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Apple researchers are seeing red

by | Feb 5, 2021

Industry standards for apple color have become increasingly rigorous, causing growers to leave apples like HoneyCrisp on the tree long after the ideal harvesting time to try to achieve the desired color. This can result in major losses in the crop and economic loss to the grower.

COLLEGE PARK, Md. — While historically, growers in the Mid-Atlantic region have enjoyed a competitive advantage by being able to produce some of the first HoneyCrisp apples that go to market, industry standards for apple color have become increasingly rigorous, causing growers to leave apples on the tree long after the ideal harvesting time to try to achieve the desired color.
This can result in major losses in the crop and economic loss to the grower.
Through two new grants, a team of researchers with the University of Maryland College of Agriculture & Natural Resources and University of Maryland Extension will examine how to effectively and efficiently use UV radiation to improve apple coloration pre- and post-harvest, educating growers on when best to harvest their apples to prevent losses while potentially improving fruit quality and food safety. 
“Both of these projects came directly from concerns we’ve heard from the growers themselves,” said Macarena Farcuh, assistant professor and Extension specialist in the Department of Plant Science & Landscape Architecture and affiliate professor with the Department of Nutrition & Food Science. “There is a big problem with getting the color that is required by the market for apples, since the 50 percent to 60 percent of red skin color is difficult to achieve in the Mid-Atlantic region because of our weather conditions.
However, leaving the apples on the tree to wait for the color the way growers have been doing has a lot of consequences.
“The fruit can become overripe, or the apples drop and you can get 10 percent to 20 percent of losses just from the tree. Then in storage, you can get up to 50-percent losses from the limited storage potential of these overripe apples, which can even cause food safety issues with more potential for Listeria outbreaks.” 
This is why the USDA National Institute of Food and Agriculture (USDA-NIFA) awarded Farcuh $300,000 to lead a team of UMD researchers and Extension agents to examine how treatment of apples in storage with UV radiation can not only potentially improve coloration post-harvest, but also provide protection against foodborne pathogens like Listeria. 
“Typically apples have a long shelf life once harvested and can be stored for months in refrigerated conditions,” said Rohan Tikekar, associate professor and Extension specialist with NFSC working on this grant. “With long periods of storage, there is always a chance that the produce might be contaminated. We know there have been outbreaks of Listeria in apples, and while washing reduces the risk of cross-contamination, it is not very effective in removing pathogenic bacteria from produce surfaces. UV radiation is already what causes many of the pigments you see in fruits as a mechanism to protect the cellular machinery from the stress of light. The idea is that UV radiation will then not only improve color, but will also kill Listeria on the surface of apples.”
According to Farcuh, as a result of the UV treatment, researchers also expect to see increases in the antioxidant capacity of the fruit and changes to phytochemical content in addition to creating a “prettier and safer” HoneyCrisp apple. Bryan Butler and Carol Allen with UME are also a part of the team, helping set up opportunities to share recommendations, best practices, and research findings with stakeholders and growers throughout the state throughout the process. Joe Sullivan, professor and associate dean for academic programs with AGNR, is also lending his 40 years of experience in the UV world to help set up treatments and determine the best UV radiation combinations to test for fruit color improvement and safety applications and to therefore present to growers. 
“Color is absolutely a food quality characteristic, but less color doesn’t mean it isn’t as good of an apple,” Farcuh said. “But the market has strict color restrictions that growers are beholden to. Looking at all aspects like color, texture, taste, and the ripening patterns and how all of these are affected will help us determine what the best options are for UV post harvest treatments.
“Sharing our findings with growers throughout the whole process will be especially important because we want to educate them on when they should be optimally harvesting their fruit; the color should not be what drives the harvesting time, but it is now because of those market standards.” 
Focusing on HoneyCrisps as an important apple variety for this region, the Joint Institute for Food Safety and Applied Nutrition with AGNR is also helping to fund the first year of a new graduate student working on this UV work in Farcuh’s Fruit Quality and Physiology Lab. Improved fruit quality, nutritional value, and safety as well as reducing fruit waste are major goals in Farcuh’s lab and work. 
“The main focus of my lab is food quality and physiology or biology from pre to post harvest practices,” says Farcuh. “But not only do fruit quality and safety directly intersect, but safety and quality both directly intersect with fruit loss and waste.
“ I feel many times we just think we have to be more efficient in producing fruit to feed a growing global population, but we forget how much fruit we are losing and wasting. My lab wants to help combat those issues.” 
With the second project Farcuh is leading, she plans to test new technology used to harness UV radiation and enhance coloration as a pre harvest practice. Supported by the Maryland Department of Agriculture Specialty Crop Block Grant Program, Farcuh will be conducting a small pilot program examining the effectiveness of a reflective ground cover called Extenday. This ground cover is placed on the ground in the orchard underneath of apple trees about three weeks prior to the desired harvest time and is used to reflect UV radiation back up into the tree and maximize UV contact with the apples. 
“We get a lot of questions about this technology in Maryland, but very few growers have adopted it, so there is a need to do some preliminary evaluation of these ground covers in our area,” said Farcuh. “My lab will be evaluating all the effects that this would have in terms of food quality in HoneyCrisp and Fuji apples with growers here and in Pennsylvania.” 
Farcuh looks forward to providing the best information possible to growers across the MidAtlantic region to reduce fruit waste, improve fruit quality and safety, and ultimately support profitable agriculture in the region. “This issue of fruit loss and waste due to apple coloration is a big issue, and we want to attack it from many different sides while examining all the costs and benefits to growers every step of the way,” said Farcuh. 

 

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