Hydrophobic interaction driving the binding of soybean protein isolate and chlorophyll: Improvements to the thermal stability of chlorophyll

True-solution-scale utilization of natural chlorophyll a in aqueous media through cooperative aggregation with phycocyanin

The challenge of applying chlorophyll(Chl) in aqueous media has been a significant obstacle to the diversified development of Chl a-related industries. This study presents the first report on the true-solution-scale utilization of Chl in aqueous media through the construction of chlorophyll a-phycocyanin (Chls-PC) composite nanoparticles. This study determined the optimal conditions for Chls-PC preparation: a composite ratio of 1:25, a solvent ratio of 1:4, and a stirring time of 1 h. Fluorescence spectroscopy, transmission electron microscope, and confocal microscopy confirmed Chl a and PC aggregation. Surface hydrophobicity and contact angle measurements showed that Chls-PC water solubility was similar to PC and much higher than Chl. Infrared spectroscopy, quantum chemical calculations, X-ray photoelectron spectroscopy, and molecular dynamics simulations elucidated the water solubilization mechanism of Chls-PC both experimentally and theoretically. This research provides theoretical guidance for the development and production of water-based products using Chl as a raw material.

Deciphering the inhibitory mechanisms of betanin and phyllocactin from Hylocereus polyrhizus peel on protein glycation, with insights into their application in bread

Protein glycation closely intertwines with the pathogenesis of various diseases, sparking a growing interest in exploring natural antiglycation agents. Herein, high-purity betacyanins (betanin and phyllocactin) derived from Hylocereus polyrhizus peel were studied for their antiglycation potential using an in vitro bovine serum albumin (BSA)-glucose model. Notably, betacyanins outperformed aminoguanidine, a recognized antiglycation agent, in inhibiting glycation product formation across different stages, especially advanced glycation end-products (AGEs). Interestingly, phyllocactin displayed stronger antiglycation activity than betanin. Subsequent mechanistic studies employing molecular docking analysis and fluorescence quenching assay unveiled that betacyanins interact with BSA endothermically and spontaneously, with hydrophobic forces playing a dominant role. Remarkably, phyllocactin demonstrated higher binding affinity and stability to BSA than betanin. Furthermore, the incorporation of betacyanins into bread dose-dependently suppressed AGEs formation during baking and shows promise for inhibiting in vivo glycation process post-consumption. Overall, this study highlights the substantial potential of betacyanins as natural antiglycation agents.

Enhancing vitamin D3 bioaccessibility: Unveiling hydrophobic interactions in soybean protein isolate and vitamin D3 binding via an infant in vitro digestion model

In the domain of infant nutrition, optimizing the absorption of crucial nutrients such as vitamin D3 (VD3) is paramount. This study harnessed dynamic-high-pressure microfluidization (DHPM) on soybean protein isolate (SPI) to engineer SPI-VD3 nanoparticles for fortifying yogurt. Characterized by notable binding affinity (Ka = 0.166 × 105 L·mol-1) at 80 MPa and significant surface hydrophobicity (H0 = 3494), these nanoparticles demonstrated promising attributes through molecular simulations. During simulated infant digestion, the 80 MPa DHPM-treated nanoparticles showcased an impressive 74.4% VD3 bioaccessibility, delineating the pivotal roles of hydrophobicity, bioaccessibility, and micellization dynamics. Noteworthy was their traversal through the gastrointestinal tract, illuminating bile salts' crucial function in facilitating VD3 re-encapsulation, thereby mitigating crystallization and augmenting absorption. Moreover, DHPM treatment imparted enhancements in nanoparticle integrity and hydrophobic properties, consequently amplifying VD3 bioavailability. This investigation underscores the potential of SPI-VD3 nanoparticles in bolstering VD3 absorption, thereby furnishing invaluable insights for tailored infant nutrition formulations.

