عنوان مقاله [English]
Background and Objectives
Tomato is one of the most important vegetable in Iran, not only because of its economics importance, but also for the nutritional value of its fruit, mainly due to the fact that they are an excellent source of natural colors and antioxidant compounds. Water quality and fruit maturity stage has a significant effect on tomato fruit quality. In the present research, we studied the response of tomato grown at different salinity levels, as well as the changes that take place during different maturity stages, in order to improve the management and harvesting of tomato and obtain fruit of a higher nutritional value.
Materials and Methods
In this study, to evaluate the effect ofsalinity and fruit ripening stage on physical, biochemical properties and shelf life of tomato fruits in hydroponics system, an experiment was carried out as factorial based on randomized complete block design with three replications at Moghan College of Agriculture and Natural Resources, during 2015. Fruits from plants grown under three saline treatments (2, 4 and 8 dS m-1) were harvested at three ripening states (mature green, purple and red colors). The nutrient solution was prepared based on full strength of Hoagland's solution containing: 5.6 mM Ca (NO3)2, 4 mM KNO3, 1 mM KH2PO4. Characteristics such as fruit fresh and dry weight, total soluble solid, firmness, flavor index, titratable acidity, soluble protein, ascorbate peroxidase activity and shelf life were measured.
The results showed that total soluble solids, juice electrical conductivity and dry matter percentage of fruits significantly increased with increasing salinity in the nutrient solution and progressed the ripening stage, but fruit water content decreased by 9%. The highest weight (147.7 g) and volume of fruits (153 cm3) were obtained in plants grown under 2 dS m-1 salinity and fruits harvested at the purple stage. Titratable acidity increased with increasing of salinity in the nutrient solution, but its content decreased at the red color stage. Firm fruit with greater shelf life was observed under 2 dS m-1 salinity and at the mature green stage. Soluble protein content in fruit was increased by increasing salinity levels in the nutrient solution, especially at the ripening stage. The application of 4 dS m-1 salinity at mature green stage increased ascorbate peroxidase activity up to 62.5% compared to 8 dS m-1 salinity and red color fruits.
These results suggest that the improvement in fruit quality induced by the salinity is achieved by some biochemical changes and the reduction of fruit water content. Increasing of salinity in the nutrient solution can be useful for improving fruit quality, especially, when fruit is harvested at the red stage. However, with increasing salinity in the nutrient solution up to 4 dS m-1 and fruit harvest in the red color stage fruits with better quality and more suitable weight can be produced.