This paper presents the development of a rapid method with ultraperformance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) for the qualitative and quantitative analyses of plant proanthocyanidins directly from crude plant extracts. The method utilizes a range of cone voltages to achieve the depolymerization step in the ion source of both smaller oligomers and larger polymers. The formed depolymerization products are further fragmented in the collision cell to enable their selective detection. This UPLC-MS/MS method is able to separately quantitate the terminal and extension units of the most common proanthocyanidin subclasses, that is, procyanidins and prodelphinidins. The resulting data enable (1) quantitation of the total proanthocyanidin content, (2) quantitation of total procyanidins and prodelphinidins including the procyanidin/prodelphinidin ratio, (3) estimation of the mean degree of polymerization for the oligomers and polymers, and (4) estimation of how the different procyanidin and prodelphinidin types are distributed along the chromatographic hump typically produced by large proanthocyanidins. All of this is achieved within the 10 min period of analysis, which makes the presented method a significant addition to the chemistry tools currently available for the qualitative and quantitative analyses of complex proanthocyanidin mixtures from plant extracts.

This paper describes the development of a rapid method with ultraperformance liquid chromatography-triple-quadrupole mass spectrometry that can specifically measure group-specific fingerprints from plant extracts for the following polyphenol groups: (1) ellagitannins, (2) gallic acid derivatives, (3) quinic acid derivatives, (4) quercetin-based flavonol glycosides, (5) kaempferol-based flavonol glycosides, and (6) myricetin-based flavonol glycosides. In addition, the method records simultaneously diode array and full scan mass spectrometry data that can be used to later characterize and quantify the main individual polyphenols if necessary. All of this is achieved within the 10 min period of analysis, which makes the presented method a significant addition to the chemistry tools currently available for the rapid analysis of complex polyphenol mixtures from plant extracts.

We developed a combination of methods to estimate the alkaline oxidative conditions of the midgut of insect larvae and to reveal the alkaline and enzymatic oxidative activities for individual phenolic compounds present in the larval host plants. First, we monitored the in vitro isomerization of 5-O-caffeoylquinic acid (5-CQA) into 3-CQA, 4-CQA and 5-CQA at pH 9.0-11.0. Then we calculated the isomer ratios of 3-CQA, 4-CQA and 5-CQA from the frass of eight species of insect herbivores fed on foliage containing 5-CQA. The isomer ratios suggested that the midgut pH of these larvae ranged from 9.4 to around 10.1. Second, we developed an in situ enzymatic oxidation method that enabled oxidation of phenolics in a frozen plant sample at 30 °C by species- and tissue-specific enzymes. Then we measured the alkaline and enzymatic oxidative activities of the individual phenolics in 20 plant species by quantifying the proportion of the compound concentration lost due to the auto-oxidation of a plant extract at pH 10 and due to the enzymatic oxidation of the frozen plant sample at 30 °C. Our results showed that both of the oxidative activity types depended primarily on the type of phenolic compound, but the enzymatic oxidative activity depended also on the plant species and tissue type. This combination of methods offers an approach to characterize a wide array of phenolics that are susceptible to oxidation by the plant enzymes and/or by the alkaline conditions estimated to prevail in the insect midgut. We propose that these kinds of compound-specific results could guide future studies on specific plant-herbivore interactions to focus on the phenolics that are likely to be active rather than inactive plant phenolics.

No abstract

No abstract