominant mechanism recognition and net effect prediction complicated. We herein reviewed the key advancement on the interaction and mechanisms of IS, including change in number of active sites for adsorbents, ion pair for metal ions, molecular aggregation and salting-out effect for organic compounds, site competition for both inorganic and organic adsorbates, and charge compensation for adsorbent-adsorbate reciprocal interactions. The corresponding fundamental theory was thoroughly described, and the efforts made by various researchers were explicated. The structural optimization of adsorbents affected by IS was detailed, also highlighting polyamine materials with exciting "salt-promotion" effects on heavy metal removal from high salinity wastewater. In addition, the research trends and prospects were briefly discussed.

Effect of high intensity ultrasound on structure and foaming properties of pea protein isolate

The effects of high intensity ultrasound (HIUS, 20 kHz, at varying amplitude 30%, 60%, 90% for 30 min) on structure and foaming properties of pea protein isolate (PPI) were investigated. No significant change was observed from the electrophoresis profiles and circular dichroism (CD) spectrum. Analyses of fluorescence spectroscopy and the amount of free sulfhydryl groups showed that HIUS induced protein molecular partial unfolding. Furthermore, HIUS decreased particle size of PPI and increased exposed hydrophobicity, resulting in a reduction of the surface tension at the air-water interface. Therefore, the foaming ability of PPI increased from 145.6% to 200.0%. The foaming stability increased from 58.0% to 73.3% with the increasing amplitude after 10 min though all reduced to 50.0% with the extension of time. That suggested that HIUS treatment has a potential to be implemented to modify foaming properties of PPI.

Stabilization and functionalization of aqueous foams by Quillaja saponin-coated nanodroplets

We report evidence for stabilization and functionalization of aqueous foams stabilized by Quillaja saponin (QS)-coated nanodroplets. In contrast to foams stabilized by QS, stabilized the foams of QS-coated nanodroplets showed superior foamability, stability and multi-functional characteristics. Specifically, the half-life time of the foam stabilized by nanodroplets was approximately 4 times that of saponin. The microstructure observation indicates the nanodroplets from assembly of saponin around oil droplet were strong attachment at the gas-liquid interface and stabling a large gas-liquid interfacial area in a hierarchical structure. The surface dynamic adsorption and large deformation rheology were performed, revealed that QS nanodroplets were almost irreversibly adsorbed at air-liquid interface and exhibited less surface desorption and high elastic-viscous response to a large mechanical deformation. These nanodroplets stabilized foams presented a large capacity for loading hydrophobic flavors and nutrients (e.g., β-carotene and curcumin), which could be used to create a new class of foam food products with sustained release of flavors and/or health benefit functionality.