Production and Characterization of a Polyphenol Enriched Date Palm Extract from California Date Palm
Authors: Alfaro‐Viquez Emilia , Ricketts Marie‐Louise , Rainey Charlene J. , Krueger Christian G. , Reed Jess D. 
Published: November 2023

Date palm (Phoenix dactylifera) is an important food cultivated in the Coachella Valley in Southern California. Medjool and deglet noor dates are the two most popular varieties and both pack an impressive list of nutrients, including vitamins, minerals, lipids and proteins. Dates are also rich in phenolic compounds including phenolic acid, flavonoids, tannins, anthocyanins and carotenoids. These compounds are associated with a variety of beneficial health effects. However, very few studies have identified the molecular mechanisms underlying these observed effects. Therefore, the aim of the present study was to produce and characterize a date palm extract (DPE) made from California dates that can then be used in subsequent in vitro and in vivo studies to elucidate the mechanisms by which dates confer beneficial health effects. California dates were harvested during the 2014 and 2015 harvest seasons and freeze‐dried date extract was produced from equal part medjool and deglet noor dates by means of liquid extraction and solid phase separation. The extracts were characterized using High Performance Liquid Chromatography (HPLC) and Matrix‐Assisted Laser Desorption Ionization Time‐of‐Flight Mass Spectrometry (MALDI‐TOF MS).

HPLC chromatograms show that the predominant polyphenols present within the extracts have spectral characteristics indicative of hydroxycinnamic acids; specifically, the UV‐Visible spectra has a maximum absorbance in the range of 320–330nm. The extracts also have spectral characteristics indicative of proanthocyanidins (PAC). Specifically, the UV‐Visible spectra have an absorbance at 280nm and resolve as a poorly eluting ‘hump’ rather than well‐defined individual peaks. The qualitative and quantitative presence of PAC in the date extract was detected by butanol‐HCl and by separation of the extract on a Sephadex LH20 column prior to HPLC and MALDI‐TOF MS analysis. This separation provides an enriched PAC fraction, which helps with the subsequent characterization of PACs, providing sufficient separation of compounds to allow for the detection of PAC oligomers from 3–7 degrees of polymerization by MALDI‐TOF MS. HPLC chromatograms of the PAC fraction at 280 nm show two broad and unresolved humps, due to the structural heterogeneity of the PAC oligomers. Furthermore, positive reflectron mode MALDI‐TOF MS exhibited a series of compounds which appear to be oligomeric in nature with repeatable extension units. We propose that this mass may correspond to suberin compounds, specifically an ester of ferulic acid with long‐chain w ‐ hydroxyfatty acids (C16, C18, C20). The pattern of MALDI peaks suggests the presence of a series of w ‐ hydroxyfatty acids varying in degree of unsaturation.

This study shows that date palm fruits are a good source of phenolic compounds mainly hydroxycinnamic acids, PAC and lipophilic polyphenols, and that this extract can be used for further in vitro and in vivo analysis.

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Funded by California Date Commission