Integration of Nondestructive Techniques with Destructive Analyses to Study Postharvest Water Stress of Winegrapes

Red Cesanese grapes were harvested at 21 Brix. Berries were destemmed manually and placed in perforated plastic trays inside a small ventilated tunnel at 10°C with 1.5 m/sec of air flow, 10°C with 2.5 m/sec of air flow, and 20°C with 1.5 m/sec of airflow as a control. Relative humidity was 45%. The experiment was stopped at 20% berry weight loss, after 26, 22, and 16 days for 10°C at 1.5 m/sec, 10°C at 2.5 m/sec, and 20°C at 1.5 m/sec, respectively. Sugar content rose to 24–25 Brix. Carbon dioxide production from chilled berries under a higher air flow rate was constantly higher (~30%) than at a lower ventilation, and similar to that of the 20°C sample. Berries lost firmness (higher deformation), increased hue angle, and decreased chroma, regardless of treatment. Berries kept at a higher flow rate had magnetic resonance images similar to those of the berries kept at 20°C, with diffuse dark areas in the mesocarp. Analysis of alcohol dehydrogenase in the direction of the oxidation of ethanol to acetaldehyde revealed significantly higher activity at 20°C than at 10°C at 20% of weight loss, and ethanol was lower. The fluorescence (Fα) pattern confirmed a different stress rate depending on temperature and flow rate. Near-infrared–acousto-optic tunable filter (NIR–AOTF) analysis revealed a different absorbance level at a specific wavelength range depending on the treatment and the rate of weight loss. A significant decrease in polyphenols occurred in 10°C samples. Flavonols and stilbenes increased significantly at 20°C, confirming a supposed higher rate of water stress at 20°C.