Natural chlorophyll: a review of analysis methods, health benefits, and stabilization strategies

Chlorophyll (Chl) is a natural pigment, widely distributed ranging from photosynthetic prokaryotes to higher plants, with an annual yield of up to 1.2 billion tons worldwide. Five types of Chls are observed in nature, that can be distinguished and identified using spectroscopy and mass spectrometry. Chl is also used in the food industry owing to its bioactivities, including obesity prevention, inflammation reduction, viral infection inhibition, anticancer effects, anti-oxidation, and immunostimulatory properties. It has great potential of being applied as a colorant and dietary supplement in the food industry. However, Chl is unstable under various enzymatic, acidic, heat, and light conditions, which limit its application. Although some strategies, such as aggregation with other food components, microencapsulation, and metal cation replacement, have been proposed to overcome these limitations, they are still not enough to facilitate its widespread application. Therefore, stabilization strategies and bioactivities of Chl need to be expected to expand its application in various fields, thereby aiding in the sustainable development of mankind.

Bovine serum albumin-liposome stabilized high oil-phase emulsion: Effect of liposome ratio on interface properties and stability

This study aimed to solve the issue of poor lipophilicity of natural bovine serum albumin (BSA) by combining with liposomes (Lips) to stabilize high oil-phase emulsions (HOPEs). The interaction between BSA and Lips was mainly driven by hydrophobic forces, followed by hydrogen bonding. The secondary structure and tertiary structure of BSA were characterized and indicated that the addition of Lips promoted the structural expansion of BSA exposing the hydrophobic groups inside. Interfacial adsorption behaviours were assessed through dynamic interfacial tension, three-phase contact angle, and quartz crystal microbalance with dissipation. These results indicated that BSA-Lips crosslinking improved wettability, promoting adsorption and rearrangement at the oil-water interface, thereby resulting in a dense interfacial layer. The emulsifying efficacy of BSA-stabilized HOPEs also displayed a distinct Lips dependency. Varying the BSA-to-Lips ratio transformed their consistency from flowing to semi-solid, reinforcing the gel network. Under optimal conditions (BSA: Lips = 1:1), the droplet size of BSA-Lips stabilized HOPEs reached a minimum with a highly uniform distribution. Moreover, a 1:1 BSA to Lips ensured outstanding storage, thermal, and centrifugal stability for the HOPEs. This work provides valuable references for the interaction between protein and Lips, guiding the development of highly stable HOPEs stabilizers.

Chlorophyl-Passivated Ytterbium-Doped Perovskite Quantum-Cutting Film for High-Performance Solar Energy Conversion and Near-Infrared Light-Emitting Diode Applications

The quantum cutting ytterbium (Yb3+)-doped CsPbX3 (X = Cl, Cl, or Br) nanocrystals, exhibiting photoluminescence quantum yields (PLQYs) exceeding 100%, hold significant promise for applications in solar energy conversion technologies and near-infrared (NIR) light-emitting diodes (LEDs). This work investigates the usage of chlorophyll (CHL), a naturally existing organic pigment, as an efficient molecular passivator to improve the performance of quantum cutting films. With the assistance of CHL, the resultant perovskite film displays an increased PLQY of 176%. The commercial silicon solar cells (SSCs) with CHL-treated perovskite films demonstrate a remarkable photon-to-current conversion efficiency improvement of 1.83% for a 330.15 cm2 area SSC device. Additionally, a CHL-modified Yb3+:CsPbCl3 film was used to create 988 nm NIR LEDs with an external quantum efficiency of 3.2%. This work provides a new, eco-friendly approach for producing high-quality, large-area Yb3+-doped perovskite film for deployment in photoelectric and night vision applications.

Non-covalent interaction between hemp seed globulin and two hemp seed phenolic compounds: Mechanism and effects on protein structure, bioactivity, and in vitro simulated digestion

This study focused on elucidating the non-covalent interactions between hemp seed globulin (GLB) and two hemp seed phenolic compounds, Cannabisin A (CA) and Cannabisin B (CB), and to explore these interactions on the protein's structure, conformation, and functionality. Fluorescence quenching and thermodynamic analysis revealed that static quenching governed non-covalent interaction processes, with hydrogen bonds and van der Waals forces functioning as major forces. This was further substantiated by molecular docking studies. The binding affinity order was CA > CB, indicating that the specific phenolic compound had a notable impact on the binding affinity. Furthermore, when complexed with CA, Tyr and Trp residues were exposed to a more hydrophilic environment than when complexed with CB. It was noted that the complexation with either CA or CB consistently affects GLB's secondary structure, particle size, and ζ-potential. GLB treated with the phenolic compounds exhibited enhanced ABTS and DPPH scavenging activities and improved digestibility compared to untreated GLB. Furthermore, the non-covalent interactions significantly increased CA's water solubility, highlighting GLB as a promising natural carrier for hydrophobic bioactive components. These findings hold potential implications for enhancing hemp seed protein applications within the food industry by positively influencing its functional properties and bioactivity.

