Walnut Protein: A Rising Source of High-Quality Protein and Its Updated Comprehensive Review

Intermolecular interactions influenced the gelation and texture improvement of sturgeon surimi gels by walnut protein isolates

Intermolecular interaction is a key factor in the fortification of surimi gels by plant protein addition. Here, the effects of different intermolecular interactions, such as ionic, covalent and non-covalent interactions, on gel structure, gelation strength and water-holding properties were investigated, using sturgeon surimi fortified by three walnut isolates, including walnut meal (WM), protein isolate (WPI) and peptide (WP), as representatives. Quantitative creep-recovery analysis and soluble protein assay demonstrated that secondary bonds, mainly hydrophobic interaction and hydrogen bond, possibly played a dominant role in walnut protein-fortified surimi gels. Hydrophobic interaction and disulfide bond benefited gelation behavior and textural strengthening by supplementation of WM and WPI. However, 1-3 % addition of WPI and WP positively influenced water retention of surimi gels due to higher hydrogen bonding level. Structural integrity of surimi gel was not destroyed, while appropriate addition of walnut proteins especially WPI improved sensory quality of sturgeon surimi product.

Integrated transcriptomics and lipidomics reveal mechanisms regulating lipids formation and accumulation in oil body during walnut seed development

BACKGROUND

Through combined analysis of the transcriptomics and lipidomics of walnut, the possible molecular mechanism of lipid formation and accumulation in oil bodies was revealed.

CONCLUSION

The formation and accumulation of lipids are critical determinants of nut quality, with walnut storing lipids primarily in oil bodies (OBs). Currently, there is still a lack of systematic research on the formation and accumulation of lipids in walnut OBs (WOBs). Therefore, this study integrated lipidomics and transcriptomics to comprehensively identify the changes in WOBs and walnut kernels at 60, 74, 88, 102, 116, and 130 days after pollination (DAP). The results showed that fatty acid content in walnut kernels and WOBs had opposite trends, especially oleic, linoleic, and linolenic. Principal component analysis of the samples and cluster analysis of differentially expressed genes (DEGs) showed that the total samples were divided into three main groups: 60-74, 88-102, and 116-130 DAP. RNA sequencing generated 33,918 unigenes (14,995 DEGs), including 228 DEGs highly related to lipid metabolism, in 18 cDNA libraries prepared from walnut kernel. These genes were mainly involved in metabolic pathways such as pyruvate metabolism, glycerophospholipid metabolism, glycerolipid metabolism, and fatty acid biosynthesis during lipid synthesis. On the other hand, the expression levels of ACC, KASII, SAD, FAD2, FAD3, and PDAT genes were downregulated at 88-130 DAP compared with 60-74 DAP, which might be the key genes regulating the reduction of free fatty acid content in WOBs. In addition, 21 FAD genes were identified, including seven SAD genes, three FAD2 genes, five FAD3 genes, one FAD5 gene, one FAD6 gene, and four FAD7/8 genes. These genes were closely related to the synthesis of unsaturated fatty acids in WOBs, especially FAD2 and FAD3. The findings offered valuable insights into the dynamic changes in lipids and genetic resources and provided a foundation for walnut quality improvement.

A breakthrough computational strategy for efficient enzymatic digestion of walnut protein to prepare antioxidant peptides

The conventional natural bioactive peptides (NBAPs) enzymatic preparation process is labor-intensive and time-consuming, limiting its application and development. This study proposes an efficient computational strategy (CAE-VD) that integrates a high-accuracy (98.18 %) deep learning model (convolutional auto-encoder, CAE) with virtual digestion (VD) to prepare NBAPs with specified activities. CAE predicts the activity of peptides generated by VD, guiding enzyme selection. CAE-VD identified alkaline protease as the most suitable enzyme for enzymatic preparation of walnut-derived antioxidant peptides compared to pepsin and trypsin, which was confirmed by DPPH and ABTS radical scavenging assays and statistical analyses of peptides. As an emerging computer technology, CAE-VD will apply to other NBAPs. This study demonstrates the efficacy of integrating deep learning with virtual digestion in guiding the enzymatic preparation of NBAPs and highlights the potential of applying advanced computational techniques in the food industry.

