BACKGROUND: Changes in instrumental color parameters, chlorophyll a and b, activity of chlorophyllase, Mg-dechelatase, peroxidase and polyphenol oxidase, total phenolic compounds and pH of spinach purée were assessed after high hydrostatic pressure (HHP) (200, 400 and 600 MPa for 5, 15 and 25 min) treatments at room temperature. RESULTS: HHP treatments induced a better retention of visual green color (-a* and L* values) and chlorophyll contents of spinach purée. As for chlorophyll degradation-related enzymes, the results indicated that chlorophyllase activity decreased at all pressures; however, Mg-dechelatase activity was dramatically activated after HHP treatment at 400 and 600 MPa. Peroxidase exhibited higher resistance to HHP; however, polyphenol oxidase, which is responsible for enzymatic browning, was suppressed progressively with increase in pressure level from 200 to 600 MPa. In addition, the pH value of HHP-treated spinach purée was increased to be close to neutral pH, which could effectively inhibit chlorophyll degradation. No significant differences (P > 0.05) were found after extending the treatment times at the same level of pressure. CONCLUSION: HHP treatments effectively prevent chlorophyll degradation and enzymatic browning in spinach purée and retain a better original fresh green color of spinach compared with conventional thermal treatment.
BACKGROUND: Changes in instrumental color parameters, chlorophyll a and b, activity of chlorophyllase, Mg-dechelatase, peroxidase and polyphenol oxidase, total phenolic compounds and pH of spinach purée were assessed after high hydrostatic pressure (HHP) (200, 400 and 600 MPa for 5, 15 and 25 min) treatments at room temperature. RESULTS:HHP treatments induced a better retention of visual green color (-a* and L* values) and chlorophyll contents of spinach purée. As for chlorophyll degradation-related enzymes, the results indicated that chlorophyllase activity decreased at all pressures; however, Mg-dechelatase activity was dramatically activated after HHP treatment at 400 and 600 MPa. Peroxidase exhibited higher resistance to HHP; however, polyphenol oxidase, which is responsible for enzymatic browning, was suppressed progressively with increase in pressure level from 200 to 600 MPa. In addition, the pH value of HHP-treated spinach purée was increased to be close to neutral pH, which could effectively inhibit chlorophyll degradation. No significant differences (P > 0.05) were found after extending the treatment times at the same level of pressure. CONCLUSION:HHP treatments effectively prevent chlorophyll degradation and enzymatic browning in spinach purée and retain a better original fresh green color of spinach compared with conventional thermal treatment.