Ferulic acid dehydrodimers in the cell walls of Beta vulgaris and their possible role in texture
1997
Waldron, K.W. | Ng, A. | Parker, M.L. | Parr, A.J.
Sugarbeet, a form of Beta vulgaris var vulgaris, fails to soften completely after heating at 100 degrees C for several hours. This is due to thermal stability of the cell-wall polymers involved in cell-cell adhesion. In contrast, beetroot softens within 25-30 min due to a relatively rapid increase in the ability of the cells to separate. Information concerning the cell-wall polymers responsible for cell-cell adhesion was obtained by subjecting sugarbeet and beetroot tissues to a range of chemical and biochemical treatments designed to cleave cell-wall chemical bonds selectively. Treatment of sugarbeet tissues with chelating agents, weak base (Na2CO3, 0.05 M) or a purified, specific endoxylanase did not facilitate vortex-induced cell separation. However, this could be induced after extraction in dilute, cold alkali (0.05-0.1 M KOH) or dilute, hot acid (0.1 M TFA, 100 degrees C). Tissues from beetroot behaved similarly. Furthermore, the cell walls of sugarbeet and beetroot were similar in yield and neutral carbohydrate composition; the cell-wall-galacturonic acid content of beetroot was 50% higher as compared with sugarbeet. They were also rich in ferulic acid (FA) and its derivatives (6-7 mg g-1 CWM), and exhibited pH-dependent autofluorescence which disappeared during alkali-induced cell separation. In sugarbeet, over 20% of the FA was in dimer form. In beetroot, however, the value was only 10%. The main FA dimers were 8-O-4'DiFA and 8,5'DiFA (benzofuran form). The results indicate that the degree of thermal stability of cell-cell adhesion and, therefore, texture in Beta vulgaris tissues is related to the degree of FA-cross linking between pectic polysaccharides.
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