Conjoint application of ultrasonication and redox pair mediated free radical method enhances the functional and bioactive properties of camel whey-quercetin conjugates

Impact of quercetin conjugation using alkaline and free radical methods with tandem ultrasonication on the functional properties of camel whey and its hydrolysates

The structural and functional properties of whey-quercetin and whey hydrolysate-quercetin conjugates synthesized using alkaline and free radical-mediated methods (AM and FRM) coupled with sonication were studied. FTIR showed new peaks at 3000-3500 cm-1 (N-H stretching regions) and the 1000-1100 cm-1 region with the conjugates. Conjugation increased the random coils and α-helix content while decreasing the β-sheets and turns. It also increased the particle size and surface hydrophobicity which was significantly (p < 0.05) higher in AM than FRM conjugates. AM conjugates had higher radical scavenging activity but lower quercetin content than FRM conjugates. Overall, the functional properties of whey-quercetin conjugates were better than whey hydrolysate-quercetin conjugates. However, hydrolysate conjugates had significantly higher denaturation temperatures irrespective of the method of production. Sonication improved the radical scavenging activity and quercetin content of FRM conjugates while it decreased both for AM conjugates. This study suggested that whey-quercetin conjugates generally had better quality than whey hydrolysate conjugates and sonication tended to further improve these properties. This study highlights the potential for using camel whey or whey hydrolysate-quercetin conjugates to enhance the functional properties of food products in the food industry.

Structural, physicochemical and digestive properties of non-covalent and covalent complexes of ultrasound treated soybean protein isolate with soybean isoflavone

The non-covalent and covalent complexes of ultrasound treated soybean protein isolate (SPI) and soybean isoflavone (SI) were prepared, and the structure, physicochemical properties and in vitro digestion characteristics of SPI-SI complexes were investigated. Ultrasonic treatment increased the non-covalent and covalent binding degree of SPI with SI, and the 240 W ultrasonic covalent complexes had higher binding efficiency. Appropriate ultrasonic treatment caused more uniform particle size distribution, lower average particle size and higher surface charge, which enhanced the free sulfhydryl groups and surface hydrophobicity, thus improving the stability, solubility and emulsifying properties of complexes. Ultrasonic treatment resulted in more disordered secondary structure, tighter tertiary conformation, higher thermal stability and stronger SPI-SI covalent interactions of complexes. These structural modifications of particles had important effects on the chemical stability and gastrointestinal digestion fate of SI. The ultrasonic covalent complexation had a greater resistance to heat-induced chemical degradation of SI and improved its chemical stability. Furthermore, the 240 W ultrasonic covalent complexes showed lower protein digestibility during digestion, and provided stronger protection for SI, which improved the digestion stability and antioxidant activity. Therefore, appropriate ultrasound promoted SPI-SI interactions to improve the stability and functional properties of complexes, which provided a theoretical basis for the development of new complexes and their applications in functional foods.

Covalent polyphenols-proteins interactions in food processing: formation mechanisms, quantification methods, bioactive effects, and applications

Proteins and polyphenols are abundant in the daily diet of humans and their interactions influence, among other things, the texture, flavor, and bioaccessibility of food. There are two types of interactions between them: non-covalent interactions and covalent interactions, the latter being irreversible and more powerful. In this review, we systematically summarized advances in the investigation of possible mechanism underlying covalent polyphenols-proteins interaction in food processing, effect of different processing methods on covalent interaction, methods for characterizing covalent complexes, and impacts of covalent interactions on protein structure, function and nutritional value, as well as potential bioavailability of polyphenols. In terms of health promotion of the prepared covalent complexes, health effects such as antioxidant, hypoglycemic, regulation of intestinal microbiota and regulation of allergic reactions have been summarized. Also, the possible applications in food industry, especially as foaming agents, emulsifiers and nanomaterials have also been discussed. In order to offer directions for novel research on their interactions in food systems, nutritional value, and health properties in vivo, we considered the present challenges and future perspectives of the topic.

Analysis of non-covalent interaction between β-lactoglobulin and hyaluronic acid under ultrasound-assisted treatment: Conformational structures and interfacial properties

Hyaluronic acid (HA) used as a food ingredient is gaining acceptance and popularity. However, the studies available for the effect of HA concentrations on the properties of β-lactoglobulin (β-LG) were limited. In this study, we investigated that the molecular characterization and functional properties of the complex formed by the non-covalent binding of β-LG and HA, as well as the ultrasound-assisted treatment at acidic pH. The optimal pH and ratio of β-LG/HA were set as 7 and 4:1, respectively. The fluorescence spectroscopy, circular dichroism spectroscopy, and molecular docking results revealed that the addition of HA and ultrasound induced a decrease in random coil and α-helix and an increase in β-sheet contents in β-LG. By the complexation with HA, the thermal stability, freezing stability, and antioxidant properties of β-LG were all improved under ultrasound treatment. The results of the present study can be useful for the modulation of HA based biopolymer complexes and the exploitation as encapsulating or structuring agents in food industry.

