The effect of thermal processing (85-130 °C) on the stability and isomerization of β-carotene in both an olive oil/carrot emulsion and an olive oil phase enriched with carrot β-carotene was studied. During processing, degradation of total β-carotene took place. Initially, total β-carotene concentration decreased quickly, after which a plateau value was reached, which was dependent on the applied temperature. In the oil/carrot emulsion, the total β-carotene concentration could be modeled by a fractional conversion model. The temperature dependence of the degradation rate constants was described by the activation energy and was estimated to be 45.0 kJ/mol. In the enriched oil phase, less degradation took place and the results could not be modeled. Besides degradation, β-carotene isomerization was studied. In both matrices, a fractional conversion model could be used to model total isomerization and formation of 13-Z- and 15-Z-β-carotene. β-Carotene isomerization was similar in both the oil/carrot emulsion and enriched oil phase as the simultaneously estimated kinetic parameters (isomerization reaction rate constant and activation energy) of both matrices did not differ significantly. The activation energies of isomerization were estimated to be 70.5 and 75.0 kJ/mol in the oil/carrot emulsion and enriched oil phase, respectively.

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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.

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During thermoforming, plastic sheets are heated and subsequently deformed through the application of mechanical stretching and/or pressure. This process directly impacts sheet properties such as material thickness in walls, corners, and bottom, crystallinity in the constituent layers, and particularly the oxygen gas permeability. The aim of this study was to quantify the impact of thermoforming on thickness and oxygen transmission rate (OTR) of selected packaging materials (polypropylene (PP); PP/ethylene-vinyl alcohol co-polymer/PP (PP/EVOH/PP); polystyrene/EVOH/polyethylene (PS/EVOH/PE); amorphous polyethylene terephtalate/PE (APET/PE); APET/PE/EVOH/PE; polyamide/PE (PA/PE); and (PE/)PA/EVOH/PA/PE). These materials were extruded in two different thicknesses and thermoformed into trays with the same top dimensions and variable depths of 25, 50, and/or 75 mm and a 50 mm tray with a variable radius of the corners. The distribution of the material thickness in the trays was visualized, showing the OPEN ACCESSPolymers 2014, 6 3020 locations that were most affected by the deep drawn process. The OTR results indicate that the calculated OTR, based on a homogeneous material distribution, can be used as a rough approximation of the measured OTR. However, detailed analysis of crystallization and unequal thinning, which is also related to the tray design, remains necessary to explain the deviation of the measured OTR as compared to the predicted one.

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