| Abstract: | Some in-vivo and in-vitro characteristics of pectin methylesterase (PME) from cell wall and whole potato tuber were determined and its role was elucidated in the pre-cooking and cooling steps of commercial dehydrated mashed potato production. The isolated cell walls contained 16.3% anhydrogalacturonic acid with a degree of esterification (DE) of 56, and 25% of tuber total PME. Cell wall pre-cooking in model systems resulted in a DE of 53.2. Native cell wall pectin solubilisation was much less than that of H-cell walls devoid of metal cations. Calcium but not Mg, supplied as Ca(Mg)-starches, retarded pectin solubilisation, while Ca-uptake by retained pectin was high when cooling followed pre-cooking. Texture measurements of potato slices pre-cooked, cooled and cooked suggested a firming effect which could be attributed to Ca-release from gelatinised starch during pre-cooking, and stabilisation of Cabridges with free COO? groups of cell wall pectin duringcooling. The role ascribed to PME in causing firming is de-emphasised. |
