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International audience; Mathematical modelling plays an important role in food engineering having various mathematical models tailored for different food topics. However, mathematical models are followed by limited information on their application in food companies. This paper aims to discuss the extent and the conditions surrounding the usage of mathematical models in the context of European food and drinks industry. It investigates the knowledge, nature and current use of modelling approaches in relation to the industry main characteristics. A total of 203 food companies from 12 European countries were included in this research.Results reveal that the country where the company operates, and size of the company, are more important predictors on the usage of mathematical models followed by the type of food sector. The more developed countries are positioned at the higher level of knowledge and use of available models. Similar pattern was observed at the micro level showing that small or medium sized companies exhibit lack of knowledge, resources and limiting usage of models.

This work focuses on the use of the Gompertz-inspired model to predict the thermal inactivation behaviour of microorganisms obtained in solid food products, validated for isothermal and non-isothermal conditions. Experiments were carried out in parsley, artificially inoculated with Listeria innocua. For the isothermal conditions tested, the predictive ability of the model was confined. The higher the temperature, the higher deviations observed (i.e. the model underestimates the inactivation behaviour). However, for the non-isothermal condition tested, the model predicted the microbial response accurately.

Ozone treatment is a non-thermal technology with promising applications in food processing. The objective of this study was to evaluate the effect of gaseous ozone at a concentration of 7.0 ± 2.4 g/L for 30 and 60 min of exposure, on some physicochemical characteristics (soluble solids content, pH, titratable acidity and color), bioactive compounds (vitamin C, total phenolics and carotenoids) and total antioxidant activity of Cantaloupe melon juice. The effectiveness of the ozone treatments in microbial survival was also assessed using Alicyclobacillus acidoterrestris spores as target spoilers of the juice (artificially inoculated). Some quality parameters were significantly affected by ozone treatments. The most relevant alterations were observed for color, vitamin C, carotenoids and total antioxidant activity. However, total phenolics content increased significantly in ozonized juices. Even though A. acidoterrestris spores reduced 2.22 ± 0.04 log cycles after 60 min of exposure, other quality related characteristics of the juice were modified. Industrial relevance The actual consumers demand for high-quality food standards have launched research to alternative and milder non-thermal processes, which have gained increasing attention and importance in the fruit juice industries. Ideally, preservation and/or processing of foods should involve technologies that prevent undesirable microbial survival and minimize quality attributes changes and nutrient losses. Thermal treatments are conventionally used to attain such targets, however, the content and the biological activity of the most health-related compounds are dramatically reduced. In this context, and particularly for the beverages industries, ozone has been exploited due to their potential for inactivating spoilage and pathogenic microorganisms while being effective in overall quality retention of the products.

Food stability is a critical parameter for both consumers and producers, since it assures safety, nutritional, and sensorial quality of foodstuffs, and at the same time maximizes shelf-life. For a long time, water activity, aw, was considered a determinant parameter in food stability and physical properties. This concept was challenged with the revolutionary approach to the study of food systems using the glass transition concept. Recently, scientific research suggests that molecular mobility is a fundamental approach to fully attain food physical properties and stability. Current literature suggests that stability can only be fully grasped if molecular mobility and structure are taken into consideration; that is, an appropriate understanding of the behavior of food products requires knowledge of its composition, structure, and molecular dynamics, through the three-dimensional arrangement of the various structural elements and their interactions. Food systems are complex mixtures of water, biopolymers, low-molecular weight ingredients, and colloid particles, and the molecular mobility between these different components reflects on the stability of such systems, determining the physical state, microstructure, and composition, which impacts food characteristics. Particularly, food water content, location, and interactions with other components are critical in microbial growth, degradation reactions, and sensorial aspects. Understanding changes in water location and mobility represents a significant step in food stability knowledge, once that water availability profoundly affects chemical, physical, and microbiological quality of foods.

