Carotene Degradation and Isomerization during Thermal Processing: A Review on the Kinetic Aspects

Kinetic models are important tools for process design and optimization to balance desired and undesired reactions taking place in complex food systems during food processing and preservation. This review covers the state of the art on kinetic models available to describe heat-induced conversion of carotenoids, in particular lycopene and β-carotene. First, relevant properties of these carotenoids are discussed. Second, some general aspects of kinetic modeling are introduced, including both empirical single-response modeling and mechanism-based multi-response modeling. The merits of multi-response modeling to simultaneously describe carotene degradation and isomerization are demonstrated. The future challenge in this research field lies in the extension of the current multi-response models to better approach the real reaction pathway and in the integration of kinetic models with mass transfer models in case of reaction in multi-phase food systems.     

Content Management Systems: Enriched learning opportunities for all?

This article examines the popular claim of Content Management Systems (CMSs) that providing a rich toolset and leaving the use under learner control is beneficial to learning. By means of a literature review, the current contribution examines whether all students are capable of using CMS tools so that their learning is enhanced. In contrast to what is assumed, the study conceptualizes tool use as a complex self-regulation strategy that cannot be taken for granted. Specifically, the article reviews empirical studies in relation to three topics: (a) personal agency in tool use, (b) performance effects of tool use and (c) influencing tool use variables. Findings reveal that not every student profited from the CMS learning opportunities; in multiple studies students differed in their tool use, and these differences had significant performance effects. Hence, these findings suggest that the pedagogical claim CMSs make is problematic. Besides this accumulated corpus of knowledge, the review revealed serious limitations in the retrieved studies which could hamper our findings. As a consequence, the review establishes a need for further research into students’ CMS tool use from an instructional design perspective. In addition to the theoretical framework, several directions for future research are given.     

Students’ tool-use within a web enhanced course: Explanatory mechanisms of students’ tool-use pattern

The popularity of content management systems (CMSs) in today’s higher education is driven by the assumption that providing a rich toolset and leaving the use of this toolset under learner control will stimulate self-regulated and deeper learning. Current evidence on students’ tool-use within CMS supported courses however tackles this assumption and indicates that CMSs may empower students’ learning only under particular learner-related conditions. The current study addresses this concern and investigates how students’ tool-use within a CMS supported course can be explained in terms of (a) students’ conceptions on the tool functionalities, (b) self-efficacy beliefs for self-regulated learning and (c) goal orientation. Data were collected within a first year undergraduate course ‘Learning and Instruction’. Students’ (n = 182) tool-use within the course was logged throughout the course episode and the influencing variables were measured through questionnaires. K-means cluster analyses revealed four clusters that reflected differences in students’ tool-choice and tool-use throughout the course. Multinominal regression analyses revealed that these tool-use differences could be explained in terms of students’ goal orientation. The study provides thus perspectives in order to capture students’ academic motivation through unobtrusive, behavioral, measures. Furthermore, questions are raised regarding the parallel between students’ tool-use pattern and study strategy use.     

Specific Heat Capacity of Nitrobenzene–Tetradecane Near the Liquid–Liquid Critical Point

High-resolution adiabatic scanning calorimetry has been used to study the specific heat capacity anomaly of the nitrobenzene–tetradecane mixture near its upper critical point. The analysis, which is based on a method that uses heat capacity and enthalpy data, yields a value of the critical amplitude ratio A ⁺/A ^? which is consistent with the universal, accepted one. The critical amplitude of the correlation length was derived via two-scale factor universality. All this information is compared to that reported in previous studies for nitrobenzene–alkane mixtures.     

Study of the bias of the MTC estimate by noise analysis due to the presence of feedback

This paper discusses the bias of the non-parametric Moderator Temperature Coefficient (MTC) estimate due to the presence of feedback. Up to now the non-parametric estimation of the Frequency Response Function (FRF) is the most commonly used method to estimate the MTC by noise analysis. This estimation method is proportional to the Cross Power Spectral Density between the total neutron flux variation and total temperature variation divided by the auto power spectral density of the total temperature variation. The estimation method is very popular since feedback is considered to be negligible in the frequency band of interest. Unfortunately this is not the case in practice. Measurements at a Nuclear Power Plant in Belgium will be used to confirm that this feedback cannot be neglected. In case of feedback the chosen estimator always results in a biased estimate when there are external neutron flux variations present. It will be seen that the ratio between the external neutron flux and external temperature variation in combination with the amplitude of the feedback determines the bias. The theoretical analysis of the bias is based on a simplified scheme of the MTC measurement setup. A simulation in MATLAB is used to confirm the theoretical results. In order to avoid a biased estimate due to the feedback we will advise to measure the external temperature variation and to use another non-parametric estimator.     

Citrate anticoagulation does not correct cuprophane bioincompatibility as evaluated by the expression of leukocyte surface molecules

BACKGROUND: Citrate, used for the anticoagulation of the extracorporeal dialysis circuit, reduces ionized calcium by chelation and has been claimed to attenuate dialyser membrane bioincompatibility. Dialysis with complement-activating cuprophane membranes is associated with leukopenia which has been related to an increase in adhesion molecule expression on the surface of circulating leukocytes. METHODS: The effect of citrate anticoagulation on the expression of CD11b, CD11c and CD45 on the surface of granulocytes and CD14 on monocytes during haemodialysis with cuprophane membranes, was evaluated by flow cytometric analysis. A comparison of standard heparin vs citrate was performed in 14 chronic haemodialysis patients. During citrate anticoagulation a calcium-free dialysate was used and citrate was infused to obtain a concentration of 4.3 mmol/l blood. The unchallenged 'baseline state' expression of the surface molecules and the increase after ex vivo stimulation with phorbol 12-myristate 13-acetate (delta-PMA) or formyl-methionyl-leucyl-phenylalanine (delta-fMLP) was studied. RESULTS: With heparin, as well as with citrate, a sharp fall in granulocyte and monocyte count was observed after 15 min of dialysis, followed by a recovery at the end of the session. The expression of CD11b, CD11c and CD45 on granulocytes increased markedly during cuprophane dialysis with a peak at 15 min; there were no differences in response between heparin and citrate anticoagulation. Delta-PMA and delta-fMLP for CD45, CD11c and CD14 showed a decrease during cuprophane dialysis vs t0; again there were no differences between heparin and citrate. CONCLUSION: We conclude that the use of citrate was not associated with reduced leukocyte activation as measured by the expression of surface molecules during cuprophane dialysis and that no effect on dialysis leukocytopenia could be registered.