The Optical Properties Of Strawberry And Its Correlation With Internal Quality

Strawberry is rich in nutritional value and loved by consumers.With the continuous improvement of living standard,people pay more and more attention to quality of strawberry.Our previous studies have shown that near-infrared spectroscopy has the ability to detect fruit quality and to identify fruit treated with expansion agents(e.g.CPPU).Fruit is a chaotic medium in optical properties.The propagation of light in such chaotic media is a complex phenomenon.The attenuation of light energy is the result of absorption and scattering of tissue.The study on the optical properties of strawberry and its correlation with internal quality is important to develop the techniques and methods for detecting strawberry quality and identifying strawberry treated with expansion agents.Therefore,single integrating sphere technique was used as the optical properties measurement method to study the optical properties of strawberry and its correlation with internal quality.The main research contents and conclusions of this study are as follows:(1)A measurement system based on single integrating sphere technique was built to measure the optical parameters(the absorption coefficient?_a and the reduced scattering coefficient?'_s).The measurement accuracy of the system in the visible/near-infrared(550-850 nm)and near-infrared(950-1650 nm)wavelength ranges was verified.The results showed that the average relative errors of the system for?_a and?'_swere 6.23%and15.26%,respectively,over the wavelength range of 550-850 nm band,were 8.23%and3.71%,respectively,over the wavelength of the 950-1650 nm band,and were 7.23%and9.48%,respectively,in the whole investigated ranges of 550-850 nm and 950-1650 nm.The established single integral sphere system could be used to measure the optical parameters of fruit accurately.(2)The effects of CPPU concentration on internal quality,cell size,and optical properties of strawberry at different growing stages(white ripening stage,color turning,and red ripening stage)were investigated.The results showed that CPPU enhanced the number and area of cells of strawberry,and significantly increased the weight of single strawberry.The effect of CPPU concentration on the soluble solid content(SSC),water content,firmness and?a at the absorption peaks of 675 nm,975 nm and 1197 nm was not significant,but CPPU resulted in the decrease of?_a at the absorption peak of 1411 nm and the decrease of?'_sat whole investigated wavelength.With the increased maturity of strawberry,there was no significant change on?_aat 975 nm and 1197 nm,while?_aat 675nm and 1411 nm gradually decreased,and?'_sgradually decreased.The?_a at 675,1197,and1411 nm had the potential in identifying the strawberry treated with CPPU and with different CPPU concentrations.The?_a of strawberry at the red ripening stage and at 675nm could be used to distinguish whether a strawberry was treated with CPPU or not,while?'_sat 675,975,1197,and 1411 nm at the color turning stage had the potential to identify strawberry treated with different CPPU concentration.(3)The correlations between the optical parameters and the internal quality of strawberry at different growing stages(white ripening stage,color turning stage and red ripening stage)over the wavelengths of 550-850 nm and 950-1650 nm were analyzed,and the prediction models for internal quality of strawberry were established based on the spectra of optical parameters.The results showed that?_ahad negative correlation with SSC and positive correlation with water content,and the absolute correlation coefficients|R|reached the maximums at the absorption peak of 1411 nm.The?'_swas negatively correlated with SSC and positively correlated with the moisture content,and the correlation was the largest at the absorption peak of 675 nm.SSC and water content mainly affect the absorption properties of strawberry.Contrasted with using the spectra of?'_sand?_a+?'_s,the established partial least squares(PLS)and support vector machine(SVM)models based on the spectra of?_ahad the best performance in predicting SSC and water content of strawberry.(4)The effects of strawberry varieties on optical properties and the relationship between optical properties and internal quality(SSC and water content)were analyzed,and the models for predicting internal quality of strawberry were established based on the spectra of optical parameters.The results showed that the variety had effect on the values of optical parameters,but it had not effect on the spectra of optical parameters.In other words,the absorption peaks of strawberry still appeared at 975,1197 and 1411 nm over the wavelength range of 950-1650 nm,and?'_sdecreased with the increase of wavelength.There was also negative correlation between?_a and SSC,but positive correlation with water content for strawberry.There was extreme values of correlation coefficients under the absorption peaks.The?_a spectrum still had the best ability to predict SSC and water content.The results of this study showed that CPPU affects the internal quality and optical properties of strawberry,and there was a close relationship between its internal quality and optical properties.The study provides information for understanding the influence of CPPU on optical properties of strawberry,the relationship between optical properties and internal quality,as well as development on the detector for CPPU treated strawberry and for internal quality.