A new technique for antioxidant walnut peptide preparation directly from walnut cake: Enzymatic preparation process optimization coupled with enzyme membrane reactor and kinetic analysis

The lack of scalable production methods limits the commercial production viability of walnut peptides. To overcome this obstacle, enzyme membrane reactors (EMRs) were used to continuously produce bioactive peptides (called CEMR) directly from walnut cake. The optimum operating conditions were pH 10.7, an [E/S] ratio of 11 %, and a temperature of 44 °C, which resulted in a peptide yield of 256.0 ± 4.66 mg/g cake and a protein conversion degree reaching 63.49 ± 0.82 %. Kinetic analysis showed that affinity between alkaline protease and walnut cake can be enhanced by EMR (km decreased, kA increased). The antioxidant results showed that the strongest antioxidant activity was detected in CEMR. The composition of amino acids and molecular weight distribution results showed that the highest content of Glu (20.20 ± 0.48 %), Asp (20.70 ± 0.95 %), and peptides with molecular weight < 1KD (51.92 %) were detected in CEMR. The results of CEMR provide a new option for simplifying the production process of walnut peptide.

Gibberellin Regulates LBD38-1 Responses to Xanthomonas arboricola pv. juglandis Infection in Walnut Bacterial Blight Pathogenesis

BACKGROUND

Plant responses to biotic and abiotic stresses are complex processes. Previous studies have shown that the LBD gene family plays important roles in plant growth and development as well as in plant defense against biotic and abiotic stresses. The expression of LBD genes was investigated in walnuts under biotic and abiotic stresses, revealing that LBD38-1 may be a key gene in the plant stress response. This study provides new insights into the roles of LBD genes in plant responses to biotic stress.

RESULTS

Forty-nine members of the JrLBD gene family were identified in the walnut genome and classified into six subfamilies. Comparative homology analysis through phylogenetic trees revealed that the presence of Group I-a and Group VI plays an important role in resistance to stressors. The expression of walnut LBD genes under cold-temperature, high-temperature, mechanical damage, and biotic stresses was analyzed via transcriptome sequencing, and the expression of JrLBD38-1 in the Group VI subfamily was particularly prominent. According to transcriptome profile analysis, JrLBD38-1 is highly expressed in different tissues of walnuts, suggesting that it plays a regulatory role in the growth and development of different tissues. The function of the Gibberellin (GA) response element in the JrLBD38-1 promoter was further analyzed and verified. These findings confirmed that GA regulated JrLBD38-1 expression changes during Xanthomonas arboricola pv. juglandis infestation of walnut leaves.

CONCLUSION

Forty-nine walnut JrLBDs were identified and classified into six subfamilies. JrLBD38-1 has GA-inducible expression, is regulated by GA under pathogenic bacterial stress, and is involved in the response to biotic stress. This function of JrLBD38-1 provides new insights into walnut disease resistance mechanisms.

Screening, identification, and mechanism of novel antioxidant peptides in walnut meal under aerobic stress

Walnut (Juglans regia L.) meal, being the primary by-product of walnut oil processing, is rich in high-quality proteins and of significant potential for development and utilization. The study used multi-stage gradient purification, liquid-quantity chromatography, and computerized virtual screening to isolate and characterize antioxidant peptides from walnut meal. Active sites and mechanism actions of antioxidant peptides were examined using oxidative damage model of HepG2 cells. Five novel peptides exhibiting high antioxidant activity were identified, among which YR-10 significantly increased the cell viability of HepG2 oxidatively damaged cells to 20.64 %. Meanwhile, YR-10 significantly reduced the ROS content to 42.54 % and apoptosis level to 11.80 % in HepG2 oxidatively damaged cells. In addition, YR-10 competed with Nrf2 for Keap1 binding site, inhibited Keap1 (13.83 %) expression, and promoted Nrf2 (27.15 %), HO-1 (34.59 %), and SOD1 (42.67 %) expression, which ultimately activated the Keap1/Nrf2/HO-1 pathway and alleviated oxidative damage.

