Relationship between colour improvement and metallo-chlorophyll complexes during blanching of peas and broccoli

ABSTRACT

The influence of adding different levels of zinc chloride ranged between 100 and 500ppm and blanching time [1,3 and 6 mins] at 85°C on the physical and structural aspects of chlorophyll pigments in peas and broccoli were investigated. It was found that when 300 and 100 ppm zinc chloride were added to the blanching water of peas and broccoli respectively to be satisfactory enough in retaining the green- colour of these vegetables. Hunter colour [-a*] values were found to be adequately represent the colour changes. These values were used to describe the results in terms of an exponential model. Raman spectroscopy was also applied to confirm the presence of Zn-chlorophyll complexes which protect the chlorophylls from converting into other derivatives. The residual zinc chloride [ppm] in the tissues of peas and broccoli after blanching was found to be 47.55 and 10.13 ppm, respectively. Therefore, double benefits regarding fortification with zinc and retaining green pigments were achieved