Preparation And Property Analysis Of Partially Hydrolyzed Guar Gum And Its Effect On Oat Protein Emulsion

Guar gum（GG）,whose main component is galactomannan,is a commonly used thickener and stabilizer.However,GG has the disadvantages of slow hydration speed and high solution viscosity,which limits its application in food.Therefore,in this study,the conversion equation was fitted by the least square method,to establish a method for detecting the absolute molecular weight of partially hydrolyzed guar gum（PHGG）using gel permeation chromatography（GPC）with differential detector.The key factors affecting the enzymatic hydrolysis of GG were regulated to prepare PHGG with different molecular weights.The properties of PHGG samples were studied by monosaccharide composition analysis,structure characterization,and thermodynamics.Furthermore,the effects of concentration,p H,and temperature on the rheological properties of PHGG and the impacts of medium and high molecular weight PHGG on the stability and microstructure of oat protein emulsion were investigated.The main conclusions are as follows:By optimizing the chromatographic column,mobile phase,column temperature,and flow rate,a method for detecting the molecular weight of PHGG by GPC was established.The chromatographic column was Ultrahydrogel^TM linear（300×7.8 mm）.The mobile phase was 0.3mol/L Na NO₃.The flow rate was 0.6 m L/min.The column temperature was 40°C.The dn/dc values of PHGG in different molecular weight ranges were determined by ASTRA software.Using the least square method,the fitting equation between the relative molecular weight parameters detected by gel permeation chromatography-differential detector（GPC-RID）and the absolute molecular weight parameters of PHGG detected by gel permeation chromatography-multiangle laser light scattering（GPC-MALLS）was established.The results elucidated that the relative molecular weight range of PHGG was 5.0×10⁵ Da<Mw<4.0×10⁶,which was consistent with the fitting equation of molecular weight parameters.The relative error between the calculated absolute molecular weight parameters and the measured values of GPC-MALLS was within±10%.With the relative molecular weight of PHGG as an indicator,β-mannanase was selected for single enzymatic hydrolysis.By investigating different enzymatic hydrolysis conditions,three key factors affecting the molecular weight of PHGG were obtained:enzyme addition,substrate concentration and enzymatic degradation time.Controlled enzymatic hydrolysis to prepare medium and high molecular weight PHGG1（8.92×10⁵ g/mol）,medium molecular weight PHGG2（5.07×10⁵ g/mol）and low molecular weight PHGG3（0.62×10⁵ g/mol）.The monosaccharide composition of GG and PHGG was determined by ion chromatography.Their structures were characterized using fourier transform infrared spectroscopy,nuclear magnetic resonance spectroscopy and X-ray diffraction.The thermodynamic properties were analyzed by differential scanning calorimetry and thermogravimetric analysis.The results indicated that the mannose/galactose ratio（M/G）of PHGG was slightly higher than that of GG.Enzymatic hydrolysis neither changed the main structure of PHGG nor introduced new functional groups,but the crystal structure changed slightly.Meanwhile,PHGG still has good thermal stability at higher temperatures.The effects of concentration,p H,and temperature on the rheological properties of PHGG with various molecular weights were investigated.The results revealed that the PHGG solution was a shear-thinning non-Newtonian fluid under different conditions.At the same concentration,the greater the molecular weight of PHGG,the greater the apparent viscosity and storage modulus.PHGG with different molecular weight and M/G required different p H conditions to form gel.PHGG1 solution forms a weak gel structure with high strength at p H6.Temperature scanning suggested that the activation energy of PHGG1 solution was smaller than that of PHGG2 and PHGG3,and the viscosity was less dependent on temperature.Moreover,the variation trend of viscoelasticity of PHGG1 solution was the same as that of GG,which was more advantageous in thermal processing.Hence,PHGG1 may be an alternative stabilizer for GG.The effects of GG and PHGG1 concentration on the stability and microstructure of oat protein emulsion were investigated.The particle size and Zeta potential analysis revealed that0.8%GG emulsion and 0.8%PHGG1 emulsion had the smallest Z-average particle size,but the emulsion PDI values were larger,indicating the existence of molecular aggregation in the system.There was no significant difference in Zeta potential between different concentrations of emulsion.The 0.8%GG emulsion was layered after 14 days of storage,while the 1%PHGG1 emulsion maintained the stability of the oat protein emulsion within 14 days.This manifested that 1%PHGG1 emulsion had better emulsification and emulsion stability.Rheological results suggested that the emulsion with PHGG was a shear-thinning non-Newtonian fluid,and the 1%PHGG1 emulsion had higher apparent viscosity and storage modulus.Laser scanning confocal microscopy observation that the microstructure of 0.8%GG emulsion had open flocculation,and the microstructure of 1%PHGG1 emulsion demonstrated that oat protein and PHGG uniformly wrapped oil droplets to formed a dense network structure.Therefore,oat protein emulsion with 1%PHGG1 had excellent storage stability and microstructure.