Effect of zinc and copper chloride on the color of avocado puree heated with microwaves

The effect of microwave heating, and zinc and copper chloride addition on the color of avocado puree was studied. Rates of color variation at different temperatures were determined by plotting a*/b* vs. time of storage. Results showed that the color was best preserved when avocado purees either with or without zinc and copper salts were microwave treated for 30 s, due to inhibition of enzymatic browning. Samples with copper chloride added showed a better color than samples with zinc chloride added, both showing a better color than the blank. This effect is attributed to the formation of chlorophyll complexes with copper and zinc cations. Also the combined effect of different concentrations of zinc and copper salts along with various pH values was evaluated through a response surface analysis. The best response was obtained in the following conditions: zinc chloride 120 ppm, copper chloride 12 ppm, and pH 5.5.