An overview of walnuts application as a plant-based

Fractionation of phenolic compounds from hickory by-products using solid phase extraction-sonication: Chemical composition, antioxidant and antimicrobial activity

Hickory is an abundant source of phenolic compounds that exhibit a diverse range of bioactivities. In this study, phenolic compounds were extracted and purified from hickory green husk (HG), hickory nutshell (HN), and hickory seed coat (HS) using solid-phase extraction and ultrasonication (SPE-US). The effects of the SPE-US treatment on the structure and properties of the phenolic compounds were then investigated, including their composition, antioxidant activity, and antimicrobial activity. The dominant phenolic substances in the different extracts after SPE-US treatment were: ellagic acid and trans ferulic acid (HS); ellagic acid and sinapic acid (HN); and rutin (HG). The HS-SPE-US1 extract exhibited the highest total polyphenol content (416 ± 11 mg GAE/g DW), total flavonoid content (47.51 ± 0.68 mg RE/g DW), Fe3+ reduction ability (74.2 ± 1.0 mmol Fe2+/g DW), radical (DPPH and ABTS) scavenging ability, and antimicrobial activity against Staphylococcus aureus.

Walnut meal improves meat quality by modulating intestinal microbes in white feather broilers

Improving the number of amino acids and unsaturated fatty acids in the diet is a good way to raise the quality of the meat. Currently, most research on the quality of broiler meat focuses on genetic traits; nevertheless, it is unclear how meat quality is regulated. This experiment was conducted to investigate the effects of different supplemental levels of walnut meal (WM) on growth performance, amino acid and fatty acid composition, microbial composition, and meat quality of white feather broilers. 1 week old white feather broilers (n = 120; Body weight 83.76 ± 2.32 g), were randomly divided into 3 treatments and 4 replicates. Walnut meal of basic diet (CK), 5 %(WM-L) and 10 %(WM-H) were added to the diets of white feather broilers, respectively. The results showed that walnut meal could increase L* 24 h (24 h brightness) of breast muscle of white feathered broilers (p < 0.05). The amount of essential amino acids (e.g., isoleucine, methionine, leucine, tryptophan, and phenylalanine), umami amino taste acids (glutamic acid), and PUFA/SFA (polyunsaturated fatty acid) (n-3PUFA and n-6 PUFA) in breast muscle increased as the dose was increased. Furthermore, walnut meal regulated amino acid flavour metabolism by increasing the relative abundance of Bacteroides, bifidobacterium, and enterococcus faecalis, according to 16S rRNA sequencing and functional prediction analysis. The correlation showed that amino acid and fatty acid composition was one of the key factors affecting pH value, meat color and tenderness of chicken. In conclusion, dietary addition of walnut meal can increase the content of essential amino acids and unsaturated fatty acids and the relative abundance of beneficial bacteria of broilers, which is of great significance for improving meat quality of white feather broilers.

Regulation of Intestinal Inflammation by Walnut-Derived Bioactive Compounds

Walnuts (Juglans regia L.) have shown promising effects in terms of ameliorating inflammatory bowel disease (IBD), attributed to their abundant bioactive compounds. This review comprehensively illustrates the key mechanisms underlying the therapeutic potential of walnuts in IBD management, including the modulation of intestinal mucosa permeability, the regulation of inflammatory pathways (such as NF-kB, COX/COX2, MAPCK/MAPK, and iNOS/NOS), relieving oxidative stress, and the modulation of gut microbiota. Furthermore, we highlight walnut-derived anti-inflammatory compounds, such as polyunsaturated fatty acids (PUFA; e.g., ω-3 PUFA), tocopherols, phytosterols, sphingolipids, phospholipids, phenolic compounds, flavonoids, and tannins. We also discuss unique anti-inflammatory compounds such as peptides and polysaccharides, including their extraction and preparation methods. Our review provides a theoretical foundation for dietary walnut supplementation in IBD management and provides guidance for academia and industry. In future, research should focus on the targeted isolation and purification of walnut-derived anti-inflammatory compounds or optimizing extraction methods to enhance their yields, thereby helping the food industry to develop dietary supplements or walnut-derived functional foods tailored for IBD patients.

Transcriptomic Analyses Reveal the Effects of Walnut Kernel Cake on Adipose Deposition in Pigs

With the rising cost of animal feed protein, finding affordable and effective substitutes is crucial. Walnut kernel cake, a polyphenol-, fiber-, protein- and fat-rich byproduct of walnut oil extraction, has been underexplored as a potential protein replacement in pig feed. In this study, we found that feeding large Diqing Tibetan pigs walnut kernel cake promoted adipose deposition and improved pork quality during pig growth. Transcriptome analysis revealed the upregulation of genes ANGPTL8, CCNP, ETV4, and TRIB3, associated with adipose deposition. Pathway analysis highlighted enrichment in adipose deposition-related pathways, including PPAR, insulin, PI3K-Akt, Wnt, and MAPK signaling. Further analysis identified DEGs (differentially expressed genes) positively correlated with adipose-related traits, such as PER2 and PTGES. Single-cell transcriptome data pointed to the specific expression of CD248 and PTGES in adipocyte progenitor/stem cells (APSCs), pivotal for adipocyte differentiation and adipose deposition regulation. This study demonstrates walnut kernel cake's potential to substitute soybean cake in pig feed, providing high-quality protein and promoting adipose deposition. It offers insights into feed protein replacement, human functional food, fat metabolism, and related diseases, with marker genes and pathways supporting pig breeding and pork quality improvement.

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.

Molecular Docking Revealed the Potential Anti-Oxidative Stress Mechanism of the Walnut Polypeptide on HT22 Cells

The preparation of novel antioxidant peptides from food raw materials is one of the research focuses, but there are fewer studies on the preparation of antioxidant peptides from walnut meal, a by-product of processing walnuts. This study analyzed the antioxidant properties and protective effects of walnut protein hydrolyzed by alkaline protease and trypsin on the oxidative stress of HT22 cells. The peptides were identified by UPLC-MS/MS, and the anti-oxidative peptides were screened based on virtual computer tools. The potential anti-oxidative stress mechanism of the walnut polypeptide on HT22 cells was explored by molecular docking. The results revealed that walnut protein hydrolysates (WPH) with molecular weights of less than 1 kDa had good antioxidant properties and inhibited oxidative damage of HT22 cells by regulating the levels of reactive oxygen species (ROS) and antioxidant enzyme catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px). Six of the ninety identified new peptides showed good solubility, non-toxicity, and bioactivity. The molecular docking results showed that the six peptides could dock with Keap1 successfully, and EYWNR and FQLPR (single-letter forms of peptide writing) could interact with the binding site of Nrf2 in the Keap1-Kelch structural domain through hydrogen bonds with strong binding forces. The results of this study provided important information on the antioxidant molecular mechanism of the walnut polypeptide and provided a basis for further development of walnut antioxidant polypeptide products.