Comparative analysis of antioxidant activities between dried and fresh walnut kernels by metabolomic approaches

Phenolic Fractions from Walnut Milk Residue: Antioxidant Activity and Cytotoxic Potential

Walnut milk residues (WMR) were investigated for the first time through their phenolic characterization including soluble (free, esterified, and etherified) phenolics and those released from their insoluble-bound form (insoluble-bound phenolic hydrolysates, IBPHs) and their antioxidant properties. Free phenolics were recovered and alkaline or acid hydrolysis were used to recover the remaining phenolic fractions. Total phenolic compounds (TPCs) and their antioxidant activity were analyzed by Folin-Ciocalteu, FRAP, and ORAC methods, respectively. Soluble phenolics (free + esterified + etherified fractions) showed a higher TPC (275.3 mg GAE 100 g-1 dw) and antioxidant activity (FRAP: 138.13 µmol TE g-1 dw; ORAC: 45.41 µmol TE g-1 dw) with respect to the IBPH. There was a significant correlation between TPC and FRAP and ORAC values regardless of the fraction and tested sample. Phenolic acids and flavonoids were identified and quantified by ultra-performance liquid chromatography-electrospray tandem mass spectrometry (UPLC-ESI-MS/MS). Gallic acid, mainly in the free form (3061.0 µg 100 g-1), was the most representative, followed by biochanin A, identified for the first time in a walnut product and mostly present in the fraction released from the esterified form (593.75 µg 100 g-1). No detrimental cytotoxic impact on Caco-2 cells was observed. Hence, WMR could be considered a potential source for the development of nutraceutical and/or antioxidant food additives.

Unraveling the metabolic profile regulation of camellia oilseeds under insect and heat stress: Insights into functional effects and mechanistic basis

There is very little information on the impacts of pre/post-harvest stresses on oilseeds. Individual and combined insect (pre-harvest) and heat stress (post-harvest) impacts on the metabolic profile of camellia oilseeds (COs) were investigated using a combination of widely-targeted metabolomics and network pharmacology. A total of 1875 metabolites were identified. In response to individual and combined stresses, 169 (insect),149 (heat), and 21 (insect + heat) metabolites were screened as differential metabolic markers (DEMs), Terpenoids, phenolic acids, and flavonoids are the most impacted metabolite species, accounting for almost 49% of total DEMs. Then network pharmacological analysis identifies 98 key active ingredients (AIs) in CO. A single stress may induce CO to impede cardiovascular system function, but the combined stress induced AI-promoting effects of CO in the urinary system. The individual and combined perturbed biological mechanisms were related to the flavonoid biosynthesis and the biosynthesis of various plant secondary metabolites pathway, respectively.

Drying enhances the antioxidant activity of Allium mongolicum Regel through the phenylpropane and AA-MA pathway as shown by metabolomics

Fresh Allium mongolicum Regel (FA) and dried A. mongolicum Regel (DA) are significantly different in antioxidant activity. However, the relevant mechanisms have not yet been explored. We evaluated the antioxidant activities of two varieties of FA and DA and characterized their metabolites using targeted metabolomics. The effect of different metabolites on the antioxidant activity of A. mongolicum Regel was investigated by multivariate analysis. A total of 713 metabolites were detected in all samples. Pearson correlation analysis demonstrated that the key primary metabolites were directly and significantly correlated with the total phenolic content (TPC) and total flavonoid content (TFC), while the secondary metabolites were directly correlated with antioxidant activity. The higher antioxidant activity of DA may be mainly attributed to the higher TPC and TFC. This study revealed the potential mechanism by which drying enhances the antioxidant activity of A. mongolicum Regel.

Metabolomic Profiling of Floccularia luteovirens from Different Geographical Regions Proposes a Novel Perspective on Their Antioxidative Activities

Floccularia luteovirens, an endemic resource of the Tibetan Plateau, possesses significant medicinal and ecological values. However, the understanding of antioxidant capacity and metabolic profiling of F. luteovirens from diverse regions remains elusive due to limited resources. Therefore, to comprehensively comprehend the antioxidant capacity and metabolite diversity of F. luteovirens, we conducted a rounded analysis of its antioxidant capacity from three distinct regions using both untargeted and targeted metabolomics. Determination of antioxidant indices, such as ferric ion-reducing antioxidant power (FRAP), total phenolic content (TPC), and flavonoid content (FC), revealed the robust antioxidant capacity of F. luteovirens. QL F. luteovirens (QLFL) exhibited no significant difference compared to ZD F. luteovirens (ZDFL); however, both were significantly distinct from XH F. luteovirens (XHFL) across multiple indices. Furthermore, a positive correlation was observed between FRAP and flavonoid content. A total of 5782 metabolites were identified and chemically classified. Metabolites of F. luteovirens varied significantly at different regions and eight key differential metabolites were screened. Phenylalanine, tyrosine and tryptophan biosynthesis, phenylalanine metabolism, and cyanoamino acid metabolism were the main different regulatory pathways. Consequently, the disparities in the antioxidant activity of F. luteovirens may primarily be ascribed to the biosynthesis and metabolism of phenylalanine, while vanillic acid could potentially serve as a pivotal metabolite influencing the antioxidative capacity of F. luteovirens by targeted metabolomics. These findings enhance our understanding of the composition of F. luteovirens and provide valuable resources for its comprehensive utilization and targeted development.

