Characterization and distribution of phenolics in carrot cell walls.

Carrot cell walls have been shown to contain significant quantities of esterified p-hydroxybenzoic acid, which is presumed to be esterified to cell wall polymers. The purpose of this study was to investigate the distribution of p-hydroxybenzoic acid and related phenolics among carrot cell wall polysaccharides. Cell wall material was prepared from fresh carrot root tissues and extracted sequentially with water, imidazole, cyclohexane- trans-1,2-diamine- N, N, N', N'-tetraacetate, Na 2CO 3, and KOH (0.5, 1, and 4 M) to leave a cellulose-rich residue. The fractions were analyzed for their carbohydrate and phenolic acid components. Selected soluble fractions were subfractionated further by graded precipitation in ethanol. The majority of the polymer fractions comprised pectic polysaccharides, with varying quantities of neutral sugars (arabinose and galactose). Hemicellulosic polymers were generally found only in the strong alkali extracts (4 M KOH). p-OH-benzoic acid was the predominant phenolic ester and was associated with most fractions analyzed; p-OH-benzaldehyde was also detected in the fractions at much lower levels. Principal components analysis of the chemical data indicated that the p-OH-benzoic acid was associated predominantly with the branched pectic polysaccharides, in contrast to the p-OH-benzaldehyde. The possible roles and functional properties of these phenolics are discussed.

Thermal stability of texture in Chinese water chestnut may be dependent on 8,8'-diferulic acid (aryltetralyn form).

Ferulic acid (FA) cross-links have been implicated in the thermal stability of texture in Chinese water chestnut (CWC) tissues. The aim of the current study has been to investigate this concept further. CWC tissue strips were measured for their mechanical properties before and after extraction in increasing strengths of alkali. The mechanical properties were related to the associated mode of fracture (cell separation or breakage) at the fracture surfaces and the phenolic composition of the cell walls. CWC tissue softened after prolonged extraction in cold alkali due to an increase in the ease of cell separation. Analysis of wall-bound phenolics demonstrated that most FA moieties, including five of the six dehydrodimers, were released before tissue strength was reduced. Loss of strength was, however, coincident with the loss of 8,8'-diferulic acid, aryltetralin (AT) form. It has been suggested that this dehydrodimer may be particularly concentrated at the edge of the cell faces. These results provide further evidence for the involvement of this dehydrodimer in conferring thermal stability of cell-cell adhesion and hence texture in CWC. However, they do not exclude the other diferulates from involvement in cell adhesion.