Abstract
This study aims to demonstrate the feasibility for classifying kiwifruit into shape grades by adding a single camera to current Chinese sorting lines equipped with weight sensors. Image processing methods are employed to calculate fruit length, maximum diameter of the equatorial section, and projected area. A stepwise multiple linear regression method is applied to select significant variables for predicting minimum diameter of the equatorial section and volume and to establish corresponding estimation models. Results show that length, maximum diameter of the equatorial section and weight are selected to predict the minimum diameter of the equatorial section, with the coefficient of determination of only 0.82 when compared to manual measurements. Weight and length are then selected to estimate the volume, which is in good agreement with the measured one with the coefficient of determination of 0.98. Fruit classification based on the estimated minimum diameter of the equatorial section achieves a low success rate of 84.6%, which is significantly improved using a linear combination of the length/maximum diameter of the equatorial section and projected area/length ratios, reaching 98.3%. Thus, it is possible for Chinese kiwifruit sorting lines to reach international standards of grading kiwifruit on fruit shape classification by adding a single camera.
Highlights
Kiwifruit is a subtropical fruit that belongs to the family Actinidiaceae and has rapidly spread from China to other parts of the world due to its easy adaptability to local climatic conditions [1].It is considered as one of the best fruits due to its high nutritive values rich in vitamin C and other mineral elements [2]
MaDES/length ratio (MLR) is 82.1%, which is higher than the reported value (79.8%) by Razavi and BahramParvar [1], but close to that (81.0%) obtained by Lorestani and Tabatabaeefar [33]
For classes I and II, they are different in the length (p < 0.05), but not in the other physical properties (p > 0.05). This is probably caused by 31.3% fruit samples of class I supposed to be classified into higher class based on the weight, but being classified into class I because of their low MiDES to MaDES ratio (MMR) values
Summary
Kiwifruit is a subtropical fruit that belongs to the family Actinidiaceae and has rapidly spread from China to other parts of the world due to its easy adaptability to local climatic conditions [1]. It is considered as one of the best fruits due to its high nutritive values rich in vitamin C and other mineral elements [2]. 47,258 hm , while the total production reached 735,748 t, which made Shaanxi the largest kiwifruit plantation area in the world [4]. 62,990 t was imported at US$171.89/t in the same year [5], which is probably caused by poor management and grading technology in China kiwifruit industry
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