New research characterizes walnut milk residue according to its phenolic content and antioxidant and cytotoxic potential using ultrahigh-performance liquid chromatography–electrospray tandem mass spectrometry (UHPLC–ESI-MS/MS).
Scientists from the University of Chile (Santiago), the University of Almería (Spain), and University of Alberta (Edmonton) characterized the soluble (free, esterified, and etherified) phenolics and insoluble-bound phenolic hydrolysates (IBPH) fractions of walnut milk residues (WMR). The study, which was published in Plants, assessed the WMR for its phenolic content and antioxidant and cytotoxic potential through analysis utilizing ultrahigh-performance liquid chromatography–electrospray tandem mass spectrometry (UHPLC–ESI-MS/MS) (1).
Found in different forms depending on their association with the food matrix, phenolic compounds are free, esterified, and etherified soluble phenolics as well as insoluble-bound phenolics (2,3) Most of the reported studies conducted previously only consider the phenolic analysis and antioxidant activity of the soluble phenolic fraction, generally evaluated after obtaining a crude extract, omitting the contribution of each of the phenolic fractions, including free, esterified, etherified soluble, and insoluble-bound phenolics (4,5). Free soluble phenolics are found within the vacuoles of the vegetal cell; insoluble-bound phenolics are bound to carbohydrates and proteins of the plant matrix cell wall by covalent bonds, which can be released by alkaline hydrolysis (6).
An edible nut of high nutritional value, walnut (Juglans regia L.), is mainly composed of unsaturated fatty acids, proteins, dietary fiber, minerals, and B-complex vitamins, in addition to vitamin E (tocopherols) and phytosterols (7-10). Walnuts also contain significant amounts of compounds of a phenolic nature which have shown potential beneficial effects on human health against chronic non-communicable diseases mediated by oxidative stress (including some types of cancer, type II diabetes, and cardiovascular diseases) and neurodegenerative diseases due to their antioxidant and anti-inflammatory capacity in in vitro and in vivo studies (11-16).
The study of this byproduct, according to the authors, is important in the context of waste reduction, optimization of natural resources, and the potential economic and health benefits of the bioactive compounds present in this residue (1). Phenolic acids and flavonoids were identified and quantified by the researchers through UHPLC–ESI-MS/MS, with gallic acid, mainly in the free form (3061.0 µg 100 g−1), being the most representative, followed by biochanin A, which reportedly was 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). The authors of the paper state that 44% w/w of the phenolics present in the walnut were not extracted during the production of walnut milk and remained in the respective residue. Therefore, the authors found that WMR could be considered as a potential source of natural antioxidants contributing to the nutraceutical and food industry in the framework of sustainable processes (1)
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References
1. Toledo-Merma, P. R.; Arias-Santé, M. F.; Rincón-Cervera, M. Á.; Porras, O.; Bridi, R.;Rhein, S.; Sánchez-Contreras, M.;Hernandez-Pino, P.; Tobar, N.; Puente-Díaz, L.; de Camargo, A. C. Phenolic Fractions from Walnut Milk Residue: Antioxidant Activity and Cytotoxic Potential. Plants (Basel) 2024, 13 (24), 3473. DOI: 10.3390/plants13243473
2. de Camargo, A. C.; Regitano-d’Arce, M. A. B.; Shahidi, F. Phenolic Profile of Peanut By-Products: Antioxidant Potential and Inhibition of Alpha-Glucosidase and Lipase Activities. Journal of the American Oil Chemists' Society 2017, 94, 959-971. DOI: 10.1007/s11746-017-2996-9