Sucrose thermal degradation is an important reaction in the food industry. When in concentrated and neutral solutions, pure sucrose presents a lag phase in the reaction. This work aimed at: (i) modelling sucrose thermal degradation autocatalytic behaviour and (ii) studying the concentration and temperature effects on kinetic parameters. Isothermal experiments were conducted at temperatures ranging from 100 to 180 °C, using solutions with varying water content (3.58-30.03 (% w/w)). The logistic and Gompertz sigmoidal equations were modified and reparameterised, in order to describe degradation behaviour with kinetic parameters with physical meaning (maximum reaction rate, kmax, and lag time, λ). In both models these parameters presented an Arrhenius type dependence on temperature. Following a mixed model effect methodology, the concentration dependence was observed on the Arrhenius parameters. This concentration effect was included in the proposed kinetic models, which were able to successfully describe experimental data.

Molecular mobility is a fundamental parameter which reflects the dynamic properties of food components and contributes to food degradation reactions comprehension. Fresh-cut fruits have become an important food market segment. However, processing of fruits promotes faster its physiological deterioration, biochemical changes and microbial degradation. The purpose of this work was to use NMR methodology as a tool to evaluate fresh-cut fruit quality, during storage at refrigerated conditions. The fresh-cut melon transverse relaxation time (T2) was measured for a period of 7 days of storage at 5 °C. The relationship between the obtained values, microstructure and quality parameters was investigated. In general, results show the existence of one class of water fluidity in the system, the one present in cells after processing. T2, a measure of this fluidity, is affected by the processing and storage time. Also, it is possible to find a close relationships between T2 and quality parameters of total colour difference (TCD), firmness and aw. As T2 increases TCD also increases, while firmness and aw decrease. These results highlight the usefulness of NMR methodology application in food science., Author Joana F. Fundo acknowledges Fundacao para a Ciencia e a Tecnologia (grant SFRH/BD/62176/2009). The authors acknowledge the Portuguese NMR Network and Strategic Project PEst-C/CTM/LA0025/2013-14. This work was supported by National Funds from FCT through project PEst-OE/EQB/LA0016/2013

A mathematical model was developed to simulate solar drying of grapes, integrating heat and mass transfer models solved by an explicit finite differences method, considering changing boundary conditions. The model simultaneously incorporated shrinkage of the product, changes in effective moisture diffusivity and dependence of thermal properties on water content and temperature. Field experiments were carried out in a mixed mode solar dryer located in the North of Portugal, with pre-blanched grapes. A good prediction of experimental solar drying curves was attained. The mathematical model can be applied for simulating solar drying of different foods, once known their specific thermo-physical properties. Simulations obtained with the developed model can be valuable for predicting accurate drying times and consequently to design, control and optimise the production of dried foods.

The entrance in the job market of Food Science and Technology (FST) professionals was examined by a web-based survey conducted in Europe. The results highlight aspects that involve both the higher education and extracurricular qualifications and underline the different needs that education and training must fulfil. The field of higher education degree and gender affected the level of responsibility and the type of activity. FST professionals cover a wide range of tasks which require expertise that cannot be covered entirely by a single degree but these professionals show that are eager to expand their knowledge and skills.

International audience; The objective of this work was to create a software application (Bugdeath 1.0) for the simulation of inactivation kinetics of microorganisms on the surface of foods, during dry and wet pasteurisation treatments. The program was developed under the Real Basic© 5.2 application, and it is a user-friendly tool. It integrates heat transfer phenomena and microbial inactivation under constant and time-varying temperature conditions. On the basis of the selection of a heating regime of the medium, the program predicts the food surface temperature and the change in microbial load during the process. Input data and simulated values can be visualised in graphics or data tables. Printing, exporting and saving file options are also available. Bugdeath 1.0 includes also a useful database of foods (beef and potato) and related thermal properties, microorganisms (Salmonella and Listeria monocytogenes) and corresponding inactivation kinetic parameters. This software can be coupled to an apparatus developed under the scope of the European Project BUGDEATH (QLRT-2001-01415), which was conceived to provide repeatable surface temperature-time treatments on food samples. The program has also a great potential for research and industrial applications.

