Cold-storage period (days) Poster code: PT 25 EFFECT OF PREHARVEST SOLAR RADIATION ON APPLE SKIN OXIDATIVE DISORDERS DURING COLD-STORAGE Laura I. Vita, Nidia F. Gonzalez, Graciela M. Colavita Instituto de Biotecnología Agropecuaria, Universidad Nacional del Comahue. Facultad de Ciencias Agrarias, Ruta 151 Km 12,5. Cinco Saltos, Río Negro, Argentina. E-mail: laura.vita@faca.uncoma.edu.ar Non-exposed tissue Superficial scald Exposed tissue Sunscald INTRODUCTION Sunscald and superficial scald are physiological disorders of apple that develop during low temperature storage. Sunscald is exclusively observed on sun-exposed section and appears originally as a yellow skin blemish on the side of the apple exposed to the sun. It often turns brown or black during the later stages of development and storage. Superficial scald is an oxidative process that appears on non-sun-exposed skin as brown or black patches during or after storage. Granny Smith apple (Malus domestica Borkh.) is the most susceptible cultivar to both postharvest disorders. They cause significant amount of cull and decrease profitability of growers and packers. The objective of this study was to evaluate apple oxidative disorders during cold-storage on different sun-exposed level tissue. MATERIALS AND METHODS During the 2013/14 harvest season, Granny Smith apples were collected from a commercial orchard located in Rio Negro Upper Valley, Argentine (39°01’S, 67°44’W; 244 m.a.s.l.) and stored in regular atmosphere at 1ºC. Sun-exposed (ET) and non-exposed tissues (NET) were compared during 0, 90, 120, 150 and 180 days of cold-storage. Sunscald and superficial scald incidence was determined visually on ET and NET respectively and expressed as percentage. α-farnesene (AF) and conjugated trienes (CT) were performed spectrophotometrically from skin hexane extract. Free radical scavenging activity was tested using the 2,2,-diphenyl-2-picryl-hydrazyl (DPPH) method, and expressed as percentage inhibition of DPPH. Lipid peroxidation was determined by assaying the thiobarbituric acid-reactive substances (TBARs). Fruit maturity was assessed by measuring firmness, total soluble solids and tritatable acidity. RESULTS After 90 days of cold-storage and 1 week at 20ºC, sunscald was observed only in ET and affected 41.4% of the fruit. Superficial scald was detected in NET and affected 66.5% of the fruit. At 180 days, these disorders enhanced to 100% (Fig. 1). In advancing storage, AF concentration increased. The highest level (125.5 nmol.cm-2 and 95.8 nmol.cm-2 for ET and NET, respectively) was measured at 120 days of storage, decreasing at 180 days. CT in ET were lower during all storage period, but increased significantly in NET after 90 days, consistent with superficial scald symptoms (Fig. 2 and Fig. 3) Fig. 5. Concentrations of lipid peroxidation products-TBARs in apple peel cv Granny Smith with different sun-exposed level. Data are the mean ± S.E. Fig. 3. Conjugated trienes (CT) concentration in apple peel cv Granny Smith with different sun-exposed level. Data are the means ± S.E. Fig. 2. α-farnesene (AF) concentration in apple peel cv Granny Smith with different sun-exposed level. Data are the means ± S.E. Fig. 4. Radical scavenging activity-DPPH in apple peel cv Granny Smith with different sun-exposed level. Data are the means ± S.E. Fig. 1. Sunscald and superficial scald incidence after 1 week at 20ºC Along all cold-storage, DPPH was significantly higher (P<0.05) in ET than NET (Fig. 4). At harvest ET showed significantly more TBARS (59.8 nmol.g-1FW) than NET (43.8 nmol.g-1FW). During storage lipid peroxidation increased, and reached at 180 days, 101.8 nmol.g-1FW in NET and 75.5 nmol.g-1FW in ET (Fig. 5). There were significant differences in fruit maturity between ET and NET. Flesh firmness and total soluble solid were higher in ET than NET throughout the sampling period (Table 1). Table 1. Fruit maturity indices in apple peel cv Granny Smith with different sun-exposed level. Cold-storage period (days) Sun- exposed level Firmness (N) Total soluble solids (ºBrix) Tritatable acidity  (%) ET 90.2 a 12.1 a 0,81 a NET 76.9 b 10.1 b 0,88 a P-value <0.0001 0,0006 0.1338 90 81.4 a 15.8 a 69.8 b 12.7 b 0,86 a 0.0002 0.0299 0.0785 120 76.0 a 15.1 a 0,77 a 64.0 b 12.6 b 0.0026 0.1955 150 73.8 a 16.1 a 0,76 a 63.6 b 14.0 b 0,84 a 0.0005 0.0023 0.0567 180 75.1 a 13.9 a 0,75 a 64.9 b 12.5 b 0,80 b 0.0042 0.0094 CONCLUSIONS These results showed that alternative physiological oxidative process may be occurring in exposed and non-exposed tissues during cold-storage and the higher antioxidants activity found in sun-exposed tissue was ineffective in preventing sunscald. Further work is needed to elucidate the processes involved in sunscald development.  Averages followed by the same letter do no differ significantly (Tukey`s Test P≤0.05)