Influence of phenolic acid content on the antioxidant capacity of hemicellulose from sorghum plant fractions

Authors: Stoklosa, Ryan; Latona, Renee; Powell, Michael; Yadav, Madhav

Submitted to: BioResources
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2020
Publication Date: 9/2/2020
Citation: Stoklosa, R.J., Latona, R.J., Powell, M.J., Yadav, M.P. 2020. Influence of phenolic acid content on the antioxidant capacity of hemicellulose from sorghum plant fractions. BioResources. 15(4):7933-7953.

Interpretive Summary: Agricultural feedstocks are mostly comprised of natural polysaccharide polymers. The most abundant polysaccharides are starches found in cereal grains, and cellulose and hemicellulose found in plant cell walls or the bran layer of cereal grains. Hemicelluloses are an important group of polysaccharides that can be utilized in many applications ranging from the production of films that can be utilized for packaging, or as an additive in food items to improve the overall nutritional value of food items. One way hemicellulose can be utilized in food items is as an additive to boost antioxidant activity. Many hemicellulose fractions contain bound phenolic acids that work as an antioxidant against free radicals. The hemicellulose fraction from agricultural feedstocks can be effectively recovered after the feedstocks are processed for biofuel generation. The recovered hemicellulose can even improve the process economics for biofuel generation if utilized as a value-added co-product. In this work we investigate the hemicellulose polysaccharide arabinoxylan (AX) for its antioxidant properties. The AX fractions were isolated and recovered from sorghum bran, sorghum biomass, and sorghum bagasse. Additionally, the phenolic acid content for each AX fraction was determined to see the effect bound phenolic acids have on antioxidant capability. Each AX fraction was dissolved in solution and tested for its antioxidant capability. Sorghum bran AX at 1 g/L concentrations produced the best antioxidant performance, but sorghum biomass and bagasse AX contained the highest fractions of phenolic acids. Moreover, at higher AX concentrations a noticeable decrease in antioxidant capability was exhibited. The reason for this decrease was hypothesized to derive from the ability of the AX fraction to form aggregated material in solution and thus hindered the AX from being an effective antioxidant agent at higher solution concentrations.

Technical Abstract: Recovered co-products from integrated biorefineries have the potential to improve overall process economics during the production of biofuels or other high value chemicals. Hemicelluloses are polysaccharides that can be recovered from several biorefinery processes and have wide ranging applications from producing food packaging materials or use as a food additive to boost nutritional value. A common hemicellulose found in many agricultural feedstocks is arabinoxylan (AX). This work investigated the antioxidant capability of AX recovered from sorghum bran, biomass, and bagasse. Bound ferulic and p-coumaric acid content were also determined for each fraction as these contents are the primary drivers for antioxidant function in polysaccharides. Sorghum bran AX produced the best reducing capability and free radical scavenger at 1 g/L solution concentration. However, sorghum biomass and bagasse AX fractions exhibited the highest ferulic and p-coumaric acid content. Furthermore, a noticeable reduction in antioxidant capability was determined for all fractions at higher AX solution concentrations. It was hypothesized that the solution properties of recovered AX, namely the polysaccharides ability to form aggregates and gel in solution, hindered the hemicelluloses function as an antioxidant.