Firming of fruit tissues by vacuum infusion of pectin methylesterase: Visualisation of enzyme action
Guillemin, Anne | Guillon, Fabienne | Degreave, Pascal | Rondeau-Mouro, Corinne | Devaux, Marie Francoise | Huber, Francoise | Badel, Eric | Saurel, Rémi | Lahaye, Marc | Laboratoire de Recherche en Génie Industriel alimentaire (LRGIA) ; Université Claude Bernard Lyon 1 (UCBL) ; Université de Lyon-Université de Lyon | Unité de recherche sur les Biopolymères, Interactions Assemblages (BIA) ; Institut National de la Recherche Agronomique (INRA) | Laboratoire d'Etudes des Ressources Forêt-Bois (LERFoB) ; Institut National de la Recherche Agronomique (INRA)-AgroParisTech | Laboratoire de Physique et Physiologie Intégratives de l'Arbre Fruitier et Forestier (PIAF) ; Institut National de la Recherche Agronomique (INRA)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)
Apple pieces were vacuum-impregnated with either a pectin methylesterase (PME) and calcium solution or with water prior to pasteurization. Pasteurized apple pieces impregnated with PME and calcium showed a significantly higher firmness. Moreover, solid state C-13 NMR spectroscopy of apple cell wall residues revealed an increase of their molecular rigidity. Exogenous PME addition involved a decrease from 82% to 45% of apple pectin degree of methyl-esterification. Microscopic observations of apple slices immunolabelled with antibodies specific for pectins showed that (i) demethyl-esterification was more intense in the cell wall region lining intercellular spaces (demonstrating a key role for these intercellular channels in the enzyme penetration in the tissue during vacuum-infusion) and that (ii) the number of calcium-dimerized deesterified homogalacturonan chains increased. The results corroborate the hypothesis that vacuum-impregnated PME action liberates free carboxyl groups along pectin chains that could interact with calcium, increasing the rigidity of pectins and finally the mechanical rigidity of apple tissue. (C) 2007 Elsevier Ltd. All rights reserved.
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