Experimental study on mechanical properties and peel separation characteristics of citrus reticulate blanco with peel clamped moving

Abstract: The mechanical properties of Satsuma mandarin are an important basis for the design and control of the automatic peeling device. In this paper, Satsuma mandarin was taken as the research object, and TMS-PRO texture analyzer was adopted. Special scissors cut along the fruit radial (fruit maximum equatorial diameter direction) and axially peeled out and pulled out different peeling widths. Citrus fruit top and pedicle were fixed in the 2 clamping edges of the fixed clamping mechanism or the longitudinal axis perpendicular to the clamping edges, and the radial part was fixed in the 2 clamping edges of the fixed clamping mechanism. Gripper clamped the peeled part of the peel. The moving probe of the texture instrument drove the gripping mechanism to move to overcome the adhesive force between peel and pulp. As the texture instrument continued to pull peel, the peel was peeled off from citrus surface. The maximum tensile force and the displacement in the separation of peel were obtained, which were as the experimental indices. The smaller the maximum separation tension, the more easily separated the skin of the citrus fruit; the separation of the larger displacement indicated that the longer the peeled peel length, the better the effect of peeling. The paper studied the peeling law of Satsuma mandarin in different pulling direction, pulling width and pulling speed by carrying out the mechanical properties test of peeling citrus. The main results were as follows: Firstly, there were 3 types of rupture during citrus peel separation (peel symmetrical tear, peel oblique tear and jagged cracks), in which the citrus peel length with symmetric cracks was the largest and the displacement was the best. Asymmetrical and jagged cracks forms of peel separation lead to shorter separation of peel, which is not conducive to achieving higher peel rate. Secondly, the stripping direction had the most significant effect on the maximum tension value of citrus fruits (P=0.006). The stripping direction also had a significant effect on the displacement (P=0.016). Results showed that the peeling strength of Satsuma mandarin had obvious anisotropy. Compared with radial direction of peeling, peeling width of the axial skin peeling is conducive to peel citrus, which can get longer peel. Thirdly, the peeling width had a significant effect on the maximal pulling force (P=0.034) and the displacement (P=0.795) in citrus fruit. When the peeling width was 25 mm, the maximum tension value was lower, 2.31 N. When the peeling width was 35 mm, the maximum tension value was larger, 2.55 N. When the peeling width was in the range of 25-35 mm, the displacement value was 47.32-48.33 mm and the fluctuation was small. Peel separation force increased as the width of the skin increased. For the existing citrus peeling machine with random cutting approach was not conducive to peeling, the ring cutting peeling should be used for the existing roller way to provide the possibility of axial peeling. At last, the maximum pulling force (P=0.043) and the separation displacement (P=0.105) were not significant. Peeling separation force increased with the increasing of pulling speed. For most of roller citrus peeling equipment, the maximum clamping force of the roller was generally much larger than the stripping force, so the citrus in the rolling process chose larger peeling width (the ring cut peel) and peeling speed, and peel separation process was more stable and efficient. In conclusion, this study provides an important basis for the design of wide-peel citrus peeling machine.