Oil-type modulation of the interfacial adsorption behavior of flavonoid-modified walnut protein hydrolysates to improve the storage stability of high internal phase Pickering emulsions

BACKGROUND

Currently, protein-polyphenol complexes have garnered increasing attention as surface-active substances in high internal phase Pickering emulsions (HIPPEs). However, the effects of the oil type and flavonoid structure on the HIPPE-stabilizing ability of protein-polyphenol complexes remain unclear. Notably, very few studies have investigated the impacts and mechanisms of different oils (olive, flaxseed, and coconut oils) and the effects of the addition of flavonoids (catechin and quercetin) on the interfacial behavior of walnut protein hydrolysates (WPHs) and the co-oxidation of protein-lipid in the resulting emulsion during storage.

RESULTS

Incorporating flavonoids was found to reduce the particle size and enhance WPH emulsification efficiency. Compared with catechin, quercetin demonstrated a greater affinity for adsorption at the oil-water interface, thereby improving the interfacial adsorption properties of WPHs across all the oil phases, although the oil type influenced the concentration of flavonoids at the interface. Excessive WPH-quercetin complex nanoparticles can form a dense multilayer at the interface and compactly pack oil droplets, endowing HIPPEs with higher viscoelasticity, greater storage stability, and stronger protection against lipid and protein oxidation than other WPH-based HIPPEs do, especially in cases of olive oil-HIPPEs.

CONCLUSIONS

Our results demonstrated that the interfacial structure of WPH-flavonoid complexes play a major role in the emulsion stabilization efficiency, followed by the type of oil. © 2024 Society of Chemical Industry.

The effect of enzymatic deamidation on the solubility and emulsifying properties of walnut protein isolate

BACKGROUND

Alkaline-extracted walnut protein isolates (WPI) exhibit limited solubility, which poses challenges for their application in the food industry. The present study investigated the effects of protein-glutaminase (PG) deamidation on the physicochemical characteristics, solubility and emulsifying properties of WPI.

RESULTS

The deamidation process of WPI was monitored by assessing the release of free ammonia and the reduction in solution turbidity. PG deamidation significantly increased the surface charge of WPI and modified its surface hydrophobicity with increasing deamidation degree (DD), resulting in a gradual improvement in solubility by approximately 50-70%. Furthermore, the emulsifying capacity of deamidated WPI (DeWPI), specifically at 0.25 h (DeWPI0.25, DD 7%) and 9 h (DeWPI9, DD 23%), was evaluated for stabilizing low internal phase emulsions (LIPEs) and high internal phase emulsions (HIPEs). LIPEs stabilized by WPI and DeWPI0.25 exhibited significant flocculation of oil droplets, leading to decreased stability against heat, salt treatment and storage compared to those stabilized by DeWPI9. DeWPI-stabilized HIPEs showed a 2-2.5-fold higher storage modulus compared to those stabilized by WPI. However, HIPEs stabilized by DeWPI0.25 displayed higher flow stress and flow strain compared to DeWPI9-stabilized HIPEs. Overall, DeWPI-stabilized HIPEs demonstrated relatively high physical stability against storage, heat treatment and high ionic strength.

CONCLUSION

PG deamidation significantly enhanced the solubility and influenced the emulsifying properties of WPI in a manner dependent on the DD. © 2024 Society of Chemical Industry.

Rapid Covalent Bonding of Walnut Protein Isolates to EGCG: Unveiling the Ultrasound-Assisted Ratio Optimization, Binding Mechanism, and Structural-Functional Transformations

The application of walnut protein isolate (WPI) and polyphenols is usually limited by low solubility. To solve the above problem, the impact of the alkaline treatment method and the ultrasound-assisted alkaline treatment method on the structural and functional properties of protein-polyphenol covalent complexes (WPI-(-)-epigallocatechin-3-gallate (EGCG), UWPI-EGCG, respectively) was explored. Fourier transform infrared spectroscopy and fluorescence spectroscopy indicated that the covalent binding of EGCG to WPI altered the secondary and tertiary structures of the protein and increased its random coil content. In addition, the UWPI-EGCG samples had the lowest particle size (153.67 nm), the largest absolute zeta potential value (25.4 mV), and the highest polyphenol binding (53.37 ± 0.33 mg/g protein). Meanwhile, WPI-EGCG covalent complexes also possessed excellent solubility and emulsification properties. These findings provide a promising approach for WPI in applications such as functional foods.