Ultrabright Fluorescent Nanorod-Based Immunochromatographic with Low Background for Advancing Detection Performance

Nanomaterials-based immunochromatographic assays (ICAs) are of great significance in point-of-care testing (POCT), yet it remains challenging to explore low background platforms and high chromogenic intensity probes to improve detection performance. Herein, we reported a low interference and high signal-to-noise ratio fluorescent ICA platform based on ultrabright persistent luminescent nanoparticles (PLNPs) Zn2GeO4: Mn, which could produce intense photoluminescence at 254 nm excitation to reduce background interference from ICA substrates and samples. The prepared immunosensor was successfully applied in T-2 toxin detection with a remarkable limit of detection of 0.025 ng/mL, which was 22-fold more sensitive compared with that of traditional gold nanoparticles. Ultimately, a portable 3D-printed detection device equipped with a smartphone analyzing application was fabricated for quantitative readout in POCT, achieving favorable recoveries in practical sample detection. This work provides a creative attempt for ultrabright PLNP-based low background ICA, and it also guarantees its feasibility in practical POCT.

Molecular Mechanisms and Applications of Polyphenol-Protein Complexes with Antioxidant Properties: A Review

Proteins have been extensively studied for their outstanding functional properties, while polyphenols have been shown to possess biological activities such as antioxidant properties. There is increasing clarity about the enhanced functional properties as well as the potential application prospects for the polyphenol-protein complexes with antioxidant properties. It is both a means of protein modification to provide enhanced antioxidant capacity and a way to deliver or protect polyphenols from degradation. This review shows that polyphenol-protein complexes could be formed via non-covalent or covalent interactions. The methods to assess the complex's antioxidant capacity, including scavenging free radicals and preventing lipid peroxidation, are summarized. The combination mode, the type of protein or polyphenol, and the external conditions will be the factors affecting the antioxidant properties of the complexes. There are several food systems that can benefit from the enhanced antioxidant properties of polyphenol-protein complexes, including emulsions, gels, packaging films, and bioactive substance delivery systems. Further validation of the cellular and in vivo safety of the complexes and further expansion of the types and sources of proteins and polyphenols for forming complexes are urgently needed to be addressed. The review will provide effective information for expanding applications of proteins and polyphenols in the food industry.

Ultrasonication significantly enhances grafting efficiency of chitosan-ferulic acid conjugate and improves its film properties under Fenton system

Ultrasonication (US)-assisted Fenton-system (US-Fenton) with different US time was developed for synthesizing chitosan (CS)-ferulic acid (FA) conjugates. The optimal US-Fenton for a suitable time was selected for preparing a film with CS-FA conjugate and its structural, functional, rheological, and physical properties were also investigated. Compared with Fenton-system, US-Fenton enhanced the grafting ratio of the conjugates, which increased firstly and then decreased as US time. The conjugate obtained by US-Fenton for 1 min (FUS1) possessed the highest grafting ratio (121.28 mg FA/g) and its grafting time was also shortened from 12 h to 1 min contrasted with Fenton grafted method. Structural characterization results showed that FA was conjugated on CS via ester and amide bonds with decreased crystallinity. Scanning electron microscopy and molecular weight analysis indicated that the degradation degree of CS-FA conjugates increased with US time. The DPPH and ABTS radical-scavenging activities of FUS1 were the closest to ascorbic acid, and it also showed the best antibacterial effect among the test conjugates. Accordingly, FUS1 was selected to obtain the film for contrasting with CS film. FUS1 film solution exhibited a decreased viscosity. In comparison to CS film, UV transmittance of FUS1 film approached zero, and its moisture, oxygen, and carbon dioxide permeabilities significantly decreased (P < 0.05). Moreover, its water solubility and tensile strength increased by 58.09% and 25.72% than those of CS film, respectively. Therefore, US-Fenton for 1 min could be a promising method for efficiently preparing active food package materials and FUS1 film possessed broad application prospects.

Sonochemical effects on fabrication, characterization and antioxidant activities of β-lactoglobulin-chlorogenic acid conjugates

The β-lactoglobulin-chlorogenic acid (LG-CA) conjugate was explored to be formed through ultrasonication, redox-pair method and their combination, the ultrasonication used a probe ultrasonic machine with a 6 mm probe at 270 W, and the frequency was 20-25 kHz. The formation of the conjugate was confirmed by SDS-PAGE with a larger molecular weight. Besides, Fourier infrared spectroscopy (FTIR) and Circular dichroism (CD) indicated changes in the secondary structure of the LG-CA conjugate. The α-helix and β-sheet contents of LG decreased and the unordered content increased significantly after the formation of covalent complexes. In addition, both the ultrasonic treatment and its combination with redox-pair method could significantly improve the antioxidant properties of LG. The former increased to 23.16 μmol Trolox/g sample, the latter 82-106 μmol Trolox/g sample. Therefore, ultrasonication could be used both individually and in combination with the redox-pair method to produce LG-CA conjugates with stronger antioxidant activities.

New insights into the ultrasound impact on covalent reactions of myofibrillar protein

In this work, two different covalent reactions, namely, alkaline reaction and free radical oxidation, were selected to compare the difference in the strengthening effects of ultrasound treatment (UDT). The grafting effects were verified by protein electrophoresis and bound gallic acid (GA) assay. Furthermore, non-covalent interactions between myofibrillar protein (MPN) aggregates were destroyed by UDT, as proved by the lower particle sizes and higher ζ-potential. Comparatively, the results from tertiary structure index and circular dichroism revealed UDT-assisted free radical oxidation could lead to better conjugates with greater structural properties. The atomic force microscope (AFME) and protein flexibility showed that MPNs appeared to display as irregular spherical particles after alkaline reaction, however, maintained fibrous structure during the free radical oxidation. Consequently, the combination of UDT and free radical oxidation were more effectively for strengthening the influence of acoustic cavitation on MPNs, of which mechanism was the changes in viscosity properties, microstructure and acoustic cavitation radicals.