Electron Microscopic Investigations of the Cell Structure in Fresh and Processed Vegetables (Carrots and Green Bean Pods)

The cell structure of fresh, blanched, boiled. dried and rehydrated tissues from carrot roots and green bean pods was examined in the scanning and/or transmission electron microscope. The secondary phloem of carrot roots represents a typical plant storage parenchyma characterized by a high starch and lipid content. Green bean pods show many characteristics of assimilation tissue (e.g. chloroplasts). but they also contain a considerable amount of starch. Blanching, boiling, de- and rehydration affect the texture of both vegetables in a similar way: swelling of cell walls. maceration of tissue during blanching and boiling coupled with a granular denaturation of cytoplasm. Drying leads to a shrinkage and twisting o f the cells and clumping of the cytoplasm. Rehydrated tissue is characterized by strong cell wall swelling, mace ration, and clumping of cytoplasm. Morphometric measurements of cell wall thicknesses after re hydration showed that various food technological process parameters may strongly influence the appearance of the rehydrated product.