Simplified Analysis and Expanded Profiles of Avenanthramides in Oat Grains.

Mike Woolman,Keshun Liu

doi:10.3390/foods11040560

Abstract

Uniquely, oats contain avenanthramides (AVAs), a group of phenolic alkaloids, exhibiting many health benefits. AVA analysis involves extraction with alcohol-based solvents and HPLC separation with UV and/or mass spectrometer detectors. There are many reported methods to extract AVAs. Almost all entail multiple extractions. The whole procedure is time- and labor-intensive. Furthermore, most quantifications are limited to three common AVAs (2f, 2p, 2c). The present study compared three extraction methods (all at 50 °C) for their effects on AVA concentrations and composition (% relative to total AVA) of oat grains. These included triplicate extractions with 80% ethanol containing 10 mM phosphate buffer (pH 2.0) (A), triplicate extractions with 80% ethanol (B), and a single extraction with 80% ethanol (C), while keeping solid/total solvent ratio at 1/60 (g/mL) and total extraction time of 60 min. Results showed that 80% buffered ethanol gave significantly lower AVA contents than 80% ethanol, while single and triplicate extractions with 80% ethanol produced the same extractability. However, the extraction method had no effect on AVA composition. Using 0.25 g sample size instead of 0.5 g saved extractants by half, without affecting AVA measurements. Consequently, a simplified method of extraction was developed, featuring Method C. The present study also expanded profiling individual AVAs beyond AVA 2c, 2p and 2f. Other AVAs identified and semi-quantified included 5p, 4p, 3f/4f, and 2pd. The simplified analysis was validated by measuring 16 selected oat grain samples. Some of these grains had relatively high contents of 4p, 3f/4f and 2pd, which have been considered minor AVAs previously.

Highlights

Compared to other cereal crops, oat (Avena sativa L.) is well known for its higher contents of oil, protein, and beta-glucan
Regardless of the minor differences among the three methods, the HPLC chromatograms of the oat grain sample obtained in the present study (Figure 2) were found to be close to that of the oat leaf sample obtained by Ren and Wise [17]), with respect to separation patterns of AVAs
Results show that all extraction methods separated individual AVAs very well (Figure 2)

Summary

Introduction

Compared to other cereal crops, oat (Avena sativa L.) is well known for its higher contents of oil, protein, and beta-glucan. Unique to oats is the natural presence of a group of phenolic alkaloids known as avenanthramides (AVAs) [2,3,4,5,6]. They were originally identified as phytoalexins produced by the plant in response to exposure to pathogens [7,8]. AVAs contain an anthranilic acid moiety conjugated to a phenylalkenoic acid moiety through an amide bond (Figure 1). The Collins nomenclature is based on letters only [2], while the modified Dimberg system is based on a combination of a number denoting the type of anthranilic acid and a letter denoting the type of phenylalkenoic acid [4,5,6,11]

Objectives

Methods

Results

Conclusion