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The activity of the pectin-modifying enzymes pectin-methylesterase (PME) and polygalacturonase (PG)
in tomato fruit was tailored by processing. Tomatoes were either not pretreated, high-temperature
blanched (inactivation of both PME and PG), or high-pressure pretreated (selective inactivation of PG).
Subsequently, two types of mechanical disruption, blending or high-pressure homogenisation, were
applied to create tomato tissue particle suspensions with varying degrees of tissue disintegration. Pro-
cess-induced pectin changes and their role in cell–cell adhesion were investigated through in situ pectin
visualisation using anti-pectin antibodies. Microscopic results were supported with a (limited) physico-
chemical analysis of fractionated walls and isolated polymers. It was revealed that in intact tomato fruit
pectin de-esterification is endogenously regulated by physical restriction of PME activity in the cell wall
matrix. In disintegrated tomato tissue on the other hand, intensive de-esterification of pectin by the
activity of PME occurred throughout the entire cell wall. PG was selectively inactivated (i.e. in high-
pressure pretreated tomatoes), with de-esterification of pectin by PME, which resulted in a high level
of Ca 2+ -cross-linked pectin and a strong intercellular adhesion. In non-pretreated tomato suspensions
on the other hand, combined PME and PG activity presumably led to pectin depolymerisation and, hence,
reduced intercellular adhesion. However, because of the high amount of Ca 2+ -cross-linked pectin in these
samples, cell–cell adhesion was still stronger than in the high-temperature blanched tomatoes, in which
the absence of PME activity during suspension preparation implied few Ca 2+ -cross-linked pectic polymers
and extensive cell separation upon tissue disruption. |
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