Extraction of avenanthramides from oats (Avena sativa) using pressurized hot water extraction

Abstract

Introduction: Avenanthramides are antioxidants present in oats, which are interesting as a food additive for functional foods.

Background: The most common method used for extraction of avenanthramides is a relative time consuming solid-liquid extraction with aqueous ethanol, which is not suitable for large scale extraction. A greener alternative could be pressurized hot water extraction (PHWE).

Aim: The aim of this project is to investigate if PHWE can be used for the extraction of avenanthramides, and to find optimal extraction conditions with regard to temperature, flow rate and amount of formic acid added to the water.

Methods: The avenanthramides were extracted with PHWE, extracted from the water phase with liquid-liquid extraction and analysed by reverse-phase HPLC with UV-detection. Optimal extraction conditions were investigated by a Box-Behnken experimental design.

Results: Optimal extraction conditions were calculated to be at 160°C and 4.5 % formic acid, with yields similar to the reference extraction method. High temperature and formic acid content partly or totally dissolved the sample matrix.

Conclusion: PHWE can be used for extracting avenanthramides in similar yield to the reference method. The drawback of the method is the large volume of the extract and the dissolution of the matrix.

Popular Abstract

Oat (Avena sativa) is a cereal that is ideal for cultivation in the Nordic countries due to its high tolerance for rain and ability to grow in cooler climate compared to other cereals. Oats contains a large number of compounds that act as antioxidants. Antioxidants, as the name suggests, are compounds that prevent oxidation, and are common additives in food to prevent it from oxidation and getting spoiled. In fact, during the early 20th century, paper coated with oat flour was used to prolong the shelf-life of food. One group of antioxidants found in oats are called avenanthramides and are the focus of this project.

The most common way of extracting avenanthramides is by mixing oat flour with 80% ethanol buffered to pH 2.8 A more environmentally sustainable and food-compatible way would be to use water for extraction. The problem is that water is too polar to extract avenanthramides since they are relative non-polar. By applying a pressure, we can get water hotter than 100°C and still keep it as a liquid. At higher temperatures, the dielectric constant of water decreases (i.e., the water appears less polar), and is more likely to dissolve avenanthramides. This extraction method is called pressurised hot water extraction (PHWE). The aim of this project was to investigate if PHWE can be used to extract avenanthramides and to find optimal conditions for extraction.

It was found that avenanthramides could be extracted with PHWE using water containing 2.5 - 5% formic acid at 160°C in similar yield as extraction with ethanol. However, some challenges remain to make this extraction effective at larger scale.

• author: Pålsson, David
• supervisor: Charlotta Turner; Cecilia Tullberg
• organization: Department of Chemistry
• course: KEMR10 20221
• year: 2022
• type: H2 - Master's Degree (Two Years)
• subject: Chemistry
• keywords: Antioxidants, Avenanthramides, Oats, Pressurised hot water extraction, Analytical chemistry
• language: English
• id: 9095140
• date added to LUP: 2022-08-01 11:52:20
• date last changed: 2022-08-01 11:52:20