title: Individual phenolic response and peroxidase activity in peel of differently sun-exposed apples in the period favorable for sunburn occurrence.
abstract: Extreme weather events like high solar radiation can cause stress in apple fruits (Malus domestica Borkh.). The aim of the study was to make a screening of individual phenols and peroxidase activity in apple peel as a response to sunburn and different sun-exposures in the period when weather conditions are suitable for sunburn occurrence. Apple fruits of 'Golden Delicious' and 'Braeburn' were sampled. Fruit temperature and color were measured prior HPLC-MS(2) and peroxidase activity analyses. Sunburned peel was darker and more yellow-red in comparison to healthy peel, which appeared yellow-green. Fruit temperature, total as well as individual flavonols and dihydrochalcones, total hydroxycinnamics and perixodase activity were highest in sunburned peel in comparison with healthy sun-exposed peel, furthermore both were different than shaded sides of both fruits and peel of apples inside the tree crown; moreover in sunburned peel dihydrochalcones were determined for the first time. Chlorogenic acid was up to 2.5 times higher, 3-hydroxy-phloretin-2'-O-xyloglucoside was up to 10 times higher and quercetin-3-galactoside was up to 33 times higher in sunburned peel, comparing to shaded sided peels. Flavanols did not show a distinct pattern. A deeper insight in phenolic response against environmental stress caused by high solar radiation and high air temperatures has been made.
authors.affiliation: Department of Agronomy, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia. Electronic address: anka.zupan@bf.uni-lj.si.
authors.forename: Anka
authors.initials: A
authors.lastname: Zupan
authors.affiliation: Department of Agronomy, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia.
authors.forename: Maja
authors.initials: M
authors.lastname: Mikulic-Petkovsek
authors.affiliation: Department of Agronomy, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia.
authors.forename: Ana
authors.initials: A
authors.lastname: Slatnar
authors.affiliation: Department of Agronomy, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia.
authors.forename: Franci
authors.initials: F
authors.lastname: Stampar
authors.affiliation: Department of Agronomy, Biotechnical Faculty, University of Ljubljana, Jamnikarjeva 101, SI-1000 Ljubljana, Slovenia.
authors.forename: Robert
authors.initials: R
authors.lastname: Veberic
mesh_terms: D027845:Malus / Q000201:enzymology / Q000378:metabolism / Q000528:radiation effects*; D010544:Peroxidases / Q000378:metabolism*; D010636:Phenols / Q000378:metabolism*; D013472:Sunlight
chemical_list: D010636:Phenols; D010544:Peroxidases
keywords: Dihydrochalcone; HPLC–MS; Individual phenols; Peroxidase; Sunburn