Effect of oxidative coupling on the thermal stability of texture and cell wall chemistry of beet root (Beta vulgaris)
1998
Ng, A. | Harvey, A.J. | Parker, M.L. | Smith, A.C. | Waldron, K.W.
The purpose of this study was to investigate whether peroxidase-mediated oxidative coupling of ferulic acid in beet root cell walls could reduce thermally induced softening by enhancing the cross-linking of polymers involved in cell adhesion. Beet root (Beta vulgaris, var. Detroit 2 crimson) tissue was incubated in the presence or absence of hydrogen peroxide (H2O2) for 18 h before cooking. Incubation in H2O2 increased the time required for tissue to soften at 100 degrees C from an average of 130 min to 650 min and resulted in a significantly higher tensile strength in heat-treated tissues (p < 0.05). This was accompanied by a large decrease in esterified cis- and trans-ferulic acid and a 2-fold increase (approximately) in 5,5'-, 8-O-4'-, and 5,8'-(benzofuran form)-diferulic acid moieties. In addition, the yield of hot-water-soluble wall polymers was much lower, consistent with increased cross-linking of the pectic polysaccharides. However, the carbohydrate composition and degree of uronide methylesterification of cell walls from H2O2-treated tissues was similar to that of fresh tissue. Incubation of control samples in the absence of H2O2 had no effect on thermal softening or phenolic chemistry of the walls. These results indicate that the H2O2-mediated changes in mechanical properties of the walls and the rate of thermal softening result from enhanced phenolic cross-linking of pectic polymers involved in cell-cell adhesion, due to oxidative coupling of ferulic acid moieties.
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