Rachis browning and water loss description during postharvest storage of ‘Krissy’ and ‘Thompson Seedless’ table grapes

Rachis browning is a serious symptom of water loss affecting the quality of table grapes (Vitis vinifera L.) during storage. It has been evaluated subjectively based on a color scale or by image analysis, while water loss, which is considered as the main factor behind this problem, is mostly measured on basis of whole-cluster weight loss, with only few studies focusing on the rachis exclusively. Our main objective was to compare the sensitivity to water loss and rachis browning of ‘Krissy’ and ‘Thompson Seedless’ cultivars under different storage conditions and using different methods of evaluation (NIR spectrometry, image analysis, colorimeter, weight loss from initial weight and relative water content). The rachises were evaluated during 3 d subjected to a combination of temperatures (0 °C or 20 °C), relative humidity (Saturated or reduced RH), and previous storage at 0 °C for 0 (HT, Harvest Time) and 30 days (ST, Storage Time). NIR spectra (896−2500 nm) were collected, and Partial Least Squares regression (PLS) models were calculated to test the correlation between the spectra and the measurements from other evaluation techniques. Results showed that ‘Krissy’ is more sensitive to dehydration symptoms than ‘Thompson Seedless’. Saturated RH combined with low temperature (0 °C) are the most suitable to reduce rachis browning and water loss during the 3 d of storage at both HT and ST. The decrease in RWC (Relative Water Content) coincided with an increase in rachis browning throughout storage. Additionally, results provided six NIRS-based prediction models for browning severity (R2 = 0.82 and 0.84), hue color (R2 = 0.68 and 0.72) and water loss (R2 = 0.63 and 0.90) in rachises of ‘Krissy’ and ‘Thompson Seedless’, respectively. These results demonstrate that the NIRS can be a suitable non-destructive method to quantify a range of rachis browning severity produced under different storage conditions.