'Sorrento' and 'Tulare' Walnut Cultivars: Morphological Traits and Phytochemical Enhancement of Their Shell Waste

Walnut processing generates considerable quantities of by-products that could be reprocessed into value-added products that have food and non-food applications. In this context, the aim of this study is to characterize the 'Sorrento' and 'Tulare' walnut cultivars using the UPOV guidelines and analyze the chemical composition and antioxidant activity of their shells. Insight into the chemical composition of the different granulometric fractions of walnut shell, obtained by sieving, was obtained following ultrasound-assisted extraction by Ultra-High-Performance Liquid Chromatography-High-Resolution Mass Spectrometry (UHPLC-HRMS). The total phenolic, flavonoid, and tannin content and antiradical capacity, obtained by DPPH and ABTS assays, and the Fe(III) reducing power of the extracts were also evaluated. The UHPLC-HRMS analysis indicated the presence of thirty-two compounds ascribable to four major classes of specialized metabolites. Furthermore, the extraction efficiency of gallic acid, ellagic acid derivatives, as well as glansreginin A, increased with the decrease in shell matrix particle size in contrast to chlorogenic acids and flavonoid glycosides. This is the first study to highlight new knowledge on the chemical composition of walnut shells. The results obtained demonstrate the feasibility of recovering valuable bioactive components from agro-waste that may be further valorized.

The Antioxidant Activities In Vitro and In Vivo and Extraction Conditions Optimization of Defatted Walnut Kernel Extract

The objective of this study was to determine the antioxidant activities of defatted walnut kernel extract (DWE) and whole walnut kernel extract (WE) in vitro and in vivo. Three spectrophotometric methods, DPPH, ABTS, and FRAP, were used in in vitro experiments, and mice were used in in vivo experiments. In addition, response surface methodology (RSM) was used to optimize reflux-assisted ethanol extraction of DWE for maximum antioxidant activity and total phenolic content. The results of in vitro experiments showed that both extracts showed antioxidant activity; however, the antioxidant activity of DWE was higher than that of WE. Both extracts improved the mice's oxidative damage status in in vivo studies. An ethanol concentration of 58%, an extraction temperature of 48 °C, and an extraction time of 77 min were the ideal parameters for reflux-assisted ethanol extraction of DWE. The results may provide useful information for further applications of defatted walnut kernels and the development of functional foods.

Effects of Packaging Materials on Structural and Simulated Digestive Characteristics of Walnut Protein during Accelerated Storage

Walnuts are rich in fat and proteins that become oxidized during the processing and storage conditions of their kernels. In this study, the effect of three packaging materials (e.g., polyethylene sealed packaging, polyamide/polyethylene vacuum packaging, and polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging) were investigated on the oxidation, structural and digestive properties of walnut kernel proteins. Results showed that the amino acid content gradually decreased and carbonyl derivatives and dityrosine were formed during storage. The protein molecule structure became disordered as the α-helix decreased and the random coil increased. The endogenous fluorescence intensity decreased and the maximum fluorescence value was blue-shifted. After 15 days of storage, surface hydrophobicity decreased, while SDS-PAGE and HPLC indicated the formation of large protein aggregates, leading to a reduction in solubility. By simulating gastrointestinal digestion, we found that oxidation adversely affected the digestive properties of walnut protein isolate and protein digestibility was best for polyethylene terephthalate/aluminum foil/polyethylene vacuum packaging. The degree of protein oxidation in walnuts increased during storage, which showed that except for fat oxidation, the effect of protein oxidation on quality should be considered. The results of the study provided new ideas and methods for walnut quality control.

Roasting treatments affect oil extraction rate, fatty acids, oxidative stability, antioxidant activity, and flavor of walnut oil

Introduction

The quality of pressed walnut oil can be improved by moderate roasting treatment.

