Heat treatments to decrease chilling injury in tomato fruit. Effects on lipids, pericarp lesions and fungal growth

Tomato fruits are sensitive to low temperature and develop chilling injury, while at nonchilling temperatures they ripen rapidly. Previously, a hot-air treatment was found to reduce the sensitivity of the fruit to low temperatures. In the present study hot air was compared to hot water and their effects on reducing chilling injury and fungal decay were investigated. Tomatoes (Lycopersicon esculentum cv. Daniella) at the breaker stage were subjected to hot air, 48 h at 38 degrees C, or various hot water dips, 30 min at 40 degrees C or 2 min at 46, 48 or 50 degrees C, before holding at 2 degrees C. The unheated tomatoes developed chilling injury and fungal infections at 2 degrees C, but not at 12 degrees C. All the heat treatments reduced chilling injury and decay in tomatoes held for 3 weeks at 2 degrees C. The outer pericarp tissue of heated tomatoes had higher phospholipid and lower sterol contents than unheated tomatoes. Heated tomatoes also had less saturated fatty acids than unheated tomatoes held at 2 degrees C, but not at 12 degrees C. Scanning electron micrograph observations showed that all the fruits had microcracks in their surface, but the unheated chilled tomatoes had also fungal growth in the cracks, while those of the heated tomato fruit did not. In the areas of chilling injury collapsed cells were present under the peel and could also support pathogen development. It is suggested that the heat treatment institutes a response to high temperature stress in the fruit tissue that leads to strengthened membranes. This prevents the loss of function and cell collapse which was found in the chilling-injured areas of affected fruit.