Vegetables like peas, beans, greens are sometimes canned. The retention of original color is of great importance effecting the marketability and consumer response.
In the process of canning, vegetables are heated to destroy spoilage disease causing microorganisms.
Such heat treatments also produce a number of of undesirable chemical and textural changes in the vegetables. The textural changes are due to partial destruction of the cell wall and cell membrane.
Blanching, plus the strong heat treatments applied to nonacid vegetables, appears to be responsible for the large vitamin losses in canning.
Heat treatments also cause chemical alteration of the green pigment chlorophyll, thus resulting in a processed vegetable with less green color.
During canning chlorophyll gets converted to pheophytin due to the high temperature used. Sometimes to retain the color and to neutralize the acid, alkali is added.
Process of canning effects on vegetables