Raisin, currant and Thompson Seedless grape phenolic compound characterization using LC‐MS‐MS‐ESI with product ion, precursor‐ion, neutral–loss analysis and selected reaction monitoring

Abstract

Raisins have a distinct phenolic profile that may be relevant to their health effects/benefits, this study characterized their profile. Thompson Seedless grapes, sun‐dried raisins, golden raisins and Zante currant raisins were extracted with methanol or acetone prior to fractionation. HPLC coupled electrospray mass spectrometry in tandem mode (LC‐ESI‐MS‐MS) with negative ion detection was used to generate a phenolic profile that was characterized/quantified using standards, mass fragmentation patterns including mass spectra in full scan mode (MS), and MS/MS (i.e. product ion, precursor ion and neutral loss). Identified phenolics included catechin, B‐type dimers , B‐type trimers, myricetin (M)‐3‐galactoside, M‐3‐glucoside, quercetin (Q)‐3‐glucuronide, rutinoside, Q‐3‐glucoside, linarin, kaempferol‐3‐O‐caffeoylate, isorhamnetin‐3‐O‐glucoside, Q, and kaempferol. Deprotonated aglycones were formed by loss of galactoside, glucoside, glucuronides, and caffeoyllate residues from their glycosides. Fragmentation patterns demonstrated several catechin derivatives; aglycons and catechins provided characteristic ions for each flavonoid family. Raisins and grapes have not until now been known to contain linarin and M‐3‐gal among other phenolics. Further study will need to determine the degree of variation within cultivars. Support: Sun‐Maid Growers of California