No abstract

The stability of phenolic compounds was followed in black currant juice at ambient temperatures (in light and in dark conditions) and at +4 °C for a year. Analyses were based on high-performance liquid chromatography-diode-array detection-electrospray ionization-mass spectrometry (or tandem mass spectrometry) and high-performance liquid chromatography-diode-array detection-electrospray ionization-quadrupole time-of-flight mass spectrometry methods supported by nuclear magnetic resonance after selective high-performance liquid chromatography isolation. Altogether, 43 metabolites were identified, of which 2-(Z)-p-coumaroyloxymethylene-4-β-d-glucopyranosyloxy-2-(Z)-butenenitrile, 2-(E)-caffeoyloxymethylene-4-β-d-glucopyranosyloxy-2-(Z)-butenenitrile, 1-O-(Z)-p-coumaroyl-β-d-glucopyranose, (Z)-p-coumaric acid 4-O-β-d-glucopyranoside, and (Z)-p-coumaric acid were novel findings in black currant juice. Hydroxycinnamic acid derivatives degraded 20-40% at room temperature during one year of storage, releasing free hydroxycinnamic acids. O-Glucosides of hydroxycinnamic acid compounds were the most stable, followed by O-acylquinic acids, acyloxymethyleneglucosyloxybutenenitriles, and O-acylglucoses. Light induced the isomerization of (E)-coumaric acid compounds into corresponding Z-isomers. Flavonol glycosides stayed fairly stable. Flavonol aglycones were derived mainly from malonylglucosides. Over 90% of anthocyanins were lost at room temperature in a year, practically independent of light. Storage at low temperatures, preferably excluding light, is necessary to retain the original composition of phenolic compounds.

Black currant juices from five different cultivars were analyzed for composition, content, and mean degree of polymerization (mDP) of proanthocyanidins (PA) by UPLC-MS/MS. Juices contained both procyanidins (PC) and prodelphinidins (PD), but the PC-% varied significantly, from 28 to 82% of the total PA. In addition, high PD-% was related to high mDP and total PA content. Enzyme-assisted processing increased significantly total PA (5-14-fold), PD-% (12-65%), and mDP (1.8-6.2-fold) in the juices of all cultivars. Enzymatic treatment increased the contents of large PAs more than those of small PAs. The contents of PA and mDP were positively associated with the mouth-drying and puckering astringent characteristics. However, the PA content did not contribute to the bitter taste. Juices from the most bitter cultivars had the lowest contents of proanthocyanidins regardless of the processing method. This finding indicates the existence of other bitter compounds in black currants in addition to PA.

No abstract

No abstract