Occurrence of tocopheryl fatty acid esters in vegetables and their non-digestibility by artificial digestion juices

Stephanie Krauß,Walter Vetter,Vanessa Darwisch

doi:10.1038/s41598-018-25997-2

Abstract

Tocopheryl fatty acid esters (TFAE) consist of tocopherols esterified to fatty acids, but only little is known about this substance class. In this study, twelve vegetable groups were screened on TFAE and contents of (free) tocopherols and TFAE were determined in red bell pepper, red chili pepper, cucumber and walnut (n = 5, respectively). Intact TFAE were separated by solid phase extraction from free tocopherols and analyzed by GC/MS. Highest TFAE values were determined in chili pepper (4.0–16 mg/100 g fresh weight, FW) and walnut (4.1–12 mg/100 g FW), followed by bell pepper (1.3–1.5 mg/100 g FW) and cucumber (0.06–0.2 mg/100 g FW). Contribution of TFAE to the total tocopherol content ranged from 7–84%. Neither the treatment with artificial digestion juices nor exposure to sunlight showed degradation of TFAE. This substance class might represent a hitherto overlooked storage form for free tocopherols in plants as they occur to be more stable. But as the ester bond in medium chain TFAE seems not to be fissile in the human body, they might not contribute in the same way as free tocopherols to the vitamin E activity of vegetables and might have to be determined separately.

Highlights

Vitamin E comprises a group of fat-soluble compounds with antioxidative activity called tocochromanols[1,2]
In solid phase extraction (SPE) fraction 2, tocopheryl fatty acid esters (TFAE) were identified by their GC/MS spectra and retention times in comparison to standard solutions
Miscellaneous tests were performed with different vegetables and fruits and TFAE were detected in all matrices except grapes, carrots, olives, almonds and hazelnut

Summary

Introduction

Vitamin E comprises a group of fat-soluble compounds with antioxidative activity called tocochromanols[1,2]. Due to their structure tocopherols insert into the amphipathic phospholipid bilayer of cellular membranes[1,3,10,11] They are able to protect membrane lipids as well as photosynthetic organs and seeds from oxidative stress[1,12,13] and are widely spread in nature[1,14]. The goal of this study was to screen more vegetables which contain high amounts of tocopherols regarding the occurrence of TFAE and to determine their composition and concentrations relative to free tocopherols For this purpose, several α- and γ-TFAE standards were synthesized. A lipid extract containing TFAE and a standard solution was treated with artificial digestion juices This experiment was performed to find out if the ester bond is cleaved during digestion and directly adds to the vitamin E activity of a vegetable or if TFAE have to be considered separately. The light stability of this substance class was investigated by exposing TFAE standard solutions to sunlight

Objectives

Methods

Results