Evaluation of The Impact of Hot Water Treatment on the Antioxidant System of Fresh Tomatoes in Chilling and Non-chilling Storage

Minimizing the effects of chilling injury during shelf-life is important for maintaining the sensory quality of fresh tomato fruit. Postharvest hot water treatments within certain limits of exposure time and temperature have been shown to increase resistance of tomatoes to chilling injury. Breaker/Turning (BT) ‘BHN-602’ tomatoes harvested in Spring and Fall 2009 were submerged in water at 25 (control) or 52 °C for 5 minutes. The BT fruit were then stored at 5 °C (chilling), 12.5 °C (putative chilling threshold), or 20 °C (non-chilling). After 1 and 2 weeks, tomatoes were transferred from 12.5 and 5 °C to 20 °C until fully ripe. Ripeness was evaluated by measuring color (CIE a*) on the blossom end of the fruit until a* reached an acceptable value. When selected as fully ripe, physicochemical analyses (acidity, pH, total soluble solids, dry matter, and sugars) were conducted. The fruit antioxidant system was evaluated by measuring ascorbic acid, hydrophilic and lipophilic phenolics, lycopene, β-carotene, hydrophilic and lipophilic ORAC, and FRAP. Decay incidence was also determined. We found that the hot-water treatment resulted in significantly higher lycopene content at all storage temperatures (P = 0.0282), whereas no other antioxidant or physicochemical measurement was found to be significantly affected by the hot-water treatment. In contrast, the storage temperature strongly affected most of the antioxidant and physicochemical analyses. We found that, in order to cope with chilling stress, tomatoes mainly increase their hydrophilic antioxidants such as ascorbic acid (P = 0.0190), hydrophilic phenolics (P = 0.0006), and total phenolics (P = 0.0007) and hence their antioxidant capacity (ORAC and FRAP, P = 0.1608 and P = 0.0019, respectively) and also their content of lipophilic phenolics, but to the detriment of their lycopene (P < 0.0001), β-carotene (P < 0.0001), sugar and dry matter content . It was observed that there was a reduction in the carotenoid content, especially lycopene, at the chilling temperature. BT tomatoes were somewhat resitant to chilling conditions, although we observed a high decay rate, particularly non-treated tomatoes at 5 °C for 2 weeks, which had 67% decay. Overall, the hot-water treatment induced an increase in lycopene content, especially at the chilling threshold temperature (12.5 °C) and had a protective effect, in terms of reduced decay, at the chilling temperature (5 °C).