Phenolic structure dependent interaction onto modified goose liver protein enhanced by pH shifting: Modulations on protein interfacial and emulsifying properties

The appropriateness of animal by-product proteins as emulsifiers is barely explored compared to their meat counterparts. This paper focused on improving interfacial and emulsifying properties of modified goose liver protein using three structurally relevant polyphenols either enhanced by pH shifting (P-catechin, P-quercetin and P-rutin) or not (catechin, quercetin and rutin). Due to its high hydrophobicity and limited steric hindrance, quercetin was more sufficient to hydrophobically interact (ΔH > 0, ΔS > 0) with MGLP than catechin and rutin. Results showed that polyphenol interactive affinity was positively correlated to surface hydrophobicity but negatively to size and aggregation extent of MGLP. Interfacial pressure and dilatational elastic modulus implied that synergistic polyphenol interaction and pH shifting favored the interfacial adsorption and macromolecular association of MGLP, particularly for P-quercetin with the values reached to 19.9 ± 2.0 mN/m and 22.9 ± 1.2 mN/m, respectively. Emulsion stabilized by P-quercetin also maintained highest physical and oxidative stabilities regarding the lowest D [4,3] (3.78 ± 0.27 μm) and creaming index (8.38 ± 0.43 %), together with highest mono- (19.51 %) and polyunsaturated fatty acid content (29.39 %) during storage. Overall, chemical structure of polyphenols may be determining in fabricating MGLP-polyphenol complexes with improved emulsion stabilization efficiency.

Mechanism of Enhancing Chlorophyll Photostability through Light-Induced Chlorophyll/Phycocyanin Aggregation

Chlorophyll (Chl) is the most abundant pigment in photosynthetic plants, but it is prone to degradation during processing and storage, limiting its usage in the food industry. This study developed a technique for increasing Chl photostability by light-induced Chl/phycocyanin (PC) triple synergistic aggregation. Under continuous illumination settings, the results revealed that the Chl retention increased to 406% compared to the control. A model of Chl/PC complexes was constructed using multiligand molecular docking, and the aggregation mechanism was investigated by quantum chemistry, which demonstrated that PC could provide an ideal central hydrophobic cavity for Chl aggregates and thus further enhance the aggregation of Chl on the basis of Chl/PC complexes. The core driver of the improved photostability of Chl is photoexcitation-induced Chl aggregates. This study enriches our understanding of the interaction mechanism between PC and Chl, and we hope that this study can provide broader ideas for the development of natural pigment products.

More simple, efficient and accurate food research promoted by intermolecular interaction approaches: A review

The investigation of intermolecular interactions has become increasingly important in many studies, mainly by combining different analytical approaches to reveal the molecular mechanisms behind specific experimental phenomena. From spectroscopic analysis to sophisticated molecular simulation techniques like molecular docking, molecular dynamics (MD) simulation, and quantum chemical calculations (QCC), the mechanisms of intermolecular interactions are gradually being characterized more clearly and accurately, leading to revolutionary advances. This article aims to review the progression in the main techniques involving intermolecular interactions in food research and the corresponding experimental results. Finally, we discuss the significant impact that cutting-edge molecular simulation technologies may have on the future of conducting deeper exploration. Applications of molecular simulation technology may revolutionize the food research, making it possible to design new future foods with precise nutrition and desired properties.

