Comparison of Alkaline/Oxidative and Hydrothermal Extraction of Wheat Bran Arabinoxylans

Abstract

The bran accounts for approximately 25% of the wheat kernel but is currently only a by-product, used as animal feed. However, due to its high arabinoxylan content it could be a valuable raw material for food production. Arabinoxylans cannot be digested in the human intestine but are intensely studied for their health-beneficial properties. These include glycemic control by formation of a highly viscous gel in the intestine, and hence delaying starch digestion, alongside an increase in short chain fatty acids. To apply sufficient amounts of arabinoxylan for health-beneficial effects, extraction and concentration is required. Alkaline/oxidative conditions are commonly used, but for potential food applications more cost-efficient methods, without hazardous chemicals, are required. Therefore, this study aimed to optimize the conditions for hydrothermal extraction (extraction time and temperature) at laboratory-scale and to compare the results to an established alkaline/oxidative method. The resulting extracts were characterized for yield, purity, arabinoxylan molecular mass, arabinose/xylose ratio, and viscosity to evaluate the quality of the method. For the hydrothermal extraction, an extraction time of 1 h at 160 °C and 6.5 bar gave the best results. However, even these optimized conditions resulted in lower extract purity and severely degraded arabinoxylans. Although further optimization of the hydrothermal process is required, the present work builds an important foundation for the development of an industrial hydrothermal extraction method.

Recycling of wheat gluten wastewater: separation, characterisation, and solution rheology of arabinoxylans

“…2b. When the temperature increased from 5 °C to 45 °C, the apparent viscosity of WEAX decreased with the rise in temperature, consistent with observations in similar AX studies (Yan et al ., 2019; Marcus et al ., 2021). This phenomenon was particularly prominent, with the apparent viscosity of WEAX at 5 °C being approximately 7.6 times greater than that at 45 °C, indicating the solution's high sensitivity to temperature changes.…”

“…As the solution temperature rises, the zero shear viscosity η 0 of WEAX solution decreases and fluctuates between 0.14 Pa·s and 0.0094 Pa·s. This change aligns with the observed behaviour of AX variants (Marcus et al ., 2021), indicating that aqueous solutions exhibit greater flowability at elevated temperatures. The apparent viscosity of WEAX also decreases with rising temperature, likely due to the enhanced deformability and flowability of the polysaccharide structure at higher temperatures (Anvari et al ., 2016).…”

Wheat bran arabinoxylans: Chemical structure, extraction, properties, health benefits, and uses in foods

“…Higher temperatures, longer durations, and acidic conditions could cause a significant depolymerization of AX and reduction of MW (Li et al., 2020). The WB AX extracted by hydrothermal extraction (160°C) was found to have a lower degree of substitution (A/X = 0.45) and lower MW (20 and 5 kDa) compared to their alkali‐extractable counterparts (A/X = 0.82; two fractions with MW of 100–120 and 5–10 kDa) (Schmidt et al., 2021). The AX in the WB layers, which have different chemical structures, may not be extracted at the same time in subcritical water.…”