Distinguishing between isomeric neoxanthin and violaxanthin esters in yellow flower petals using liquid chromatography/photodiode array atmospheric pressure chemical ionization mass spectrometry and tandem mass spectrometry

Abstract

Liquid chromatography-photodiode array atmospheric pressure chemical ionization mass spectrometry (LC-PDA-APCI-MS) is used for the analysis of various carotenoid pigments in plants. Among them, it is difficult to distinguish between the isomeric violaxanthin/neoxanthin esters. METHODS:The yellow pigments of tomato petals were extracted with acetone, and the extracts were kept at −30℃ to settle out the contaminating triacylglycerols physically. The supernatants were analyzed using LC-PDA-APCI-MS with a high-resolution orbitrap MS for their exact masses. The expected carotenoid esters were calculated with the combination of carotenoids and fatty acids, and they were matched with the experimental exact masses. The fatty acid structures in the carotenoid esters were also identified using collision-induced dissociation (CID) MS/MS. The isomeric violaxanthin/neoxanthin esters were distinguished using CID MS/MS from their in-source dehydrated product ions as pseudoprecursor ions. RESULTS: The in-source dehydrated ions [M−H2O+H] + of neoxanthin diesters predominated over their protonated molecules [M+H] + in the LC-MS. By contrast, the protonated molecules of violaxanthin diesters predominated. The 92 u loss product ions [M−H2O−C7H8+H] + were observed from the dehydrated violaxanthin diesters, but they were not generated from the dehydrated neoxanthin diesters in the CID MS/MS of their dehydrated pseudoprecursor ion [M−H2O+H] + . CONCLUSIONS:The allene allyl carbocation in neoxanthin diesters was generated from dehydration after preferential protonation at the hydroxy group. The epoxide group of violaxanthin diesters opens easily after protonation; however, the dehydration did not proceed at this stage. The 92 u loss of C7H8 was explained by the intramolecular [2+2] cycloaddition, which proceeded preferentially in dehydrated violaxanthin diesters because the carbocations in the dehydrated species were conjugated to the polyene and those double bonds were depolarized in the CID MS/MS. Therefore, the isomeric neoxanthin/violaxanthin diesters were

The Carotenoid Esterification Gene BrPYP Controls Pale-Yellow Petal Color in Flowering Chinese Cabbage (Brassica rapa L. subsp. parachinensis)

“…Carotenoids can be acylated by different fatty acids, generating a large number of possible carotenoid ester compounds ( Schweiggert et al, 2016 ; Mariutti and Mercadante, 2018 ). Lutein esters, such as lutein caprate, 5,6epoxy-luttein dilaurate, lutein dilaurate and lutein laurate, are also the well-known predominant carotenoids in petals of marigold ( Rodrigues et al, 2019 ) and tomato ( Watanabe et al, 2021 ). Carotenoid esters are also generated by acylation of fatty acids (Fas), and esterification does not change the carotenoid chromophore; thus, all carotenoid esters present the same UV-VIS spectrum and color of free-carotenoid ( Mercadante et al, 2017 ; Rodrigues et al, 2019 ).…”

The Compositional Aspects of Edible Flowers as an Emerging Horticultural Product

“…However, specific carotenoids are able to perform other functions through additional mechanisms, such as β-carotene that is converted into vitamin A, or some xanthophylls, such as lutein and zeaxanthin, that protect human vision by absorbing specific wavelengths of light [126]. Despite the diversity of carotenoids present in nature, the yellow xanthophylls (lutein, β-cryptoxanthin, and zeaxanthin), and epoxide xanthophylls (violaxanthin, antheraxanthin, neoxanthin) are the main carotenoids found in the flowers [127].…”