The influence of ions, starch, buffer strength and pH on solubilization of pectic galacturonan from potato cell wall material during boiling was studied. The ions enhanced β-eliminative degradation of galacturonan, but calcium, copper (II) and iron (II) cations slowed down the solubilization at pH 6.1. Magnesium was ineffective. Citrate, malate and phytate anions favoured it. Maceration of potato tissue disks by pectic lyases and model cooking experiments demonstrated the ability of calcium ions to retain intercellular cohesion of potato tissue even when pectic galacturonan had been severely degraded. In a pH range of 6.1-6.5, β-eliminative pectin degradation was shown by specific periodate thiobarbituric acid staining to occur in cell wall and potato tissue boiling.<p/>Specific gravity graded potato tubers were analysed chemically. In addition to starch, citrate, phosphorus, potassium, magnesium, pectic galacturonan and pH increased but malate, calcium and intercellular cohesion decreased with increasing sp. gr. There was a complex causal relationship between chemical composition and intercellular cohesion. Both were influenced by physiological age. Potato pectinesterase was partially characterized. Because of activation of this enzyme or leaching of ions, intercellular cohesion could be greatly enlarged in preheating experiments. Literature on structure and insolubility of pectic substances in plant cell walls and on intercellular cohesion of the cooked potato was reviewed.
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