Preparation Of Microencapsulated Glucose Oxidase And The Improvement On Quality Of Wheat Flour

The gluten in wheat flour is neither strong nor weak ubiquitously in our country, with less wheat varieties with excellent baking quality. The study is to prepare a safe and efficient flour improver under the premise of baking quality and safety. At present, glucose oxidase (GOD), whose improvement effect has been widely recognized, is considered to be "the most promising agent of green gluten flour", but there are still some drawbacks. Firstly, as a fast oxidizer, GOD catalyzes fast and large amount of H₂O₂ is generated during the dough formation process, which produces a large number of disulfide bonds to break free thiol (-SH) and be oxidized again, and this strong and fast cross-linking reaction is not selective, not conducive to post-polymerization of glutenin molecules and affecting the improvement effect.Secondly, GOD is less stable in dough, prone to degeneration and inactivation. Based on this, we embedded GOD using emulsion-internal gelation method with alginate -chitosan as wall material, improving the quality of GOD from three respects. Firstly, GOD was isolated from the outside environment by microencapsulation, improving the stability of the enzyme. Secondly, there is a swelling process for CAGC after adding water to the flour, delaying the oxidation onset. Lastly, diffusion resistance of substrate glucose from the microcapsules slows down the H₂O₂ generation rate.First, the preparation process of sodium alginate-chitosan micro-capsulated glucose oxidase (CAGC) was systematically studied. The effects of concentration of sodium alginate, CaCO₃ dosage, concentration of Span 80, stirring speed and water-oil ratio on the particle size distribution and sphericity of calcium alginate beads (CA), as well as the chitosan molecular weight, concentration and pH on the CAGC microencapsulation efficiency and the amount of protein loaded were investigated. The ultimate optimum microencapsulation conditions are as follows: alginate concentration 1.5%, CaCO₃ 4.0mg/mL, water to oil ratio of 1:5, Span 80 2.0% and stirring speed 1000 rpm, under these conditions the CA gel beads presented average particle size [D4,3] as 87.332μm, with good sphericity. The CA as the core of microcapsules, the chitosan with molecular weight 200,000 as the wall material, chitosan concentration of 1.5%, complex coacervation reaction pH 4.0, 60min reaction time generated the microencapsulation efficiency of 81.7%, protein loading capacity of 37.7mg/g, the volume of the prepared CAGC average size of [D4, 3] for 59.332μm,wall thickness of about 13.22μm and 4℃storage half-life of 105 days. Confocal laser microscopy showed that GOD evenly distributed in the inside of CAGC and the microcapsule presented membrane integrity and uniform thickness.Wet CAGC was dried using spray drying technology to improve the storage stability at room temperature and practical convenience. The final product yield and enzyme activity retention rate reached 72.19% and 80.64%, through response surface optimization. Decay Kinetic equation of dry CAGC has been built under 4℃, 25℃and 45℃, by which the corresponding enzyme activity half-life as 240 days, 190 days and 74 days.The effects of CAGC on the wet gluten content (WG), water-soluble and water insoluble protein-SH content (W-SH, DS-SH), dough properties, tensile properties, dynamic rheological properties and micro-structure were investigated. The results showed that CAGC did not exert its oxidative capacity during the dough formation process due to swelling stage, delaying the enzyme functioning and significantly improving the dry and harden phenomenon of dough with the rapid oxidation of GOD. However, the oxidation capacity of CAGC gradually embodied, reflected in WG content increases, W-SH and SDS-SH content decreased and improved viscoelasticity of dough, holding gas recovery and fermentation capacity. Compared with un-microencapsulated GOD, CAGC has starting time lag, low oxidization and extended action time, leading to increased oxidization degree after insulation and promoting the dough gluten chains cross-linking and dough gluten network structure.The variations of the dough height, gas holdup, CO2 spilled out of time, and W-SH and SDS-SH content were studied during the dough fermentation with different CAGC dose, with GOD and KBrO₃ as control. And the effects of CAGC on the dough gluten network structure and bread quality were analyzed through bread baking and texture analysis. The results showed that CAGC continuously oxidized W-SH and SDS-SH during fermentation, leading to formation of disulfide bonds and improved gas-holding capacity of dough, increased bread specific volume and quality of bread core. Furthermore, the difference of GOD and KBrO₃ in improving the quality of wheat flour was discussed as well as the advantages of CAGC compared with GOD, with the oxidization model as a benchmark.The diffusion rate inside the microcapsules and the molecular weight cutoff of linear polymer and spherical molecules was investigated with PEG of different molecular weight as spreading substrate and the curves for dry CAGC expansion and glucose diffusion, laying the foundation for the establishment of the actual catalytic rate of CAGC in dough system.Integrating the effects of CAGC on the dough components, rheological properties, fermentation capacity and bread baking etc, we established the correlation between the parameters and bread quality through distance analysis, analyzed the principle of microencapsulation to increase the GOD stability and discussed the mechanism of CAGC slow oxidation relative to GOD.