Biochemical changes in fresh and processed orange juice

Oranges (Washington Navel, Citrus sinensis) were harvested from an experimental orchard, and after washing, half of them were stored as whole at 6, 15 and 30°C for 4 weeks. The other half were squeezed and the fresh juice samples were stored in hermetically sealed dark bottles at 6, 15 and 30°C for 4 weeks before and after pasteurization at 95°C, 30 s. Three of the samples were analyzed after 0, 1, 2, 3 and 4 weeks storage time for Vitamin C, total phenol content, antioxidant activity and pectinmethylesterase activity (PME), dry matter, pH and total soluble solid (TSS). Dry matter, pH and TSS values of the samples did not vary at all storage temperatures during 4 weeks. Pasteurization of freshly squeezed orange juice at 95°C, 30 s, resulted a 8.58 % decrease in vitamin C content. The ascorbic acid content of the juices decreased during storage, faster at 30°C than at 6°C and 15°C. The mean life of ascorbic acid in freshly squeezed juice was reached at 30°C, 4 weeks storage whereas pasteurized juice and whole orange juice exhibited greater shelf life. Antioxidant capacity (FRAP assay) was decreased 16.53 %, total phenol was decreased 7.17 % and PME activity 68 % due to the pasteurization process, 95°C, 30 s. After 4 weeks storage at 6°C, the antioxidant activity in whole orange juice, freshly squeezed juice and pasteurized juice, were decreased by 30.53 %, 27.47% and 23.20 %, respectively. Total phenol contents of whole orange juice at 6 and 15°C were not significantly different, but at 30°C there was an appreciable decrease in concentration at the end of 4 weeks storage. PME activity loss was observed in all samples due to the time and temperature of storage studied.