Towards a better understanding of the pectin structure–function relationship in broccoli during processing: Part II — Analyses with anti-pectin antibodies |
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Authors: | Stefanie Christiaens Sandy Van Buggenhout Evelien Vandevenne Ruben Jolie Ann M Van Loey Marc E Hendrickx |
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Affiliation: | aLaboratory of Food Technology, Leuven Food Science and Nutrition Research Centre (LFoRCe), Department of Microbial and Molecular Systems (M2S), Katholieke Universiteit Leuven, Kasteelpark Arenberg 22, P.O. Box 2457, 3001 Leuven, Belgium |
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Abstract: | To investigate the structure–function relationship of pectin during (pre)processing, broccoli samples (Brassica oleracea L. cultivar italica) were subjected to one of the following pretreatments: (i) low-temperature blanching (LTB), (ii) LTB in combination with Ca2+ infusion, (iii) high-pressure pretreatment (HP), (iv) HP in combination with Ca2+ infusion, or (v) no pretreatment (control sample), whether or not in combination with a thermal treatment of 15 min at 90 °C. Anti-homogalacturonan antibodies were used to perform in situ (microscopy) and ex situ (immuno-dot assays) analyses on broccoli pectin which resulted in information concerning the localisation of defined pectic domains in broccoli cell walls and pectin's structure. Water-soluble pectin appears to contain unbranched, high-esterified pectin and some pectic polymers with abundant side chains that are less esterified. Ionically cross-linked pectin, on the other hand, contains low-esterified pectin with either highly branched or unbranched domains. The in situ visualisation of pectin in broccoli suggested that de-esterification of pectin by PME during LTB as well as during HP mainly takes place in the tricellular junctions of adjacent cells in broccoli tissue. Ca2+-cross-linked pectin could be found in cell walls lining intercellular spaces and was particularly abundant at the corners of intercellular spaces, indicating its important role in cell–cell adhesion. Both LTB and HP created pectin–Ca2+-cross-links in parts of the cell wall where these cross-links were originally absent. The influence of thermal processing and the effect of pressurisation on the pectic components in the cell wall could also be visualised using the antibodies. |
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Keywords: | Abbreviations: AIR alcohol-insoluble residue CSP chelator-soluble pectin DE degree of esterification FITC fluorescein isothiocyanate GalA galacturonic acid HG homogalacturonan HG&ndash GalA homogalacturonan&ndash galacturonic acid HP high-pressure pretreatment LTB low-temperature blanching MPBS phosphate-buffered saline containing milk powder NSP sodium-carbonate-soluble pectin PBS phosphate-buffered saline PME pectin methylesterase RG-I rhamnogalacturonan-I RG-II rhamnogalacturonan-II Rha rhamnose T thermal treatment WSP water-soluble pectin |
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