Non-uniformity in process quality was investigated during in-pack thermal sterilization of food products. This was accomplished through the combined application of the Monte Carlo procedure and a reliable mathematical method for process evaluation. Despite the large coefficients of variation found, the optimum quality process could be designed. The influence of the statistical variability of heating rate index on the retention of green beans' color was studied and an optimum temperature range was found between 125 and 135 °C. The variability in hardness of sterilized white beans, resulting from uncertainties of the combined effect of heating rate index and initial hardness of beans, was also evaluated by simulation. In this case, an optimum global temperature range between 120 and 135 °C was found, independently of the rotation, F0 value and surface heat transfer coefficient assumed.

Frozen green beans ( Phaseolus vulgaris , L.) thawing is one of the operations that compromises significantly quality. The present research aims at studying the effects of thawing, at environmental and refrigeration temperatures, on the quality profile of a frozen green beans package. Quality losses were computationally evaluated, using a simulation system based on object-oriented technologies. Simulations show that sensory parameters, such as flavour and colour, are more sensitive to thawing at environmental temperatures, than nutritional parameters, such as vitamin C and starch contents. The study demonstrates that green beans quality retention is also influenced by packaging materials, with different degrees of thermal insulation, and environmental conditions, such as temperature and surface heat convection coefficients. Important conclusions are discussed on shelf-life limiting quality parameters during thawing and temperature abuses, as well as on thawing green vegetables to maximise their quality profile. Results emphasise that the principle of high-temperature–short-times is not directly applicable to frozen green beans thawing. Furthermore, simulations lead to the conclusion that overall quality profile is maximised by thawing under refrigeration temperatures.

The microbiological safety of fresh produce is a significant concern of consumers and industry. After applying at an inoculated level (6–7 log CFU/mL) of Listeria monocytogenes on Iceberg lettuce, the antilisterial properties of balsamic vinegar from Modena, white wine vinegar and acetic acid solutions were investigated. Different proportions of the vinegars, acetic acid (58.7 g/L), and deionized water were evaluated to determine the role of those solutions at the stage of washing Iceberg lettuce to remove L. monocytogenes . The maximum observed log reduction of L. monocytogenes was 2.15 ± 0.04 for balsamic vinegar (50% (v/v)), 1.18 ± 0.06 for white wine vinegar ((50% (v/v)) and 1.13 ± 0.06 for acetic acid ((50% (v/v)). Washing with water only reduces 0.05 ± 0.04 log CFU/mL of L. monocytogenes numbers. Listeria reductions observed for balsamic vinegar are similar or higher than those of chlorine-based sanitizers evaluated in other studies with lettuce. In the case of balsamic vinegar solutions, Listeria inhibition followed a linear reduction according to the model: Log ( N / N 0 ) = −4.09 × balsamic vinegar proportion % (v/v) − 0.13; R ² = 0.95. Balsamic vinegar washings may be a promising method for reducing other foodborne pathogens present in produce or other foods, at home and retail environments.

This study was developed with the purpose to investigate the effect of polysaccharide/plasticiser concentration on the microstructure and molecular dynamics of polymeric film systems, using transmission electron microscope imaging (TEM) and nuclear magnetic resonance (NMR) techniques. Experiments were carried out in chitosan/glycerol films prepared with solutions of different composition. The films obtained after drying and equilibration were characterised in terms of composition, thickness and water activity. Results show that glycerol quantities used in film forming solutions were responsible for films composition; while polymer/total plasticiser ratio in the solution determined the thickness (and thus structure) of the films. These results were confirmed by TEM. \NMR\ allowed understanding the films molecular rearrangement. Two different behaviours for the two components analysed, water and glycerol were observed: the first is predominantly moving free in the matrix, while glycerol is mainly bounded to the chitosan chain., Authors Joana F. Fundo and Mafalda A.C. Quintas acknowledge Fundacao para a Ciencia e a Tecnologia (grants SFRH/BD/62176/2009 and SFRH/BPD/41715/2007, respectively), and Portuguese NMR Network.

