Freeze‐thaw (And Blanch) Damage to Vegetable Ultrastructure

The parenchyma cells of three vegetable tissues varying in starch content as well as in textural response to freeze‐thawing were studied ultrastructurally before and after controlled freeze‐thaw regimes. Similar tissue samples were also studied after blanching and after the blanch‐freeze‐thaw combination. Subcellular structures were altered more drastically by blanching than by freeze‐thawing. There was much less fine structural disruption in the high starch tissue (green pea cotyledon) than in the tissues of lower starch content (spinach leaf and green bean pod) following all processing treatments. As judged by sensory evaluation, peas also underwent less textural change on processing than the other tissues studied. The minimal ultrastructural change observed in peas may be associated with certain cell characteristics: high starch content, abundant protoplasmic structure, and resultant low degree of vacuolation. It is concluded that ‐ of these ‐ the starch granule component is the major contributor to texture. This probably applies in the case of most processed vegetable tissues of relatively high starch content. The protective role of cellular starch is discussed in relation to fine structure retention and to texture.