APPLE DAMAGE AND COMPRESSIVE FORCES IN BULK BINS DURING ORCHARD TRANSPORT

Abstract

Mechanical damage occurs in postharvest handling primarily in two modes, impact forces and compressiveforces. When apples are handled in bulk bins, the compressive forces are static when stationary or dynamic during thehandling and transport process. Developing an understanding of the characteristics of the actual compressive forces andinteractions between apples, will enable bulk systems to be designed to eliminate potentially damaging forces. Prototypelow profile force sensors were developed to measure static and dynamic compressive forces on individual fruit in bulkbins. The sensors provide a uniform sensitivity over a 73 mm (2.9 in.) diameter surface. Using 10 sensors, compressiveforces were measured in the floor of five bulk bin designs (one hardwood, one plywood and three plastic) as they weretransported over a 1.3 km (0.8 mile) orchard course using a short tined tractor-mounted fork-lift. The compression datacollected was used to develop force spectral density (FSD) representations for each force sensor. Damage-free appleswere placed on the floor of each bin, and accumulated damage was measured. Bruise damage was higher in all bindesigns for test fruit positioned at the section of the bin floor furthest from the tractor. The range of bruise damaged fruitwas 15.0 to 47.5% and graded 67.5 to 92.5% U.S. Extra Fancy. The magnitude of compressive forces measured with eachsensor was inconsistent among bin designs; however, higher forces were recorded in the middle of the bin and the end ofthe bin away from the tractor. Predominant FSD levels were found at frequencies between 1.0 to 2.0 Hz and 3.5 to 4.5 Hzfor all 5 bin designs. Bruise damage best correlates to the amplitude of FSD at a frequency of 4 Hz.