Seasonal changes in oranges and the effect of canning and storage on the constituents of the juice

Seasonal changes in the Persian orange (Citrus sinensis var. Sia-Varaz) and the effect of canning and storage on the juice were studied. The major factors under consideration were the physical characteristics: weight, size, volume of juice, colour of peel; and chemical characteristics: free sugars, vitamin C, free amino acids and lipid content. In order to determine the optimum state of maturity of the orange, samples were harvested at regular monthly intervals and analysed. 1. Throughout fruit development there was a continuous increase of juice, fruit size, and total soluble solids while total acidity decreased. These parameters were sufficiently different to enable the separation of the development cycle into three distinct phases: Cell division, Cell enlargement and Maturation of the fruit. Colour break from yellow to orange occurred between December and January but the oranges were assessed to be mature for harvesting by February and March. 2. Five sugars were identified: xylose, galactose, fructose, glucose and sucrose. Xylose soon disappeared while galactose was only found in minor quantities. Sucrose and reducing sugar content increased with fruit development. In the mature orange the ratio of suerose : glueose : fructose was very close to 2:1:1.3. While vitamin C content per 100 g pulp showed no significant change over the period of study the amount per orange pulp increased approximately four-fold. 4. Seventeen amino acids were identified. Increase in proline and arginine during December and January may be used as an indication of the onset of maturation. 5. Changes in lipid constituents were noted but, in general, no definite pattern could be established. The processing procedure involved heating the juice at 98°C for 30 seconds and then sealing in lacquered A1 cans. Analyses were carried out at two-monthly intervals. 6. Although total free sugars, vitamin C and colour of the juice were not affected by processing, significant increases in total free amino acids and lipids were noted.7. Storage of canned juice at 7°C for twelve months showed no significant effect on total free sugars, vitamin C, free amino acids and flavour. However, total lipid was significantly decreased after eight months. Storage of canned juice at 30°C brought about significant losses of total free sugars after twelve months, of vitamin C after two weeks, and of free amino acids after two months, and of total lipids after two months. The flavour of the juice, judged by a taste panel, had deteriorated significantly after one month's storage.