Methods

This study compared physicochemical characteristics and antioxidant ability of walnut oils pressed from differently roasted pretreated walnuts, analyzed the correlation among these indicators by using Pearson correlation coefficient and correlation coefficient heatmap, and evaluated the volatile organic compounds (VOCs) of walnut oil under optimal pretreatment roasting conditions using headspace-gas chromatography-ion mobility spectrometry (HS-GC-IMS).

Results

Hierarchical cluster analysis (HCA) and principal component analysis (PCA) were able to remarkably distinguish walnut oil produced by different roasting processes. In addition, correlation analysis showed that there was a significant impact among indicators. There were 73 VOCs were identified in the optimum roasted treated walnut oil, consisting of 30 aldehydes, 13 alcohols, 11 ketones, 10 esters, 5 acids, 2 oxygen-containing heterocycles, 1 nitrogen-containing heterocycle and 1 other compound. GC-IMS results showed that aldehydes contributed significantly to the volatile flavor profile of walnut oil, especially (E)-2-heptenal, (E)-2-pentenal and hexenal.

Discussion

The properties of walnut oil based on varying roasting pretreatment of walnut kernels were significantly differentiated. Roasting at 120°C for 20 min is a suitable pretreatment roasting condition for pressing walnut oil. Roasting at 120°C for 20 min is a suitable pretreatment roasting condition for pressing walnut oil.

Hypoglycemic and antioxidative activity evaluation of phenolic compounds derived from walnut diaphragm produced in Xinjiang

Walnut diaphragm is defined as a dry wood septum located between the walnut shell and kernel. In this work, seven phenolic compounds from walnut diaphragm were purified and characterized, and their antioxidant activities and mechanisms of hypoglycemia were investigated. Compounds 1-7 were tested for DPPH, ABTS scavenging ability, and FRAP assay to evaluate the antioxidant activity. α-Amylase inhibition assay was introduced to assess the hypoglycemic activity, and the mechanism was investigated by kinetic analysis, CD spectrum, and molecular docking. Compound 6 showed the strongest antioxidant ability, while compound 1 exhibited the strongest inhibition of α-amylase by changing the secondary structure of α-amylase in a mixed competitive inhibition mode. Molecular docking test predicted that the tetrahydropyran part in compound 1 may contribute to its hypoglycemic effect. This study furnishes a new theoretical reference for the utilization and development of walnut diaphragm into a health food with antioxidant and hypoglycemic properties. PRACTICAL APPLICATIONS: The finding of this research may serve as a basis for the subsequent development of walnut diaphragm into instant tea-based health food or added to other food carriers to achieve auxiliary antioxidant and hypoglycemic effects. This study revealed that polyphenolic components were the material basis for the antioxidant and hypoglycemic effects of walnut diaphragm, which could be identified as landmark chemical components for controlling quality standards in the development of walnut diaphragm, thus accelerating the research process of quality standards for walnut diaphragm-related products. Furthermore, the studies on the mechanism of hypoglycemic activity supply more credible data to support the development of walnut diaphragm into a safe and consumer-friendly health food. With abundant resources and clear efficacy, walnut diaphragm has great development prospect and application value.

Ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry based untargeted metabolomics to reveal the characteristics of Dictyophora rubrovolvata from different drying methods

Dictyophora rubrovolvata is a highly valuable and economically important edible fungus whose nutrition and flavor components may vary based on drying methods. Herein, an untargeted ultraperformance liquid chromatography-quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF/MS) metabolomics method combined with multivariate analysis was first performed to characterize the metabolomics profiles of D. rubrovolvata upon different drying treatments, viz., coal burning drying (CD), electrothermal hot air drying (ED), and freeze drying (FD). The results indicated that 69 differential metabolites were identified, vastly involving lipids, amino acids, nucleotides, organic acids, carbohydrates, and their derivatives, of which 13 compounds were confirmed as biomarkers in response to diverse drying treatments. The Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis illustrated that differential metabolites were significantly assigned to 59, 55, and 60 pathways of CD vs. ED, CD vs. FD, and FD vs. ED groups, respectively, with 9 of the top 20 KEGG pathways shared. Specifically, most of lipids, such as fatty acyls, glycerophospholipids and sphingolipids, achieved the highest levels in D. rubrovolvata after the CD treatment. ED method substantially enhanced the contents of sterol lipids, nucleotides, organic acids and carbohydrates, while the levels of amino acids, prenol lipids and glycerolipids were elevated dramatically against the FD treatment. Collectively, this study shed light on metabolomic profiles and proposed biomarkers of D. rubrovolvata subjected to multiple drying techniques, which may contribute to quality control and drying efficiency in edible fungi production.