Heating and vegetable colour

Several industrial processes associated with heating may have an impact on colour. Vegetables are blanched, cooked, boiled, canned, pastenrised or dehydrated. Vegetables are also brined or fermented using processes that may cause colour changes. 

Pasteurisation (60-85°C) is associated with destruction of vegetative microorganisms (Williams et al., 1986). Pasteurisation of vegetable products is primarily used in juice processing. 

Brining and fermentation include preservation by the use of acids. Acids are added in the brining process. In fermentation, however, the process can be self-driven (natmal) or acids can be added to drive the process towards optimal conditions. 

Walker (1964) proposed that the ratio of chlorophyll to pheophytin could be used as a colour index for heated green vegetables. Reflectance measruements of 

10 Changes in relative eontent of pheophytin in Brussels sprouts and tobacco leaves after 20 minutes heating at 60, 70, 80 and 90°C. Data from Haisman and Clarke 

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