Effect of Cooking and Pre-Cooking on Cell-Wall Chemistry in Relation to Firmness of Carrot Tissues

The aim of this work was to investigate heat-induced changes in cell wall polysaccharides of carrot in relation to texture. Discs of fresh carrot (Daucus carota cv Amstrong) tissue were subjected to cooking (100¡C, 20 min), with or without a pre-cooking treatment (50¡C, 30 min). Alcohol-insoluble residues were prepared from the tissues and were extracted sequentially with water, NaCl, CDTA, and 0É5 M KOH to leave a residue. These were analysed for 23 their carbohydrate compositions, their degree of methyl esteriÐcation and the molecular size of selected soluble polysaccharides. Cooking caused tissues to soften. This involved cell separation, an increase in waterand salt-soluble, highmolecular-weight pectic polysaccharides and a concomitant decrease in the pectic polymers in all wall extracts and the residue. Pre-cooking prior to cooking enhanced cellÈcell adhesion and reduced the extent of softening. This was accompanied by a general reduction in the degree of methylesteriÐcation of cell-wall pectic polymers, and a decrease in the cooking-induced modiÐcation to all pectic fractions. The Ðrming e†ect of pre-cooking could be reversed by extracting the precooked] cooked tissue with CDTA, a chelating agent. The role of Ca2` cross-linked polymers and pre-cooking in the enhancement of Ðrmness are discussed.