Effect Of Bruises On Optical And Physicochemical Properties Of Fruit During Storage

Fruit is often bruised by pressing,vibration,impacting and collision in the process of harvesting,transportation,processing and storage.After the mechanical damage of the fruit,fungi and bacteria will more easily erode the flesh of the fruit,which can accelerate the senescence and decay of the fruit,and further infect other undamaged fruit,causing great economic losses.At present,there have studies on the detection of bruised fruit based on near infrared spectroscopy and hyperspectral technology,but the spectrum is a comprehensive reflection of the absorption and scattering of photons in fruit tissue.Different types of bruise have different effects on physicochemical properties and flesh tissue of fruit.However,it is not clear whether different types of bruise have the same effects on optical parameters of the same fruit,and which optical parameters was more obviously affected by bruise.In order to explore the mechanism of identifying bruised fruits based on spectroscopy,this paper set up the system to measurement optical properties parameters based on the technology of integrating sphere.The effects of pressing and impacting bruises on absorption coefficient(?_a),reduced scattering coefficient(?_s'),microstructure,color,the soluble solids content(SSC),moisture content(MC)and firmness(FI)of kiwifruit,peach and pear in storage period after bruising were studied by using the non-bruised samples as control,and analyzing the correlation between the optical parameters and the physicochemical properties.The main research contents and conclusions were described as follows:(1)An integrating sphere system was established to measure the optical property parameters of fruits.The reliability of the system in the range of 950-1650 nm was verified by using pure water and Intralipid-20%solution.The results showed that the average relative error of?_a and?_s'in the range of 950-1650 nm are 8.23%and 3.71%,respectively.The system error measured by the integrating sphere system constructed in this study is similar to the measured results in other literatures,which proves the reliability of this system.(2)The changes of microstructure,color,SSC,MC and FI of non-bruised,pressing and impacting bruised samples of kiwifruit,peach and pear during storage were researched.The results showed that the cells of the peach and pear were smaller and more compact compared with the kiwifruit.In addition,the bruises resulted in the cell rupture and damage of three fruits,and the cell gap became larger.Meanwhile,the degree of cell damage would increase with time.The L*,a*and b*values of the peel and flesh of kiwifruit were little affected by bruises,but the L*value of the peel and flesh of non-bruised peach was significantly higher than bruised ones,and the other values were not significantly affected by bruises.The L*and b*values of the peel of non-bruised pear were significantly higher and a*value was significantly lower than bruised ones.While the L*value of the flesh of non-bruised pear was significantly higher and a*and b*values were significantly lower than bruised ones.The SSC of three fruits had an increasing trend during storage,except that the SSC of the impacting bruised peach had a decreasing trend during storage,and the MC and FI of three fruits all had a decreasing trend during storage.Meanwhile,the SSC and MC of three fruits were not significantly affected by bruises,except that the SSC of non-bruised peach was significantly higher than impacting bruised ones during storage of 1,2 and 3 days.However,the bruises significantly reduced the FI of the kiwifruit and peach,and the FI of pear stored for 5 days(P?0.05).It was also found that the FI of kiwifruit,the SSC of peach and the color of pear was most affected by bruises among the three kinds of fruits.(3)The changes of the?_a and?_s'of non-bruised,pressing and impacting bruised samples of kiwifruit,peach and pear in the range of 950-1650 nm during storage was researched.The results showed that the?_a of kiwifruit,peach and pear was not significantly affected by pressing and impacting bruises,and it was difficult to identify the invisible bruises of kiwifruit,peach and pear by?_a.However,the?_s'of non-bruised samples was significantly higher than that of bruised samples of kiwifruit in 950-1360 nm,peach in 950-1650 nm and pear in 950-1400 nm respectively.Which was caused by the cell rupture and the separation between cells.Therefore,?_s'has the potential to identify the invisible bruises in kiwifruit,peach and pear.At the same time,the penetration depth of the non-bruised samples was less than that of the bruised samples of kiwifruit in 950-1360 nm,peach in 950-1650 nm and pear in 950-1400 nm respectively.(4)The correlation between optical parameters and physicochemical properties of non-bruised,pressing and impacting bruised samples of kiwifruit,peach and pear in the range of950-1650 nm were researched.The results showed that the correlation coefficients between the optical parameters and the physicochemical properties of three kinds of fruits had peaks or trunks around 1450 nm,and the correlation coefficients between?_a or?_s'and MC and FI were similar,but contrary to the correlation coefficients of SSC.The correlation coefficients between optical parameters and physicochemical properties of different fruits and the same fruit with different bruises were different.(5)SPA and CARS methods were used to extract characteristic wavelength from the pretreated data after?_a,?_s'and?_a+?_s'were pretreated by SG,SNV,MSC,SG+SNV and SG+MSC.Finally,PLS-DA model was established to identify the invisible bruises of peach and pear.The results showed that the PLS-DA model,which extracted the characteristic wavelength of SG pretreated?_s'with SPA,had the best recognition effect in the invisible bruises identification of peaches and pears,and the accuracy of the prediction set was 76.92%and 97.50%,respectively.The results indicate that pressing and impacting bruises damaged the microstructure of kiwifruit,peach and pear,and significantly reduced the FI of kiwifruit and peach,as well as the FI of pear stored for 5 days.As a result,the?_s'of nondestructive samples was significantly higher than that of bruised ones,but the bruises had no significant effect on?_a.Therefore,the?_s'has great potential in identifying bruised kiwifruit,peach and pear from non-bruised ones,this study provides a theoretical basis for detecting bruised fruit based on optical properties.