Postharvest rind colour and antioxidant composition of ‘Marsh’ grapefruit harvested from different canopy positions of the tree

Rind biochemical composition affects citrus fruit response to postharvest physiological stresses. Effect of canopy position within the tree on rind colour and antioxidant composition of ‘Marsh’ grapefruit was investigated during 9 weeks of postharvest storage. Fruit from inside canopy (IC) and outside canopy (OC) were harvested from KwaZulu-Natal (KZN) and Mpumalanga (MP) provinces in South Africa. Colour indices were measured using calibrated colorimeter while total phenolics concentration (TPC) was determined by Folin-Ciocalteu method. Canopy position had significant effect on fruit rind quality. At harvest, OC fruit from Mpumalanga province were more luminous (L* = 83.1) than IC fruit (L* = 81.1). At KZN IC fruit were less luminous (L* = 78.9) compared to OC fruit (L* = 79.8). The albedo of OC fruit from KZN had higher levels of TPC (2.9 mg gallic acid equivalent GAE g^-1) than IC fruit (2.8 mg GAE g^-1). This trend was observed at subsequent sampling times during postharvest storage until week 6 when the maximum TPC in OC (4.9 mg GAE
g^-1) and IC fruit (3.8 mg GAE g^-1) were reached, followed by a decline. Conversely, OC fruit from MP had lower TPC (2.1, 2.3, 2.9, 2.5 mg GAE g^-1) than IC fruit (2.3, 2.9, 2.9, 2.8 mg GAE g^-1) at weeks 0, 3, 6 and 9 in cold storage, respectively. However, TPC of the flavedo followed a consistent increasing trend until week 6, followed by a decline. OC fruit had higher flavonoids concentration (0.6 and 0.7 mg quercetin equivalent (QTE) g^-1) than IC fruit (0.5 and 0.5 mg QTE g^-1) from KZN and MP, respectively. This study provides baseline information to improve the understanding of how canopy position affects rind quality.