Inhibitory effects of chlorophylls and its derivative on starch digestion in vitro

Chlorophylls (Chls) have been shown to help regulate blood glucose levels. In this study, the effects of Chls and its derivative, pheophytin a (Phe a), on starch digestion in vitro were investigated. Chls significantly decreased starch hydrolysis while increasing resistant starch content (p < 0.05). SEM revealed that Chls either existed in free form or was absorbed and embedded on the surface of starch granules. Spectroscopic analysis and molecular docking demonstrated that Chls had a dual effect: (1) the phytol chain of Chls formed a double helix structure with starch, which may hinder the starch-enzyme contacts; and (2) the porphyrin ring of Chls interacted with amino acid residues of α-amylase and α-glucosidase to change the characteristics of enzymes, thereby inhibiting their activities. The investigation may serve as motivation for developing healthful starchy foods rich in Chls and enhancing the selection of foods for diabetics and hyperglycemias.

Influence of hemin on structure and emulsifying properties of soybean protein isolate

Hemin has potential application value in plant-based meat analogues. However, mechanisms of interaction between hemin and plant protein are unclear. In this study, soy protein isolate (SPI) was applied to examine these interactions using multi-spectroscopic and molecular docking techniques. Additionally, the influence of hemin on emulsification of SPI was also explored. Fluorescence and UV-Vis spectra showed quenching of SPI by hemin was static, resulting in conformation changes on the surface amino acid residues, around which hydrophobicity was significantly reduced from 425.9 ± 16.2 to 108.9 ± 1.8 (p < 0.05). FTIR and CD spectra results suggested the protein secondary structure altered, and the content of α-helix and random coils increased by 1.13% and 1.43%, respectively. Furthermore, emulsifying properties of SPI were strengthened with increased hemin. This work improves our understanding of interactions between SPI and hemin and offer a theoretical basis for application of heme in plant-based meat analogues.

Fabrication of a novel antioxidant emulsifier through tuning the molecular interaction between soy protein isolates and young apple polyphenols

Soy protein isolates (SPI) exhibit weaker emulsifying properties than those of animal proteins, thereby limiting their wide applicability. In this study, a novel plant-based antioxidant emulsifier was developed using SPI and young apple polyphenols (YAP), and its underlying interaction mechanisms were discovered using multispectral technology and molecular docking. YAP physically bound to SPI through hydrogen bonds and hydrophobic interactions, which significantly enhanced the free radicals scavenging, reducing, and metal ion chelating abilities of SPI by introducing free hydroxyl groups. Moreover, SPI modified by YAP exerted better emulsifying performance owing to a looser protein structure, reflected by a higher random coil and a lower α-helix content. In addition, YAP may bridge adjacent SPI molecules, promoting the adsorption and anchoring of SPI at the oil-water interface. SPI-YAP complexes are promising antioxidant emulsifiers that can be used to nano-deliver functional oils and nutrients, thereby broadening SPI and YAP applications in the food industry.

A Comparative Study of Binding Interactions between Proteins and Flavonoids in Angelica Keiskei: Stability, α-Glucosidase Inhibition and Interaction Mechanisms

Flavonoids are easily destroyed and their activity lost during gastrointestinal digestion. Protein-based nanocomplexes, a delivery system that promotes nutrient stability and bioactivity, have received increasing attention in recent years. This study investigated the stability, inhibitory activity against α-glucosidase and interaction mechanisms of protein-based nanocomplexes combining whey protein isolate (WPI), soybean protein isolate (SPI) and bovine serum albumin (BSA) with flavonoids (F) from A. keiskei using spectrophotometry, fluorescence spectra and molecular docking approaches. The results show that the flavonoid content of WPI-F (23.17 ± 0.86 mg/g) was higher than those of SPI-F (19.41 ± 0.56 mg/g) and BSA-F (20.15 ± 0.62 mg/g) after simulated digestion in vitro. Furthermore, the inhibition rate of WPI-F (23.63 ± 0.02%) against α-glucosidase was also better than those of SPI-F (18.56 ± 0.02%) and BSA-F (21.62 ± 0.02%). The inhibition rate of WPI-F increased to nearly double that of F alone (12.43 ± 0.02%) (p < 0.05). Molecular docking results indicated that the protein-flavonoids (P-F) binding occurs primarily through hydrophobic forces, hydrogen bonds and ionic bonds. Thermodynamic analysis (ΔH > 0, ΔS > 0) indicated that the P-F interactions are predominantly hydrophobic forces. In addition, the absolute value of ΔG for WPI-F is greater (−30.22 ± 2.69 kJ mol−1), indicating that WPI-F releases more heat energy when synthesized and is more conducive to combination. This paper serves as a valuable reference for the stability and bioactivity of flavonoids from A. keiskei.

