Effect Of Ana-rLOX And RGOx-m On Frozen Non-fermented Dough Quality And Its Application On Frozen Noodles

Lipoxygenase(LOX)is classified as oxidoreductases.LOX can catalyze polyunsaturated fatty acid(PUFA)containing cis,cis-1,4-pentadiene structure,resulting in the formation of hydroperoxides with a conjugated double bond.These hydroperoxides with high activity are important intermediates in many chemical reactions.Therefore,they can be widely used during food processing.Currently,the researches about LOX are mainly focused on investigating the effect of soybean rich in LOX on the quality of flour and bread.It has been reported that LOX has good strengthening and bleaching effects.Glucose oxidase can catalyze glucose to produce ξ-D-glucose lactone and hydrogen peroxide under aerobic conditions.Hydrogen peroxide has strong oxidizing ability to oxidize the thiol(-SH)of gluten molecules to a disulfide bond(-S-S-),thus strengthening gluten significantly.Therefore,glucose oxidase is regarded as the most promising alternative to potassium bromate.This thesis was based on the previous studies about expression of recombinant lipoxygenase(Ana-rLOX)and recombinant glucose oxidase(rGOx-m)in our laboratory.Wheat flour Yangmai 13 was used as experimental materials,and the effects of Ana-rLOX and rGOx-m on frozen non-fermented dough were explored.At the same time,response surface methodology was used to optimize the proportion of two enzymes in frozen non-fermented dough.Moreover,the quality improvement of frozen noodles induced by the two enzymes was also evaluated.The main results are shown as follows:1.Effect of rGOx-m on wheat flour.The effect of rGOx-m on wet gluten content,dough farinographical properties,tensile properties and dynamic rheological properties was studied.It was found that wet gluten content,development time and stability time increased progressively after rGOx-m addition.When the rGOx-m addition in flour and dough were 0.8 U/g,the development time and stability time increased by 2.0 min and 2.3 min.Meanwhile,wet gluten extraction yield increased significantly compared with the control sample(P<0.05).RGOx-m mainly affected the tensile resistance of dough.When the rGOx-m addition was 0.8 U/g in flour and dough,the tensile resistance of dough increased by 94.9%at 90 min and 77.9%at 135min.Furthermore,rGOx-m addition increased G’ and G" of dough,since rGOx-m can make gluten network more powerful.RVA experiments showed that peak viscosity increased when rGOx-m was added,while trough viscosity and final viscosity reduced.2.Effect of Ana-rLOX and rGOx-m on the properties of frozen non-fermented dough and optimization of two enzymes’ proportion in frozen non-fermented dough.The effect of Ana-rLOX and rGOx-m on wet gluten content,water loss rate,color,tensile properties,dynamic rheological properties was studied and response surface methodology was used for optimization.To be exact,the addition of Ana-rLOX and rGOx-m can significantly increase wet gluten content(P<0.05)and reduce the frozen non-fermented dough’s water loss rate(P<0.05).Ana-rLOX can also bleach the frozen non-fermented dough.When the addition was 50 IU/g,L*increased by 2.11 compared with the control sample.Ana-rLOX and rGOx-m addition increased G’and G" of frozen non-fermented dough.Furthermore,Ana-rLOX and rGOx-m addition can significantly improve the tensile resistance of frozen non-fermented dough.Response surfacoptimization showed that when the amounts of Ana-rLOX and rGOx-mwere 16.13 IU/g and 0.70 U/g,the tensile area reached 136cm,which was consistent with the predicted result(135.416 cm2).In addition,the tensile area of frozen non-fermented dough containing enzyme mixture was higher than that of frozen non-fermented dough containing single enzyme.SEM microstructure showed that the frozen non-fermented dough containing enzyme mixture can form a large fiber bundle structure.Dynamic rheological results showed that the G’ and G" of sample with enzyme mixture increased significantly compared with the frozen non-fermented dough with single enzyme.3.Quality improvement of frozen noodles using enzyme mixture.The effect of enzyme mixture on the quality of frozen noodle after processing and during storage was studied.When enzyme mixture was added,the hardness,elasticity and L*increased by 23.8%,37.9%and 5.0%,respectively,compared to control sample.After 30 day storage,the properties of frozen noodles added with enzyme mixture were maintained well,indicating that enzyme mixture can preserve frozen noodle quality during storage.Scanning electron microscopy(SEM)experiments showed that after 20 day storage at-18 ℃,gluten membrane structure can be easily observed in frozen noodles containing enzyme mixture.Parts of the gluten network structure remained intact.These results indicated that the addition of enzyme mixture can effectively enhance the gluten network structure,alleviate the damage of gluten network structure during crystallization and re-crystallization,and protect the frozen noodle quality and structure.