Assessment of rind quality of 'Nules Clementine' mandarin during postharvest storage: 1. Vis/NIRS PCA models and relationship with canopy position

- A link between fruit canopy position and rind biochemical profile was established.
- Bagged fruit inside the canopy had higher incidence of rind breakdown disorder.
- Shaded fruit had lower rind dry matter and higher postharvest weight loss.
- Vis/NIRS PCA displayed clusters that separated fruit according to canopy position.

This research was conducted to examine the relationships between fruit position in the canopy, limited light by fruit bagging, rind biochemical composition and susceptibility of 'Nules Clementine' mandarin to rind breakdown disorder (RBD) during storage. A secondary aim of this study was to explore diffuse reflectance visible and near infrared spectroscopy (Vis/NIRS) as a non-destructive technique to sort mandarin fruit based on preharvest canopy position. Vis/NIRS signals of fruit from four orchards in the Western Cape Province in South Africa (Citrusdal, Paarl, Porterville and Stellenbosch) were obtained using a LabSpec® spectrophotometer. In all four orchards, bagged fruit inside the canopy had significantly (p < 0.001) higher incidence of RBD compared to unbagged outside fruit. Concomitant to this, bagged fruit inside the canopy had significantly higher postharvest weight loss and lower dry matter (DM) content in the rind tissue, suggesting involvement of these parameters in fruit susceptibility to RBD. Bagged fruit inside the canopy harvested from Porterville and Paarl had higher concentration of non-structural carbohydrates (fructose, glucose, and sucrose) than outside fruit without bagging. In Stellenbosch, fruit from the outside position without bags had lower rind sucrose (95.3 mg/g DM) compared to inside bagged fruit (114.9 mg/g DM) but higher glucose concentration (92.0 mg/g DM) compared to inside bagged fruit (66.9 mg/g DM). Principal component analysis (PCA) of Vis/NIRS signals was executed to separate fruit according to canopy position. The projection of the samples in the PCA score plots displayed clusters that allowed distinction between fruit from different preharvest treatments. The ability of PCA to discriminate inside and outside fruit using Vis/NIRS signal suggests the potential of this technology to discriminate fruit based on their susceptibility to RBD.