Study On The Quality Degradation Mechanism Of Tibetan Hulless Barley Under Different Storage Conditions

With the growing demand for pollution-free high-quality cereals,grains became the staple food of a healthy and nutritious diet.Hulless barley is not only the leading crop of Tibetan areas and the main food for the herdsmen,but also the best food in the grains.The amount of 20%of hullesss barely due to the unsuitable storage and quality deterioration of the problem,which leads to the loss of 5?11 million tons per year.In recent years,the state in the grain storage preservation technology has been improved.Therefore,the effective,green and healthy preservation techniques of food have become increasingly urgent.At present,the utilization of controlled atmosphere storage and low temperature storage has been attracted more attention in food and agriculture scientists.In this thesis,the effects of temperature and CO2 controlled atmosphere storage on the quality of hulless barley were studied compared to natural sealed storage.Through differential proteomics analysis,the molecular mechanisms for preservation of huless barley during storage were stated at proteomics lever by using the iTRAQ marker combined with LC-MS/MS.The main contents and results are as follows:Firstly,the changes in physical and chemical properties of hulless barley during storage were investigated.Low temperature storage and CO2 controlled atmosphere storage were more effective in slowing down the increase of fatty acid value and peroxide value,indicating that low temperature and high concentration of CO2 were at a advantage in inhibiting the oxidation of fatty.Low temperature storage showed the most effective effect on the loss of moisture,the decrease of bound water and the increase of loosely bound water.CO2 controlled atmosphere storage effectively delayed the decrease of free sulfhydryl and the change of color,which indicated that the CO2 controlled atmosphere storage has a good protective effect on the freshness of hulless barley.Secondly,biochemical characteristic changes of hulless barley during storage were studied.Low temperature storage and CO2 controlled atmosphere storage can significantly lower the decrease rate of water soluble protein and the decrease of a-amylase activity.Low temperature storage can effectively reduce the activities of lipase,while the inhibition of lipase activity was more obvious in low temperature and CO2 controlled atmosphere storage.The higher the temperature,the less obvious the effect.C02 controlled atmosphere storage can effectively reduce the activity of catalase,the lower the temperature,and the better quality of the hulless barley.Thirdly,the changes in flavor substances of hulless barley during storage were studied.A total of 51 volatile compounds were detected,including 22 species of hydrocarbons,followed by aldehydes,ether phenols,alcohols,esters,acids and ketones.The relative contents of volatile components such as acids,esters,alcohols and ketones in the process of storage of hulless barley were gradually increased,while the relative contents of volatile components of hydrocarbons and aldehydes were decreased.It was indicated that the formation of flavor is the result of the interaction of different volatile substances during hulless barley storage.In addition,the deeper aging of hulless barley,the more obvious change of flavor substances.The last,the proteomic changes of the 0 d,25? 300 d,25?+CO2 300 d of hulless barley sample were studied.It was found that there were 3433 kinds of proteins in hulless barley,and the relative molecular mass was between 20?60 kDa,and the isoelectric point was between 4.5 and 7.Most of the length of the protein peptide contains 6 to 15 amino acids,and the longer length of the peptide,the less coverage of the peptide increases and the smaller number of proteins.The results showed that there were 132 differential expressed proteins in 25?/0 group,and 144 differential expressed proteins in 25?+CO2/0 group.These differential proteins mainly have ion binding function,oxidoreductase activity,and 25?/0 group also has ribosomal structural components,enzyme activity,25?+CO2/0 group also has transglycosyl transferase activity.These differential proteins were mainly involved in carbohydrate metabolism and biosynthesis biological processes,and 25?/0 group was involved in stress response,cell nitrogen complex metabolic process,25?+CO2/0 group was involved in translation,cell amino acid metabolism process and transport.The 25?/0 group was mainly located in the intracellular and ribosome,the up-regulated proteins in the organelles and cells,down-regulated proteins more concentrated in the cytoplasm of 25?+CO2/0 group and 25 ?/25?+CO2 group.28 differential expressed proteins associated with aging were found in these differential proteins,which were involved in 39 metabolic pathways.37 differential proteins associated with CO2 were found,involving 60 metabolic pathways.These differential proteins were associated with nitrogen metabolism,fatty acid degradation,fatty acid metabolism,pyruvate metabolism,aromatics degradation,glycolysis,amino acid biosynthesis,and pentose phosphate metabolic pathways.The expression of differential expressed proteins were different under different temperature and regulation conditions.Under 25? the up-regulated proteins involved in energy metabolism and glycolysis were more,indicating that high temperature was not conducive to maintaining the quality of hulless barley.CO2 controlled atmosphere storage can reduce amino acid metabolism and glucose metabolism.Elevated catalase expression,indicating that CO2 controlled atmosphere can slowed the rate of aging in hulless barley,but can not inhibit aging.The change of protein and the interaction between proteins in hulless barley directly affected the storage resistance of hulless barley.