Reaction kinetics in food extrusion: methods and results

Extrusion cooking is a highly efficient food processing technology. During the extrusion process, there are many desirable and undesirable reactions which will determine final product quality. While being heated and sheared simultaneously, food raw materials experience a non-isothermal process and their residence time in the extruder is distributed. All these factors contribute to the difficulties in determining the kinetic parameters for those reactions. Therefore, this paper attempts to review the reaction kinetics in food extrusion. First of all, the kinetic models for the reactions are outlined. After elucidating how to determine reaction time in an extruder, the methodological approaches for determining the reaction order, rate constant, and activation energy of a reaction under isothermal or non-isothermal conditions with or without residence time distribution (RTD) are presented. Then, different models relating the rate constant to its various impact factors, with especially focusing on shear stress, are reviewed. Subsequently, how shear stress is estimated in an extruder, is illustrated. In the last part of this paper, the reported data of rate constant, reaction order, and activation energy for the reactions occurring during food extrusion are summarized, with detailed impacts of temperature, moisture content, shear stress, and determination method on these kinetic parameters. Finally, future research needs are suggested.     

Kinetics of quality changes during food frying

This paper deals with kinetics of quality changes during food frying. The quality parameters of interests include color, texture, viscoelastic properties, volume/density, and nutraceuticals (Omega 3 fatty acids). The kinetic theory and determination methodology under isothermal/non-isothermal conditions are also reviewed. This paper presents the reported reaction rate constant, order of reaction, and activation energy for specific quality changes including phenomenological observations and important speculations. The changes of color, textural, and viscoelastic properties generally followed a first order reaction. In some studies, activation energy analysis could have been improved by applying corresponding system temperatures for the quality change reactions of interest. The kinetic information on volume/density changes and thermal degradation of nutraceutical is still limited to experimental observations of the changes.     

Tribological Shear Conversion of Starch

Tribological (powdery friction) conversion (cooking) of starch as followed by DSC measurements was studied in a capillary rheometer. The crumbly extrudates with <20% conversion were analyzed to obtain a kinetic model and its parameter values suitable to describe the phenomena of tribological conversion of starch. Such conversion of starch followed zeroth order kinetics. An Arrhenius type activation energy plot described the shear energy initiated conversion well. The shear activation energy of starch conversions due to tribological shearing of powders was lower than that found for overall (tribological plus rheological) conversions. These findings can help develop more accurate and realistic models for starch conversion and similar processes and help elucidate their mechanisms.     

STATISTICAL EVALUATION OF ARRHENIUS MODEL AND ITS APPLICABILITY IN PREDICTION OF FOOD QUALITY LOSSES

To minimize quality losses occurring during processing and storage and to predict shelf-life, quantitative kinetic models, expressing the functional relationship between composition and environmental factors on food quality, are required. The applicability of these models is based on the accuracy of the model and its parameters. In this paper, the calculation of the Arrhenius parameters and the accuracy of the derived model were compared, using three statistical methods, namely: linear least squares, nonlinear least squares and weighted nonlinear least squares. Results indicated that the traditional two-step linear method, was the least accurate and the derived energy of activation and the pre-exponential factor had the largest confidence interval. The latter was shown to have a profound effect on the precision of the calculated rate constant and the predicted shelf life. Based on previous reports that indexes of deterioration     

REHYDRATION KINETICS OF MICROWAVE-DRIED OKRAS AS AFFECTED BY DRYING CONDITIONS

The aim of the present work was to understand the effect of drying conditions (microwave output powers and sample amounts) and rehydration temperature on rehydration kinetics of microwave-dried okras. Four different models, Peleg's, Weibull, first order and exponential association, were applied to experimental data, and the corresponding parameters of the models were obtained. In addition, the kinetic parameters of the models were correlated with the ratio of microwave output power to sample amount and temperature. Although all the models applied provided a good agreement with the experimental data with high values of the coefficient of determination of R ², the first-order kinetic model was chosen as the appropriate model because of its simplicity. By using the kinetic parameters of this model, the activation energy for rehydration kinetics was estimated as 1.15 kJ/mol.

