Effect Of CPPU On Optical Properties Of Kiwifruit And Discrimination Of Expanded Kiwifruit

Kiwifruit is a very appreciated fruit for consumers due to its harmonious sourness and sweetness,delicious taste and rich nutrients.Forchlorfenuron(CPPU)is the most widely used plant growth regulator applied on kiwifruit.It can improve the yield of kiwifruit and the rate of fruit setting.However,many researches indicate that CPPU cause many negative effects to fruit.For example,the treatment of CPPU reduced the internal quality such as soluble solids content(SSC),acidity,firmness and storage time.The abnormal fruit rate increased and the fruit shape index decreased when the used CPPU concentration was too high.Moreover,the potential effect of CPPU on people health is not clear.In recent years,the abuse of CPPU is very serious in kiwifruit production.It is,therefore,of great importance to develop an efficient and nondestructive method to discriminate the CPPU-treated kiwifruit from untreated ones for the healthy development of kiwifruit industry.Nowadays,spectroscopy technique has been applied in discriminating CPPU treated-kiwifruit and showed a relatively good result,while the acquired spectrum using the spectroscopy technique is a comprehensive information that includes both absorption and scattering.Therefore,the mechanism of interaction between light and tissue cannot be explained by the spectroscopy technique,and the physical significance of information carried by light from the tissue is also not clear.To explore the mechanism of discriminating CPPU-treated kiwifruit by spectroscopy technique,an optical properties measurement system based on single integrating sphere was developed,and the effect and mechanism of CPPU on optical properties of kiwifruit during growth and storage stage was investigated.In addition,to explore the major difficulties on the discrimination of CPPU-treated kiwifruit,the studies on discriminating kiwifruit treated with different CPPU concentrations based on micro spectrometer and discriminating CPPU-treated kiwifruit based on multi-varieties kiwifruit together were conducted.The main results were described as follows:(1)An optical properties measurement system based on single integrating sphere was built,and the stability and accuracy of system were validated with different concentrations of Intralipid solution.The results showed that the relative standard deviation of the total diffuse reflectance(MR)and total diffuse transmittance(MT)of 22.7%-phantom solution were 0.28%and 0.29%,respectively.The relative standard deviation of the MR and MT of0.908%-phantom solution were 1.46%and 0.16%,respectively.Additionally,the validation error of absorption coefficient(?a)and reduced scattering coefficient(?'s)was comparable with the error reported in other researches.It showed that the measurement system of optical properties had a good stability and accuracy.(2)The effect of CPPU on optical properties of kiwifruit during growth was investigated over the wavelength range of 950-1650 nm,and the relationship of optical properties with physicochemical properties and cell size was analyzed.The results showed that,at the same growth stage,the?a values of kiwifruit treated with 5,10,and 15 mg/L CPPU concentrations were significantly higher than those of CPPU untreated kiwifruit at both 970 and 1190 nm(P?0.05).The flesh's?'_s of kiwifruit treated with 0,5,and 15 mg/L CPPU concentrations had significant difference between each other at 1190 nm for most of the growth stages(P?0.05).Contrasted with CPPU-untreated kiwifruit,the CPPU-treated kiwifruit had higher SSC and moisture content,lower firmness,and larger cell.The results suggest that the?a of flesh around 970 and 1190 nm have potential for discriminating CPPU-treated kiwifruit from untreated ones,while the?'s around 1190 nm are potential for discriminating kiwifruit treated with different CPPU concentrations.(3)The effect of CPPU on optical properties of kiwifruit during storage was investigated over the wavelength range of 950-1650 nm,and the relationship of optical properties with physicochemical properties and cell size was analyzed.The results showed that,for most of the storage stages,there was no significant difference(P?0.05)on flesh's?a among kiwifruit treated with different CPPU concentrations at the absorption peaks of970,1190 and 1390 nm,and the flesh's?'_s had significant difference(P?0.05)between the kiwifruit treated with 0,5 and 15 mg/L CPPU concentrations.For most of the storage stages,the average?'s of skin of untreated kiwifruit were lower than those of CPPU-treated kiwifruit.The CPPU-treated kiwifruit had higher moisture content,lower firmness,and larger cell than CPPU-untreated kiwifruit.The results suggest that,at kiwifruit storage stage,the?'s of flesh around 1190 nm have potential for discriminating kiwifruit treated with different CPPU concentrations.(4)A near infrared spectroscopy system was built based on a micro spectrometer.The spectra of‘Huayou'and‘Hayward'kiwifruit treated with 0,5,10 and 15 mg/L CPPU concentrations were acquired in 950-1650 nm,and the discrimination models of kiwifruit treated with different CPPU concentrations were established.The results showed that,for‘Huayou'kiwifruit,the extreme learning machine(ELM)models had the best performance,followed by support vector machine(SVM)models,and the partial least squares discriminant analysis(PLS-DA)models had the worse result.For‘Hayward'kiwifruit,SVM models obtained the best performance,followed by ELM and PLS-DA models.The accuracy rate of predication set of the best discrimination models for‘Huayou'and‘Hayward'kiwifruit were 84.9%and 92.5%,respectively.It indicates that the near infrared spectroscopy system based on a micro spectrometer can accurately discriminate kiwifruit treated with different CPPU concentrations.(5)The near infrared spectra of 10 mg/L CPPU-treated kiwifruit and CPPU-untreated ones for variety‘Huayou',‘Hayward'and‘Xuxiang'were acquired,and the discrimination models of CPPU-treated kiwifruit were established based on characteristic wavelengths and universal wavelengths(UWs)for single variety and multi-varieties,respectively.The results showed that the number of characteristic wavelengths selected by stability competitive adaptive reweighted sampling(SCARS)algorithm were 36,81,81 and 40 for‘Huayou',‘Hayward',‘Xuxiang'and multi-varieties,respectively.Twenty UWs were found in the four characteristic wavelengths sets selected using SCARS.For the same modeling method,the results of models based on full spectra were comparable with those based on characteristic wavelengths selected by SCARS,and they both performed better than those based on UWs.However,the UWs in this research had a stronger applicability,which can simultaneously be used for the discrimination of CPPU-treated kiwifruit of‘Huayou',‘Hayward',‘Xuxiang'and multi-varieties together.Generally,the accuracy rate of predication set of the best discrimination models for‘Huayou',‘Hayward',‘Xuxiang'and multi-varieties kiwifruit were 100%,100%,96.4%and 99.2%,respectively.It indicates that the near infrared spectroscopy technique can be used to discriminate CPPU-treated kiwifruit not only for single variety but also for multi-varieties.The UWs selected in this research can be simultaneously used as the characteristic wavelengths of both single variety and multi-varieties for the discrimination of CPPU-treated kiwifruit.