Pecan (Carya illinoinensis (Wangenh.) K. Koch) nuts as an emerging source of protein: extraction, physicochemical and functional properties.

BACKGROUND: The increasing demand for sustainable alternatives to traditional protein sources, driven by population growth, underscores the importance of protein in a healthy diet. Pecan (Carya illinoinensis (Wangenh.) K. Koch) nuts are currently underutilized as plant-based proteins but hold great potential in the food industry. However, there is insufficient information available on pecan protein, particularly its protein fractions. This study aimed to explore the physicochemical and functional properties of protein isolate and the main protein fraction glutelin extracted from pecan nuts. RESULTS: The results revealed that glutelin (820.67 ± 69.42 g kg-1) had a higher crude protein content compared to the protein isolate (618.43 ± 27.35 g kg-1), while both proteins exhibited amino acid profiles sufficient for adult requirements. The isoelectric points of protein isolate and glutelin were determined to be pH 4.0 and pH 5.0, respectively. The denaturation temperature of the protein isolate (90.23 °C) was higher than that of glutelin (87.43 °C), indicating a more organized and stable conformation. This is further supported by the fact that the protein isolate had a more stable main secondary structure than glutelin. Both proteins demonstrated improved solubility, emulsifying, and foaming properties at pH levels deviating from their isoelectric points in U-shaped curves. Compared to the protein isolate, glutelin displayed superior water and oil absorption capacity along with enhanced gelling ability. CONCLUSION: The protein isolate and glutelin from pecan nuts exhibited improved stability and competitive functional properties, respectively. The appropriate utilization of these two proteins will support their potential as natural ingredients in various food systems. © 2024 Society of Chemical Industry.

L-Theanine Improves the Gelation of Ginkgo Seed Proteins at Different pH Levels.

L-theanine (L-Th), a non-protein amino acid naturally found in teas and certain plant leaves, has garnered considerable attention due to its health benefits and potential to modify proteins such as ginkgo seed proteins, which have poor gelling properties, thereby expanding their applications in the food industry. The objective of this study was to investigate the impact of varying concentrations of L-Th (0.0%, 0.5%, 1.0%, and 2.0%) on the gelling properties of ginkgo seed protein isolate (GSPI) at various pH levels (5.0, 6.0, and 7.0). The GSPI gels exhibited the highest strength at a pH of 5.0 (132.1 ± 5.6 g), followed by a pH of 6.0 (95.9 ± 3.9 g), while a weak gel was formed at a pH of 7.0 (29.5 ± 0.2 g). The incorporation of L-Th increased the hardness (58.5-231.6%) and springiness (3.0-9.5%) of the GSPI gels at a pH of 7.0 in a concentration-dependent manner. However, L-Th did not enhance the gel strength or water holding capacity at a pH of 5.0. The rheological characteristics of the GSPI sols were found to be closely related to the textural properties of L-Th-incorporated gels. To understand the underlying mechanism of L-Th's effects, the physicochemical properties of the sols were analyzed. Specifically, L-Th promoted GSPI solubilization (up to 7.3%), reduced their hydrophobicity (up to 16.2%), reduced the particle size (up to 40.9%), and increased the ζ potential (up to 21%) of the sols. Overall, our findings suggest that L-Th holds promise as a functional ingredient for improving gel products.

Alkali-Induced Phenolic Acid Oxidation Enhanced Gelation of Ginkgo Seed Protein.

The effect of alkali-induced oxidation of three phenolic acids, namely gallic acid, epigallocatechin gallate, and tannic acid, on the structure and gelation of ginkgo seed protein isolate (GSPI) was investigated. A mixture of 12% (w/v) GSPI and different concentrations of alkali-treated phenolic acids (0, 0.06, 0.24, and 0.48% w/w) were heated at 90 °C, pH 6.0, for 30 min to form composite gels. The phenolic treatment decreased the hydrophobicity of the GSPI sol while enhancing their rheological properties. Despite a reduced protein solubility, water holding capacity, stiffness, and viscoelasticity of the gels were improved by the treatments. Among them, the modification effect of 0.24% (w/v) EGCG was the most prominent. Through the analysis of microstructure and composition, it was found to be due to the covalent addition, disulfide bond formation, etc., between the quinone derivatives of phenolic acids and the side chains of nucleophilic amino acids. Phenolic acid modification of GSPI may be a potential ingredient strategy in its processing.

Biotinylated caffeic acid covalent binding with myofibrillar proteins in alkaline conditions: Identification of protein-phenol adducts and alterations in protein properties.