Fabrication, Characterization, and Emulsifying Properties of Complex Based on Pea Protein Isolate / Pectin for the Encapsulation of Pterostilbene

In this study, pectin (PEC) and pea protein isolate(PPI) was successfully used to create complexes as a novel delivery system for pterostilbene (PT). When the mass ratio of PEC to PPI was 0.5, the particle size and ζ-potential of PPI-PEC-PT were 119.41 ± 5.68 nm and -23.26 ± 0.61 mV, respectively, and the encapsulation efficiency (EE) of PT was 90.92 ± 2.08%. The photochemical stability of PT was enhanced after encapsulation. The results of the molecular docking and multispectral analysis demonstrated that the PPI and PT binding was spontaneous and mostly fueled by hydrophobic interactions. The hydrophobicity of PPI was significantly decreased and the emulsification activity and emulsion stability were significantly improved after production with PEC and PT. The best emulsification impact was demonstrated by the PPI-PEC-PT complex. PPI-PEC is an effective PT delivery material, and the PPI-PEC-PT complex is a new functional emulsification material with significant potential in liquid and semi-liquid food and health products.

Spray-dried and freeze-dried protein-spinach particles; effect of drying technique and protein type on the bioaccessibility of carotenoids, chlorophylls, and phenolics

The effects of protein carrier and drying technique on the concentration and bioaccessibility of lipophilic compounds (lutein, β-carotene, chlorophylls a and b) and hydrophilic flavonoids in freeze-dried (FD) or spray-dried (SD) spinach juice and protein-spinach particles were investigated. Carotenoid and chlorophyll contents were highest in FD spinach juice without protein (147 and 1355 mg/100 g, respectively). For both SD and FD protein-spinach particles, SPI best protected carotenoids and chlorophylls (123 and 1160 mg/g, respectively), although the bioaccessibility of lipophilic compounds in WPI particles was higher than SPI particles (p < 0.05). For flavonoids, the drying technique was more important than the type of carrier, since FD particles had higher total flavonoids than SD. However, SD particles had higher bioaccessibility for most flavonoids (40-90 %) compared to FD (<20 %). The drying method and protein carrier can be designed to produce protein-spinach ingredients with desired concentration of compounds and bioaccessibility.

Study on the binding behavior and functional properties of soybean protein isolate and β-carotene

This study focused on the non-covalent interaction between soybean protein isolate (SPI) and β-carotene (BC). The conformational changes of SPI with β-carotene in varying proportions (BC/SPI: 2%, 4%, 6%, 8%, and 10%) were investigated by multi-spectroscopy and molecular docking. Results showed that the quenching mode is static quenching and binding affinity increased with temperature. The stoichiometry was 1:1, indicating there was only one binding site in SPI. The binding was based on entropy and primarily driven by hydrophobic interactions and its binding constant was in the order of 104 L⋅mol–1. The addition of the β-carotene affected the secondary structure of SPI resulting in an increase in α-Helix and a decrease in random coil and β-turn content, indicating protein aggregated and hydrophobic interactions occurred. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) verified that no new larger molecular weight substance was formed and no covalent interaction existed. Molecular docking corroborated that electrostatic and hydrophobic interactions were both involved in the formation of complexes, where hydrophobic interaction was the dominant one. Moreover, β-carotene improved 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, foaming capacity, and emulsifying stability of SPI. These findings provide useful information about the interaction mechanism of SPI and β-carotene, which contributes to the further development and application of SPI products rich in β-carotene in the food industry.