Complexation between curcumin and walnut protein isolate modified by pH shifting combined with protein-glutaminase

The poor techno-functional properties of walnut protein isolate (WPI) limit its application as carrier to improve bioavailability of curcumin. In this study, WPI was modified by pH-shifting (PS) and protein-glutaminase (PG). Changes on the physicochemical and structural characteristics of WPI and effects on complexation with curcumin were investigated. Treatment of PS plus PG increased electrostatic repulsion of WPI with altered secondary and tertiary structure. Solubility of WPI was greatly improved from 18.09% to 52.90%. The increased flexibility resulted in reduced particle size and increased exposure of hydrophobic groups. The improved amphiphilicity of WPI provided more binding sites for complexation with curcumin. Encapsulation efficiency of curcumin was increased from 32.50% to 94.48%. Interestingly, the formed complexes were able to protect curcumin from degradation with improved storage stability and bioaccessibility. Thus, PS plus PG could serve as effective modification strategy for utilization of WPI as a promising delivery vehicle for hydrophobic bioactives.

Plant protein-derived anti-breast cancer peptides: sources, therapeutic approaches, mechanisms, and nanoparticle design

Breast cancer causes the deaths of approximately 685,000 women annually, posing a severe threat to women's health. Consequently, there is an urgent need for low-cost, low-toxicity and effective therapeutic methods to prevent or mitigate breast cancer progression. PDBP are natural, non-toxic, and affordable substances and have demonstrated excellent anti-breast cancer activities in inhibiting proliferation, migration, and invasion, and promoting apoptosis both in vitro and in vivo, thus effectively preventing or inhibiting breast cancer. However, there are no comprehensive reviews summarizing the effects and mechanisms of PDBP on the treatment of breast cancer. Therefore, this review described the inhibitory effects and mechanisms of active peptides from different plant protein sources on breast cancer. Additionally, we summarized the advantages and preparation methods of plant protein-derived anticancer peptide-encapsulated nanoparticles and their effects in inhibiting breast cancer. This review provides a scientific basis for understanding the anti-breast cancer mechanisms of PDBP and offers guidance for the development of therapeutic adjuvants enriched with these peptides.

Characterization and functional properties of walnut protein fibrils for enhanced bioaccessibility of CoQ10 and ALA

Emulsion-based delivery systems have garnered significant attention in terms of encapsulation and delivery of the hydrophobic bioactive compounds in recent years. This study investigated the formation of walnut protein fibrils (WPF) through acid-heat treatment for varying durations. Emulsions stabilized by WPF were prepared for the codelivery of CoQ10 and ALA. The emulsifying properties and interfacial distribution characteristics of WPF were compared and the differences in the stability of the emulsions were studied. Prolonged treatment duration resulted in secondary structural alterations, including an increase in β-sheet content (from 39.42 % to 45.87 %). Fibrillation increased protein interfacial adsorption, leading to WPF stabilized emulsions with better storage stability, resilience to environmental stress fluctuations and oxidative stability. In summary, compared to unmodified walnut protein, WPF10 stabilized emulsion already significantly enhanced the bioaccessibility of CoQ10 and ALA. The potential delivery system may facilitate the incorporation of hydrophobic active substances and functional fatty acids into beverage products.

