Horticulture Fact Sheet
H-00-051
The University of Georgia College
of Agricultural and Environmental Sciences
Cooperative Extension Service
Kathryn C. Taylor, Stone Fruit Horticulturist, Horticulture
Department, CAES,
University of Georgia, 21 Dunbar Rd., Byron, GA 31008
Injury to the peach peel that causes peel discoloration is cumulative. Therefore, each improvement that can be made to reduce discoloration will pay off in better post harvest quality. Steps can be taken in the field and the packing house to improve post harvest quality. A checklist of factors that when mishandled accumulate to decrease overall peel quality follows.
1- Have the peaches received a great deal of rainfall just prior to harvest? If so the fruit swells and is not as resistant to handling and mechanical injury. Injured areas are sites of dehydration during cool storage and will be revealed as discolored areas on the peel. Pay attention to weather forecasts prior to harvest. If heavy rains are predicted, pick a little early, to minimize the adverse effect of excess rain.
2- Was fungicide with potential for injury used prior to harvest? In preliminary studies performed in 1998, it should be noted that levels of captan residue were high on non-packed fruit that showed 8-10 percent discoloration. The source trees were treated with captan several weeks prior to harvest. Additionally, we've found that trees suffering from fungal gummosis are more likely to bear stained or bleached peel where the gum has dripped on the fruit. These fruit are also more likely to be affected by sooty mold. Consider this problem when selecting varieties ('Summergold' appears highly susceptible). All practices that reduce stress (especially irrigation and weed management) reduce gummosis and reduce gumming in affected trees.
3- Is fruit handling conducive to excessive injury? Rough handling during picking, non-smooth picking containers, and "bumpy" transport (due to rough roads and high transport speeds) to the packing house all contribute to increased peel discoloration. Wooden crates can be lined with bubble wrap or other padding materials. Trailers can be fitted with shocks to reduce bumping on rough roads. Think about reducing the height of fall as fruit are dropped from picking bags into bins. Use wet dumps rather than dry dumps onto the packing line.
4- Does your hydrocooler pH check out? Maintain hydrocooler pH between 5.5 and 6.5. A commercial buffer such as Decco 311 buffer concentrate is effective in maintaining this range.
5- How is your chlorine holding up? At pH 5.5-6.5 a free chlorine level of 25-50 ppm is ideal for reducing microbial populations without damaging the peel. Although, as little as 1 ppm is sufficient to kill microbes, more is advisable to insure that the level stays above 1 ppm over the course of the day during packing.
6- Is iron a problem? It can be if it is present above 10 ppm. Maintenance of 5.5-6.5 pH will aid in the avoidance of discoloration due to the presence of iron in the hydrocooler water. Fruit abrasion and high pH are associated with increased discoloration when iron levels are greater than 50 ppm. Keep in mind that certain pesticides, e.g. phosmet and Benlate are high in iron (2-2000 ppm). Thus during the hydrocooling operation, iron is continually being added to the hydrocooling tank. Peel discoloration can be limited by increased turnover of hydrocooler water.
7- Do you have ammonia leaks? A leakage of ammonia coolant will raise the pH of the hydrocooler water. Have your refrigeration system checked if sudden increases in pH occur after adjustment to the appropriate level.
8- Did you prerun the drying rollers? Precondition new drying rollers by running fruit for a period of time to break them in prior to extensive use.
9- Latex or polyurethane on your rollers? Polyurethane is the material of choice for rollers. When compared to latex, fruit run over polyurethane have less discoloration.
10- Have you checked the packing line for injury points? We can assess your line for sites of potential bruising or other forms of injury. Contact your county extension office to access this service. We will provide pointers on how to improve those locations on your line. The final drop into the shipping container is often a point of great potential injury. Padding can be added to the box or placed beneath the box to produce some cushion as fruit impact the box surface. Baffles can be placed above the box to reduce the velocity of the fruit as it enters the box.
Crisosto, C.H., R.S. Johnson, KR. Day, B. Beede, H. Andris. 1999. Contaminants and injury induce inking on peaches and nectarines. California Agriculture 53(1):19-23.
Mitchell, F.G., A.A. Kader. 1989. Factors affecting deterioration rate. In: Peaches, Plums, and Nectarines: Growing and Handling for Fresh Market (J.H. LaRue and R.S. Johnson, eds). University of California Publication #3331.
Ridley, J.D., L.O. Van Blaricom, E.T. Sims, Jr. 1976. Postharvest treatment influences discoloration of fresh peaches. Clemson University Cooperative Extension Bulletin #560.
H-00-051/July, 2000
The University of Georgia and Ft. Valley State University, the U.S. Department of Agriculture and counties of the state cooperating. The Cooperative Extension Service, the University of Georgia College of Agricultural and Environmental Sciences offers educational programs, assistance and materials to all people without regard to race, color, national origin, age, sex or disability.
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Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, The University of Georgia College of Agricultural and Environmental Sciences and the U.S. Department of Agriculture cooperating.
Gale A. Buchanan, Dean and Director