The thermal degradation kinetics of both components of vitamin C, ascorbic acid (AA) and dehydroascorbic acid (DHAA), were determined in a nectar of Cupuacu (Theobroma grandiflorum) with 25% of pulp and 15% of sugar in water. AA was assayed by HPLC and the results showed that AA degraded into DHAA. A reversible first order model described well the AA degradation data, with an activation energy of 74±5 kJ/mol and k 80 ∘ C =0.032±0.003 min −1 . DHAA kinetic behavior suggested a consecutive first order reaction where DHAA was the intermediate product of AA degradation. A mechanistic model was derived to predict DHAA concentration. Rate constants were replaced by the Arrhenius equation in the model to evaluate the temperature dependence and the kinetic parameters for AA degradation, previously determined, were used. An activation energy of 65±9 kJ/mol and a k80∘C of 0.013±0.003 min −1 were estimated. The present findings will help to predict the best Cupuacu nectar processing conditions that minimize degradation of an important quality factor such as vitamin C.

Optimisation of thermal processes relies on adequate degradation kinetic models for food safety and quality. In order to use peach puree as a model food to further validate calculated optimal conditions, isothermal experiments, using peach puree, were performed between 110°C and 135°C. Colour was quantified using the L , a , b system. Two combinations of these parameters, La / b and Total Colour Difference (TCD), were used to evaluate the total colour change. A one-step non-linear regression was performed on all data using the Arrhenius model. The changes in the L and b values followed a first-order reaction with activation energies of 107 ± 7 and 109 ± 8 kJ/mol, respectively. The fractional conversion model was applied to a , La / b and TCD resulting in activation energies of 106 ± 13, 106 ± 10 and 119 ± 9 kJ/mol, respectively.

A mathematical model was developed to describe the pasteurization, by hot filling, of fruit purees. The model assumed that the puree reaches instantaneously a hot-fill temperature and, after introduced into the container, cooling by conduction takes place. The heat transfer was modelled by a finite differences method. Vitamin C and pectinesterase were used as quality and pasteurization criteria, respectively. Specific filling temperatures combined with container dimensions are required to achieve a target pasteurization value. However, only some of the adequate conditions offer final products with maximum quality. Several simulations were carried out to investigate the effect of filling temperature, container shape, type of cooling medium and pasteurization value on final quality retention expressed as vitamin C retention. Using statistical factorial analysis the most important parameters affecting quality were filling temperature and pasteurization value, followed by cooling medium. Shape was not considered significant ( p > 0.05). Best quality was achieved with higher hot filling temperatures and small pasteurization values.

Ethylene oxide is a dominant agent in the sterilization of medical devices due to its effectiveness and compatibility with most materials. The advantages and disadvantages, as well as its recommended uses, are explored in this chapter. The variables and their relevance on process optimization are described, the types of processing cycles are detailed and emphasis is given to the design and validation of the sterilization process.

The impact of sodium hypochlorite and hydrogen peroxide (H 2O 2 at 1 and 5%) solutions on Listeria innocua in red bell peppers, total mesophiles in strawberries and total coliforms in watercress was studied. Quality attributes such as colour, firmness and pH were studied for all products; total anthocyanins content was determined for strawberries. Sensorial analyses were also carried out for all products. Results showed that H 2O 2 (5%) provided the highest reductions of microbial loads. Besides H 2O 2 (1%) had a lower impact, it was more effective than water-washings. Sodium hypochlorite solutions lead to microbial reductions comparable to water risings. In terms of quality, H 2O 2 (5%) was the solution with higher negative impact on products' colour. For strawberries, such colour alterations were also detected by sensorial analyses. The anthocyanins content decreased significantly. Overall it was found that H 2O 2 (1%) was a good sanitizer solution, since microbial reduction was attained while quality factors did not suffer considerable alterations.

The effect of non-thermal technologies (ozone in aqueous solution, ultrasound and ultraviolet C radiation) and washings with chemical solutions (sodium hypochlorite and hydrogen peroxide) on safety and quality features of strawberries was studied. These treatments were applied before fruit storage at two different temperatures (4 and 15 °C). The overall impact on microbial loads (total mesophiles, and yeasts and moulds) and selected quality attributes (colour, firmness, pH, total anthocyanins and ascorbic acid content) was assessed. During storage under refrigerated temperature, washing with hydrogen peroxide solutions resulted in strawberries with lower microbial loads, when compared to the other treatments. However, it produced significant key quality attributes losses, such as colour and total anthocyanins content. The results presented show that ozone and ultrasound are promising alternatives to thermal treatments. The application of such technologies, before refrigerated storage of strawberries, allowed a satisfactory retention of all quality characteristics analysed, while being efficient in controlling microbial contamination.