Design and characterization of EGCG conjugated walnut protein cold-set gels for quercetin encapsulation

While heat treatment is a conventional method for the gelation of alkaline-extracted walnut protein isolates (AWPI), it can limit the incorporation of heat-sensitive ingredients. This study explored a novel approach to fabricate cold-set gels from epigallocatechin-3-gallate (EGCG) conjugated AWPI (AWPI-EGCG). EGCG conjugation effectively inhibited the thermal gelation of AWPI while promoting the formation of soluble aggregates upon heat treatment. AWPI-EGCG cold-set gels were then successfully fabricated through acidification with glucono-δ-lactone (GDL). The rheological study revealed that the storage modulus and yield stress of the cold-set gels were positively correlated with the GDL concentration and the EGCG conjugation degree. However, higher concentrations of GDL were associated with the reduced yield strain of the gels. Texture analysis indicated an increase in gel hardness with increasing GDL concentration, accompanied by a decrease in springiness. Microstructural examination by scanning electron microscopy revealed that the AWPI-EGCG cold-set gels with 0.3 % GDL exhibited smaller pores with thinner and smoother internal walls, while those with 0.9 % GDL exhibited relatively larger pores with thicker and denser walls. In addition, the AWPI-EGCG cold-set gels showed promising quercetin encapsulation capacities and controlled release properties.

Integrated Transcriptomic and Proteomic Analysis of Nutritional Quality-Related Molecular Mechanisms in "Longjia", "Yangpao", and "Niangqing" Walnuts (Juglans sigillata)

In this study, "Longjia (LJ)" and "Yangpao (YP)"exhibited higher contents of major nutrients compared to "Niangqing (NQ)" walnuts. The combination of transcriptome and proteome by RNA sequencing and isotope labeling for relative and absolute quantification techniques provides new insights into the molecular mechanisms underlying the nutritional quality of the three walnut species. A total of 4146 genes and 139 proteins showed differential expression levels in the three comparison groups. Combined transcriptome and proteome analyses revealed that these genes and proteins were mainly enriched in signaling pathways such as fatty acid biosynthesis, protein processing in endoplasmic reticulum, and amino acid metabolism, revealing their relationship with the nutritional quality of walnut kernels. This study identified key genes and proteins associated with nutrient metabolism and accumulation in walnut kernels, provided transcriptomic and proteomic information on the molecular mechanisms of nutrient differences in walnut kernels, and contributed to the elucidation of the mechanisms of nutrient differences and the selection and breeding of high-quality walnut seedlings.

Plant-based proteins: clinical and technological importance

Healthy and sustainable diets have seen a surge in popularity in recent years, driven by a desire to consume foods that not only help health but also have a favorable influence on the environment, such as plant-based proteins. This has created controversy because plant-based proteins may not always contain all the amino acids required by the organism. However, protein extraction methods have been developed due to technological advancements to boost their nutritional worth. Furthermore, certain chemicals, such as bioactive peptides, have been identified and linked to favorable health effects. As a result, the current analysis focuses on the primary plant-based protein sources, their chemical composition, and the molecular mechanism activated by the amino acid types of present. It also discusses plant protein extraction techniques, bioactive substances derived from these sources, product development using plant protein, and the therapeutic benefits of these plant-based proteins in clinical research.

Effect of succinylation-assisted glycosylation on the structural characteristics, emulsifying, and gel properties of walnut glutenin

In this study, we examined the effects of various sodium alginate (ALG) concentrations (0.2%-0.8%) on the functional and physicochemical characteristics of succinylated walnut glutenin (GLU-SA). The results showed that acylation decreased the particle size and zeta potential of walnut glutenin (GLU) by 122- and 0.27-fold, respectively. In addition, the protein structure unfolded, providing conditions for glycosylation. After GLU-SA was combined with ALG, the surface hydrophobicity decreased and the net negative charge and disulfide bond content increased. The protein structure was analyzed by FTIR, Endogenous fluorescence spectroscopy, and SEM, and ALG prompted GLU-SA cross-linking to form a stable three-dimensional network structure. The results indicated that dual modification improved the functional properties of the complex, especially its potential protein gel and emulsifying properties. This research provide theoretical support and a technical reference for expanding the application of GLU in the processing of protein and oil products.

