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 ß-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.

Quantifying the influence of thermal process parameters on in vitro ß-carotene bioaccessibility: a case study on carrots.

This study describes a detailed and systematic investigation on the effect of thermal processing in terms of temperature and time (kinetic study) on ß-carotene in vitro bioaccessibility in carrots. ß-Carotene in vitro bioaccessibility increased with increasing processing temperature and time until steady-state conditions were reached after prolonged heating. The bioaccessibility values in steady-state conditions were temperature dependent. The experimental bioaccessibility data could adequately be modeled with a fractional conversion model. For the first time, modeling of processing-induced bioaccessibility changes is reported in literature. The results of the present kinetic study were used to estimate the impact of industrially relevant thermal processes on ß-carotene bioaccessibility in carrots by simulation. It was shown that, to achieve a high ß-carotene bioaccessibility, processing of carrots is essential (i.e., on the one hand, intense thermal processing or, on the other hand, mild thermal processing combined with intense mechanical processing).

Effect of pilot-scale aseptic processing on tomato soup quality parameters.

UNLABELLED: Tomatoes are often processed into shelf-stable products. However, the different processing steps might have an impact on the product quality. In this study, a model tomato soup was prepared and the impact of pilot-scale aseptic processing, including heat treatment and high-pressure homogenization, on some selected quality parameters was evaluated. The vitamin C content, the lycopene isomer content, and the lycopene bioaccessibility were considered as health-promoting attributes. As a structural characteristic, the viscosity of the tomato soup was investigated. A tomato soup without oil as well as a tomato soup containing 5% olive oil were evaluated. Thermal processing had a negative effect on the vitamin C content, while lycopene degradation was limited. For both compounds, high-pressure homogenization caused additional losses. High-pressure homogenization also resulted in a higher viscosity that was accompanied by a decrease in lycopene bioaccessibility. The presence of lipids clearly enhanced the lycopene isomerization susceptibility and improved the bioaccessibility. PRACTICAL APPLICATION: The results obtained in this study are of relevance for product formulation and process design of tomato-based food products.

Lycopene degradation and isomerization kinetics during thermal processing of an olive oil/tomato emulsion.

The stability of lycopene in an olive oil/tomato emulsion during thermal processing (80-140 °C) was studied. Initially, the degradation of total lycopene (all-E plus Z-forms) occurred quickly at temperatures above 100 °C. However, a nonzero plateau value, depending on the processing temperature, was attained after longer treatment times. Besides degradation, the isomerization of total-Z-lycopene as well as the individual isomerization of all-E-, 5-Z-, 9-Z-, and 13-Z-lycopene was studied in detail. After prolonged heating, the isomer conversion reached a temperature-dependent equilibrium state. The degradation of total lycopene and the isomerization could be described by a fractional conversion model. The temperature dependency of the corresponding reaction rate constants was quantified by the Arrhenius equation. The activation energy of degradation was estimated to be 28 kJ/mol, and the activation energy of overall (all-E and total-Z) isomerization was estimated to be 52 kJ/mol.

Beta-carotene isomerization kinetics during thermal treatments of carrot puree.

The effect of thermal processing on the stability of beta-carotene in carrot puree was investigated in a broad temperature range (80-150 degrees C). Heat induced changes in the stability of beta-carotene resulting in the conversion into its cis-isomers until an equilibrium state was reached after prolonged heating. By using nonlinear one-step regression analysis, the overall isomerization of all-trans-beta-carotene and the formation of individual cis-isomers could be modeled with a fractional conversion model. The Arrhenius equation was used to describe the temperature dependence of the reaction rate constants. As indicated by the low activation energies for all compounds (11 kJ mol(-1)), the isomerization rate constants showed little sensitivity toward the treatment temperature. The temperature dependence of the equilibrium concentration values after prolonged heating (C(f)) varied for the different compounds, but in all cases, a linear relation between the C(f) values and the treatment temperature could be noted. Although isomerization was observed as a result of thermal processing, it could be concluded that during industrially relevant heating processes, the retention of all-trans-beta-carotene in plain carrot puree was relatively high, which is most likely due to the presence of the protecting food matrix.

Mechanical and thermal pretreatments of crushed tomatoes: effects on consistency and in vitro accessibility of lycopene.

The effects of mechanical and thermal treatments on the consistency and in vitro lycopene accessibility of crushed tomatoes were evaluated. Different crushing intensities and a subsequent heat treatment carried out as a heat shock (95 degrees C for 8 min) or a boiling step (100 degrees C for 20 min) were examined. Additional homogenization was compared with milder crushing regarding the effect on lycopene content and in vitro accessibility. Textural properties, polygalacturonase and pectinmethylesterase activity, pectin degree of methoxylation, lycopene content, and in vitro lycopene accessibility were evaluated. Microstructure was studied using both light and transmission electron microscopy. Crushing and subsequent heating affected the pectin degree of methoxylation and the consistency of the crushed tomatoes. The mechanical and thermal treatments did not affect the lycopene content to any great extent; however, in vitro accessibility seemed to improve with extensive crushing followed by heating. Crushing or homogenization in itself was not enough to increase in vitro lycopene accessibility.