Suberin. A component of citrus peel extracts

Flavanone glycosides have been traditionally recovered from citrus peels and commercialized as herbal supplements. Commercial recoveries of these citrus peel flavonoids typically involve initial water extractions, and in certain cases the removal of pectin by ion-exchange resins. A consistent feature of high-performance liquid chromatography (HPLC) chromatograms of such aqueous peel extracts is significantly elevated broad baselines. These baselines suggest the occurrence of wide populations of possibly similar chemical entities. In this study, isolations of these materials by either ultrafiltration or LH20 column chromatography led to the recoveries of fractions, termed 'baseline fractions' particularly enriched in the peel materials responsible for these elevated baselines. The goal of this study was to isolate the material responsible for these elevated baselines and to conduct an initial chemical characterization and possible identification of this portion of citrus peel water extracts.

The water-soluble component of these baseline fractions was determined to be protein as determined by its Fourier-transform infrared (FTIR) spectroscopy. The remaining major components of these baseline fractions were freely soluble in methanol, and the FTIR and nuclear magnetic resonance (NMR) spectra of these components were indicative of the plant polymer, suberin. Size exclusion chromatography showed this material to largely occur between 10 and 60 kDa as would be expected for this plant polymer.

It is proposed in this study that suberin is responsible for the broad elevated HPLC baselines of citrus extracts. Furthermore, this multifunctional chemical cell wall material may possibly contribute to the overall biological effects attributed to flavanone-enriched citrus peel supplements, in which this material frequently occurs. Published 2025. This article is a U.S. Government work and is in the public domain in the USA. Journal of the Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.