Psychometric Qualities of the Educational Identity Processes Scale (EIPS)

CC BY 4.0In the educational domain, the development of identity becomes especially salient during school transition phases. To assess the specific identity processes that match the adolescents’ experiences before and after the school transition, the Educational Identity Processes Scale (EIPS) was developed. The present study aimed to test the psychometric qualities of the EIPS by examining its factor structure, the internal and convergent validity of the identity dimensions, and whether the questionnaire was measurement invariant over time. The pre-transition version was tested in a Dutch sample (N = 242 early adolescents) and the post-transition version was tested in a Lithuanian sample (N = 1,268 mid-adolescents). Findings indicated good psychometric qualities for both the pre- and post-transition versions of the EIPS. Additionally, context dependencies were observed, as distance to the transition influenced the meaning of specific identity processes and determined whether specific processes could be considered as part of normative development

Process-structure-function relations of pectin in plant-based foods: the use of anti-homogalacturonan antibodies in an integrated methodological approach.

Pectin has been identified as a critical structural component of plant cell walls contributing to tissue integrity and rigidity. As a result, this polysaccharide strongly determines the textural/rheological quality of fruit- and vegetable-based products. Pectin s functional properties depend on its molecular fine structure, which can be altered enzymatically as well as non-enzymatically. Several modifications in pectin structure occur during food processing, rendering pectin a major point of interest for food technologists seeking to tailor the textural/rheological properties of plant-based food products. So far, the process-structure-function relation of pectin in food matrices has predominantly been investigated via the physicochemical analysis of isolated cell-wall material with the consequent loss of most spatial information. Today, monoclonal anti-pectin antibodies, originally generated in the context of plant cell wall biology, provide a new range of opportunities as they allow the precise localisation of defined structural pectic domains in intact cell walls in plant tissues. Antibodies binding to the homogalacturonan (HG) domain of pectin are of particular interest for food technologists as HG in general and its degree of methyl-esterification (DM) in particular strongly determine the functionality of pectin in food matrices. The current study aimed at the implementation of these anti-HG antibodies in an integrated methodological approach in order to unravel the structure-function relation of pectin during processing of plant-based foods.In a first step, the potential of the anti-HG antibodies to investigate the effect of processing on pectin in fruits and vegetables was explored. Specifically, the binding specificity of these probes towards pectins and methoxylated polygalacturonic acids with defined degree and pattern of methyl-esterification was determined via immuno-dot assays and, moreover, a microscopic method to use these monoclonal antibodies in situ in plant-based food systems was developed and implemented. Subsequently, four different case studies (on broccoli tissue, broccoli purée, carrot purée and tomato suspensions) were performed in which the traditional physicochemical analysis of isolated cell-wall material was combined with the ex situ and in situ application of anti-HG antibodies to acquire in-depth insight into the process-structure-function relations of pectin. Broccoli, carrot and tomato were subjected to various thermal, high-pressure and mechanical treatments changing pectin s structure and, hence, its functional properties. Thermal processing of broccoli and carrot was demonstrated to result in a thermosolubilisation and ß-eliminative depolymerisation of pectin. The induced weakening of the intercellular adhesion could be related to texture softening of broccoli tissue, whereas syneresis phenomena were limited in broccoli and carrot purées. In situ visualisation of pectin with anti-HG antibodies JIM7 and LM20 showed that, after thermal processing, highly methyl-esterified, water-soluble pectic polymers became detached and loosely bound to the cell wall. Conversely, pretreatments stimulating the endogenous pectin methylesterase (PME) activity were shown to cause a decrease in the DM of pectin and, correspondingly, an increase in Ca2+-cross-linked pectin at the expense of loosely bound water-soluble pectin. The resulting stronger intercellular adhesion could be linked to a reduced texture degradation during subsequent thermal processing of broccoli tissue and a higher resistance of broccoli and carrot tissue to physical disintegration during purée preparation. For carrot, this alteration in pectin structure was reflected in a purée with a high consistency and a large degree of separation between serum and pulp. Anti-HG antibody PAM1 revealed that process-induced pectin demethoxylation by endogenous PME mainly took place at the tricellular junctions of adjacent cells in broccoli and at discrete regions of the inner face of the cell wall adjacent to the plasma membrane in carrot. In tomato, process-induced pectin changes did not only depend on the activity of PME, but also on the activity of the depolymerising enzyme polygalacturonase (PG). In case PG was selectively inactivated, i.e. in high-pressure pretreated tomatoes, de-esterification of pectin by PME also resulted in a high level of Ca2+-cross-linked pectin and a stronger intercellular adhesion, similar as in broccoli and carrot. Immunolabeling showed that in intact tomato fruit, pectin de-esterification was endogenously regulated by the physical restriction of PME activity in the cell wall matrix, whereas in disintegrated tomato tissue intensive demethoxylation of pectin could occur throughout the entire cell wall. Finally, high-pressure homogenisation, an intense shear treatment used for tissue disruption, affected pectin solubility depending on the plant matrix. This thesis shows that anti-HG antibodies are valuable tools in elucidating the process-structure-function relations of pectin in food matrices by providing the opportunity to explore local changes in pectin structure in situ. The obtained results form a sound basis to control the textural/rheological properties of plant-based food products and to identify targets for food-structure engineering.nrpages: 143status: publishe

