A Screening Method for the Identification of Glycosylated Flavonoids and Other Phenolic Compounds Using a Standard Analytical Approach for All Plant Materials

Abstract

A screening method was developed for the systematic identification of glycosylated flavonoids and other phenolic compounds in plant food materials based on an initial, standard analytical method. This approach applies the same analytical scheme (aqueous methanol extraction, reverse phase liquid chromatographic separation, and diode array and mass spectrometric detection) to every sample and standard. This standard approach allows the cross-comparison of compounds in samples, standards, and plant materials previously identified in the published literature. Thus, every analysis contributes to a growing library of data for retention times and UV/vis and mass spectra. Without authentic standards, this method provides provisional identification of the phenolic compounds: identification of flavonoid backbones, phenolic acids, saccharides, and acyls but not the positions of the linkages between these subclasses. With standards, this method provides positive identification of the full compound: identification of subclasses and linkages. The utility of the screening method is demonstrated in this study by the identification of 78 phenolic compounds in cranberry, elder flower, Fuji apple peel, navel orange peel, and soybean seed.

Strategies for differentiation of isobaric flavonoids using liquid chromatography coupled to electrospray ionization mass spectrometry

“…One approach found in the literature for achieving this utilizes basic and acidic hydrolysis in such a way that substituents are cleaved off, more or less completely, before chromatographic analysis. [8,[20][21][22] One limitation with this approach is that information about the number of flavonoids with a specific aglycone could not directly be obtained. Furthermore, C-linked substituents are more resistant against hydrolysis [8] , thus identity of those aglycones will not be obtained.…”

“…[8,[20][21][22] One limitation with this approach is that information about the number of flavonoids with a specific aglycone could not directly be obtained. Furthermore, C-linked substituents are more resistant against hydrolysis [8] , thus identity of those aglycones will not be obtained. As can be seen when comparing lut-7-glu, and lut-8-Cglu (entry 14 and 15 in Table 3), the O-glucoside readily fragments using both methods 1 and 2, whereas no fragments could be seen for the C-glucoside although the loss of the glucoside can be seen with method 2.…”

“…When comparing the MS 3 spectra, obtained during a LC run, from cy-3-glu 8, kaempf-3-glu 11 and lut-7-glu 14 (see Figure 4) one can first notice that 11 has more fragments of (comparably) high intensity than the others (8,14). These fragments would be m/z 165 ( 0,2 A + ), be concluded that MS 3 spectra, i.e.…”

“…However, selection of ionization mode, positive or negative, will have an influence on the type of information that could be achieved but also on the sensitivity. In the literature a number of different screening or fingerprint methods have been reported, [7][8][9][10][11][12][13] where some have used, positive ionization mode, [12,13] while other have use negative ionization. [9,10] Information from pos/neg mode provides complementary information and thus some work has been done utilizing both ionization modes.…”

“…[9,10] Information from pos/neg mode provides complementary information and thus some work has been done utilizing both ionization modes. [8,11,14] Generally, in the literature, it is considered that negative ionization provides best sensitivity [9,14,15] but it could also be found that positive ionization are more useful for structure elucidation [11,14,15] . Co-elution of different flavonoids are often encountered in LC making characterizing the flavonoid composition difficult, especially since standards are not always available.…”