The effects of freezing process and frozen storage at isothermal (−7, −15 and −25 °C) and non-isothermal (accelerated life testing with step-stress methodology; temperature range from −30 to −5 °C) conditions on pumpkin quality were investigated. Storage temperature conditions were selected to embrace the limits practiced in the cold chain. Quality changes, such as texture, colour CIE Lab and vitamin C (ascorbic acid) content, were evaluated for both frozen storage regimes. The freezing process (that included a pre-blanching step) and subsequent frozen storage had significant impacts on all quality parameters analysed. A fractional conversion kinetic model was adequate in colour, texture and vitamin C data fits. The storage temperature effect was successfully described by the Arrhenius law. This study shows that non-isothermal frozen storage has a marked effect on pumpkin quality.

Ozone is a strong sanitizer that can be applied as a convenient washing-treatment to foods. The main objective was to study the ozone impact on Listeria innocua in red bell peppers, total mesophiles in strawberries and total coliforms in watercress. Modelling microbial load reduction throughout treatment time and due to ozone effect were also targets. The microbiological reductions observed for ozonated samples were higher than the ones obtained for water dipping. However, total coliforms/watercress were less sensitive to both deionized-water and ozonated-water washings. A Weibull-based model was adequate in describing microbiological reductions and may contribute to design more effective sanitizing processes.

The kinetics of peroxidase thermal inactivation, total phenolic content degradation, and colour (CIE L∗a∗b∗) and texture changes were studied in a temperature range of 70–90 °C for carrots (Daucus carota L.). Peroxidase inactivation, total phenolic content degradation and the lightness colour (L∗ parameter) change were successfully described by a first-order reaction model. The redness and yellowness colour (a∗ and b∗ parameters, respectively) and texture (firmness and energy parameters) changes presented a fractional conversion kinetic model behavior. The temperature effect was well described by the Arrhenius law. All the blanching conditions recommended to reduce peroxidase inactivation to an acceptable level (90% loss of its original activity) ensured good quality retention. However, to obtain a high quality carrot product a balance must be made between colour and total phenolic content losses. Therefore, blanching at 80 °C for 6 min is suggested as a compromise condition to maximize quality. The overall study indicated that colour is a critical parameter to optimize carrot hot water blanching condition.

A computer program was developed, aiming at estimating water diffusivity parameters in a dynamic drying process with grapes, assessing the predictability of corresponding non-isothermal drying curves. It numerically solves Fick’s second law for a sphere, by explicit finite differences, in a shrinking system, with anisotropic properties and changing boundary conditions. Experiments were performed in a pilot convective dryer, with simulated air conditions observed in a solar dryer, for modelling the process. The equivalent radius of grapes decreased 30% until the end of the process, stressing the need to include shrinkage in mass and heat transfer models. It was observed that macroscopic shrinkage reflects cellular shrinkage, if plotted versus the normalised water content. Diffusivity values ranged between 1 × 10−16 and 1 × 10−10 m2/s. The developed methodology yields very good prediction of dynamic drying curves., The authors Ines N. Ramos and Teresa R.S. Brandao would like to acknowledge, respectively, PRAXIS XXI PhD Grant No. 18543/98 and Post-Doctoral Grant SFRH/BPD/11580/2002, to Fundacao para a Ciencia e a Tecnologia, Portugal.

Watercress is an herb traditionally consumed fresh. If frozen, would be readily available to consumers. However, pathogenics resistant to frozen storage are a safety concern in this new product. in this study watercress was artificially contaminated with Pseudomonas aeruginosa ATCC 27853 and Enterococcus faecalis ATCC 29212. Their survival was evaluated after blanching, frozen storage and temperature fluctuations of the frozen product. The blanching caused a reduction of about 2 log cfu per gram of product of total viable count (TVC) and about 1.7 and 1.3 log cfu per gram of product of P. aeruginosa and E. faecalis, respectively. P. aeruginosa seemed to be more sensitive to temperature abuses than E. faecalis. After 3 months, TVC was still observed with a reduction of about 3 log cfu per gram of product. At the end of the study, exposure to freeze-thaw cycles resulted in death or injury of the microorganisms. These findings on the behaviour of two microorganisms of concern in frozen watercress will help improving the safety and cold chain settings for this product. (C) 2008 Elsevier Ltd and IIR. All rights reserved.