PRACTICAL APPLICATIONS

Drying, in general, is a means of removal of water from the material. The purpose of drying food products is to allow longer periods of storage with minimized packaging requirements, reduce shipping weights, and preserve seasonal plants and make them available to consumers during the whole year. Besides these advantages, some important changes take place, as structural and physicochemical modifications, which affect the final product quality during dehydration. Rehydration is a complex process aimed at the restoration of raw material properties when dried material contacted with water, and can be considered as a measure of the injury to the material caused by drying. The objective of rehydration study is to attain as many products in their original characteristics as fast as possible. An improved knowledge of rehydration kinetics would significantly enhance the feasibility of this process.     

Is Food Safety Compatible with Food Waste Prevention and Sustainability of the Food Chain?

In a context where the sustainability of food chains and food waste prevention are subjects of interest for public authorities and professionals, it is important to assess if these new objectives of food policy are compatible with food safety. The objective of this work was to develop a global model for a ready-to-eat meat product that provides three different outputs, i.e. energy consumption, percentage of spoiled products and exposure levels of Listeria monocytogenes. First a cold chain model was developed. The cold chain model was then coupled with (i) predictive microbiology models and (ii) energy consumption models for cold equipments. Various scenarios were tested for assessing the consequences of potential changes in cold chain equipment on safety, food waste and energy cost. This global approach could help policy makers in decision making.     

Kinetic models of quality parameters of spreadable processed Gouda cheese during storage

The aim of the study was to prepare mathematical models based on the Arrhenius equation as predictive tools for the assessment of changes in quality parameters during the storage of spreadable Gouda cheese at temperatures of 8, 20 and 30 °C. The activation energy value and the chemical reaction rate constant enabled the construction of kinetic models, which helped to estimate the direction and rate of changes. Moreover, the activation energy (E_a) of the quality parameters was used to determine the sequence of their vulnerability during storage. The value of activation energy corresponding to temperature changes resulted in the following order of susceptibility of the quality parameters: ΔC?>?ΔE?≈?water activity?>?texture parameters?>?pH?>?colour?>?sensory parameters?>?rheological parameters. The research showed limited applicability of the mathematical models for estimation of quality parameters referring to spreadable processed Gouda cheese.     

The Relative Activation Energy of Food Materials: Important Parameters to Describe Drying Kinetics

An effective drying model should be accurate and require a small number of experiments to generate the parameters. The relative activation energy of various food materials, important drying kinetic properties used in the reaction engineering approach, is evaluated and summarized. The reaction engineering approach is then implemented to model the global and local drying rates of food materials. By using the relative activation energy, the reaction engineering approach describes the (R² higher than 0.99) global drying rate of food materials well. The reaction engineering approach can be coupled with a set of equations of conservation of heat and mass transfer to model the local drying rate of food materials. The relative activation energy is indeed proven to be accurate to model the local drying rate. While the predictions are accurate, the reaction engineering approach is very effective in generating the drying parameters since the relative activation energy can be generated from one accurate drying run. Different drying conditions of the same material with similar initial moisture content would result in the similar relative activation energies. The drying kinetics parameters generated here are readily used for design of new equipment, evaluating the performance of existing dryers, and monitoring the product quality.     

CONSIDERATIONS IN CALCULATING KINETIC PARAMETERS FROM EXPERIMENTAL DATA

Engineers require quantitative models to design and optimize processes. In the food industry, these process models become very complex because of the unique physical/chemical characteristics and variability of the raw material. Furthermore, frequently data describing rates of reactions and/or changes in foods are generated by food scientists who are not thoroughly familiar with reaction models. Analysis of those data to obtain parameters for reaction models thus becomes critical. In this paper, calculating kinetic parameters from experimental data is examined, and suggestions are presented for determining reaction rates and temperature dependence.     