In this study, the effects of covalent interactions between myofibrillar proteins (MP) and caffeic acid (CA) were investigated. Protein-phenol adducts were identified by biotinylated caffeic acid (BioC) used as a substitution of CA. The total sulfhydryls and free amines content were decreased (p < 0.05). The α-helix structure of MP increased (p < 0.05) and MP gel properties enhanced slightly at low dosages of CA (10 and 50 µM), and both were impaired significantly (p < 0.05) at high dosages of CA (250 and 1250 µM). Two prominent adducts of myosin heavy chain (MHC)-BioC and Actin-BioC were identified by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE), which gradually increased at low concentrations of BioC (10 and 50 µM), and raised significantly at the concentration of 1250 µM. According to the correlation analysis, MHC-BioC and Actin-BioC adducts showed a significant negative correlation with gel properties, such as G', hardness, and water holding capacity (WHC) (p < 0.01), which indicated that the covalent interactions between MP and CA significantly affected the quality of meat products.

Enhanced gelling properties and hydration capacity of ginkgo seed proteins by genipin cross-linking.

The present study investigated the effects of genipin cross-linking on the gelling properties of ginkgo seed protein isolate (GSPI). Cross-linking of GSPI was achieved with different concentrations (0, 0.05, 0.1, 0.2, 0.4, 0.6% w/v) of genipin at pH 6.0. Compared to pure GSPI, genipin treatment led to lower solubility, surface hydrophobicity, and fluorescence intensity, while promoted protein aggregation. Cross-linked GSPI gels exhibited markedly improved gelling properties and water holding capacity (WHC), with up to 2.1-fold increases in gel hardness and 1.3-fold increases in WHC over non-treated GSPI gel. Electrophoresis and Fourier-transform infrared spectroscopy confirmed the cross-linking. Moreover, microstructural examination showed that cross-linking with genipin resulted in protein aggregation and more porous gel matrix. Overall, genipin cross-linking demonstrated great potential for the enhancement of gelling properties of ginkgo seed protein. The current research may expand the utilization of ginkgo seeds in food applications.

Fabrication and characterization of self-assembled whey protein isolate/short linear glucan core-shell nanoparticles for sustained release of curcumin.

The aim of this research was to prepare a bistratal nanocomplex with a high loading capacity (LC) and harsh environment stability for controlled release of curcumin (Cur) in gastrointestinal conditions. Whey protein isolate (WPI)/short linear glucan (SLG) core-shell nanoparticles were fabricated by self-assembly for the delivery of Cur. The results showed that Cur@WPI@SLG nanoparticles had a relatively high LC (12.89 %) and small particle size (89.4 nm). The nanocomplex remained relatively stable in extreme pH conditions (2-4 and 8-10), high temperatures (60-70 °C), and ionic strength (<400 mM). Core-shell nanostructures facilitated the sustained release of Cur in simulated gastrointestinal conditions. In addition, the nanocomplex had little cytotoxicity at high concentrations, yet significantly enhanced the DPPH scavenging activity and reducing power of Cur. This delivery system will significantly improve the sustained release effect of Cur and broaden the application of hydrophobic nutrients in foods.

Physicochemical and Microstructural Characterization of Whey Protein Films Formed with Oxidized Ferulic/Tannic Acids.

Protein-based biodegradable packaging films are of environmental significance. The effect of oxidized ferulic acid (OFA)/tannic acid (OTA) on the crosslinking and film-forming properties of whey protein isolate (WPI) was investigated. Both of the oxidized acids induced protein oxidation and promoted WPI crosslinking through the actions of quinone carbonyl and protein sulfhydryl, and amino groups. OTA enhanced the tensile strength (from 4.5 MPa to max 6.7 MPa) and stiffness (from 215 MPa to max 376 MPa) of the WPI film, whereas OFA significantly increased the elongation at break. The water absorption capability and heat resistance of the films were greatly improved by the addition of OTA. Due to the original color of OTA, the incorporation of OTA significantly reduced light transmittance of the WPI film (λ 200-600 nm) as well as the transparency, whereas no significant changes were induced by the OFA treatment. Higher concentrations of OTA reduced the in vitro digestibility of the WPI film, while the addition of OFA had no significant effect. Overall, these two oxidized polyphenols promoted the crosslinking of WPI and modified the film properties, with OTA showing an overall stronger efficacy than OFA due to more functional groups available.

Ginkgo Seed Proteins: Characteristics, Functional Properties and Bioactivities.

