Diverse mechanical properties and microstructures of sorghum bran arabinoxylans/soy protein isolate mixed gels by duo-induction of peroxidase and calcium ions

Authors: YAN, JINXIN - China Agricultural University; ZHANG, BOYA - China Agricultural University; FENG, LIPING - China Agricultural University; YAN, WENJIA - China Agricultural University; WU, FEIFEI - China Agricultural University; LV, PENG - Hebei Academy Of Agriculture & Forestry; JIA, XIN - China Agricultural University; Yadav, Madhav; YIN, LIJUN - China Agricultural University

Submitted to: Food Hydrocolloids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2020
Publication Date: 4/18/2020
Citation: Yan, J., Zhang, B., Feng, L., Yan, W., Wu, F., Lv, P., Jia, X., Yadav, M.P., Yin, L. 2020. Diverse mechanical properties and microstructures of sorghum bran arabinoxylans/soy protein isolate mixed gels by duo-induction of peroxidase and calcium ions. Food Hydrocolloids. https://doi.org/10.1016/j.foodhyd.2020.105946.
DOI: https://doi.org/10.1016/j.foodhyd.2020.105946

Interpretive Summary: Arabinoxylans (AXs) are carbohydrate polymers present in the cell wall of grains and their processing by-products. AXs can be extracted from sorghum bran, which is a low valued by-product of sorghum grains milling in ethanol industries. In addition to their major carbohydrate components, AXs also contain a small amount of phenolic compounds. Several studies have reported that AXs can be connected to each other through phenolic groups to form hydrogels when treated with an enzyme called “laccase”. However, the hydrogels formed by simple enzyme treatment may not be strong enough to encapsulate drugs or bioactive compounds. To solve this problem, we have prepared a multiple network mixed gel by using a mixture of sorghum AXs and soy protein isolate (SPI). The gel formation of AXs and SPI was initiated by crosslinking them with the enzyme (peroxidase) and metal ion (calcium). During such gel formation, the AXS and SPI become intertwined with each other and form a multiple network gel. The mechanical properties, texture characterization, flow behaviors and microscopic analysis of these gels were studied. These studies indicated that these new hydrogels have regular and dense inner structure with a smooth surface. They are also stronger than the gel prepared with AXs or WPI. Thus, this technique of multiple network gel formation can be useful in preparing hydrogels with greater strength and more uniform structure. These findings will help to increase the utilization of sorghum bran AX and WPI in food and pharmaceutical applications and may benefit US sorghum and soy beans growers. The utilization of these products may ultimately improve the markets for sorghum and soy beans processing by-products. The production of new mixed gel products may also benefit the U.S. consumers, food and pharmaceutical industries and ultimately the U.S. economy.

Technical Abstract: This study investigated the molecular characteristics and rheological properties of arabinoxylans (AX) extracted from three different red sorghum brans from Shandong, Shanxi and Hebei Province in China. It was found that only the Shandong sorghum bran AX, with its high ferulic acid content and low Ara/Xyl ratio, could form a functional gel. Subsequently, this AX and soy protein isolate (SPI) were used to prepare mixed gels using two crosslinking agents, namely peroxidase and calcium ions. Dynamic rheological tests showed that the doubly induced AX-SPI mixed gel had higher storage modulus (G') and loss modulus (G'') than mixed gel by only peroxidase or AX gel induced by one or two crosslinking agents. In addition, TPA analysis confirmed that the doubly induced mixed gel was harder and more elastic than the other gels. FT-IR spectroscopy further confirmed that, in addition to the presence of AX intermolecular covalent cross-linked gel network by peroxidase and the connection of SPI intermolecular gel network via salt bridge (Ca2+), a partial covalent cross-linking network between AX and SPI existed in the doubly induced mixed gel. Microstructure observation of the gels revealed that the doubly induced AX-SPI mixed gel had a more regular, uniform and dense inner structure than the AX single network gel. Gels with different mechanical properties and network structures could be prepared by adjusting the order of addition of the crosslinking agents.