Measure of mechanical impacts in commercial blueberry packing lines and potential damage to blueberry fruit

Blueberry fruit is susceptible to bruising from mechanical impact. Bruised fruit has shorter postharvest shelf life and softens rapidly in cold storage than non-bruised fruit. A blueberry packing line consists of a hopper for transferring fruit in field containers onto a conveyor line that moves fruit into trash removal equipment, electronic sorter, inspection line, and finally onto clamshell-filling equipment. Blueberry fruit drops as it is transferred from one equipment to the next on the packing line. The mechanical impacts that occur on blueberry packing line equipment were measured quantitatively with a miniature, instrumented sphere called the blueberry impact recording device (BIRD) at 11 packing houses in the United States in 2013 and 2014. The BIRD sensor recorded impacts at transfer points or wherever there was a vertical drop on the packing line. The potential for impact damage was determined in four cultivars ('Farthing', 'O'Neal', 'Reveille' and 'Star') by dropping fruit from different heights. The measured data revealed that the largest impacts (∼230 g) were recorded when the sensor dropped into the hopper above the clamshell filler on eight empty lines. The cumulative peakG data showed strong correlation with overall drop height, indicating that reducing the overall drop height on a packing line could reduce the impact level. When the transfer points were padded with Poron foam sheet, significantly lower levels of impact were recorded by the sensor. The BIRD sensor also recorded lower impacts when it was run with fruit on the packing line. The severity of bruise damage resulting from fruit being dropped was related to the impact data recorded by the BIRD sensor. Using peakG-velocity change plot and the fruit bruising rate, several large impacts sufficient to cause bruising were identified, (e.g., >20% of cut surface area indicating bruise damage in 76% of 'Reveille' fruit). This paper quantitatively measured the mechanical impact on blueberry packing lines for the first time and the information will assist in improving the design and configuration of blueberry packing line equipment. These changes should result in reducing the magnitude and frequency of mechanical impacts and bruise damage in blueberry fruit.