What’s Considered Good Fruit Quality for Fresh Blueberries Harvested by the OTR Harvesters?

By Wei Q Yang, OSU-NWREC and Fumi Takeda, USDA-ARS

There is an increased use of the over-the-row (OTR) mechanical harvesters to pick blueberries for fresh market across the country. This is no surprise because of the harvest labor savings with using OTR harvesters. However, fresh fruit quality often suffers from machine harvest, so does shelf life of cold-stored fruits. Finding ways to improve the fresh quality of blueberries harvested by machine is a long-standing goal of growers, though there are no set quality standards to follow.

Let’s first understand why berry quality is reduced during machine harvesting. The culprit is the excessive internal bruising damage (IBD) in fruit created by mechanical harvesters. The process goes like this: Berries on the bush enter the body of the OTR harvester and are met by rapidly moving shaking rods to vibrate canes in an up/down or circular motion. The cane movement causes mature berries to detach and fall to a catching surface of OTR harvesters and then intoa conveyor collection system. The fruits are transported onto the transfer belt which brings fruits to the top of the OTR harvester. After fruits go through a trash blower, they drop onto a conveyor belt moving towards the collection flats. Although this sounds like a straightforward process, there are many moving parts that create physical impact forces damaging fruits. Using a Blueberry Impact Recording Device (BIRD) developed by Dr. Li of the University of Georgia, these impact points were very well defined with the polycarbonate catch plates of the OTR machine and accounted for more than 30 percent of total mechanical damage. The magnitude of this impact was extremely high on the catch plates to cause the most significant IBD in fruits. An obvious solution is to modify the hard catch surface in the OTR harvester with softer surfaces. The design of a soft surface can be achieved by either incorporating netted material or suspending “rubber” sheets without hard surfaces under the material for catching the fruit (Takeda and Wolford, US Patent No. 9,750,188). The challenges are that the soft materials must meet food safety standards as well as the durability to be used in the field. The currently available soft catch system on the market is OXBO’s SOFTSurface® kit.

In several field experiments conducted in 2020, the reduction of fruit IBD by using the SOFTSurface® kit versus without it ranged from 15 to 80 percent depending on blueberry cultivars and how the harvester was operated, such as machine settings and timing of harvest. There was an average of a 15-24 percent increase in good quality fruits with no damage by using the SOFTSurface® kit. However, sorters on the packing line were not effective in removing blueberries with internal bruise damage because after sorting, there were still more than 30 percent of fruits with 20 percent or more IBD in the fresh packs. In fact, using a non-destructive hyperspectral imaging system to inspect the sorted fruits, it revealed that a wavelength of ~1,150 nm was highly superior for detecting or discriminating fruit IBD and distinguishing between damaged and undamaged tissues. To the best of our knowledge, all commercial optical sorters currently on the market use light emission ≤ ~850 to 960 nm, which is less adequate to sort out fruits with IBD. As a result, packed fruits harvested by machine may always have some fruits with significant IBD, affecting the shelf life of stored fruits. The question is if there is an acceptable level of IBD for fruits to be packed for cold storage.

Our research of fruit IBD since 2015 with machine-harvested blueberries found that if there were more than 70 percent of fruits with less than 10 percent IBD in the fresh pack, there were still 50 percent of good fruits after 3-4 weeks cold storage depending on cultivars. Blueberry cultivars ‘Draper’, ‘Legacy’ and ‘Last Call’ generally had a slower IBD development (better quality) during cold storage, while ‘Liberty’ had a much faster rate of IBD development (poor quality). Obviously, the more fruits with less IBD (preferably less than 10 percent) are in the fresh pack, the better the fruit quality after weeks of cold storage. Because of the current challenges to sort out fruits with more than 20 percent IBD, the quality of machine-harvested fruits is still in doubt until better sorting equipment becomes available. Therefore, the success of machine harvesting blueberries for the fresh market demands not only the OTR harvester with soft catch surfaces, but also better sorting equipment.