Dual aggregation in ground state and ground-excited state induced by high concentrations contributes to chlorophyll stability

Chlorophyll (Chl) has great application potential in food colouring and nutritional supplementation. Since Chl is easily degraded, stability protection is vital to its application. Herein, a dual aggregation mechanism induced by high concentrations to improve Chl stability was proposed. As a result, the Chl retention at high concentrations increased to 323.92% of that at low concentrations. To explain aggregation, the Chl dimer was observed by atomic force microscopy, and a stable structural model of the Chl a "sandwich" dimer was established. It was proven that Chl dimer stability was dominated by van der Waals (vdW) interactions, while monomer orientation during aggregation was dominated by electrostatic interactions. Charge transfer (CT) was also shown to be a key interaction in the dimer. Excitation at 393 nm was first proposed for CT identification. This research hopes to provide new ideas for the design of food ingredients in human health promotion.

The Effect of Glycosylated Soy Protein Isolate on the Stability of Lutein and Their Interaction Characteristics

Lutein is a natural fat-soluble carotenoid with various physiological functions. However, its poor water solubility and stability restrict its application in functional foods. The present study sought to analyze the stability and interaction mechanism of the complex glycosylated soy protein isolate (SPI) prepared using SPI and inulin-type fructans and lutein. The results showed that glycosylation reduced the fluorescence intensity and surface hydrophobicity of SPI but improved the emulsification process and solubility. Fluorescence intensity and ultraviolet–visible (UV–Vis) absorption spectroscopy results showed that the fluorescence quenching of the glycosylated soybean protein isolate by lutein was static. Through thermodynamic parameter analysis, it was found that lutein and glycosylated SPI were bound spontaneously through hydrophobic interaction, and the binding stoichiometry was 1:1. The X-ray diffraction analysis results showed that lutein existed in the glycosylated soybean protein isolate in an amorphous form. The Fourier transform infrared spectroscopy analysis results revealed that lutein had no effect on the secondary structure of glycosylated soy protein isolate. Meanwhile, the combination of lutein and glycosylated SPI improved the water solubility of lutein and the stability of light and heat.

Efficient Green Light Acclimation of the Green Algae Picochlorum sp. Triggering Geranylgeranylated Chlorophylls

In analogy to higher plants, eukaryotic microalgae are thought to be incapable of utilizing green light for growth, due to the “green gap” in the absorbance profiles of their photosynthetic pigments. This study demonstrates, that the marine chlorophyte Picochlorum sp. is able to grow efficiently under green light emitting diode (LED) illumination. Picochlorum sp. growth and pigment profiles under blue, red, green and white LED illumination (light intensity: 50–200 μmol m⁻² s⁻¹) in bottom-lightened shake flask cultures were evaluated. Green light-treated cultures showed a prolonged initial growth lag phase of one to 2 days, which was subsequently compensated to obtain comparable biomass yields to red and white light controls (approx. 0.8 g_DW L⁻¹). Interestingly, growth and final biomass yields of the green light-treated sample were higher than under blue light with equivalent illumination energies. Further, pigment analysis indicated, that during green light illumination, Picochlorum sp. formed unknown pigments (X1-X4). Pigment concentrations increased with illumination intensity and were most abundant during the exponential growth phase. Mass spectrometry and nuclear magnetic resonance data indicated, that pigments X1-X2 and X3-X4 are derivatives of chlorophyll b and a, which harbor C=C bonds in the phytol side chain similar to geranylgeranylated chlorophylls. Thus, for the first time, the natural accumulation of large pools (approx. 12 mg g_DW⁻¹) of chlorophyll intermediates with incomplete hydrogenation of their phytyl chains is demonstrated for algae under monochromatic green light (Peak λ 510 nm, full width at half maximum 91 nm). The ability to utilize green light offers competitive advantages for enhancing biomass production, particularly under conditions of dense cultures, long light pathways and high light intensity. Green light acclimation for an eukaryotic microalgae in conjunction with the formation of new aberrant geranylgeranylated chlorophylls and high efficiency of growth rates are novel for eukaryotic microalgae. Illumination with green light could enhance productivity in industrial processes and trigger the formation of new metabolites–thus, underlying mechanisms require further investigation.

