Study On The Properties Of Some Sulfur-containing Amino Acids In Garlic

This study investigated the effect of different immersion liquids on sulfur-containing volatile substances in garlic?Allium sativum L.?products,the combination of dynamic purging system?DHS?and gas chromatography-mass spectrometry?GC-MS?was used to determine the volatile components from the sulfur-containing amino acids of garlic in oil,vinegar and water.Three sulfur-containing amino acids that can produce volatile substances were synthesized,and their interaction with proteins?such as bovine serum albumin?was determined by fluorescence spectroscopy and synchronous fluorescence spectroscopy.Meanwhile,three sulfur-containing amino acids were determined with DPPH,hydroxyl radical scavenging,reduction ability of potassium ferricyanide,antioxidant capacity of fats and oils by UV.Furthermore,thermal decomposition curves of sulfur-containing amino acids were determined by differential scanning calorimetry?DSC?and thermodynamic parameters were calculated.The main research results are as follows:1.Three kinds of immersion liquid treatments affect the types and content of volatile components in garlic.Eight kinds of volatile components are identified in oil immersion liquid,vinegar immersion liquid,water immersion liquid,such as diallyl disulfide?DADS?,3-vinyl-1,2-dithiacyclo-4-cyclohexene,2-vinyl-4H-1,3-dithiane,?E?-1-allyl-2-?prop-1-en-1?disulf-ane,five kinds of volatile components such as trisulfide,di-2-propenyl?DATS?,3H-1,2-dithiole are identified in oil immersion garlic,and four kinds of volatile components such as DATS and3H-1,2-dithiol in vinegar immersion garlic,and 3-methyl-3H-1,2-dithiole are identified in water immersion liquid.Total absolute content of peak area of sulfur-containing volatile components:oil immersion liquid?50.45×10⁸ in term of peak area?>vinegar immersion liquid?28.14×10⁸?>water immersion liquid?14.88×10⁸?.2.S-allyl cysteine?SAC?,S-allyl cysteine sulfoxid?SACS?and S-allyl mercapto cysteine?SAMC?were synthesised by using TLC,HPLC,HPLC-MS,HRMS,IR and ¹H-NMR and other structural identification methods,the purity of the products is greater than 95%.3.Quenching effect of SAC and SACS on bovine serum albumin?BSA?is dynamic quenching and the quenching effect is not good,while SAMC is static quenching.The binding constants of SAMC at 298 K?310 K.s are 6.18×10³,5.54×10³ L/mol,respectively.Its binding site to BSA is 1:1?it closer binds to tryptophan residues?,and both are mainly electrostatic attraction.The thermodynamic parameter?H is-7.06 kJ/mol,?G at 298 K?310 K are-21.63,-22.21 kJ/mol,?S at corresponding temperature are 48.89,46.99 J/mol/K,and the binding distance is 1.61 nm.4.The order of free radical scavenging rates are:SAMC>SACS>SAC,and the IC₅₀0 of SAMC is 1.1706 mg/mL in DPPH free radical scavenging experiments,.the sequence of free radical scavenging rates are:SACS>SAMC>SAC in the hydroxyl radical scavenging experiment,.In the reduction experiment of potassium ferricyanide,the order of reducing ability are:SACS>SACS>SAMC;in the antioxidant experiment of oil and fat,the order of antioxidant capacity are:SAC>SACS>SAMC.5.The most probable mechanism functions of methionine,cysteine,cystine and SAC are calculated as the functions of No.16,No.12,No.23 and No.23,respectively by using the thermodynamic equations of integral and differential.The activation energies in the integral form are 987.57,144.69,120.88,106.56 kJ/mol,respectively.The pre-exponential factors lnA are212.46,32.14,25.72,24.51,respectively;the activation energies in the differential form are953.36,209.47,189.26,161.10 kJ/mol,the pre-exponential factors lnA were 204.36,48.41,39.27,34.76,respectively.SACS and SAMC are complicated by thermal decomposition,and their mechanism function,activation energy,and pre-exponential factor can not be calculated.Taken together,the above results are reported for the first time,it provides a theoretical basis for the study of the flavor of garlic and the nature of sulfur-containing amino acids in garlic.