Skin burning is a type of skin discoloration that has become a frequent problem on specific susceptible peach and nectarine cultivars. Rejections due to skin burning can reach as high as 50%. Our results from observations over several years indicate that peach and nectarine skin discolorations, field inking and skin burning, are both triggered by a combination of physical damage during harvesting-hauling combined with different postharvest stresses. However, although field inking and skin burning disorders have similar symptoms, they have different triggers and different biological mechanisms of development and therefore it is important to understand the differences between both cosmetic skin disorders.
Skin burning symptoms appear as brown and/or black areas that are restricted to the skin. In contrast to field inking, these symptoms are mainly triggered during packing operations, principally at the brushing-washing point, although abrasion that occurred prior to packing will also contribute to its development. Specifically, the damage is triggered by exposure to high pH and/or dehydration caused by high-velocity, forced-air cooling during packing. Symptoms can be observed very soon after packing, but the symptoms rapidly increase during cold storage due to dehydration. In fact, it has been observed that most of the intense skin damage in packed fruit occurred on the exposed part of the fruit above the tray receptacle and no damage occurred under the price-look-up (PLU) sticker. Our studies demonstrated that fruit skin phenolics in susceptible cultivars and breeding lines are not stable at high pH leading to phenolic transformations. These transformations at different pH values result from copigmentation of phenolics with anthocyanins resulting in a change in color of the anthocyanin compound and therefore discoloration of the skin.
Different susceptibilities to skin burning have been observed among peach and nectarine cultivars, depending mainly on the specific phenolics in their skin tissues.
- Minimize physical damage or abrasion on the fruit surface during pre- and/or post-harvest operations. Handle fruit gently, use air-ride suspension on trailers, avoid long hauling distances and keep harvest containers free of dirt.
- In a standard packing operation, washing water pH in the brushing-washing or hydrocooling operation should be continuously maintained around 6.5-7.0. The installation of automated systems using oxidation-reduction potential (ORP) to monitor and/or adjust active/effective chlorine and pH levels is critical to increase disease control effectiveness and decrease potential skin burning development.
- Based on our results, we recommend dry packing (without brushing or a chlorine rinse) for highly susceptible peach or nectarine cultivars.
- Avoid high air velocities during forced-air cooling for skin burning susceptible peach or nectarine cultivars. For these susceptible cultivars, we suggest cooling the fruit by room cooling, without forced-air.
- As a long-term solution, we suggest screening peach and nectarine breeding parents for their susceptibility to copigmentation.
Cantin, C.M., Day, K., Crisosto, G.M. and Crisosto, C.H. 2009. Update on white flesh peach and nectarine skin burning discoloration. Central Valley Postharvest Newsletter 18(2): 2-5.
Crisosto, C.H., Cantin, C. M. and Suslow, T. 2009. The importance of adjusting your water chlorine pH during your brush-washing operation for the San Joaquin Valley stone fruit industry. Central Valley Postharvest Newsletter 18(3): 1-5.
Cantín, C.M., Tian, T., Xiaoqiong, Q. and Crisosto, C.H. 2011. Copigmentation triggers the development of skin burning disorder on peach and nectarine fruit [Prunus persica (L.) Batsch]. Journal of Agricultural and Food Chemistry, 59, 2393-402. dx.doi.org/10.1021/jf104497s.