Reliable estimation of the key variables and of their rates of change in the alcoholic fermentation

International audienceThe paper establishes a rigorous probabilistic framework for the reconciliation of apparently conflicting data from various physical and chemical measurements related to the key biological variables of alcoholic fermentation: the ethanol and the residual sugar concentrations. The analysis is carried out on a database consisting of 15 beer fermentation experiments, for which off-line determinations of ethanol concentration, fermentable sugar concentration, wort density and refractive index are available, as well as on-line records of evolved CO2. The basic reconciliation method uses mass balance and monotonicity constraints derived from the biological knowledge of the fermentation process. In order to provide interpolated values and rate estimates, smoothness requirements are added. The reconciliation procedure gives more reliable estimates than any given measurement, detects outliers, helps fixing problems in the experimental setting and is also applicable on line

Prediction of Confidence Limits for Diacetyl Concentration During Beer Fermentation

International audienceA dynamic model for diacetyl production and reduction was developed based on experimental data from 14 laboratory-scale (15-L) lager beer fermentations carried out in various conditions of temperature (10–16°C), top pressure (50−850 mbar), initial yeast concentration (5−20 million cells per milliliter) and initial wort gravity (1,036−1,099 g/L). Uncertainties due to measurement errors, model parameters, and batch-to-batch variability were described in a probabilistic framework. The model predicts a probability distribution for the final diacetyl concentration from which a median value and an upper boundary, at a specified confidence level, are derived. It is demonstrated that in-line diacetyl measurements at early stages of fermentation greatly reduce the uncertainty about the final diacetyl level in each specific batch.Predicción de los Límites de Confianza para la Concentración de Diacetilo en Cerveza Durante la Fermentación Se desarrolló un modelo dinámico para la producción y reducción de diacetilo durante la fermentación, basado en datos experimentales de 14 fermentaciones en el laboratorio (15 L) con cerveza lager; estas fermentaciones se realizaron en diferentes condiciones de temperatura (10-16°C), sobrepresión (50–850 mbar), concentración inicial de levadura (5–20 millones de células por mililitro) y densidad inicial del mosto (1,036–1,099 g/L). Las incertidumbres debido a los errores de medición, los parámetros del modelo y la variabilidad de lote a lote, fueron descritas en un marco probabilístico. El modelo pronostica una distribución de probabilidad para la concentración final del diacetilo, de cual se deriva un valor de la mediana y del límite superior de la concentración, a un nivel de confianza especificada. Se demuestra que las mediciones de diacetilo en línea en las fases iniciales de la fermentación reducen de manera significativa la incertidumbre de la concentración final de diacetilo de cada lote

An Interactive Tool for the Optimization of Freeze-Drying Cycles Based on Quality Criteria

International audienceAmong existing dehydration methods, freeze-drying has unique benefits for the stabilization and preservation of biological activity of pharmaceutical products but remains an expensive and time-consuming process. A user-friendly software tool was developed, allowing for interactive selection of process operating condition profiles in order to maximize process productivity while insuring product quality preservation. The software is based on a dynamic, one-dimensional heat and mass transfer model, which can accurately represent both the primary and secondary drying stages and the gradual transition between them. The model was validated in a wide range of operating conditions: − 25 to + 25°C shelf temperature and 10 to 34 Pa total pressure. By comparing a reference sucrose solution with a formulated pharmaceutical product containing polyvinylpyrrolidone (PVP), it is shown that controlling product properties such as glass transition temperature and sorption isotherm can reduce the minimum achievable cycle duration by 12 h (33%)

Modélisation du pH, de l'extrait sec et de la minéralisation du caillé pendant l'égouttage d'un fromage à pâte molle

International audienceThe influence of the temperature at the rennet addition (31.2, 32.0 and 32.8 °C) and of the starter type on the soft cheese drainage process was studied. Off-line measurements of pH, calcium and phosphorous concentrations, as well as dry matter of the curd were performed in parallel with on-line measurements of the weight and pH of the whey. Only the starter type was found to have a significant influence on the curd and whey pH, on the calcium concentration in the curd and on the calcium/dry matter ratio. Correlations were established between weight of the whey and dry matter of the curd, as well as between pH of the whey and physico-chemical measurements in the curd. Linear regressions gave satisfactory results only when performed separately for each type of starter. Artificial neural networks allowed the building of common models for both starters and predicting curd pH, calcium concentration and the calcium/dry matter ratio using the pH of the whey at one hour after moulding.Au cours de l'égouttage en moule de fromages à pâte molle, des mesures de pH, de concentrations en calcium et phosphore ainsi que de l'extrait sec du caillé ont été effectuées parallèlement aux mesures en ligne de la masse et du pH du sérum. Les effets de la température d'emprésurage (31,2 ; 32,0 et 32,8 °C) et de la nature des levains ont été évalués sur l'évolution de ces grandeurs. Seule la nature des levains présente un effet significatif sur les évolutions du pH du caillé et du sérum, sur la concentration en calcium du caillé et sur le rapport Ca ++ /extrait sec. Des corrélations sont établies entre la masse de sérum égoutté et l'extrait sec du caillé ainsi qu'entre le pH du sérum et les grandeurs physico-chimiques mesurées dans le caillé. Dans ces relations, les régressions linéaires multiples n'apportent des résultats corrects que lorsqu'elles sont établies séparément, en fonction du levain utilisé. La mise en oeuvre de réseaux de neurones artificiels permet d'établir un modèle unique pour l'ensemble des variables recherchées

Critical water activity and amorphous state for optimal preservation of lyophilised lactic acid bacteria

