Identification of Polymethylene-Interrupted Polyunsaturated Fatty Acids (PMI-PUFA) by Solvent-Mediated Covalent Adduct Chemical Ionization Triple Quadrupole Tandem Mass Spectrometry

Pine nuts and other edible gymnosperm seeds contain unusual, bioactive polymethylene-interrupted polyunsaturated fatty acids (PMI-PUFAs), a subset of nonmethylene-interrupted PUFA with (-CH₂-)_n≥2 intervening between double bonds. Conventional methods for structure elucidation of PMI-PUFAs require special derivatization risking rearrangement artifacts. Here we introduce a facile solvent-mediated (SM) covalent adduct chemical ionization (CACI) system modified with a triple quadrupole MS, which distinguishes PMI-PUFAs from their analogues in direct methyl ester form. The prominent Δ5 desaturated PMI-PUFAs exhibit characteristic fragmentation at C_6-7 to yield ω diagnostic ions and share their fragmentation pattern with normal methylene interrupted PUFAs for the α diagnostic ion. H^• transfer upon CID dissociation of PMI-PUFAs was found to be dependent on the relative position of isolated lone double bonds and cleavage points. Ginkgo and five species of pine nuts were characterized for their unique Δ5 fatty acid profile, without the need for chemical standards.

Potentially High Value Conjugated Linolenic Acids (CLnA) in Melon Seed Waste

Conjugated linolenic acids (CLnAs) are natural phytochemicals with known and potential bioactivities in mammals. Established CLnA sources are limited to a few common fruit seeds, notably pomegranate seeds and cherry pits, and the search for alternatives is impeded in part by cumbersome methods for reliable measurement. We investigated CLnA contents in lower value fruit seeds with a recently available facile mass spectrometry method, solvent-mediated chemical ionization, enabling and quantitative analysis. We report for the first time the detection of CLnAs in cantaloupe and honeydew seeds at levels of 2 mg CLnA/g seed kernel. Based on the combined waste stream for these muskmelons of about 1.4 billion pounds in the USA annually, we estimate that the available CLnAs amount to 37.5 tons, similar to cherry pits. Our results suggest the potentially enhanced economic value of a specific class of bioactives that may be extracted from discarded food processing waste.