The effects of blanching treatment on peroxidase inactivation, colour and texture of pumpkin (Cucurbita maxima L.) were studied in the temperature range of 75-95 °C. Peroxidase inactivation followed a first-order Arrhenius model, where the activation energy and rate of the reaction at a reference temperature of 85 °C were 86.20 ± 5.57 kJ mol-1 and 0.27 ± 0.01 min-1, respectively. During blanching, pumpkin became darker and softer with processing time. The degradation of colour (evaluated throughout CIE L*a*b* colour system, with chroma index and total colour difference) and texture parameters (firmness and energy) showed a fractional conversion model kinetics, being the temperature effect on kinetic parameters well described by the Arrhenius law. The results of this work are a good tool to further optimise pumpkin blanching conditions.

Multiresponse modelling is a powerful tool for studying complex kinetics of reactions occurring in food products. This modelling technique uses information of reactants and products involved, allowing insightful kinetic parameters estimation and helping in clarifying reaction mechanisms. One example of a complex reaction that occurs in food processing is the caramelisation reaction. Caramelisation is the common name for a group of reactions observed when carbohydrates are exposed to high temperatures. The objective of this work was to apply multiresponse regression in developing a mathematical mechanistic model that describes sucrose thermal degradation and caramelisation products formation in highly concentrated sucrose solutions, with different water contents and under various temperatures. Results demonstrated the usefulness of multiresponse modelling in understanding reaction mechanisms in food matrices. A mechanistic model for the caramelisation reaction was proposed, which successfully described the experimental data of concentrated solutions in the 30.03 to 12.20% (w/w) water content range. Furthermore, good predictions of temperature and water content effects were achieved. For extremely low water content systems (3.58% (w/w)), the proposed mechanistic model failed to describe experimental data, indicating different reaction pathways. Industrial relevance Caramelisation is one reaction occurring during heat treatment in high sugar content food products. Understanding the mechanism of caramelisation reaction and the effect of the environmental conditions on different reaction steps may help in the design of products and processes, in order to prevent or promote such occurrence. This work also uses an advanced modelling technique that can be used in any food system for any reaction occurring during processing.

Listeria innocua was subjected to thermal inactivation and the extent of heat-injured cells was quantified. Cultures were heated in liquid medium for different times, using temperatures in the range of 52.5 to 65.0 °C, and plated on Tryptic Soy Agar with 0.6% yeast extract (TSAYE) used as non-selective medium and on TSAYE plus 5% NaCl (TSAYE + NaCl) and Palcam agar with selective supplement (Palcam agar) as selective media. The difference observed in counts in non-selective and in selective media gave an indication of cell injury during the heat treatment. D- and z- values were calculated for all conditions considered. For each temperature, D-values obtained using non-selective recovery procedures were higher than the ones obtained using the two selective media. When comparing the selective media, it can be concluded that Palcam agar allowed recovery and growth of thermally injured cells and so it was less inhibitor than TSAYE + NaCl. Another important result was the influence of temperature on the degree of cellular injury. As temperature increases, the degree of heat-injured cells also increases, and consequently concern has to be taken with the temperature and the counting medium used in food processing studies. The results of this work clearly demonstrated that selective media used for Listeria monocytogenes enumeration/detection might not be suitable for the recovery of heat-injured cells, which can dangerously underestimate the presence of this foodborne pathogen.