Ginkgo biloba L. is an ancient plant relic, which is known as a "living fossil", and is widely cultivated in China. This plant with medical potential and health benefits has drawn the attention of researchers. Ginkgo seeds are rich in protein. Ginkgo seed proteins (GSPs) have good functional properties over many other seed proteins, which have the potential to be utilized as food ingredients. Moreover, GSP contains no restricted amino acids and is easy to be separated. Several GSP isolate with various bioactivities, such as antimicrobial and antioxidative activities, have been purified and evaluated for their bioactive potential. In this review, the separation methods and bioactivities of GSP were summarized, physicochemical characteristics and functional properties were comprehensively reviewed and compared with other seed proteins. Some food applications of GSP were also briefly introduced. Besides, some suggestions and prospects were discussed in this review.

Modification of structure and functionalities of ginkgo seed proteins by pH-shifting treatment.

Modification and improvement of protein functionalities are important for expanding the applications of proteins in food. The objective of this study was to investigate the effects of pH-shifting treatments on the structural and functional properties of ginkgo seed protein isolate (GSPI). GSPI was exposed to acidic (pH 2.0-4.0) and basic (pH 10.0-12.0) pHs for 0, 0.5, 1, 2, and 4 h and subsequently neutralized for refolding. The pH-shifting treatments significantly increased GSPI solubility by 43-141% except for the treatment at pH 2.0, which decreased protein solubility by 16-39%. All pH-shifting treatments more than doubled the surface hydrophobicity of GSPI and significantly improved the emulsifying activity. The highest emulsifying activity was observed in the pH 2.0-treated GSPI, which was 4.9-fold higher than the control. Acid-induced GSPI degradation likely promoted protein adsorption to the oil-water interface. In summary, the pH-shifting-modified GSPI may serve as a promising emulsifier in various food systems.

Fabrication of pickering high internal phase emulsions stabilized by pecan protein/xanthan gum for enhanced stability and bioaccessibility of quercetin.

The stabilizing effect of pecan protein (PP)/xanthan gum (XG) complex on the Pickering high internal phase emulsion (HIPE) has been examined in this study. Shear viscosity of HIPEs increased with respect to XG concentration due to the formation of hydrogen bonds between PP and XG. Confocal laser scanning microscopy (CLSM) imaging showed fairly even distribution and polygonal shapes of oil droplets (30-70 µm). When used to encapsulate quercetin, this Pickering HIPE exhibited high retention rate and improved gel strength. Furthermore, the interface film of PP/XG on oil-water interface contributed to the high retention of quercetin in Pickering HIPEs when exposure to heat, iron ions, and hydrogen peroxide in aqueous phase. The bioaccessibility of quercetin after in vitro simulated digestion were also improved by HIPE encapsulation than that in oil. To conclude, PP/XG complex stabilized HIPEs may be suitable delivery systems for improving colloidal stability and bioaccessibility of hydrophobic bioactives.

Highly sensitive detection of lipopolysaccharide based on collaborative amplification of dual enzymes.

In this work, a novel electrochemical biosensor is developed for facile and highly sensitive detection of lipopolysaccharide (LPS) based on collaboration of dual enzymes for multiple-stages signal amplification. Through ingenious design, the specific recognition of target LPS is transformed to the exonuclease III (Exo III)-assisted interface DNA cycling collaborated with the terminal deoxynucleotidyl transferase (TdT)-catalyzed DNA extension, finally inducing significant electrochemical signal concerned with the concentration of LPS. This paper mainly discusses the detection principle, optimization of key factors, and the analytical performance of the biosensor. With the efficient signal amplification, the biosensor shows high sensitivity with a good linearity and a low limit of detection of 1 pg mL-1 for LPS. Moreover, the developed biosensor can clearly discriminate LPS from interferents and show high specificity for LPS detection. This biosensor has also been successfully employed to measure LPS in real food samples, suggesting potential opportunity for application in food safety detection.

Liposome co-encapsulation as a strategy for the delivery of curcumin and resveratrol.

