Diverse rheological properties, mechanical characteristics and microstructures of corn fiber gum/soy protein isolate hydrogels prepared by laccase and heat treatment

Authors: DENG, CHANGNING - China Agriculture University; LIU, YAN - China Agriculture University; LI, JINLONG - China Agriculture University; Yadav, Madhav; YIN, LIJUN - China Agriculture University

Submitted to: Food Hydrocolloids
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2017
Publication Date: 2/1/2018
Publication URL: http://handle.nal.usda.gov/10113/5611583
Citation: Deng, C., Liu, Y., Li, J., Yadav, M.P., Yin, L. 2018. Diverse rheological properties, mechanical characteristics and microstructures of corn fiber gum/soy protein isolate hydrogels prepared by laccase and heat treatment. Food Hydrocolloids. 76:113-122.

Interpretive Summary: Corn fiber gum (CFG) is a carbohydrate polymer present in the cell wall of corn kernels. CFG can be extracted from corn fiber, which is a low valued by-product of the dry or wet milling corn ethanol industries. In addition to their major carbohydrate components, CFG also contains a small amount of phenolic compounds. Several studies have reported that CFGs 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 and act as their delivery vehicle in human body. To solve this problem, we have prepared double network hydrogels by using a mixture of CFG and soy protein isolate (SPI). The hydrogel formation of CFG and SPI were initiated with the enzyme and heat treatment respectively in the same mixture. During such hydrogel formation, the CFG and SPI hydrogels become intertwined with each other and form a double network hydrogel. The mechanical properties, flow behaviors and microscopic analysis of these hydrogels were compared. These studies indicated that these new hydrogels have regular and dense inner structure with a smooth surface. They are also stronger than the hydrogel prepared with CFG or WPI. Thus, this technique of double network hydrogel formation can be useful in preparing hydrogels with greater strength and more uniform structure. These findings will help to increase the utilization of these CFG and WPI polymers in food and pharmaceutical applications and may benefit US corn and soy beans growers. The utilization of these products may ultimately improve the markets for corn and soy beans processing by-products. The production of new hydrogel products may also benefit the U.S. consumers, food and pharmaceutical industries and ultimately the U.S. economy.

Technical Abstract: Two types of corn fiber gum (CFGs) were extracted from corn fibers (CFs) obtained from wet or dry corn milling processing. Both CFGs could form hydrogels when induced via laccase, but CFGs isolated from wet milled CFs exhibited higher storage modulus (G') and better mechanical strength as obtained from rheological testings. Afterwards, CFGs from wet milled CFs and soy protein isolate (SPI) were used to fabricate CFG-SPI double network (DN) hydrogel using laccase and heat treatment processes, in which CFG solution formed the first gel network through laccase oxidation, while SPI formed the second network through heating. When compared with single network (SN) CFG-SPI hydrogel, the DN CFG-SPI hydrogel looked more firm and uniform with better elasticity. The rheological testings showed that both the storage modulus (G') and loss modulus (G'') of DN hydrogel were higher than SN hydrogels of CFGs or SPI. Moreover, the CFG-SPI DN hydrogels were harder than SPI hydrogels and exhibited better deformation ability compared to CFG hydrogels. The results from scanning electron microscopy indicated that these CFG-SPI DN hydrogels had more regular, denser inner structure and smoother surfacees than SN hydrogels.