Submitted to: Foods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/11/2022
Publication Date: 2/16/2022
Citation: Woolman, M.J., Liu, K. 2022. Simplified analysis and expanded profiles of avenanthramides in oat grains. Foods. 11(4). Article 560. https://doi.org/10.3390/foods11040560.
Interpretive Summary: Compared to other cereal crops, oat is well known for its higher contents of oil and protein and rich presence of beta-glucan. Furthermore, unique to oats is the natural presence of a group of phenolic alkaloids known as avenanthramides (AVAs), which have been shown to provide health benefits in mammals, including anti-oxidation, anti-inflammation, anti-atherosclerosis, and anti-cancer properties. Analysis of AVAs typically involves extraction with an alcohol-based solvent and separation by liquid chromatography. There are many variations in AVA extraction methods among reports, but almost all investigators make repeated extractions, which is time and labor intensive. In some cases, a rotary evaporator is used to dry extracts, which makes quantitative measurement difficult to achieve. Although a few tried to optimize their extraction procedures for maximum AVA contents, none has investigated the effect of AVA extraction on composition of AVAs (% relative to total) in oats. Furthermore, so far about 35 AVAs have been identified from oat grains, but only AVA 2c, 2p, and 2f are commonly quantified. The present study simplified AVA extraction by using a single extraction procedure and replacing the rotary evaporator with a vacuum oven, without affecting AVA contents and composition (% of each AVA relative to total AVAs). It also provided semi-quantification of a few other AVAs in oat grains, in addition to the common three.
Technical 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.