Curcumin and resveratrol are natural compounds whose strong antioxidant activities are highly beneficial in the human diet. Unfortunately, their physicochemical properties result in poor stability in their chemical and antioxidant activities, which limits their utilization in food and pharmaceutical applications. In this study, liposomal nanoencapsulation was developed as a strategy to overcome these limitations and improve the antioxidant effects of these compounds. The physicochemical characteristics of co-encapsulated liposomes were evaluated and compared to formulations containing each compound individually. Liposomes co-encapsulating curcumin and resveratrol presented a lower particle size, lower polydispersity index and greater encapsulation efficiency. The formulation of liposomes co-loading curcumin and resveratrol at 5 : 1, exhibited the lowest particle size (77.50 nm), lowest polydispersity index (0.193), highest encapsulation efficiency (reaching 80.42 ± 2.12%), and strongest 2,2-diphenyl-1-picrylhydrazyl scavenging, lipid peroxidation inhibition capacity and reducing power. Additionally, liposomes loading both curcumin and resveratrol displayed a higher ability during preparation, storage, heating and surfactant shock than those loaded with individual polyphenol. Infrared spectroscopic and fluorescence techniques demonstrated that the curcumin mainly located in the hydrophobic acyl-chain region of liposomes, while the resveratrol orientated to the polar head groups. These orientations could have synergistic effects on the stabilization of liposomes. Our findings should guide the rational design of a co-delivery liposomal system regarding the location and orientation of bioactive compounds inside the lipid bilayer.

Physicochemical and functional properties of γ-aminobutyric acid-treated soy proteins.

Gamma-aminobutyric acid (GABA) is a non-protein amino acid with various health benefits. GABA enrichment in soy products such as tempeh, doenjang, and soymilk have been reported. However, no study has explored how GABA interacts with soy proteins and affects their properties. The current study investigated the physicochemical and functional properties of soy proteins in a 4% (w/v) slurry treated with 0.2-1.0% of GABA at 80, 90, and 100 °C. The addition of GABA significantly (P < 0.05) reduced the average particle size and increased the ζ-potential and intrinsic fluorescence intensity of the soy protein slurries. GABA treatment resulted in concentration-dependent increases (P < 0.05) in soy protein solubility, viscosity, rheology, emulsifying and foaming properties. This study, for the first time, investigated the effects of GABA on the properties of soy proteins. The findings would be useful in soy product formulation when GABA is added as a functional ingredient.

Production of recombinant beta-amylase of Bacillus aryabhattai.

In this study, the effects of carbon source, nitrogen source, and metal ions on cell growth and Bacillus aryabhattai ß-amylase production in recombinant Brevibacillus choshinensis were investigated. The optimal medium for ß-amylase production, containing glucose (7.5 g·L-1), pig bone peptone (40.0 g·L-1), Mg2+ (0.05 mol·L-1), and trace metal elements, was determined through single-factor experiments in shake flasks. When cultured in the optimized medium, the ß-amylase yield reached 925.4 U mL-1, which was 7.2-fold higher than that obtained in the initial medium. Besides, a modified feeding strategy was proposed and applied in a 3-L fermentor fed with glucose, which achieved a dry cell weight of 15.4 g L-1. Through this cultivation approached 30 °C with 0 g·L-1 initial glucose concentration, the maximum ß-amylase activity reached 5371.8 U mL-1, which was 41.7-fold higher than that obtained with the initial medium in shake flask.

Sensitive detection of chloramphenicol based on Ag-DNAzyme-mediated signal amplification modulated by DNA/metal ion interaction.

We here report a novel method for antibiotic detection by making use of DNA/metal ion interaction coupled with Ag-DNAzyme cleavage-mediated signal amplification. Taking the analysis of chloramphenicol (CAP) as an example, upon the specific recognition between the antibiotic CAP and its aptamer, the secondary structure of the DNA aptamer shaped by C-Ag+-C base mismatches will be altered, liberating the pre-captured Ag+. Subsequently, the free Ag+ provided as a cofactor can activate the Ag-DNAzyme, which behaves recycled cleavage of substrate DNA on the electrode surface for signal amplification. The more CAP is present, the more Ag+ is released, thus more Ag-DNAzyme can be activated to achieve a higher electrochemical signal. Therefore, the target-responsive variation of electrochemical signal enables the sensitive detection of CAP. The proposed method is cost-effective only with plain metal ion as modulator. It has also been challenged with real food samples, indicating the potential to be a promising tool for food safety detection.

Rheology and microstructure of myofibrillar protein-olive oil composite gels: effect of different non-meat protein as emulsifier.

