Roles of the ascorbate–glutathione cycle, pigments and phenolics in postharvest ‘sunscald’ development on ‘Granny Smith’ apples (Malus domestica Borkh.)

Antioxidant Metabolism and Gene Expression during “Stain” Development on ‘Fuji’ Apples during Cold Storage

“…Antioxidant metabolites. Ascorbic acid (AsA) and total glutathione (GSH) determinations were carried out by extracting peel tissue (five replicates of five fruit each) with 1 M HClO 4 as described by Hernandez et al (2014). In brief, supernatants were divided into two aliquots of 400 mL for AsA and GSH determinations, 200 mL of 0.1 M HEPES/ KOH (pH 7.0) added, and pH adjusted with 6 M K 2 CO 3 to pH 4.0-5.0 for AsA and 6.0-7.0 for GSH.…”

“…Antioxidant enzyme activities. For all enzyme activity assays, frozen peel tissue (five replicates of five fruit each) was extracted using MES/KOH buffer (pH 6.0) containing KCl, CaCl 2 , and AsA as described by Hernandez et al (2014). Catalytic activity for each enzyme was determined by monitoring the change in optical density (OD) using a spectrophotometer (Agilent Technologies, model 8453, Santa Clara, CA).…”

“…As with sunscald of 'Granny Smith' apples (Contreras et al, 2008;Hernandez et al, 2014;Lurie et al, 1991), ''stain'' development is associated with sun exposure in the orchard as well as sunburn incidence and severity (Fan and Mattheis, 1998;Felicetti and Schrader, 2010;Schrader et al, 2003Schrader et al, , 2008. Fuji apples are highly susceptible to ''stain,'' although it can occur on other cultivars including Royal Gala and Honeycrisp apples.…”

“…Phenolic compounds rapidly accumulate on sunexposed peel in response to direct sunlight (Felicetti and Schrader, 2008;Yuri et al, 2010). Phenolic compounds also appear to be directly involved in sunscald development in 'Granny Smith' apples during cold storage (Hernandez et al, 2014). The antioxidative capacity and regeneration of ascorbate by the AsA-GSH pathway ostensibly has an indirect role in sunscald development by improving defense against postharvest oxidative stresses (Hernandez et al, 2014).…”

“…Phenolic compounds also appear to be directly involved in sunscald development in 'Granny Smith' apples during cold storage (Hernandez et al, 2014). The antioxidative capacity and regeneration of ascorbate by the AsA-GSH pathway ostensibly has an indirect role in sunscald development by improving defense against postharvest oxidative stresses (Hernandez et al, 2014). During this process, quercetin oxidation and accumulation of its brown products may be responsible for the symptoms (Jimenez and Garcia-Carmona, 1999).…”