Deliberate processing of carrot purées entails tailored serum pectin structures

A combination of mechanical tissue disintegration techniques (i.e. blending and high pressure homogenization) and heat treatments (i.e. high and low temperature) was deliberately applied in processing carrot purées. The chemical structure of serum pectin and its influence on the consistency of the differently prepared purées were evaluated. High temperature treatment of carrot pieces prior to high pressure homogenization (HTT+ HPH) resulted in high apparent molar mass (MM) serum pectin, while the reverse order of purée preparation (HPH+HTT) generated a relatively lower MM. The exceptional high apparent MM of HTT+HPH sample is possibly related to proteins bound to pectin. The importance of the order of heat treatment and tissue disruption was also reflected in largely different carrot purée consistencies in which HTT +HPH was more consistent. Low temperature treated (LTT) carrot purées, whereby endogenous pectin methyl-esterase was stimulated, had less consistent purées and low molar mass serum pectins.status: publishe

Thermal and high pressure high temperature processes result in distinctly different pectin non-enzymatic conversions

Pectin is a common, extremely complex and process sensitive polysaccharide in plant cell walls with many uses as an additive in the food and biomedical industry. Process induced chemical changes in pectin result in various effects on its functionality. An in-depth study is presented of the effects of thermal compared to HP/HT (high hydrostatic pressure combined with high temperature) processing on pectin nano-structure and characteristics. The results obtained emphasized the necessity of taking into account pectin association and conformation in solution when analyzing molecular weight changes. At a pH of 6.3, a decrease in molecular weight was observed for both thermal and HP/HT treated samples but with partially different reasons. While for the thermally treated samples the reduction in molecular weight was mostly due to pectin depolymerization for the HP/HT treated samples a significant effect was observed for conformational changes induced by electrostatic repulsion caused by the complete demethoxylation of the polymer. On the contrary due to conformational changes, an increase in the observed molecular weight was noticed for HP/HT treated samples at a pH of 4.4. The study also clearly shows the necessity of combining an absolute molar mass determination method like multiangle laser light scattering (MALLS) in studies on the effect of processing on pectin.publisher: Elsevier articletitle: Thermal and high pressure high temperature processes result in distinctly different pectin non-enzymatic conversions journaltitle: Food Hydrocolloids articlelink: http://dx.doi.org/10.1016/j.foodhyd.2014.01.018 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.status: publishe

The effect of pectin on in vitro B-carotene bioaccessibility and lipid digestion in low fat emulsions

In this work, we investigated how pectin with different DM, with or without the presence of an additional emulsifier (L-α-phosphatidylcholine), influences on the one hand the in vitro bioaccessibility of β-carotene, loaded in the oil phase of an oil-in-water emulsion, and on the other hand the lipid digestion. As a consequence, the relation between the β-carotene bioaccessibility and the lipid digestion was investigated as well. For this research, two types of oil-in-water emulsions have been investigated. The first type contained 5% olive oil enriched with β-carotene and water in which only 2% citrus pectin (CP) (with a DM of 99%, 66% or 14%) was dissolved. In this type, only pectin is present that can function as emulsifier. The second type contained 5% enriched oil and water in which 1% L-α-phosphatidylcholine and 0 or 2% CP (with a DM of 99%, 66% or 14%) were dissolved. Results show that the influence of pectin DM on the in vitro β-carotene bioaccessibility (incorporation of β-carotene in the micelles) and the lipid digestion (incorporation of free fatty acids (FFAs) and monoacylglycerols (MAGs) in the micelles) was dependent on the presence of phosphatidylcholine but was less dependent on the particle size (distributions) or the viscosity. In the emulsions with phosphatidylcholine, an increase of on the one hand the incorporation of β-carotene and on the other hand the incorporation of FFAs and MAGs in the micelles was seen by decreasing the DM of the citrus pectin from 99% to 66%, whereas both incorporations decreased again by decreasing the DM further to 14%. In the emulsions without phosphatidylcholine, an increase of the incorporation of β-carotene into the micelles was seen by decreasing the DM. On the contrary, the incorporation of FFAs and MAGs into the micelles remained. This means that there was a clear relation between the incorporation of β- carotene and the incorporation of FFAs and MAGs in the micelles for the emulsions without phosphatidylcholine, whereas this was not the case for the emulsions containing phosphatidylcholine.status: publishe

