Rheology and microstructure of gels based on wheat arabinoxylans enzymatically modified in arabinose and xylose

Authors: MARQUEZ-ESCALANTE, JORGE - Center For Research In Food And Development (CIAD); CARVAJAL-MILLAN, ELIZABETH - Center For Research In Food And Development (CIAD); Yadav, Madhav; KALE, MADHUVANTI - Z-Trim Holdings, Inc; RASCON-CHU, AGUSTÍN - Center For Research In Food And Development (CIAD); GARDEA, ALFONSO - Center For Research In Food And Development (CIAD); VALENZUELA-SOTO, ELISA - Center For Research In Food And Development (CIAD); LÓPEZ-FRANCO, YOLANDA - Center For Research In Food And Development (CIAD); LIZARDI-MENDOZA, JAIME - Center For Research In Food And Development (CIAD); FAULDS, CRAIG - Inland Northwest Research Alliance, Inra

Submitted to: Journal of the Science of Food and Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/6/2017
Publication Date: 1/1/2018
Publication URL: http://handle.nal.usda.gov/10113/5883641
Citation: Marquez-Escalante, J.A., Carvajal-Millan, E., Yadav, M.P., Kale, M., Rascon-Chu, A., Gardea, A.A., Valenzuela-Soto, E., López-Franco, Y., Lizardi-Mendoza, J., Faulds, C.B. 2018. Rheology and microstructure of gels based on wheat arabinoxylans enzymatically modified in arabinose and xylose. Journal of the Science of Food and Agriculture. 98:914-922.

Interpretive Summary: Arabinoxylans (AX) are carbohydrate polymers present in all plant cell walls. They can be extracted from low value agricultural and industrial by-products such as cereal brans, crop residues and distiller’s dried grains (DDGS), which is a byproduct of the ethanol industry. Some AXs can form strong covalently bound gels that have potential applications as drug delivery matrices. This study specifically focused on using a technique called Atomic Force Microscopy (AFM) to study the structure of the gel and the effect of the molecular structure of the AX on the structure of its gels. By treating AX with an enzyme, samples with varying amounts of branching were prepared and subsequently gelled. It was found that decreasing the number of branches affected the gel structure, making it more compact. Based on the actual dimensions calculated from the AFM images, the number of molecules participating in each gel strand was calculated and found to increase with decreasing degree of substitution. This study is the first to report successful AFM imaging of AX gels, and it represents a unique method to obtain valuable three dimensional images to better understand their structure. The results of this study improve our understanding of AX gels, and will help further utilization of these polymers, in food and pharmaceutical applications. Thus these results may benefit farmers because utilization of these products will ultimately improve the markets for agricultural by-products. It will also benefit the U.S. consumers, food and pharmaceutical industries and ultimately the U.S. economy.

Technical Abstract: Atomic force microscopy (AFM) was used to investigate the microstructure of laccase-induced arabinoxylan (AX) gels for the first time. The effect of the degree of substitution (DS) of AX on gel microstructure was investigated by AFM. AX with three DS values (0.68, 0.61 and 0.51) were enzymatically tailored without affecting any other structural characteristics of this polymer. The AFM image of AX gels with DS of 0.68 showed a sponge-like microstructure, which appeared to be constituted of connected strands of several AX chains. At lower DS values, AX formed gels exhibited a more compact and robust microstructure with connected strands, which appeared to constitute a higher number of AX chains. These results suggest that lower DS values favor the aggregation of AX chains and that physical interactions play an important role, along with covalent bonds in the three-dimensional polymeric network.