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

¹ Department of Food Science and Technology, University of Tuscia, Viterbo, Italy; ² Chemical Methodologies Institute, CNR, Montelibretti, Rome, Italy; ³ Research Center for Soil Plant System, CRA, Rome, Italy; and ⁴ Department of Food Engineering, Polytechnic University of Cartagena, Cartagena, Spain.

^* Corresponding author (email: mencarel{at}unitus.it; tel: +39 761 357494; fax: +39 761 357498)

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 (F) 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.

Key words: grape, dehydration, temperature, air flow, polyphenols, ADH, MRI, NIR