Studies On The Emulsifying Properties And Interfacial Viscoelasticity Of Structural Lipid-modified Corn Fiber Gum

Corn fiber gum?CFG?,also called hemicellulose B or arabinoxylan,is a kind of natural polysaccharide extracted from corn fiber or corn bran.CFG possesses the characteristics of highly branched structure,good water solubility and low solution viscosity,and has been considered as a potential replacer of gum arabic with wider application prospects due to its good emulsifying capability.The further improvement of the emulsifying activity of CFG via physical or chemical methods has attracted much attention,and it is also a main route to achieve the high value utilization of this corn by-product to extend its application.Structured lipids?SLs?are functional lipids that provide basic nutrition and special physiologic functions.Glyceryl monooleate?GMO?and Diolein?DO?are two types of biocompatible and biodegradable SLs.While GMO has anti-oxidant,anti-diabetic and anti-atherosclerotic activity,DO is of unique physiological benefits including suppressive effects on hypertriglyceridemia,obesity and body fat accumulation.In this work,a new hydrophobic modification strategy was proposed for CFG.In order to further improve the long-term emulsification stability of CFG and endow the derivatives with the special properties of GMO/DO,CFG was chemically modified with GMO and DO,respectively.Chemical modification of CFG is expected to provide theoretical supports and techniques to promote and broaden the industrialized application of CFG.The main research contents are summarized as follows:?1?Two types of structural lipids of GMO and DO,were firstly synthesized by enzymatic esterification,respectively,and then each of them was grafted onto CFG molecules via esterification to obtain two kinds of CFG derivatives of GMO-CFG and DO-CFG.The structures of both of the derivatives were characterized by ¹H-NMR and FT-IR analysis,and their degrees of substitution were determined by ¹H-NMR analysis.?2?Comparative studies were made on the bulk rheological properties,surface tension and interfacial tension of CFG and GMO-CFG/DO-CFG.Experimental results indicated that while CFG behaved as a Newtonian fluid,both GMO-CFG and DO-CFG exhibited Newtonian fluid behavior at low concentrations but exhibited shear thinning properties at high concentrations.The apparent viscosity of the aqueous derivative solution depends on the degree of hydrophobic modification,increasing with the increase of DS and emulsifier concentration.Compared with CFG,both GMO-CFG and DO-CFG derivatives shown more effective reduction abilities to surface tension and interfacial tension.?3?The interfacial shear rheology of the CFG and GMO-CFG/DO-CFG adsorption layers at the oil/water interfaces was analyzed and compared.The influences of DS and emulsifier concentration on the interfacial rheological properties were considered.Interfacial viscoelasticity was measured by using several test modes?time sweep,frequency sweep and steady shear?.Results showed that all of the CFG,GMO-CFG and DO-CFG emulsifiers formed pure viscous films at the soybean oil/water interface with a fast adsorption kinetics,and their complex moduli increased with increasing DS.The relationship of the shear viscosity and complex viscosity of the interfacial films was in accordance with the Cox-Merz rule,indicating that the emulsifier molecules didn't form microstructures in the interfacial layers.The adsorption kinetics of CFG and GMO-CFG indicated that the emulsifying activity of CFG can be enhanced greatly by hydrophobic modification.The adsorption layers are of high viscoelasticity with a large adsorption amount and the desorption of GMO-CFG was less prone to occurrence.?4?The stability of soybean oil emulsions prepared by CFG,GMO-CFG and DO-CFG emulsifiers was evaluated by droplet size and distribution analysis,confocal microscopy observation,zeta potential analysis,centrifugal acceleration stability analysis and spin-spin relaxation time?T₂?measurements.The influences of DS and emulsifier concentration were also considered.The results demonstrated that the emulsifying activity and emulsion stability of GMO-CFG/DO-CFG were greatly improved.The emulsion stability was enhanced with the increase of DS.?5?The emulsification and stabilization mechanism of CFG and GMO-CFG/DO-CFG were discussed and proposed.The increase of the content of hydrophobic component in CFG by grafting GMO/DO molecules is the essential benefit to advance the interfacial activity of CFG and reduce the oil/water interfacial tension.Compared with CFG,both GMO-CFG and DO-CFG can form viscous interface films with a higher modulus at the oil/water interface,which can effectively reduce the aggregation of droplets caused by the breakage of the interface films,thus improving the emulsion stability.