Pectin methylesterase, polyphenol oxidase and physicochemical properties of typical long-storage cherry tomatoes cultivated under water stress regime

BACKGROUND: The selection of cherry tomato genotypes with extended shelf-life and resistant to water stress is an important aspect of Sicilian agriculture. The aim of the present study was to evaluate the effects of watering regime on the expression of enzymatic activities (pectin methylesterase (PME, EC 3.1.1.11) and polyphenol oxidase (PPO, EC 1.14.18.1)) and the physicochemical properties of typical long-storage cherry tomatoes in order to propose a solution strategy suitable for Sicilian cultivation. RESULTS: PPO activity seemed to be related to the watering regime employed, showing a maximum under normal watering conditions. PME activity also decreased greatly with increasing water stress (loss of activity ranging from 22.31 to 82.01%). Water stress induced an increase in titratable acidity (up to 68.7% in cultivar 'Giallo piccolo a punta') and, above all, in dry matter and total soluble solids (increases ranging from 24.08 to 91.68% and from 5.93 to 40.90% respectively). Possible solution strategies for cultivation of tomato genotypes with extended shelf-life are (a) selecting the local type that presents the lowest levels of PME and PPO ('Pizzutello') or (b) modifying the watering regime in order to induce commercial cultivars employed in intensive cultivation (e.g. 'Naomi') to better protect themselves from degradative enzymatic activities. CONCLUSION: It appears that the adoption of high watering levels, leading to a more marked expression of degradative enzymatic activities, could result in cherry tomatoes with a high susceptibility to undesirable browning and softening reactions.