Study On Changes And Mechanism Of Gluten Aggregation In Newly Harvested Wheat During Postharvest Maturation

The processing quality of newly harvested wheat is not stable.Under suitable storage temperature and humidity conditions,after a certain period of storage,the postharvest maturation process will improve the processing quality and edible quality of wheat.As a storage protein in wheat grains,wheat gluten protein plays a very important role in affecting wheat quality and processing characteristics.During the postharvest maturation process of newly harvested wheat,wheat gluten protein aggregates,forming a tighter gluten network,which changes the viscoelasticity and hardness of gluten,thereby changing the processing quality of wheat.The mechanism for the change of wheat gluten protein aggregation characteristics is mainly the cross-linking between proteins.The intra-or intra-molecular covalent bonds are formed between the polypeptide chains of gluten protein,so that the proteins are connected to each other to form large aggregates.The change may not only be closely related to the content and structure of gluten protein,but protein disulfide isomerase(PDI),which can help the correct formation of protein disulfide bonds,also plays an important role.This project selected the medium-gluten wheat Panmai 8 widely grown in Henan Province as the experimental material to simulate the storage of three main grain ecological regions in China: Mengxin ecological region 15℃ 50% RH(WT1);North China ecological region 20℃ 65% RH(WT2);Central China ecoregion 28℃ 75% RH(WT3).In order to explore the mechanism of quality change during postharvest maturation of newly harvested wheat,based on the analysis of changes in gluten protein aggregation characteristics during postharvest maturation of newly harvested wheat,changes in gluten protein structure,gene expression change rules and protein disulfide isomerase activity were analyzed.The result shows:During the postharvest maturation process of newly harvested wheat,the peak formation time(PMT)in the GlutoPeak graph gradually increased;the peak torque(BEM)changed little;the peak area(EnMT)gradually increased.This indicates that the gluten aggregation time gradually increases,which may improve the rheological properties of the gluten;the gluten extension resistance increases,the ductility decreases,and the gluten strength increases.The gluten peak area can be used to analyze the quality change of newly harvested wheat duringpostharvest maturation.The gluten aggragation characteristics are the best when stored under WT3 until about 14 weeks,and the wheat quality is the best.During the postharvest maturation of newly harvested wheat,the content of each protein component changed with storage time and storage conditions,and the total amount of protein did not change significantly during postharvest maturation;the content of gliadin in gluten protein decreased,and glutenin and glutenin macropolymers(GMP)content increased;and the experimental materials stored under WT3 until the 14 th week had the most significant change.At the same time,the content of free sulfhydryl groups in glutenin macromers decreased significantly,and the content in WT3 experimental materials was the least.SDS-PAGE analysis of the molecular weight distribution of glutenin macropolymers(GMP)showed that the distribution phenomenon under WT3 was affected by storage time,temperature and humidity.With the extension of the postharvest maturation time,the HMW-GS content in the experimental materials increased,and LMW-GS content reduced.The particle size distribution,secondary structure,and microstructure of GMP of newly harvested wheat during the postharvest maturation all changed to some extent.Among them,the change of GMP particle size is similar to its content and molecular weight distribution.With the increase of post-storage time,the smaller particles gradually decrease,and the larger particles gradually increase.The conversion of large-diameter particles to large-diameter particles is more convenient for the aggregation of large-diameter particles.Under the storage conditions of WT1 and WT2,the secondary structure of GMP was not significantly changed.Under WT3 storage conditions,the trend of decreasing α-helix content and increasing β-sheet content was the most significant.The ratio is the smallest.Obviously,under the scanning electron microscope under three storage conditions,GMP aggregated,and gradually aggregated from a single irregular particle to form a compact,smooth and flat large aggregation.WT3 condition can accelerate the aggregation.During postharvest maturation of newly harvested wheat,wPDI can promote the accumulation of wheat gluten protein,and its gene expression,redox activity and secondary structure have changed to a certain extent.With the increase of postharvest maturation time,the up-regulated genes of w PDI increased and the expression of related genes increased.Themost up-regulated genes of wPDI were newly added at the 8th week of WT3 storage condition;the increase of the content of α-helix in the secondary structure may be directly proportional to the oxidation activity and inversely proportional to the reduction activity of wPDI.In summary,the more up-regulated genes of wPDI,the more wPDI can be expressed,and under the action of wPDI,more disulfide bonds can be formed;at the same time,the higher the oxidation activity of wPDI,the catalytic oxidation of free thiol to two The greater the amount of sulfur bonds,the greater the amount of large polymers formed by disulfide bond connections,and the more prominent the gluten aggregation characteristics..