3. Zhang, Y. G.; Kan, H.; Chen, S. X.; Thakur, K.; Wang, S.; Zhang, J. G. et al. Comparison of Phenolic Compounds Extracted from Diaphragma juglandis Fructus, Walnut Pellicle, and Flowers of Juglans regia Using Methanol, Ultrasonic Wave, and Enzyme Assisted-Extraction. Food Chem. 2020, 321, 126672. DOI: 10.1016/j.foodchem.2020.126672
4. Kafkas, E.; Attar, S. H.; Gundesli, M. A.; Ozcan, A.; Ergun, M. Phenolic and Fatty Acid Profile, and Protein Content of Different Walnut Cultivars and Genotypes (Juglans regia L.) Grown in the USA. International Journal of Fruit Science, 2020, 20 (s3), S1711-S1720. DOI: 10.1080/15538362.2020.1830014
5. Slatnar, A.; Mikulic-Petkovsek, M.; Stampar, F.; Veberic, R.; Solar, A. Identification and Quantification of Phenolic Compounds in Kernels, Oil and Bagasse Pellets of Common Walnut (Juglans regia L.). Food Res. Int. 2015, 67, 255-263. DOI: 10.1016/j.foodres.2014.11.016
6. Shahidi, F.; Yeo, J. Insoluble-Bound Phenolics in Food. Molecules 2016, 21 (9), 1216. DOI: 10.3390/molecules21091216
7. Abdallah, I. B.; Tlili, N.; Martinez-Force, E.; Rubio, A. G.; Perez-Camino M. C.;Albouchi, A.; Boukhchina, S. Content of Carotenoids, Tocopherols, Sterols, Triterpenic and Aliphatic Alcohols, and Volatile Compounds in Six Walnuts (Juglans regia L.) Varieties. Food Chem. 2015, 173, 972-978. DOI: 10.1016/j.foodchem.2014.10.095
8. Croitoru, A.; Ficai, D.; Craciun, L.; Ficai, A.; Andronescu, E. Evaluation and Exploitation of Bioactive Compounds of Walnut, Juglans regia. Curr. Pharm. Des. 2019, 25 (2), 119-131. DOI: 10.2174/1381612825666190329150825
9. Wang, P.; Zhong, L..; Yang, H.; Zhu, F.; Hou, X., Wu, C. et al. Comparative Analysis of Antioxidant Activities Between Dried and Fresh Walnut Kernels by Metabolomic Approaches. LWT 2022, 155, 112875. DOI: 10.1016/j.lwt.2021.112875
10. Shahidi, F.; Pinaffi-Langley, A. C. C.; Fuentes, J.;Speisky, H.; de Camargo, A. C. Vitamin E as an Essential Micronutrient for Human Health: Common, Novel, and Unexplored Dietary Sources. Free Radic. Biol. Med. 2021, 176, 312-321. DOI: 10.1016/j.freeradbiomed.2021.09.025
11. Wu, S.; Shen, D.; Wang, R.; Li, Q.; Mo, R.; Zheng, Y. et al. Phenolic Profiles and Antioxidant Activities of Free, Esterified and Bound Phenolic Compounds in Walnut Kernel. Food Chem. 2021, 350, 129217. DOI: 10.1016/j.foodchem.2021.129217
12. Alasalvar, C.;Huang, G.; Bolling, B. W.; Jantip, P. A.; Pegg, R. B.; Wong, X. K. et al.Upcycling Commercial Nut Byproducts for Food, Nutraceutical, and Pharmaceutical Applications: A Comprehensive Review. Food Chem. 2024, 142222. DOI: 10.1016/j.foodchem.2024.142222
13. Carvalho, M.; Ferreira, P. J.; Mendes, V. S.; Silva, R.; Pereira, J. A.; Jerónimo, C.; Silva, B. M. Human Cancer Cell Antiproliferative and Antioxidant Activities of Juglans regia L. Food Chem. Toxicol. 2010, 48 (1), 441-447. DOI: 10.1016/j.fct.2009.10.043
14. Guasch-Ferré, M.; Hernández-Alonso, P.; Drouin-Chartier, J. P.; Ruiz-Canela, M.; Razquin, C.; Toledo, E. et al. Walnut Consumption, Plasma Metabolomics, and Risk of Type 2 Diabetes and Cardiovascular Disease. The Journal of Nutrition 2021,151 (2), 303-311. DOI: 10.1093/jn/nxaa374
15. Kris-Etherton, P. M. Walnuts Decrease Risk of Cardiovascular Disease: A Summary of Efficacy and Biologic Mechanisms. The Journal of Nutrition 2014, 144 (4), 547S-554S. DOI: 10.3945/jn.113.182907
16. Ni, Z. J.; Zhang, Y. G.; Chen, S. X.; Thakur, K.; Wang, S.; Zhang, J. G. Exploration of Walnut Components and Their Association with Health Effects. Critical Reviews in Food Science and Nutrition 2022, 62 (19), 5113-5129. 10.1080/10408398.2021.1881439
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