Effect of Soybean Protein Isolate-7s on Delphinidin-3-O-Glucoside from Purple Corn Stability and Their Interactional Characterization

Anthocyanins are abundant in purple corn and beneficial to human health. Soybean protein isolate-7s (SPI-7s) could enhance the stability of anthocyanins. The stable system of soybean protein isolate-7s and delphinidin-3-O-glucoside complex (SPI-7s-D3G) was optimized using the Box–Behnken design at pH 2.8 and pH 6.8. Under the condition of pH 2.8, SPI-7s effectively improved the sunlight-thermal stabilities of delphinidin-3-O-glucoside (D3G). The thermal degradation of D3G conformed to the first order kinetics within 100 min, the negative enthalpy value and positive entropy value indicated that interaction was caused by electrostatic interaction, and the negative Gibbs free energy value reflected a spontaneous interaction between SPI-7s and D3G. The interaction of SPI-7s-D3G was evaluated by ultraviolet visible spectroscopy, circular dichroism spectroscopy and fluorescence spectroscopy. The results showed that the maximum absorption peak was redshifted with increasing the α-helix content and decreasing the β-sheet contents, and D3G quenched the intrinsic fluorescence of SPI-7s by static quenching. There was one binding site in the SPI-7s and D3G stable system. The secondary structure of SPI-7s had changed and the complex was more stable. The stabilized SPI-7s-D3G will have broad application prospects in functional foods.

Integration of the Metabolomic and Transcriptome Analysis Reveals the Remarkable Compounds of G. bicolor Young and Mature Leaves under Different Iron Nutrient Conditions

Gynura bicolor (Roxb. ex Willd.) DC. (G. bicolor) is a functional vegetable rich in iron (Fe) and widely grown in Asia (e.g., Japan and China). Because most Fe in the soil exists in the form of insoluble oxides or hydroxides, it is difficult for plants to obtain Fe from the soil. A comparative metabolomic and transcriptome study was carried out to investigate the effect of Fe deficiency on metabolite synthesis and gene expression in young and mature leaves of G. bicolor. Fe deficiency caused chlorosis and decreased the chlorophyll content in young leaves. The metabolomic results for young leaves showed that l-glutamate and 4-hydroxybutanoic acid lactone significantly increased and decreased, respectively. The transcriptome results showed that the expression levels of genes involved in ferric reduction oxidase 7 and 14-kDa proline-rich protein DC2.15-like were significantly upregulated and downregulated, respectively. However, Fe deficiency had little effect on mature leaves.

Interactions between puerarin/daidzein and micellar casein

Puerarin (PUE) and daidzein (DAI) are polyphenols with extensive biological activities. In the present study, the interactions between PUE/DAI and micellar casein (MC) were investigated, and the physicochemical properties of their complexes were analyzed. The results of fluorescence spectrum analysis and molecular docking revealed that the main interactions between DAI and MC were hydrophobic forces, while that between PUE and MC was hydrogen bonding. The FTIR and XRD analyses confirmed the formation of complexes between MC and PUE/DAI. After binding to PUE/DAI, the size of MC increased. The weight loss rate of MC decreased after complexing with PUE/DAI, but its morphology was not extensively modified. The DPPH radical scavenging capacities of PUE-MC and DAI-MC complexes were higher than those of free PUE/DAI in both water and ethanol. In vitro release experiments showed that the release rate of PUE/DAI was inhibited by MC under simulated intestinal conditions. PRACTICAL APPLICATIONS: The low water solubility and poor bioavailability of PUE and DAI limit their application. Micellar casein has high affinity for PUE and DAI. After encapsulated by micellar casein, the release rates of PUE and DAI were prolonged during simulated intestinal digestion. The results would provide useful information for improving the solubility and bioavailability of PUE and DAI, and broadening the use of them in the food and pharmaceutical industry.

Synergistic effects and antityrosinase mechanism of four plant polyphenols from Morus and Hulless Barley

Sanggenone C, oxyresveratrol, catechin and l-epicatechin exist in Morus and Hulless Barley as natural polyphenols with antityrosinase activity. Little research on their synergistic and structure-function relationships of them has been reported in recent years. In this paper, the inhibition mechanisms of these four plant polyphenols were investigated by enzyme kinetics, HPLC, fluorescence spectra, and molecular docking methods. The results showed that oxyresveratrol (IC₅₀ = 1.096 ± 0.048 μg/mL), sanggenone C (IC₅₀ = 13.360 ± 1.029 μg/mL), l-epicatechin (IC₅₀ = 55.730 ± 1.762 μg/mL), and catechin (IC₅₀ = 148.500 ± 3.355 μg/mL) exhibited tyrosinase inhibition activity. When sangenone C (14 μg/mL) was mixed with l-epicatechin (56 μg/mL) at 4:1 (40 μL + 10 μL), the highest tyrosinase inhibition was achieved. Molecular docking showed that the number and position of phenolic hydroxyls of polyphenols were the key for tyrosinase inhibition activity. This study provided new ideas for the application of these four plant polyphenols from Hulless Barley and Morus as tyrosinase inhibitors in food preservation.