Predicting mycotoxins in foods: A review

The need to ensure the microbiological quality and safety of food products has stimulated interest in the use of mathematical models for quantifying and predicting microbial behaviour. For 20 years, predictive microbiology has been developed for predicting the occurrence of food-borne pathogens, although these tools are dedicated to bacteria. Recently, the situation has changed and a growing number of studies are available in the literature dealing with the predictive modelling approach of fungi. To our knowledge the present one is the first review focussed on predictive mycology and food safety, including mycotoxins; existing kinetic and probability models applied to mycotoxigenic fungi germination and growth, and mycotoxin production are reviewed.     

西式快餐条件下煎炸油氧化稳定性及其不饱和脂肪酸氧化动力学研究

为了解煎炸油在煎炸过程中的氧化动力学规律,考察了5种常见煎炸油在西式快餐条件下的氧化稳定性,并对煎炸油中主要不饱和脂肪酸（亚麻酸、亚油酸及油酸）的氧化动力学进行研究。结果表明,煎炸过程中,棕榈油的茴香胺值、全氧化值的生成速率及碘值降低幅度最小,相比其他4种煎炸油具有更好的氧化稳定性。大豆油和菜籽油中亚麻酸的反应规律均同时符合0级和1级反应动力学模型;棕榈油、菜籽油、葵花籽油及稻米油中亚油酸的反应规律均同时符合0级和1级反应动力学模型,大豆油中亚油酸符合1级反应动力学模型;棕榈油、大豆油、菜籽油及葵花籽油中油酸的反应规律均同时符合0级和1级反应动力学模型;模型相应的决定系数R2在0.886~0.987之间,均大于0.85,模型拟合程度均较好。表明所构建煎炸油不饱和脂肪酸氧化动力学模型是可行的。     

Generating Maillard reaction products in a model system of d-glucose and l-serine by continuous high-intensity ultrasonic processing

In this paper, a continuous ultrasonic processing system was established and firstly applied to a Maillard reaction (MR) model system of d-glucose and l-serine. Furthermore, the effects of high-intensity ultrasound assisted MR were compared with those of thermally induced MR through kinetic modelling. The ultrasonic MR had higher depletion rates of reactants as well as higher generation rates of intermediate and final MR products (MRPs) at relatively low processing temperatures (55 and 60 °C). However, both rates were lower for ultrasonic MR than thermal MR when the temperature was raised to 70 and 75 °C. Moreover, the ultrasonic MR had significantly lower activation energy compared with thermal MR. Lastly, three pyrazines, two amines and five O-containing flavour compounds were only produced in ultrasonic MR, not in thermal MR. The difference in flavour generation was attributed to the extremely high, albeit momentary, temperature and pressure condition produced by high-intensity ultrasound.Industrial relevanceUltrasound-assisted processing, a novel technology for non-thermal processing, has been utilized as an alternative to conventional thermal processing. High, albeit momentary, temperature and pressure that are generated by high-intensity ultrasound during processing provide a favourable environment for a number of chemical reactions. Moreover, strong shear stress, turbulence and agitation are among the unique characteristics generated by high-intensity ultrasound, which help to keep excellent mixing during food processing. In our study, a continuous ultrasonic processing system was established so as to achieve a good temperature control as well as to minimize the loss of volatile products during processing, which are major concerns to any liquid-based processing with ultrasound. Furthermore, a Maillard reaction (MR) model system of d-glucose and l-serine under the continuous ultrasonic processing were studied and compared to the most common batch processing of thermal MR through kinetic investigation at the same processing temperature and time conditions. The kinetic models that focused on reactants, intermediates, and final MR products (i.e. melanoidins and flavour compounds), and the kinetic parameters obtained for the MR system may enable controlling the reaction at industrial scale. The different flavour profile that was generated in ultrasonic MR points to new approaches to the food flavour industry to produce more alternatives and varieties.     

A kinetic study of the release of vanillin encapsulated in Carnauba wax microcapsules

Thermal release of vanillin encapsulated in Carnauba wax microcapsules was studied by isothermal thermogravimetric analysis at 443, 453, 473, and 483 K. The thermal analysis data were analyzed kinetically and it was found that they can be satisfactorily described mathematically by the Avrami-Erofe’ev kinetic model A3. However, application of the isoconversional Friedman’s method showed that the activation energy of the vanillin release changes significantly with the degree of conversion, implying that the release is not a single-step reaction but a complex kinetic process. Nonetheless, the activation energies throughout the process remain relatively low (below 40 kJ mol⁻¹), meaning that the Carnauba wax as a carrier can easily release vanillin in food processing.     