Modulation of cecal microbiota and fecal metabolism in mice by walnut protein

Walnut meal is a by-product of walnut oil pressing, in which the protein content is more than 40%, which is an excellent food raw material, but at present, it is basically used as animal feed or discarded, which results in a great waste of resources, and its modulating effect on the intestinal microbiota is not clear. In this study, we used supercritically extracted walnut meal as a raw material, prepared walnut meal isolate protein (WP) by alkaline extraction and acid precipitation, and systematically analyzed its structure by Fourier infrared spectroscopy (FTIR), Raman spectroscopy (Raman), and scanning electron microscopy (SEM); meanwhile, we explored the effects of WP on the cecal bacterial flora and fecal metabolites of mice by microbiological and metabolomic techniques. The results showed that the protein content of WP prepared using alkaline extraction and acid precipitation was as high as 83.7%, in which arginine and glutamic acid were abundant, and it has the potential to be used as a raw material for weight-loss meal replacement food; FTIR and Raman analyses showed that the absorption peaks of WP's characteristic functional groups were obvious, and that the content of the α-helix and β-fold in the secondary structure was greater than 30%, which indicated that it was structurally stable; differential scanning calorimetry (DSC) and SEM analyses showed that WP is a typical spherical particle, its denaturation temperature is 73.6 °C, and it has good thermal stability. Supplementation of WP significantly altered the composition of the intestinal flora in mice, with an increase in beneficial bacteria and a decrease in harmful bacteria; the strongest modulation of the intestinal flora was achieved by altering the composition of the intestinal flora and by increasing the number of Akkermansia (p < 0.01), which consequently affects the function of the microbiota. Based on LC-MS metabolomic results, we identified a total of 87 WP-regulated metabolites, mainly enriched in the bile secretion pathway, which had the highest relevance, followed by benzoxazine biosynthesis. In summary, walnut protein is an important plant protein and has a positive impact on intestinal health, which may provide new ideas for the development of functional foods.

Walnut peptide alleviates obesity, inflammation and dyslipidemia in mice fed a high-fat diet by modulating the intestinal flora and metabolites

Introduction

Obesity is a chronic disease in which the body stores excess energy in the form of fat, and intestinal bacterial metabolism and inflammatory host phenotypes influence the development of obesity. Walnut peptide (WP) is a small molecule biopeptide, and the mechanism of action of WP against metabolic disorders has not been fully elucidated. In this study, we explored the potential intervention mechanism of WP on high-fat diet (HFD)-induced obesity through bioinformatics combined with animal experiments.

Methods

PPI networks of Amino acids and their metabolites in WP (AMWP) and "obesity" and "inflammation" diseases were searched and constructed by using the database, and their core targets were enriched and analyzed. Subsequently, Cytoscape software was used to construct the network diagram of the AMWP-core target-KEGG pathway and analyze the topological parameters. MOE2019.0102 was used to verify the molecular docking of core AMWP and core target. Subsequently, an obese Mice model induced by an HFD was established, and the effects of WP on obesity were verified by observing weight changes, glucose, and lipid metabolism levels, liver pathological changes, the size of adipocytes in groin adipose tissue, inflammatory infiltration of colon tissue, and intestinal microorganisms and their metabolites.

Results

The network pharmacology and molecular docking showed that glutathione oxide may be the main active component of AMWP, and its main targets may be EGFR, NOS3, MMP2, PLG, PTGS2, AR. Animal experiments showed that WP could reduce weight gain and improve glucose-lipid metabolism in HFD-induced obesity model mice, attenuate hepatic lesions reduce the size of adipocytes in inguinal adipose tissue, and reduce the inflammatory infiltration in colonic tissue. In addition, the abundance and diversity of intestinal flora were remodeled, reducing the phylum Firmicutes/Bacteroidetes (F/B) ratio, while the intestinal mucosal barrier was repaired, altering the content of short-chain fatty acids (SCFAs), and alleviating intestinal inflammation in HFD-fed mice. These results suggest that WP intervenes in HFD-induced obesity and dyslipidemia by repairing the intestinal microenvironment, regulating flora metabolism and anti-inflammation.

Discussion

Our findings suggest that WP intervenes in HFD-induced obesity and dyslipidemia by repairing the intestinal microenvironment, regulating flora metabolism, and exerting anti-inflammatory effects. Thus, WP may be a potential therapeutic strategy for preventing and treating metabolic diseases, and for alleviating the intestinal flora disorders induced by these diseases. This provides valuable insights for the development of WP therapies.