Evaluation of Pomological Characteristics and Fruit Quality of Ten Orange (Citrus sinensis) Cultivars on Sour Orange (Citrus aurantium) Rootstock

Oranges are the second most widely consumed fruit in the world after apples. The quality of citrus fruits depends not only on the appearance of the fruit size, shape, color and absence of disease and any surface damage, but also on the flavor, richness of food, vitamins, seedlessness and fruit aroma. The present study investigated the fruit qualitative differences between the ten orange varieties (Thomson Navel, Tarocco, Mars Early, Frost Novel, Local, Italian, Khorram Abadian, Hamlin, Morbeld and Moro Valencia) that grafted on sour orange rootstock, in the Jiroft region. The aim of this study was introducing the fruit qualitative characteristics and nutritional value of ten orange cultivars on the sour orange rootstock in climate conditions of Jiroft region, for fresh uses and processing. Also, determine the capabilities of each cultivar in antioxidant content and antioxidant capacity to introduce the properties of these cultivars to researchers in the food and pharmaceutical industries.

Fruit weight was determined by digital scales. The volume of the fruit was obtained by moving the water. The 0.1 mm caliber device was used to measure skin thickness, length and fruit diameter. To measure the thickness of the fruit skin, a cut was first separated from the middle part of the fruit and its thickness was recorded in mm. The total number of hollow and healthy seeds was counted and was recorded as seed number. The juice percentage was calculated by calculating the percentage of juice mass to fruit mass. A manual refractometer was used to measure the total soluble solids, and thesodium hydroxide titration method was used to measure the titration acidity. The flavor index or maturity index was obtained from the TSS/TA ratio and technology index was calculated by multiplying the percentage of TSS in the percentage of juice. Vitamin C measured by the iodometric method. The antioxidant activity of juice was determined based on the DPPH method. Carotenoid and chlorophyll pigments in juices and skins, were calculated using the Liechtensteiner pigmentation method. The experiment was done as a randomized complete block design in three replications. Statistical analysis of the data was performed using SAS software and means were compared using Duncan's multiple range test at 5% of probability level.

The results showed that Thomson Novell, Frost Novell and Italian cultivars had the highest freshness quality in terms of appearance characteristics (fruit weight, volume, and length, number of seeds, and fruit shape index) among the ten cultivars evaluated. All cultivars were in the physiological maturity stage and were suitable for the juice industry due to their high technology index. The range of vitamin C varied 57 - 109 mg per 100 ml juice and the range of antioxidant capacity varied 65 - 94%. Morbeld, Valencia Morocco, Frost Novell and Mars Early cultivars had higher nutritional value due to higher vitamin C, and Hamlin, local, Tarocco and Frost Navel had higher antioxidant capacity. Khorramabadian cultivar had higher carotenoid pigments in juice and skin.

Therefore, most of the studied cultivars had high freshness and nutritional value, but among them, Frost Novell cultivar, considering the amount of vitamin C, antioxidant capacity, technology index and appearance characteristics in the higher statistically groups  and was in the lower statistical group in terms of number of seeds, therefore was selected as the best cultivar.