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.     

Diffusion of homologous model migrants in rubbery polystyrene: molar mass dependence and activation energy of diffusion

Published diffusion prediction models for the diffusion of additives in food packaging simplify reality by having a small number of parameters only. Therefore, extrapolation of such models to barrier polymers, larger ranges of temperature and/or additive molecular weight (M_W ) is questionable. Extra data is still required to generalize these existing prediction models. In this paper, diffusion of a specifically designed homologous set of model additives (from 236 to 1120 g mol^?1) was monitored in two polystyrenes in the rubbery state (from 100 to 180°C): syndiotactic semi-crystalline polystyrene and its amorphous equivalent. Variations in associated diffusion coefficient D and activation energy Ea with migrant M_W and temperature were surprisingly low. Comparison of experimental behaviour with model predictions was performed. In their actual form, none of the models is capable of describing all experimental data, but there is evidence of convergence of the different approaches.     

Microwave Heating Distributions in Slabs, Spheres and Cylinders with Relation to Food Processing

Relatively simple mathematical models for microwave energy penetration in food products were applied, based on Lambert's law and taking into account internal reflections. With these models direct insight in microwave heating distributions in products with basic geometries and homogenous composition can be gained. Effects of changes in product composition with relation to dielectric properties and changes in product size can be predicted. The model was not designed to give an exact and detailed prediction of temperature distributions during microwave heating. However, it can simulate microwave heating of various food products and be useful for designing heat treatments.     

Effect of high pressure homogenization (HPH) on the rheological properties of tomato juice: Time-dependent and steady-state shear

High pressure homogenization (HPH) is a non-thermal technology that has been widely studied as a partial or total substitute for the thermal processing of food. Although microbial inactivation has been widely studied, there are only a few works in the literature reporting the physicochemical changes caused in fruit products due to HPH, especially those regarding the rheological properties. The present work evaluated the effect of HPH (up to 150 MPa) on the time-dependent and steady-state shear rheological properties of tomato juice. HPH reduced the mean particle diameter and particle size distribution (PSD), and increased its consistency and thixotropy. The rheological results were in accordance with the PSD observed. The rheological properties of the juice were evaluated by the Herschel–Bulkley and Falguera–Ibarz models (steady-state shear) and Figoni–Shoemaker and Weltman models (time-dependent). The parameters of these equations were modelled as a function of the homogenization pressure. The models obtained described the experimental values well, and contributed to future studies on product and process development.     

谷物干燥过程中的品质变化动力学

干燥导致谷物的品质特性发生变化,了解谷物干燥过程中的品质变化动力学对有效预测和控制烘后谷物品质十分必要。本文描述该过程的动力学模型、以及动力学结果进行了汇总分析。根据幂律动力学方程,谷物干燥中品质特性变化的级数在0~2之间,活化能多在100×103~400×103J/mol之间。幂律模型对有些变化过程并不适用。     

Kinetic Modeling of Food Quality: A Critical Review

ABSTRACT: This article discusses the possibilities to study relevant quality aspects of food, such as color, nutrient content, and safety, in a quantitative way via mathematical models. These quality parameters are governed by chemical, biochemical, microbial, and physical changes. It is argued that the modeling of such quality aspects is in fact kinetic modeling. Therefore, attention is paid to chemical kinetics, and its possibilities and limitations are discussed when applied to changes occurring in foods. The discussion is illustrated with examples from the literature. A major difficulty is that principles from chemical kinetics are strictly speaking only valid for simple elementary reactions, and foods are all but simple. Interactions in the food matrix and variability are 2 complicating factors. It is discussed how this difficulty can be tackled, and research priorities are suggested to come to better models in food science, and thereby to a better control of food quality.