Laurent Bouvier

Predicting the distribution of whey protein fouling in a plate heat exchanger using the kinetic parameters of the thermal denaturation reaction of β-lactoglobulin and the bulk temperature profiles

Fouling of plate heat exchangers (PHE) is a severe problem in the dairy industry, notably because the relationship between the build-up of protein fouling deposits and the chemical reactions taking place in the fouling solution has not yet been fully elucidated. Experiments were conducted at pilot scale in a corrugated PHE, and fouling deposits were generated using a model β-lactoglobulin (β-LG) fouling solution for which the β-LG thermal denaturation reaction constants had been previously determined experimentally. Then 18 different bulk temperature profiles within the PHE were imposed. Analysis of the fouling runs shows that the dry deposit mass per channel versus the ratio R=kunf/kagg (with kunf and kagg representing, respectively, the unfolding and aggregation rate constants computed from both the identification of the β-LG thermal denaturation process and knowledge of the imposed bulk temperature profile into the PHE channel) is able to gather reasonably well the experimental fouling mass data into a unique master curve. This type of representation of the results clearly shows that the heat-induced reactions (unfolding and aggregation) of the various β-LG molecular species in the bulk fluid are essential to capture the trend of the fouling mass distribution inside a PHE. This investigation also illustrates unambiguously that the release of the unfolded β-LG (also called β-LG molten globule) within the bulk fluid (and the absence of its consumption in the form of aggregates) is a key phenomenon that controls the extent of protein fouling as well as its location inside the PHE.

Denaturation Kinetics of Whey Protein Isolate Solutions and Fouling Mass Distribution in a Plate Heat Exchanger

Few investigations have attempted to connect the mechanism of dairy fouling to the chemical reaction of denaturation (unfolding and aggregation) occurring in the bulk. The objective of this study is to contribute to this aspect in order to propose innovative controls to limit fouling deposit formation. Experimental investigations have been carried out to observe the relationship between the deposit mass distribution generated in plate heat exchangers (PHE) by a whey protein isolate (WPI) mainly composed of β-lactoglobulin (β-Lg) and the ratio between the unfolding and aggregation rate constants. Experiments using a PHE were carried out at a pilot scale to identify the deposit distribution of a model fouling solution with different calcium contents. In parallel, laboratory experiments were performed to determine the unfolding/aggregation rate constants. Data analysis showed that (i) β-Lg denaturation is highly dependent on the calcium content, (ii) for each fouling solution, irrespective of the imposed temperature profile, the deposit mass in each channel and the ratio between the unfolding and aggregation rate constants seem to be well correlated. This study demonstrates that both the knowledge of the thermal profile and the β-Lg denaturation rate constants are required in order to predict accurately the deposit distribution along the PHE.

Damage in Agitated Vessels of Large Visco-Elastic Particles Dispersed in a Highly Viscous Fluid

UNLABELLED Many food recipes entail several homogenization steps for solid particles in hot or cold viscous liquids, such as pureed fruit and sugar, jam or sauce with mushroom pieces. Unfortunately, these unavoidable processes induce damage to the solid particles. To date, little is known of the extent and nature of the damage caused. Consequently, few clear guidelines are available for monitoring solid particle integrity when mixing solid/liquid suspensions in an agitated tank. In this study, an attempt is made to quantify the impact of various physical parameters including the influence of the rotational speed of the impeller and the processing time on particle attrition, when a suspension of large visco-elastic particles in a highly viscous fluid is mixed under isothermal condition. Pectin gel particles were immerged in a viscous liquid and homogenized for various times and rotational speeds, while the evolution of the particles morphological parameters was monitored. Then, a set of dimensionless numbers governing the attrition mechanism is established and some empirical process relationships are proposed to correlate these numbers to the morphological characteristics and mass balance ratios. From the conditions observed, it is clear that 2 dimensionless ratios could be responsible for a change in the damaging mechanisms. These 2 ratios are the Froude and impeller rotation numbers. Finally, in the conditions tested, mass balance ratios appear to be mainly sensitive to the impeller rotational number, while the shape ratios are both impacted by the Froude and impeller rotational numbers. PRACTICAL APPLICATION Damage to solid particles suspended in a stirred vessel reduce the final product quality in industrial cooking processes. Examples of this are fruit in jam or sauces with mushroom pieces. The attrition phenomenon was measured and the influences of the impeller rotational speed and processing time were evaluated quantitatively in function of dimensionless numbers. This study contributes key elements for the monitoring of damage to solids with a view to retaining solid integrity.

Corrigendum to “Denaturation Kinetics of Whey Protein Isolate Solutions and Fouling Mass Distribution in a Plate Heat Exchanger”

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Continuous Monitoring of Whey Protein Fouling Using a Nonintrusive Sensor

Abstract In this work, a nonintrusive device to monitor fouling of a plate heat exchanger is presented. This device is composed of a flat electrical resistance covering a thermocouple located on the external face of a tubular holding section. The tubular holding section is placed immediately after the investigated plate heat exchanger, constituting the heating zone for which fouling monitoring is required. The principle of detection consisted in following the evolution of the measured temperature with time when a fixed thermal heat flux imposed by the resistance is dissipated through the temperature sensor. The measured temperature is supposed to vary with time since the inner temperature on the inner surface of the holding tubular zone is linked to the fouling growth. It is shown that the device response is highly correlated to the fouling occurring in the plate heat exchanger and could be a promising way for monitoring fouling rate (cheap and easy to implement avoiding cleanability drawbacks).