Evaluation of Quality Characteristics of Thomson Orange Produced in Golestan Province

Background and objectives: The losses of horticultural products encompass both quantitative and qualitative losses from production to consumption. Three factors—harvesting time, storage, and climate—impact fruit quality and, consequently, lead to losses. Various indices are utilized to determine the proper harvesting time, with the most important ones for oranges being the maturity index (TSS/TA), total soluble solids (TSS), and extract content. Considering the weather conditions in each area, all these indices should be determined when the fruit is ripe. Additionally, fruit storage is contingent on production conditions such as climate, orchard management, harvesting time, and storage conditions. Due to the lack of necessary information about oranges produced in Golestan province, this research was conducted to determine fruit quality at harvesting time as well as after storage.

Materials and methods: In this study, considering the extent of citrus orchards and climatic diversity in Golestan province, the province was divided into three areas (west, Kordkoy and Bandarqs), center (Aliabad and Gorgan) and east (Azadshahr)..In each area some orchards with similar management were selected. Fruits were harvested from a number of trees in each orchard at two times (first half of the harvesting season, when less than 10% of the fruit surface discolored and the bottom half, when more than 90% of the fruit surface discolored). Then, samples from each area were mixed at each harvesting date and finally a mixed sample was obtained. Fruits were stored at 4-6 °C and 85-90% relative humidity. Characteristics related to fruit quality, such as titratable acidity (TA), total soluble solids (TSS), Maturity Index (TSS/TA), acidity, ascorbic acid, total sugar, reducing sugar and sucrose according to the method described by the Iran National Standards Organization (No 2685 and 14617-2) at harvesting time, after two and four months of storage Was examined. Data were analyzed by using factorial statistical design.

Results: The results showed that harvesting location had significant effect (p≥0.01) on TA and TSS as well as maturity index (p≥0.05) but had no significant effect (p≥0.01) on ascorbic acid, total and reducing sugar content. Harvesting time also affected TA, maturity index and ascorbic acid (p≥0.01) but had no effect on TSS, total and reducing sugar. Storage period affected qualitative characteristics of fruits included TA, TSS, maturity index, ascorbic acid and reducing sugar, except total sugar. The results showed that TA, ascorbic acid, TSS, maturity index, total sugar, reducing sugar and sucrose were in the range of 0.76-1.76 gram in100 mL juice, 11.4-40.16 milligram in100 gram juice, 8.88- 11.43 Brix, 6.34-13.34, 5.76-9.16 gram in100 gram juice, 3.01- 4.54 gram in 100 gram juice and 3.10-4.83 gram in100 gram juice, respectively.

Conclusion: The fruits of the center of province had the highest amount of extract, total acid and lowest acidity, soluble solids and maturity index. The second harvesting time also reducing total acid and increased maturity index. The storage duration also increased the amount of extract, acidity, ascorbic acid, total soluble solids, maturity index and reducing sugar and decreased total acid and sucrose. Based on the results, it can be stated that samples from the center area should be picked up later than the other two sites to achieve better quality. Although storage duration had led to changes in some of the characteristics investigated, it can be stated that the fruit of the Golestan orchards had the potential of storage for four months.