Prediction and evaluation of the 3D structure of Macadamia integrifolia antimicrobial protein 2 (MiAMP2) and its interaction with palmitoleic acid or oleic acid: An integrated computational approach

This study investigated the physicochemical properties and 3D structure of Macadamia integrifolia antimicrobial protein 2 (MiAMP2) and its interaction with palmitoleic acid (POA) or oleic acid (OA) in macadamia oil. The 3D structure of MiAMP2 was constructed for the first time by ab initio modelling using the TrRosetta server. The results showed that MiAMP2 was highly hydrophilic and had seven disulfide bonds and higher α-helix and β-sheet/turn contents. Molecular simulation showed that the hydrophobic pocket of MiAMP2 created a favourable environment for the binding of POA and OA. Free energy landscape and independent gradient model (IGM) analyses revealed that hydrogen bonds and van der Waals forces were the major driving forces stabilizing complexes formed by MiAMP2 and POA or OA. The present study provides a theoretical basis and new insight for the future development and utilization of macadamia nut protein in the food industry.

pH-Dependent complexation between β-lactoglobulin and lycopene: Multi-spectroscopy, molecular docking and dynamic simulation study

This study aims to investigate the effect of pH levels (pH 7.0 and pH 8.1) on binding ability of β-lactoglobulin (β-LG) with lycopene (LYC) and elucidate interaction mechanisms using multi-spectroscopy and molecular docking study. β-LG at pH 8.1 showed a stronger binding affinity to lycopene than that at pH 7.0 according to binding constant, binding number, energy transfer efficiency, and surface hydrophobicity. Lycopene bound to protein mainly by van der Waals force in the form of static quenching mode and preferred to interact with β-LG at the top of barrel for both pH levels. Molecular dynamic simulation revealed that β-LG/LYC complex at pH 8.1 was more stable than at pH 7.0. β-LG/LYC complexes formed at pH 8.1 showed significantly higher ABTS radical scavenging activity than samples at pH 7.0 (p < 0.05). Data obtained may contribute valuable information for preparing a whey protein-based delivery system for lycopene.

Improving the Thermostability and Activity of Transaminase From Aspergillus terreus by Charge-Charge Interaction

Transaminases that promote the amination of ketones into amines are an emerging class of biocatalysts for preparing a series of drugs and their intermediates. One of the main limitations of (R)-selective amine transaminase from Aspergillus terreus (At-ATA) is its weak thermostability, with a half-life (t _1/2) of only 6.9 min at 40°C. To improve its thermostability, four important residue sites (E133, D224, E253, and E262) located on the surface of At-ATA were identified using the enzyme thermal stability system (ETSS). Subsequently, 13 mutants (E133A, E133H, E133K, E133R, E133Q, D224A, D224H, D224K, D224R, E253A, E253H, E253K, and E262A) were constructed by site-directed mutagenesis according to the principle of turning the residues into opposite charged ones. Among them, three substitutions, E133Q, D224K, and E253A, displayed higher thermal stability than the wild-type enzyme. Molecular dynamics simulations indicated that these three mutations limited the random vibration amplitude in the two α-helix regions of 130-135 and 148-158, thereby increasing the rigidity of the protein. Compared to the wild-type, the best mutant, D224K, showed improved thermostability with a 4.23-fold increase in t _1/2 at 40°C, and 6.08°C increase in T 50 10 . Exploring the three-dimensional structure of D224K at the atomic level, three strong hydrogen bonds were added to form a special "claw structure" of the α-helix 8, and the residues located at 151-156 also stabilized the α-helix 9 by interacting with each other alternately.