The effect of heat and the combined heat/ultrasound (thermosonication) treatment on the inactivation kinetics of peroxidase in watercress (Nasturtium officinale) was studied in the temperature range of 40–92.5 °C. In the heat blanching processes, the enzyme kinetics showed a first-order biphasic inactivation model. The activation energies and the rates of the reaction at a reference temperature for both the heat-labile and heat-resistant fractions were, respectively, Ea1 = 421 ± 115 kJ mol−1 and Ea2 = 352 ± 81 kJ mol−1, k 1 84 . 6 ° C = 18 ± 14 min - 1 and k 2 84 . 6 ° C = 0 . 24 ± 0 . 14 min - 1 . The initial relative specific activity for both isoenzyme fractions were also estimated, being C01 = 0.5 ± 0.08 μmol min−1 mg protein−1 and C02 = 0.5 ± 0.06 μmol min−1 mg protein−1, respectively. The application of thermosonication was studied to enable less severe thermal treatments and, therefore, improving the quality of the blanched product. In this treatment the enzyme kinetics showed a first-order model. The activation energy, the rate of reaction at a reference temperature and the initial relative specific activity were, respectively, Ea3 = 496 ± 65 kJ mol−1, k 3 87 . 5 ° C = 10 ± 2 min - 1 and C03 = 1 ± 0.05 μmol min−1 mg protein−1, proving that the enzyme became more heat labile. The present findings will help to design the blanching conditions for the production of a new and healthy frozen product, watercress (Nasturtium officinale), with minimized colour or flavour changes along its shelf life.

Development of effective heat treatments is crucial to achieve food products safety, and predictive microbiology is an excellent tool to design adequate processing conditions. This work focuses on the application of a modified Gompertz model to describe the inactivation behaviour under time-varying temperature conditions at the surface of a food product. Kinetic studies were carried out assuming two different heating regimes, typically used in surface pasteurisation treatments, and compared with isothermal conditions. Parameters were estimated on the basis of generated pseudo-experimental data. It was concluded that the heating period greatly affects microbial inactivation and parameter estimation. If a slow heating treatment is used, the process time should be extended to achieve a given microbial load when compared to a fast heating process. This is explained by the fact that, in the slow heating rate process the temperature was below the lowest temperature for inactivation for a much longer time, in comparison with the fast heating regime. 2005 Elsevier Ltd. All rights reserved.

Microstructural changes in cells of Ruby grape (Vitis vinifera) quarters were monitored during first stage of convective air drying, under a stereo-microscope. A gradual overall shrinkage of grape cells was observed during the process. The cellular parameters: area, perimeter, major and minor axis length, Feret diameter, elongation, roundness and compactness, were quantified by image analysis. It was verified that cell dimensions suffered modifications during drying, but their shape remained unchanged. These microstructural changes showed a smooth exponential decrease with time, and a first-order kinetic model was satisfactorily fitted to the data. Temperature increased the rate of cellular shrinkage and this effect followed an Arrhenius type behaviour. Increasing temperature from 20 to 60 °C resulted in a 350% increase of the area change rate. For the parameters related to cellular dimensions, the magnitude of the values were 10-3 min-1 for the rate of change at 40 °C and 3 kJ/mol for the activation energy.

A mathematical model was developed to describe the heat transfer during the sterilisation of conduction heating foods inside three dimensional two division rectangular packs. The model uses a standard explicit finite differences method with non-capacitance surface nodes and simulates different pack sizes, food properties and surface heat transfer resistances at the package lid and walls. Taking into account the cooling phase, the sterility value was calculated as a function of position in order to identify the location of the least lethality point. The most important variables affecting the position of this point are the product heating rate and the surface heat transfer coefficients. For low heating rate values this critical point moves towards the surface. When different food products are sterilised in simultaneously the quality degradation of foods in this type of package is also a point of discussion.

Two objective functions—volume average retention and volume average cook-value—commonly used to optimize the overall quality and nutrient retention of heat-preserved foods, were studied and optimal processing conditions based on the two approaches were compared. Case studies from the literature were run and tested for the two objective functions. The influence of the decimal reduction time (at the reference temperature, Dref value) of the quality factor on the optimal processing temperature was evaluated. For high Dref values, e.g. for vitamins, the two objective functions give the same results and the Dref value has a minor influence on the optimum processing conditions. For low Dref values, such as for texture and colour, the optimal sterilization temperature is affected by this parameter and the use of volume average cook-value, as objective function, does not take this effect into account, which may result in underestimation of the optimal processing temperature.