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Title: Some thoughts about an unusual set of phenols in calamondin leaves and orange juice

item Manthey, John

Submitted to: Subtropical Technology Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 9/15/2007
Publication Date: 10/18/2007
Citation: Manthey, J.A. 2007. Some thoughts about an unusual set of phenols in calamondin leaves and orange juice. Subtropical Technology Conference Proceedings. 58:18

Interpretive Summary:

Technical Abstract: Antioxidant phenols are thought to be responsible for much of the anti-inflammatory properties of orange juice. In addition to this, the compounds may be active against some plant pathogenic bacteria; possibly the canker organism, Xanthomonas axonopodis pv citri. This possibility led to our investigation of these compounds in Calamondin leaf tissue. Several main classes of flavonoids and related phenols occur in Calamondin leaves, including polar hydroxycinnamates, flavone glycosides, flavanone glycosides and polymethoxylated flavones. Crude separations of these classes of compounds were made by low-pressure reversed-phase column chromatography, and cursory structural analyses were achieved by HPLC-mass spectroscopy. Among these compounds, an unusual set of seemingly related UV-absorbing compounds of intermediate polarities was detected and further isolated. HPLC analysis of this set of compounds produced a "humptogram", and this suggested that this unusual set of compounds is composed of a very large number of minor-occurring constituents. The UV spectra of the combined compounds further suggest that they are comprised mainly of mixed flavones and hydroxycinnamates. Nothing else is known about these compounds, but it is significant that this set of compounds represents a substantial portion of the total phenolics in calamondin leaves. This is also true of the powerful anitoxidant phenols in orange juice. It has been noted that similar "humptograms" occur in the HPLC of total phenol extracts of chocolate, pine bark, and cranberry. These plant materials contain widely varying mixtures of proanthocyanidin oligomers, which make up major portions of the humptograms in their respective HPLCs. These oligomers have been extensively studied for their potential beneficial biological activities in human cells. Thus, it is tempting to speculate that the citrus compounds might also be comprised of complex sets of mixed oligomers, not necessarily proanthocyanidins, but rather of flavones and hydroxycinnamates. Such oligomers may arise from oxidative coupling in citrus plant tissues abundant in these many diverse polyphenols.