FT-IR spectroscopy, a reliable method for routine analysis of the degree of methylesterification of pectin in different fruit- and vegetable-based matrices

The use of Fourier transform infrared (FT-IR) spectroscopy as a method for routine analysis of the degree of methylesterification (DM) of pectin was validated. The relationship between the ratio of the intensity of the peak at around 1740cm(-1) (due to ester carbonyl group stretching) to the sum of the intensities of the peaks at around 1740 and 1630-1600cm(-1) (due to carboxylate group stretching) and the DM of pectin in model and real systems was investigated. In model systems of low to medium DM with low added protein (⩽20%), accurate DM determinations were obtained without spectra deconvolution whilst for medium to high DM pectin with high added protein (⩾30%), peak deconvolution was vital. In real systems, good DM determinations were obtained without peak deconvolution except for broccoli-derived samples. Considering that broccoli is a protein-rich vegetable, better determinations of the DM were obtained using deconvoluted FT-IR spectra.publisher: Elsevier articletitle: FT-IR spectroscopy, a reliable method for routine analysis of the degree of methylesterification of pectin in different fruit- and vegetable-based matrices journaltitle: Food Chemistry articlelink: http://dx.doi.org/10.1016/j.foodchem.2014.12.033 content_type: article copyright: Copyright © 2014 Elsevier Ltd. All rights reserved.status: publishe

Microscopic evidence for Ca2+ mediated pectin-pectin interactions in carrot-based suspensions

This study explored the use of fluorescently labeled pectin to obtain evidence for Ca(2+) mediated pectin-pectin interactions in situ. Specifically, carrots were either blanched at low temperature (LTB) or blanched at high temperature (HTB) to activate or inactivate endogenous pectin methylesterase, respectively. Consequently, pectin in tissue particles of LTB and HTB carrots exhibited low degree of methylesterification (DM) and high DM, respectively. Pectin present in the LTB carrot serum exhibited a lower DM, was more branched, and showed a higher molar mass compared to HTB carrot serum pectin. Ca(2+) mediated pectin-pectin interactions were influenced by serum pectin molecular structure, increased with increasing pH and Ca(2+) concentration, and decreasing DM. Presence of more linear pectin in the serum created a competition, leading to less intense interactions between labeled pectin and pectin at tissue particle surfaces. Generally, the most intense Ca(2+) mediated pectin-pectin interactions were observed for pectin of LTB carrot particles.publisher: Elsevier articletitle: Microscopic evidence for Ca2+ mediated pectin–pectin interactions in carrot-based suspensions journaltitle: Food Chemistry articlelink: http://dx.doi.org/10.1016/j.foodchem.2015.04.135 content_type: article copyright: Copyright © 2015 Elsevier Ltd. All rights reserved.status: publishe

Electrostatic pectin-pectin interactions and in vitro bioaccessibility of calcium and iron in particulated tomato-based suspensions

This study explored the pectin structure-function relationship in tomato-based suspensions. Particularly, electrostatic pectin-interactions were investigated and subsequently linked to the in vitro bioaccessibility of Ca and Fe-ions in tomato-based suspensions. Process tomatoes were either treated at high-pressure (HP) to selectively maintain pectin methylesterase enzyme (PME) or blanched at high temperature (HB) to inactivate all the endogenous pectin-degrading enzymes. The samples were disintergrated into purée and incubated to allow the action of PME (if any). Structure characterisation showed that pectin in HP tomato tissue particles was of a lower degree of methylesterification (DM) compared to pectin in HB tomato tissue particles. Pectin in HP tomato serum was of a lower DM, was less linear and was of a lower molar mass compared to the high DM, highly linear and high molar mass pectin in the HB tomato serum. Exploring the pectin-interactions revealed that Ca2+ mediated pectin-pectin interactions in reconstituted HP tomato-based systems were stronger than in HB tomato-based systems. These interactions were influenced by the molecular structure of pectin in the serum fraction of the tomato suspensions, and improved with increasing Ca2+ and pH. Investigation of the essential mineral content showed that HP and HB tomato-based suspensions contained similar amounts of Ca and Fe-ions (9.8 ± 0.8 and 0.39 ± 0.1 mg/100 g of purée, respectively). Ca and Fe-ions were more bio-accessible in HB tomato-based suspensions (two times) than in HP tomato-based suspensions and the bioaccesibility of ions decreased with increasing electrostatic pectin-interactions.status: publishe