Browsing by Author "Christiaens, Stefanie"

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In situ pectin engineering as a tool to tailor the consistency and syneresis of carrot purée
(Elsevier, 2012) Christiaens, Stefanie; Buggenhout, Sandy Van; Chaula, Davis; Moelants, Katlijn; David, Charlotte C.; Hofkens, Johan; Loey, Ann M. Van; Hendrickx, Marc E.
To investigate whether in situ pectin engineering would be a helpful tool in tailoring the consistency and syneresis of vegetable purées, carrot was selected as a plant tissue in which the textural properties are largely influenced by pectin methylesterase-induced pectin changes. The effect of low-temperature and high-temperature blanching, as well as the effect of two types of mechanical disruption, blending and high-pressure homogenisation, on the flow properties of carrot purée was explored. The influence of these different purée preparation steps on pectin was examined via physicochemical analysis of fractionated walls and isolated polymers, and via anti-pectin antibodies entailing in situ and ex situ analyses. Purée prepared by blending non-pretreated carrots showed a rather high consistency and pronounced syneresis. Treatments that solubilise pectin, such as high-pressure homogenisation and, in particular, high-temperature blanching, limited syneresis phenomena. In contrast, when the intercellular adhesion in carrot tissue was strengthened via low-temperature blanching, the degree of syneresis increased. High-pressure homogenisation was useful to reduce the carrot tissue particle size and, consequently, resulted in a lower consistency carrot purée. Low-temperature blanching on the other hand increased the consistency of carrot purée as the higher level of intercellular adhesion presumably led to an increased resistance to particle disintegration upon blending or high-pressure homogenisation
Unravelling process-induced pectin changes in the tomato cell wall: An integrated approach
(Elsevier ltd., 2011) Christiaens, Stefanie; Buggenhout, Sandy Van; Houben, Ken; Chaula, Davis; Loey, Ann M. Van; Hendrickx, Marc E.
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.