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United States Department of Agriculture

Agricultural Research Service

Title: Novel Fatty-Acid Esters of P-Coumaryl Alcohol in Epicuticular Wax of Apple Fruit

Authors
item Whitaker, Bruce
item Schmidt, Walter

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: May 14, 2001
Publication Date: N/A

Technical Abstract: During a study of alpha-farnesene accumulation and oxidation in the skin of cold-stored apple fruit, hexane extracts of epicuticular wax from >Gala= apples were noted to have an unusual, broad absorbance maximum at about 258 nm, which led us to isolate and identify the primary UV- absorbing compounds. Column and thin-layer chromatography steps yielded a fraction that gave a series of paired, 260-nm-absorbing peaks on C18- HPLC. These were shown to be a family of phenolic fatty-acid esters, for which retention times increased with increasing fatty-acid chain length and paired peaks were esters of two related phenolics with the same fatty-acid moiety. Alkaline hydrolysis of the esters released two water-soluble phenolics separable by C18-HPLC. Electrospray MS gave a molecular mass of 150 for both, and proton-NMR plus UV absorbance spectra identified them as E and Z isomers of p-coumaryl alcohol (p-CA). Gradient HMQC-NMR of the HPLC-purified stearate ester of E-p-CA indicated that fatty-acid esterification occurs at the gamma-OH rather than at the 4-OH on the phenyl ring. To our knowledge, this is the first report of fatty-acid esters of monolignols as a natural plant product. The mechanism of fatty-acid esterification and the physiological role of these compounds are presently unknown. They did, however, show moderate antioxidant activity in two different assays, which suggests that they may be beneficial in the human diet.

Last Modified: 4/16/2014
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