Evaluation of the Effects of Calcium Nitrate and Potassium Phosphite on the Storage Life and Some Quality Traits of Thomson Navel Orange

Oranges belong to the Citrus (family Rutaceae) and are an important source of antioxidants, including phenolic compounds and vitamin C. These compounds have a protective effect against various diseases such as cancer and cardiovascular. Since there is a possibility of decay and rot of Citrus in all stages of harvest and post-harvest, the use of mineral elements may have an important effect on increasing the quality of the fruit and its shelf life. This effect varies depending on the species and cultivar of Citrus. Mineral elements, especially potassium and calcium, affect fruit growth and Citrus fruit quality.

To investigate the effect of spraying, a research was conducted in Qaemshahr city in 2019, which in this study, manual foliar application of calcium nitrate (0, 2 and 4 g / l) and potassium phosphite (0, 1.5 and 3 g / l) was done in the late October in three stages with a week interval. Then, one week after the last treatment, the harvesting operation was performed with garden shears. After washing, the fruits were kept in normal temperature for 3 months. Various parameters such as morphology (percentage of weight loss, firmness, percentage of decay, etc.), biochemical (total soluble solids (TSS), titratable acidity (TA) and acidity of fruit juice (pH)), antioxidant (percentage of inhibition and vitamin C), enzyme (ascorbate peroxidase and superoxide dismutase) and marketability traits were evaluated.

The results showed that the application of higher concentrations of calcium nitrate and potassium phosphite improved the measured traits at harvest day. The use of these materials has also increased the shelf life and quality of the fruit during storage. Fruits treated with calcium nitrate and potassium phosphite had more antioxidant properties on the day of harvest. The highest amount of vitamin C and inhibition percentage were observed in the treatment of 4 g / l calcium nitrate and 3 g / l potassium phosphite at harvest day. Treated fruits were more firm and less rotten during storage than control ones. Also, the treated fruits had more soluble solids and titratable acidity. Also, during storage, the quality of the fruit and its marketability decreased, but fruits treated with calcium nitrate and potassium phosphite received higher scores from the evaluators. The use of calcium increases the strength of the membrane and reduces the activity of enzymes that relax the cell wall, which therefore increases the firmness of the fruit and reduces the weight loss and rot of fruits during storage. The use of potassium phosphite has also been effective in reducing caries. Calcium along with potassium play a role in photosynthesis and cause the accumulation of sugars. Vitamin C is associated with a decrease during storage, due to the use of ascorbic acid as an ascorbate peroxidase cofactor. Finally, it seems that the marketability of the fruit has increased due to the increase of quality traits such as sugars, due to the use of calcium nitrate and potassium phosphite.

The storage of Thomson Novel oranges was affected by the treatments used, and the highest firmness, weight and quality characteristics of the fruit were obtained in the highest amount of calcium nitrate and potassium phosphite. Also, the rate of caries has decreased significantly with the use of these treatments.