Development and evaluation of an apple infield grading and sorting system

Authors: ZHANG, ZHAO - North Dakota State University; LU, YUZHEN - Mississippi State University; Lu, Renfu

Submitted to: Postharvest Biology and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/6/2021
Publication Date: 5/26/2021
Citation: Zhang, Z., Lu, Y., Lu, R. 2021. Development and evaluation of an apple infield grading and sorting system. Postharvest Biology and Technology. 180. Article 111588. https://doi.org/10.1016/j.postharvbio.2021.111588.
DOI: https://doi.org/10.1016/j.postharvbio.2021.111588

Interpretive Summary: Apple infield pre-sorting is intended to segregate inferior or processing quality fruit from fresh quality fruit, so that growers can implement different postharvest storage and packing procedures for these apples to achieve cost savings. Currently, infield sorting is still not adopted by apple growers in U.S., due to the lack of appropriate technology. In this paper, we report on the development of an apple infield grading and sorting system, which consists of a low-cost imaging-based grading module, an integrated fruit singulation, rotation and transport mechanism, and paddle sorters. Laboratory tests were conducted for ‘Golden Delicious’ and ‘Red Delicious’ apples to evaluate the system performance in terms of grading repeatability, fruit bruising and sorting accuracy at three sorting rates of 7.5, 9.0 and 10.5 fruit per second. Results showed that the grading repeatability rates of the system for intra- and inter-lane grading were 90% and 81%, respectively. The system achieved 99% or higher sorting accuracies at the three sorting rates. One hundred percent (100%) of the sorted fruit were graded ‘Extra Fancy’, and at least 55% of the sorted apples incurred no bruising at all after grading and sorting. The developed infield grading and sorting system is compact and robust in performance, and it can meet commercial infield sorting needs.

Technical Abstract: Infield pre-sorting is intended to remove processing (inferior) fruit that are not suitable for the fresh market, so that growers could handle sorted apples differentially in postharvest storage and packing to achieve cost savings. To achieve this goal, we developed an apple infield grading and sorting system, in which fruit singulation, rotation, and transportation were achieved by using simple, compact pitch-variable screw conveyors, fruit grading (size and color) was accomplished with a low-cost imaging system, and fruit sorting was done by using paddle sorters. Experiments were conducted for ‘Red Delicious’ and ‘Golden Delicious’ apples to evaluate the overall performance of the infield grading and sorting system in terms of grading repeatability (i.e., chances of each apple that would be graded into the same quality grade in multiple runs and different lanes), bruising damage, and sorting accuracy (consistency between the imaging-based grading results and destinations). Results showed that the grading repeatability rates of the system were above 90% and 81% for intra- and inter-lane grading, respectively. The system achieved above 99% sorting accuracies for the system throughputs of 7.5, 9.0, and 10.5 fruit per second, while 100% of sorted apples were graded ‘Extra Fancy’ and at least 55% of the apples incurred no bruising damage at all after grading and sorting. The developed infield grading and sorting system is compact and robust in performance, and it can meet commercial infield sorting needs.