Studies On Extraction,Isolation And Antioxidant Activities Of Melanoidins From Black Garlic

Black garlic(BG)is soft and the taste is sweet,withouting the pungent flavor of raw garlic.The main source of the black color in BG is the melanoidins produced by the Maillard reactions.Melanoidins can not only improve food flavor,but also have many functional activities.At present,the researches about melanoidins are mainly based on the function of the model melanoidins,and only a few of researches are about the compositions and structures of food melanoidins.In this paper,the BG melanoidins were isolated,and the related components,structure s and antioxidant activities of melanoidins were studied.The study would be helpful to better understand the complex melanoidins in food.The effects of various factors on the extraction efficiency were investigated by single factor and orthogonal design experiment.The best extraction conditions were determined as follows:extraction solvent was 10%ethanol,feed liquid was 1:3,extraction temperature was 70?and extraction time was 1h.High(>50 k Da,M₄),medium(10-50 k Da,M_3;1-10 k Da,M₂)and low molecular weight(<1 k Da,M₁)fractions were obtained by ultrafiltration and relative molecular weights of the fractions were measured by GPC.Pure melanoidins were obtained by Na Cl dissociation.The pyrolysis-gas-mass spectrometry(Py-GC-MS)analysis of the chemical composition of BG melanoidins showed that the highest relative content was furans,followed by thiophenes and alkanes.Elemental analysis indicated that the C/N value of M₁was the largest,while the content of N and S was the lowest.HPLC was used to detect the related constituents of melanoidins,and the results displayed that the amino acid content of M₄ was the lowest,presumably due to the consumption of amino acids in Maillard reactions during the processing of BG.Fructose,glucose and sucrose were detected in M₁ and M₂,while M₃and M₄contained only fructose.The presence of free chlorogenic acid was detected only in M_1.The high to low orde of 5-HMF content was:M₄>M₃>M₂>M₁.The average particle size range of each fraction was relatively concentrated with different topographical features.The fractions had characteristics UV spectrum and fluorescence spectroscopy.IR showed significant amide I bands and characteristic absorption bands of sugars in BG melanoidins;The ¹³C-NMR and ¹H-NMR spectrum further confirmed that the melanoidins had rich carbohydrate components;X-ray diffraction patterns showed that there were no crystals before dissociation of BG melanoidins and there appeared crystallinity after dissociation.The results showed that at the same concentration,the free radical scavenging activities were from high to low as M₁>M₂>M₃>M_4,while the reducing power from high to low as M₄>M₃>M₂>M₁.