Unveiling the "hidden quality" of the walnut pellicle: A precious source of bioactive lipids

Authors: ABBATTISTA, RAMONA - University Of California, Davis; FEINBERG, NOAH - University Of California, Davis; SNODGRASS, ISABEL - University Of California, Davis; Newman, John; DANDEKAR, ABHAYA - University Of California, Davis

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/30/2024
Publication Date: 6/18/2024
Citation: Abbattista, R., Feinberg, N.G., Snodgrass, I.F., Newman, J.W., Dandekar, A.M. 2024. Unveiling the "hidden quality" of the walnut pellicle: A precious source of bioactive lipids. Frontiers in Plant Science. 15. https://doi.org/10.3389/fpls.2024.1395543.
DOI: https://doi.org/10.3389/fpls.2024.1395543

Interpretive Summary: Walnut consumption has been widely associated with various health benefits including improved cardiovascular and neurological health. While attributed to the vast array of phenolic antioxidants and abundant polyunsaturated fatty acids, not all clincial outcomes related to walnut consumption can be explained by these molecular hallmarks. An untargeted metabolomics profiling of the walnut pellicle (seed coat) revealed a myriad of unusual lipids, including oxylipins and endocannabinoids, that have known potent bioactivities as mammals. Given the potential value of this tissue and its “bioactive” lipid fraction for human health, we sought to quantify these compounds in waste by-products of mechanized walnut processing in California. An impressive repertoire of bioactive lipids were found in high concentrations making this low-value agriculture waste a promising candidate for valorization and translation into high-value, health-promoting products. This “hidden quality” of the walnut pellicle may encourage further consumption of walnuts, and walnut industries may benefit from a revaluation of abundant pellicle-enriched waste streams, leading to increased sustainability and profitability through waste upcycling.

Technical Abstract: Tree nut consumption has been widely associated with various health benefits, with walnuts, in particular, being linked with improved cardiovascular and neurological health. These benefits have been attributed to walnuts’ vast array of phenolic antioxidants and abundant polyunsaturated fatty acids. However, recent studies have revealed unexpected clinical outcomes related to walnut consumption, which cannot be explained simply with the aforementioned molecular hallmarks. An untargeted metabolomics profiling of the walnut pellicle (seed coat) revealed a myriad of unusual lipids, including oxylipins and endocannabinoids, that have known potent bioactivities as mammalian signaling molecules and homeostatic regulators. The discovery of these compounds in the pellicle, which likely enhances the seeds’ defenses due to their antimicrobial properties, represents a potential explanation for these unexpected clinical outcomes of walnut consumption. Given the potential value of this tissue and its “bioactive” lipid fraction for human health, we sought to quantify the amounts of these compounds in waste by-products of mechanized walnut processing in California. An impressive repertoire of these compounds was revealed, and in notably significant concentrations, making this low-value agriculture waste a promising candidate for valorization and translation into high-value, health-promoting products. This “hidden quality” of the walnut pellicle may encourage further consumption of walnuts, and walnut industries may benefit from a revaluation of abundant pellicle-enriched waste streams, leading to increased sustainability and profitability through waste upcycling.