Study On New Detection Methods For Furfurals In Dairy Products

Milk and dairy products can provide a wealth of nutrition benefits,such as high-quality protein,calcium and a variety of essential nutrients.However,higher content of furfurals,including furfural and 5-hydroxymethylfurfural,are generated by the degradation of saccharides as a result of thermal processing and long-term storage of milk products.Furfurals are used to indicate the damage of dairy foods.Therefore,it is of vital importance to develop a simple,fast,and sensitive method to research the presence of furfurals in milk products.Currently,the commonly used method for the detection of furfural in dairy products is chromatography.However,the chromatography methods showed several drawbacks such as high cost,use of toxic reagents,the requirement of sophisticated equipment and the need for specially trained people.The electrochemical method features high sensitivity,simplicity of operation,low cost,and short analysis times.Surface-enhanced Raman Scattering（SERS）technology uses the surface enhancement effect produced by rough substrates such as Au or Ag,which can increase the detection signal by several orders of magnitude.SERS can also achieve non-destructive determinations.These two methods are rarely used in the detection of furfural in dairy products.In this paper,two electrochemical electrodes were developed for the rapid detection of furfural in dairy products based on electrochemically reduced graphene oxide and three-dimensional graphene-like structure,respectively.Additionally,gold nanoparticles（Au NPs）substrates were also prepared by solvothermal reduction method,and the SERS enhancement effect of the substrates on 5-hydroxymethylfurfural（5-HMF）was investigated.The main contents are summarized as follows:（1）An electrochemical sensor was developed for the cathodic determination of furfural by one-step electrochemically reduced graphene oxide（ErGO）modified glassy carbon electrode（GCE）.The morphology and chemical constituents of the obtained ErGO/GCE were characterized by scanning electron microscopy（SEM）,transmission electron microscopy（TEM）,X-ray diffraction（XRD）,Raman and X-ray photoelectron spectroscopy（XPS）.The results found that the fast and green electrochemical reduction process effectively eliminated the oxygen-containing groups in the GO and produced the reduced graphene with high surface area and promoted electron transfer kinetics.In addition,the ErGO based modified electrode displayed excellent responses for furfural in Na₂HPO₄-Na H₂PO₄ solution（p H=9.18）with a wide linear range from 2 to 2015μM and a low detection limit of 0.4μM（S/N=3）.The reduction mechanism of furfural was also discussed.Furthermore,the feasibility of the modified electrode was confirmed by the determination of furfural in three milk samples and generated acceptable outputs.（2）A furfural sensor was fabricated based on 3D graphene-like surface（3DGrls）by applying+3 V voltage to the surface of the pencil graphite electrode（PGE）in a neutral Na₂SO₄ solution for 300.The results of SEM,XRD,XPS,Raman and electrochemical impedance（EIS）show that 5 minutes of electrochemical pretreatment created a 3D graphene-like surface with a large specific surface area and a fast electron transfer rate without any hazardous chemicals added.The results also found that the electrochemical response of 3DGrls/PGE for furfural is 24 times bigger than that of PGE.The reduction current of furfural has a good linear relationship with its concentration in the range of 4～9710μM（R²=0.9660）,and the detection limit is0.61μM（S/N=3）.Moreover,3DGrls/PGE can also be used for the rapid electrochemical detection of furfural in dairy products,with a recovery of 93.2%～100.3%.（3）A SERS sensor with Au nanoparticles（Au NPs）as the substrate,which was synthesized by the citrate-reduction method,was developed for 5-HMF sensing.The sensor exhibited a linear range from 0.02 to 100 m M with a detection limit of 14μM（S/N=3）.Moreover,the proposed SERS sensor displayed an excellent application in real dairy samples.