Study On The Reaction Products Of Asparagine And Glucose At High Temperature Hydrothermal Conditions

High-temperature hydrothermal (HTH) is an emerging technique in extractionand modification of the valuable components, which is widely used in the industrialand food processing industry. Hightemperature hydrothermal extraction technique isone kind of separation technology which is cost-effective, safe and harmless to theenvironment. Studies have shown that, there are chemical reactions like Maillard andcaramelization during the extraction of natural materials. These reactions not onlylead to the production of some new active subatances with antioxidant activity, butalso production of harmful products, such as acrylamide. However, current studiesstill focused on salutary field of HTH, but limited knowlege on the generation ofhazardous substances and the relationship between active substances and hazardouscomponents was gained. In this study, the system of asparagine-glucose was studied,and we evaluated the properties of MRPs，the formation of acrylamide, melanoidinsand revealed the relationships between properties and formation, then obtainedapproaches to optimize food processing by HTH (low abundance of acrylamide,better palatability, and more potentially nutritional benefits). The main researchcontents and the conclusions were as following:(1) An improved method to detect the formation of acrylamide in Glu/Asn modelsystem using HPLC equipped with a UV detector was established. The optimumchromatographic detection conditions: sample loop onto a250mm×4.6mm,5μmPhenomenex C18column, injected sample volume:10μL, the detection wavelengthwas205nm, and eluted isocratically at30℃with5%methanol in water at a flowrate of0.4mL/min. In conclusion, this method has been certified as a new, low costalternative for routine analysis of acrylamide in this test.(2) The effects of high temperature hydrothermal on the generation ofacrylamide at various conditions were investigated. At lower temperatures, theincreased heating time was conducive to acrylamide formation. Increasing heatingtemperature and prolonging heating time significantly decreased the acrylamide concentration. When the system were at pH8and10, the formation of acrylamidewas promoted, however, at another pH value, the acrylamide content all decreased.Comparing with the higher ratio of glucose and asparagines, the lower ratio wasbeneficial to the higher acrylamide formation. The acrylamide formation was notdetected in the heated asparagine without glucose at160℃.(3) The effects of hightemperature hydrothermal on the formation ofmelanoidins at various conditions were evaluated. At higher temperature, prolongingheating time and higher glucose/asparagine ratio were conducive to the melanoidinsformation. The highest formation level of melanoidins was reached at initial pH10.(4) The effects of high temperature hydrothermal at various conditions on theantioxidants activity of MRPs were studied. At120℃and140℃, the DPPH radicalscavenging activity and reducing power increased with the extension of heating time.At160and180℃, the DPPH radical scavenging activity leveled off with longerheating time，while reducing power was slightly reduced after heating for a long time.It is concluded that the reducing power component was instable. At the ratio betweenglucose and lower than0.5, the DPPH radical scavenging activity and reducing powerincreased with the extension of heating time; At the ratio between glucose andasparagine higher than1, the DPPH radical scavenging activity leveled off withlonger heating times, while reducing power was reduced slightly. The higher level ofreducing power and DPPH radical scavenging activity was obtained respectively atinitial pH10and8.(5) The effects of high temperature hydrothermal at various conditions on theA294, A420, color and fluorescence of MRPs. When the temperature was lower than160℃, the A294, A420increased with the extension of heating time, while a slightreduction was observed after heating for a long time at180℃. The correlationbetween A294curves and A420curves suggests that a large proportion of theintermediate products are precursors of brown polymers. A steady increase offluorescence was observed at120℃and140℃, while a reduction was observed at160℃and180℃and the reduction at160℃was found to be more rapidly than180℃, suggesting that the fluorescent molecules are rather stable at hightemperature. L*of MRPs was decreased with the extension of heating time and temperature. b*and△E was changed in the opposite trend. a*was increased withthe increasing of heating time at≤160℃and changes in the opposite trend at180℃suggesting that the red molecules was instable.(6) The relationships between products and properties of MRPs wereinvestigated. There was close linear correlation between melanoidins and antioxidantactivity, which suggested that melanoidin was the major antioxidant of MRPs. Therewas fine linear correlation between acrylamide and antioxidant activity, whichconcluded that antioxidative compounds and acrylamide formed in the similar stagesof the Maillard reaction with a similar rate. There was close linear correlationbetween a*and acrylamide while there was no obvious correlation betweenfluorescent and melanoidins, antioxidants activity and acrylamide.