Reduction of Sunburn in 'Golden Delicious' Apple (Malus domestica L.) Fruit using a Hydrophilic Biofilm

A unique elastic, hydrophilic organic Biofilm was developed in the College of Pharmacy at Oregon State University in 2008 and refined in 2009/10. A U.S. Patent was awarded in 2011 for the use of the Biofilm for the prevention of fruit sunburn. From 2009 to 2011 several different UV protectants, including cinnamaldehyde, zinc sulfate, and kaolin (Surround^(R)) were used in conjunction with the elastic Biofilm to determine whether sunburn of apple fruit could be signficantly reduced. In vitro tests were undertaken between 2009 and 2011. In 2009 and 2010, 'Golden Delicious' apple fruit were sampled monthly, from May until August, from a commercial orchard trained to a central leader in Milton-Freewater, OR. In 2011, fruit were sampled weekly from early June till early August. All fruit were subjected to intense ultraviolet radiation for up to 8 hours totaling 12,500 KJoules•m^-2. Fruit color changes including chroma, hue,  and Hunter L, a and b readings were recorded both before and after treatments. A time, UV, temperature interaction was needed to induce discoloration of fruit skins and fruit were only susceptible to sunburn after the red base color associated with fruit set had faded to green. Furthermore, temperature, UV and visible light radiation were recorded in the field in 2011 and modeling of these in relation to in vivo sunburn will be reported on. Two full cover applications of 1 gal per acre of the Biofilm in conjunction with 25 lbs of Surround^(R) per 100 gallons of water per acre applied in late spring and early summer provided better protection to the fruit than five applications of Surround^(R).  Both treatments were superior to the untreated control in preventing sunburn. The effects on yield, packouts, and postharvest quality will also be reported.