Synchronous Front-face Fluorescence Spectroscopy For Adulteration Determination Of Coffee And Turmeric Powders

Synchronous front-face fluorescence spectroscopy(SFFFS)is a rapid and non-destructive analysis technique with high sensitivity and selectivity.With the development of chemometrics and the widespread use of fluorescence spectroscopy,the potential of SFFFS for food safety research has largely increased.By rotating the sample holder at an angle,the method measures and collects fluorescence generated by molecules on the surface of the sample only,so that the fluorescence signal is no longer dependent on the penetration of the excitation light in the sample,and only the molecules on the sample surface are excited,avoiding the shortcoming of traditional right-angle fluorescence.This technology can also be applied to opaque,non-clear or solid samples.Coffee is currently one of the most popular and largely consumed beverages in the world and is one of the most valuable basic goods in the world(second only to petroleum).Turmeric is a perennial herb of Curcuma L,native to South Asia and India.Its brown rhizome has a unique flavor and commonly used for coloring and flavoring food in Southeast Asia,as well as in the local medical treatment.Both foods are relatively expensive due to their unique color and flavor characteristics and irreplaceability.Hence the huge benefits have attracted a large number of illegal businesses to manufacture and sell counterfeits.This paper uses SFFFS to rapidly and non-destructively determine the adulteration of coffee powder and turmeric powder,which provides a new idea for the detection of adulteration of two foods.The main contents are as follows:(1)Exploration of sample treatment and fluorescence conditions:The influence of moisture content and particle size on the front-face fluorescence spectral measurement of soybean flour,maize flour and coffee powder.The results showed that the fluorescence intensities of the dried samples with more uniform particle sizes were stronger.After sieved by 60 mesh,soybean flour,maize flour and coffee powder with particle size less than 0.3mm were selected to reduce the error.In order to make the color of the roasted soybean and maize flour closer to that of pure coffee powder,mixed soybean samples roasted at 220°C for 40 min and mixed corn samples roasted at 240°C for 20 min were selected as adulterants.(2)SFFFS was used to detect the adulteration of coffee powder with roasted soybean and maize flours.For the two adulterants,54 adulterated samples were prepared respectively.For each adulterant,together 162 data points for constructing the model were obtained,and the concentration of adulterants was 0-40%.Through pretreatment to reduce the error in detection,the obtained results are combined with chemometric methods such as principal component analysis(PCA),linear discriminant analysis(LDA)and partial least squares regression(PLSR)to qualitatively discriminate and quantitatively analyze the adulteration of coffee powder.The determination coefficients(R~2)of the model established by quantitative analysis are in the range of 0.904–0.952,and all root mean square errors(RMSE)are no more than 4%.The relative errors of prediction(REP)are 20.1%and 17.3%for maize and soybean flours,respectively.The corresponding RPD are 3.5 and 3.9,respectively.(3)Detection of turmeric powder samples adulterated with maize flour was achieved by SFFFS.For the first time,competitive absorption between curcumin in turmeric powder and phenolic acids in maize flour was found.Eight brands of turmeric powder from different producing areas were collected in the experiment.Maize flour was added into these turmeric powders to give adulterated samples.The prediction model was constructed by PLS regression through fluorescence spectroscopy and chemometric.The prediction determination coefficient(R_P~2)of the model is>0.95,RMSEP<6%,REP<15%and RPD>5,and the limit of detection(LOD)is about 8%.The model is verified by spiked samples,and the results are ideal,and the recovery is 80-120%.