BACKGROUND: Heat-induced composite gels were prepared with 20 g kg-1 (2%) myofibrillar protein (MP) sol and 100 g kg-1 (10%) olive oil pre-emulsified by MP or non-meat protein in 0.6 mol L-1 NaCl, at pH 6.2. The effect of different non-meat protein (soy protein isolate, egg-white protein isolate and sodium caseinate) pre-emulsions on the rheological properties and microstructure of MP gel was evaluated. RESULTS: Adding emulsion enhanced the gel strength of MP gel except for the soy protein isolate (SPI) as emulsifier group, but all emulsion group markedly improved (P < 0.05) the water-holding capacity and the storage modulus (G') of MP gels. SDS-PAGE show that some non-meat protein bands partially participated in the formation of MP composite gels with different kinds of emulsion added. Micrographs revealed that these emulsions made the gels become denser and more compact with subtle diverse effects. CONCLUSION: Different meat or non-meat proteins as emulsifier have varied impacts on the rheology and microstructure of MP gels, indicating the potential and feasibility of these non-meat proteins as emulsifiers to modify the textural properties in comminuted meat products. © 2017 Society of Chemical Industry.

Identification of Rosmarinic Acid-Adducted Sites in Meat Proteins in a Gel Model under Oxidative Stress by Triple TOF MS/MS.

Triple TOF MS/MS was used to identify adducts between rosmarinic acid (RosA)-derived quinones and meat proteins in a gel model under oxidative stress. Seventy-five RosA-modified peptides responded to 67 proteins with adduction of RosA. RosA conjugated with different amino acids in proteins, and His, Arg, and Lys adducts with RosA were identified for the first time in meat. A total of 8 peptides containing Cys, 14 peptides containing His, 48 peptides containing Arg, 64 peptides containing Lys, and 5 peptides containing N-termini that which participated in adduction reaction with RosA were identified, respectively. Seventy-seven adduction sites were subdivided into all adducted proteins including 2 N-terminal adduction sites, 3 Cys adduction sites, 4 His adduction sites, 29 Arg adduction sites, and 39 Lys adduction sites. Site occupancy analyses showed that approximately 80.597% of the proteins carried a single RosA-modified site, 14.925% retained two sites, 1.492% contained three sites, and the rest 2.985% had four or more sites. Large-scale triple TOF MS/MS mapping of RosA-adducted sites reveals the adduction regulations of quinone and different amino acids as well as the adduction ratios, which clarify phenol-protein adductions and pave the way for industrial meat processing and preservation.

Effect of different packaging films on postharvest quality and selected enzyme activities of Hypsizygus marmoreus mushrooms.

Freshly harvested Hypsizygus marmoreus mushrooms were packaged using different packaging films, and physiological changes associated with postharvest deterioration, together with the activities of selected enzymes thought to play a role in senescence, were monitored during subsequent storage for 16-24 days at 4 degrees C and 65-70% relative humidity. A biaxially oriented polypropylene film (BOPP) maintained the postharvest appearance of the mushrooms most effectively by significantly reducing the incidence of unsightly aerial hyphae on the pileal surface and restricting mushroom softening. These samples also exhibited smaller initial decreases in soluble protein, smaller increases in reducing sugar content, and lower levels of malondialdehyde accumulation during early storage. Smallest increases in proteinase activity were recorded in samples wrapped with BOPP and polyoletin packaging, and superoxide dismutase and polyphenol oxidase levels were significantly higher and lower, respectively, in the former. Choice of packaging can significantly affect postharvest quality loss in H. marmoreus and improve mushroom shelf life.

Effect of 60Co-irradiation on postharvest quality and selected enzyme activities of Hypsizygus marmoreus fruit bodies.

Hypsizygus marmoreus fruit bodies were exposed to different doses of (60)Co gamma-irradiation, stored at 4 degrees C and 65-70% relative humidity, and various physiological changes associated with postharvest deterioration, as well as the activities of selected enzymes widely considered to play a role in the process of senescence, were monitored over a subsequent storage period of 25 days. Exposure to 0.8 kGy irradiation was clearly beneficial in maintaining the postharvest appearance of the mushroom sporophores compared to non-irradiated samples and fruit bodies exposed to higher doses (1.2-2.0 kGy) of irradiation. Samples treated with 0.8 kGy also exhibited smaller initial declines in soluble protein, smaller increases in reducing sugar content, and lower levels of malondialdehyde accumulation during the early storage period. Smallest increases in proteinase activity were recorded in samples dosed with 0.8 and 2.0 kGy, and levels of superoxide dismutase were significantly higher in samples exposed to 0.8 kGy compared with non-irradiated controls. Large initial increases in catalase activity were detected in samples irradiated with 0.8, 1.2, and 1.6 kGy and, although enzyme levels gradually decreased in all samples during further storage, residual levels after 25 days were still severalfold higher in irradiated samples compared with controls. The data increase the current understanding of the effects of gamma-irradiation on the biochemical changes associated with postharvest senescence and should lead to more targeted strategies for reducing postharvest quality loss in H. marmoreus and other mushrooms.