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The aim of present study was to compare antioxidant properties and investigate the possibility of synergism or antagonism interaction between green tea and oak extracts. Green tea extract in all concentrations had a significant (p<0.05) higher effect than BHT in  DPPH free radical scavenging assay and total antioxidant capacity, and in two concentration in reducing power, and in all of the assays was better than oak extract; While only in DPPH free radical scavenging assay the oak extract was better than BHT. Among different combinations of these two extracts, synergism was found in three combination according to DPPH free radical scavenging assay, four combination in total antioxidant capacity assay and all combination in reducing power assay. In the peroxide value assay, the chosen combination showed antagonism, although it was significantly (p<0.05) more effective than BHT in soy bean oil stability. The result shows that it is possible to use these natural antioxidant as substitute of synthetic antioxidant BHT.

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The Juice clarification is an important operation in the fruit processing industry. Sour Orange is a source of vitamin C that is cultivated in the north of Iran. Since turbidity of this fruit after juice extraction affects on quality, shelf-life and concentration of juice; clarification and removing of turbidity-causing factors is important. In this study, the effect of membrane parameters including pressure (1.2-2.2 bar) and temperature (25-35 ºC) on the quality characteristics of sour orange during membrane clarification was investigated. The response surface methodology (RSM) by Design-Expert Software was used to optimize the clarification conditions. Results of the experiments showed that the Browning index was raised by increasing of temperature, but vitamin C content, Total antioxidant activity value and clarity was decreased in this condition. The Browning index was decreased by increasing of pressure; however, no significant effect was observed on the other quality characteristics. Results of process optimization indicated that the best condition to maximize of vitamin C content, total antioxidant and clarity and to minimize of Browning index achieved at 25 ºC and 1.7 bar. In this condition the vitamin C content, Browning index, Total antioxidant activity and clarity was 24.9 (mg/100 cc juice), 0.106, 87.97% and 97.1%, respectively.