Effects Of Ultra-high Pressure On Aroma Compounds In Fresh Orange Juice And Its Controlling Measures On Off-flavour

Orange juice is favored by consumers because of its nutrient-rich. At present, the thermal sterilization process seriously damage the natural flavor of orange juice. Ultra-high pressure technology is the most promising substitute for heat sterilization in juice industry. Our laboratory successfully developed the orange juice product by ultra-high pressure to maximize the juice to keep the natural flavor. However, orange juice will produce a slight off-flavor after high pressure treatment. In order to further improve the smell quality of fresh juice, this paper was focused on the causes and the formation mechanism of off-flavor. Based on these studies, the ways how to reduce the production of off-flavour were also found. Main research finding was following:1. Fresh orange juice processed by ultra-high pressure could produce a slight off-flavor as a result of the productions ofα-terpineol and carvone.α-terpineol was created by hydration reaction of limonene and linalool degradation, while carvone was created by oxidation reaction of limonene.2. Pressure (x1), temperature (x2), treatment time (x3) were three significant factors influencing the degradations of limonene and linalool under high pressure and there were positive effect on degradation with increasing of three factors. The relationship of linalool (Y1) or limonene (Y2) concentrations between three factors could be expressed by the regression equation as follows:3. Metal ions as a catalyzer influencing oxidation of limonene under high pressure, could significantly speed up the degradation of limonene; while it did not play an important role on the hydration of limonene and degradation of linalool.4. At pH2.8 ~ 5.2, there was a negative effect on limonene degradation with increasing of pH values; at pH5.2 ~ 6.0, there was a positive effect on limonene degradation with increasing of pH values; at pH2.8 ~ 6.0 between, there was a negative effect on linalool degradation with increasing of pH values. The relationship of linalool (Y1) or limonene (Y2) concentrations between the pressure (x1) and pH values (x4) could be expressed by the regression equation as follows:5. When some limonene (0.15‰, w/v) was added to orange juice before ultra-high pressure processing, the smell quality of treated-juice could effectively improved.6. Vacuum degassing (vacuum degree of 0.095 MPa, 3 min) could significantly reduce the the reaction of limonene oxidation while it did not play an important role on the hydration of limonene and degradation of linalool.7. protein which could chelated metal ions in orange juice have a significant impact on the oxidation reaction, resulting in a significant reduction of limonene degradation under high pressure, while there was no significant effect on the hydration of limonene and degradation of linalool. Protein was added to orange juice with a concentration of 30μg/mL.