Cd

era'

Ki Ki

TABLE 9.1 (continued)

Processing and Stability of Chlorophylls

Model/Ref.

Effect of

Observations

Ki Ki oo

Pea/Canjura et at. (1999)20

Blanching and Zn addition

Broccoli juice/ van Loey et al. (1998)19

Broccoli juice/ Weemaes et al. (1999)21

High pressure treatment and heating

High pressure treatment and heating

A relationship is found between the zinc added and the zinc absorbed by the pea. Blanching is performed at 83°C/5 min/300 mg/1 of ZnCl2. Zn-pheophytin a is both formed and degraded during the thermal treatments, while Zn-pyropheophytin a is only formed as heating time and temperature increase.

In comparison to controls, all Zn-treated tissues show color improvement.

Changes in reflectance values confirm that as holding time increases, sample greenness increases. For the Zn-treated samples at all temperatures, a decrease in the color difference value over time is observed, indicative of regreening and color loss improvement. It is concluded that the use of metal salts may be viable for preservation of green color in vegetables.

Chlorophyll degradation follows a kinetic degradation of first order. Chlorophyll a is less thermostable than chlorophyll b. The degradation rate is dependent on the temperature and is accurately described by the Arrhenius relationship; for chlorophyll a, chlorophyll b, and total chlorophyll content, the activation energies are 63, 80, and 67 kJ/mol, respectively.

Chlorophylls show an extreme stability toward pressure processing, even after treatment times of 4 h at 800 MPa and 40°C. Only high-pressure treatments combined with temperatures exceeding 50°C have a significant reduction in chlorophyll concentration. Thus, it is suggested that high-pressure processing below 50°C can offer a major advantage as a preservation method in comparison with classical pasteurization processes to obtain vegetable products that keep their original fresh green color.

Greenness is marginally affected by pressure at low temperatures (30-40°C). At 800 MPa and slightly higher temperatures (50-60 °C), first-order degradation of green color is observed. The greenness loss is suggested to be due to chlorophyll-pheophytin conversion with no further pheophytin degradation. Pheophytin is degraded further at higher temperatures (> 70°C). For broccoli juice, high-pressure processing in combination with temperatures below 50°C is recommended, where degradation of green color would be limited. Pressure treatment at 800 MPa and 50°C resulted in only about 10% greenness loss.

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