International audienceThe aim of this study was to investigate the influence of the water activity on the stability of lyophilised lactic acid bacteria, especially in the solid glassy region. Lactobacillus bulgaricus CFL1 was co-lyophilised with sucrose and stored under controlled relative humidity at 25 °C. Glass transition temperature (T g), water activity, water content and loss of specific acidification activity during storage were determined. The rates of bacteria degradation were analysed as a function of water activity and as a function of the temperature difference between storage temperature and T g. Above T g , the degradation rate appeared related to the physical changes of the amorphous matrix. Below T g , the optimal stability of the lyophilised bacteria was observed in the intermediate water activity range 0.1–0.214. An integrated analysis of the relationships between water activity, T g , water content and biological activity appeared as a promising approach for optimising the freeze-drying process and predicting the storage stability

Mapping the physiological states of Carnobacterium maltaromaticum obtained” by applying stressful fermentation conditions

This work received funding from the European Union´s Horizon 2020 research and innovation programme under grant agreement No 777657Mapping the physiological states of Carnobacterium maltaromaticum obtained” by applying stressful fermentation conditions. 4. Microbial Stress: from systems to molecules and bac

Influence of culture conditions on the technological properties of Carnobacterium maltaromaticum CNCM I-3298 starters

The aim of this study is to investigate the effect of a broad spectrum of culture conditions on the acidification activity and viability of Carnobacterium maltaromaticum CNCM I‐3298, the main technological properties that determine the shelf‐life of biological time‐temperature integrator (TTI) labels. Cells were cultivated at different temperatures (20–37°C) and pH (6–9·5) according to a modified central composite design and harvested at increasing times up to 10 h of stationary phase. Acidification activity and viability of freeze‐thawed concentrates were assessed in medium mimicking the biological label. Acidification activity was influenced by all three culture conditions, but pH and harvest time were the most influential. Viability was not significantly affected by the tested range of culture conditions.Carnobacterium maltaromaticum CNCM I‐3298 must be cultivated at 20°C, pH 6 and harvested at the beginning of stationary phase to exhibit fastest acidification activities. However, if slower acidification activities are pursued, the recommended culture conditions are 30°C, pH 9·5 and a harvest time between 4–6 h of stationary phase. Quantifying the impact of fermentation temperature, pH and harvest time has led to a predictive model for the production of biological TTI covering a broad range of shelf‐lives

Model-based real time operation of the freeze-drying process

Background: Freeze-drying or lyophilization is a dehydration process employed in high added-value food and biochemical goods. It helps to maintain product organoleptic and nutritional properties. The proper handling of the product temperature during the operation is critical to preserve quality and to reduce the process duration. Methods: Mathematical models are useful tools that can be used to design optimal policies that minimize production costs while keeping product quality. In this work, we derive an operational mathematical model to describe product quality and stability during the freeze-drying process. Model identification techniques are used to provide the model with predictive capabilities. Then, the model is used to design optimal control policies that minimize process time. Results and conclusion: Experimental measurements suggest splitting the process into two subsystems, product and chamber, to facilitate the calibration task. Both models are successfully validated using experimental data. Optimally designed control profiles are able to reduce the process duration by around 30% as compared with standard policies. The optimization task is introduced into a real time scheme to take into account unexpected process disturbances and model/plant mismatch. The implementation of the real time optimization scheme shows that this approach is able to compensate for such disturbances

Effect of freeze-dryer design on heat transfer variability investigated using a 3D mathematical model

International audienceIn the freeze-drying process, vials located at the border of the shelf usually present higher heat flow rates which in turn result in higher product temperatures than central vials. This phenomenon, named edge vial effect, can result in product quality variability within the same batch of vials and between batches at different scales. Our objective was to investigate the effect of various freeze-dryer design features on the heat transfer variability. A 3D mathematical model previously developed in COMSOL Multiphysics and experimentally validated was used to simulate heat transfer of a set of vials located at the edge and in the centre of the shelf. The design features considered were the loading configurations of the vials, the thermal characteristics of the rail, the walls and the shelves and some relevant dimensions of the drying chamber geometry. The presence of the rail in the loading configuration and the value of the shelf emissivity strongly impacted on the heat flow rates received by the vials. Conversely, the heat transfer was not significantly influenced by modifications of the thermal conductivity of the rail, the emissivity of the walls and by the geometry of the drying chamber. The developed model revealed to be a powerful tool to predict the heat transfer variability between edge and central vials for the cycle development and scale-up and to compare various freeze-dryer design features

Use of a multi-vial mathematical model to design freeze-drying cycles for pharmaceuticals at known risk of failure

[EN] Freeze-drying is a dehydration method suitable for the stabilization of heat-labile pharmaceutical products, such as vaccines. Due to the vial-to-vial variability of heat and mass transfer during the process, the value of the critical process parameters (e.g., product temperature, sublimation rate) may be different between vials and batches often present significant product quality heterogeneity. The aim of this work was the development of a dynamic, multi-vial mathematical model making it possible to predict risk of failure of the process, defined as the percentage of vials potentially rejected by quality inspection. This tool could assist the design of freeze-drying cycle.This work was sponsored by GlaxoSmithKline Biologicals SA which was involved in all stages of the study conduct and analysisScutellà, B.; Trelea, IC.; Bourlés, E.; Fonseca, F.; Passot, S. (2018). Use of a multi-vial mathematical model to design freeze-drying cycles for pharmaceuticals at known risk of failure. En IDS 2018. 21st International Drying Symposium Proceedings. Editorial Universitat Politècnica de València. 315-322. https://doi.org/10.4995/IDS2018.2018.7421OCS31532