Study On Mechanism Of Apple Fresh Browing And Methods Of Nondestructive Measurement Using Near-Infrared Spectroscopy

Apple is one of the four major fruits.China is the first main producing country in theworld and the total production of apple is 25 300 000 t in 2006.But the export amount is only1.5 percent of total production for its poor quality,lower industrialization standard dragglingdetection methods and isolate evaluation standard which is not consistent with the firstcountry of apple total yield.At present,there is very severity of the apple flesh browning inthe storage time,and the routine analytical methods used for fruit internal qualitymeasurement are destructive,expensive,complex,labor consume and off line by nature.It isvery urgent to find mechanism and mathematic models used to nondestructively measurementapple internal quality.Therefore,the research establishes the mathematic models fornondestructive measurement flesh browning of apple using near-infrared spectroscopy basedon browning mechanism,which it has the important theoretical meaning and applied value.Choosing red'Fuji'apple as materials and taking aim at browning mechanism andnondestructive detection techniques,the paper studies browning mechanism,near-infraredspectrum characteristic,affecting factors of detection and the optimal working parameters.Anoptimal nondestructive detection model for apple flesh browning is proposed.The mainresults of the dissertation involved:(1) The mechanism of apple flesh browning was investigated in several stages.Theenzymatic browning,maillard reaction and AsA oxidizing reaction were analyzed in thedifferent storage time of apples.It would be concluded that apple flesh browning is inducedby maillard reaction before 80 days and by enzymatic browning after 80 days.AsA oxidizingreaction was very subordinate owing to AsA minim in apples.(2) The cell microstructural changes of the different lrowning apple flesh degrees wereobserved with JEFM-1230 transmission electron microscopy.Results show that cellmicrostructural changes were similar between browning and senescence,for example,cellwall distortion,incipient plasmolysis,membrance disaggregation,chloroplast translatingstarch granules,and mitochondrion membrance breaking,and so on.With browningaggravation,plasmodesmata density and number descend,and structure became chaos orrupture.Disaggregation of cell organs (vacuole,plastid,mitochondrion) and cytoplasm membrances and destructin of cell region structure lagged flesh browning.Therefore,enzymatic browning owing to destructin of cell region structure was not exclusive reason,butmaillard reaction was essence of earlier browning.(3) The near-infrared spectrum measurement factors including testing distance,sampletemperature,sampling position,surface colour and storage time were researched.Testingdistance,sampling position and storage time had significant influence on apple near-infraredspectrum,but sample temperature and surface colour did not have significant influence.(4) The instrument parameters of the effects on spectrum measurement were analyzedand the best matching parameters used to FT-NIR measurement were as the following:instrument signal energy was 5V,scan resolution was 8 cm^-1 and scan number is 64.It wouldbe concluded that the calibration models used the best matching parameters will give the bestprediction accuracy.The optimal working parameters could not only satisfy with applequality detection,but also simplify operation,reduce cost,improve detective efficency.(5) Outlier and similar sample diagnosis and eliminating algorithms based on clusteranalysis of Euclidean distance were put forward,and established qualitative model with 170effective representative samples.Eorror identical ratio of the model declined from 53% to29%.The paper analyzed the different spectral pretreatment methods influenced on the applebrowning qualitative model.The results indicated that the SNV+SD pretreatment was the bestmethod with 22% eorror identical ratio.The different selected spectral range was used tooptimize the calibration models.The best calibration models of apple browning was at thewavenumber of 10500 cm^-1～6960cm^-1,6760 cm^-1～5300 cm^-1,5100 cm^-1～4500 cm^-1 with19% eorror identical ratio.Comparative analysis on the apple browning qualitative model ofstandard methord and factorization method was researched and factorization method was thebest algorithm.The eorror identical ratios of the best calibration model of browning were16% on calibration set and 19% on validation set,respectively.(6) The apple browning quatitative nondestructive measurement method was put forward.The methord could not only measure browning degrees of apple,but also predict and warn thefruit inner browning.Choosing representative modeling samples by eliminating outlier andsimilar sample,the calibration models used to non-destructive measurement of the fleshbrowning were developed by partial least square (PLS) regression combined withmultiplicative scatter correction (MSC).The best calibration model of apple samples gaveRMSECV 0.082,RMSEP 0.084,the cross validate R² 0.871,and the outer validate R² 0.853.The results revealed that the model prediction was more accurate and could accurately predictunknown samples.(7) The experiment proved up the characteristic fingerprints of apple flesh browning 8822 cm^-1,7085 cm^-1,7000 cm^-1,6694 cm^-1,5800 cm^-1,5322 cm^-1,4650 cm^-1,and thenondestructive measurement model was established by using MLR regression based on thefingerprints.The model can predict apple flesh browning accurately with RMSECV0.077,RMSEP 0.079,the cross validate R² 0.908,and the outer validate R² 0.878.Theprecision of the mathematical model optimized by MLR can obviously improved thehigh-correlation coefficient of prediction model and the low prediction standard error.A newmethod that could evaluate apple flesh browning rapidly,visually,simply and feasiblywas developed.