The aim of this study was to experimentally determine the mixing times of viscous fluids placed in a soft container where they were mixed by the vibrations of the tank wall. In parallel, mechanistic ...models were established to link the inlet parameters of the crank/slider device responsible for the tank wall vibrations to the mixing times. The mechanistic models are based on dimensional analysis. Either momentum change (change in instantaneous velocity with which the slider comes in contact with the soft elastic reactor) or impulse (force transmitted by the piston) is introduced as an intermediate parameter in the relevant list of physical quantities in order to take the intensity of mechanical solicitation induced by the beater into account. These two intermediate parameters were theoretically computed on the basis of knowledge about the geometrical parameters and the rotational speed of the crank/slider device. The experimental results showed that the mixing time strongly depends on momentum change (or impulse) induced by the beater and its striking frequency. Empirical correlations are proposed, and good agreements between experimental and predicted values were obtained as the standard deviation is lower than 20% for the whole data set.
Dairy fouling is a ubiquitous problem in food processing, however, the fouling mechanism is not fully understood and investigations arose mainly from experiments with model systems that contained ...only whey proteins, typically reconstituted from whey protein isolate powder (WPI). The effect of casein on fouling has been rarely considered despite it is the major component of milk proteins. To fill this gap, whey protein-based model fluids containing different casein concentrations and fixed content of added calcium were prepared, leading to various Casein/WPI mass ratios. The effect of Casein/WPI on β-lactoglobulin (BLG) denaturation at molecular level and subsequent fouling behavior in the pilot-scale plate heat exchanger during pasteurization treatment was investigated. It was shown that Casein/WPI significantly affects the fouling behavior: at low Casein/WPI, fouling mass dropped dramatically until a minimum value was reached located at Casein/WPI of 0.2. While at higher Casein/WPI, fouling mass increased with elevated Casein/WPI. Element mapping of the fouling layer also reveals that different structures and fouling mechanisms occur depending on Casein/WPI ratio. Finally, it was established that contrary to WPI solutions, BLG thermal denaturation is poorly correlated to decrease/extent of fouling for casein protein-based solutions showing that the presence of casein deeply modifies mineral and protein interactions and fouling build-up.
•Casein mitigates whey protein fouling at low casein/whey ratio.•Casein participates in fouling build-up at high casein/whey ratio.•β-lactoglobulin denaturation does not dominate fouling when casein is present.•Calcium phosphate particles act as binding agents for fouling to occur.
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•Plant protein-based infant formulas (IFs) can be produced close to a milk-reference.•The protein source has an impact on the in vitro digestibility of IFs.•Pea and faba bean IFs ...showed in vitro digestibility close to a milk-reference.•Rice and potato IFs showed lower in vitro digestibility compared to a milk-reference.
Infant formulas (IFs) are the key nutritional source for infants who cannot be breastfed. There is currently a growing interest in these sensitive products in order to control their quality and to design their composition with regard to nutritional balance. In a context of sustainable development and increasing growth of the world population, it seems essential to search for alternative to animal protein in food today. Plant proteins offer interesting nutritional and functional benefits thanks to the latest improvement through research and development. In this context, five model IFs were developed with identical composition, except that 50% of the proteins were either whey proteins in the “milk-reference IF”, pea, faba bean, rice or potato proteins in the four “plant IFs” tested. The IFs were evaluated using an in vitro static gastro-intestinal model simulating infant conditions. The protein hydrolysis degree (DH) and the amino acid bioaccessibility (AAB) were used as indicators of protein digestibility. Results showed that both DH and AAB were very similar between the milk-reference IF, pea and faba bean IFs, but significantly lower for the rice and potato IFs. This study provides new insights into the impact of protein sources on IF digestibility.
Caking of lactose: A critical review Carpin, M.; Bertelsen, H.; Bech, J.K. ...
Trends in food science & technology,
07/2016, Letnik:
53
Journal Article
Recenzirano
Caking is a recurrent problem in various industries, whether it occurs during the production, storage or transport of powders. Caked powder results in longer processing times and decreased product ...quality, leading to significant economic loss. Several caking mechanisms have been described in the literature. However, they are often difficult to take into account in an industrial context, given the many parameters which influence the overall caking phenomenon.
This review describes the three relevant caking mechanisms for food powders in general. Focussing on predominantly crystalline lactose powder, we discuss how each of these mechanisms can explain caking and be prevented in the industrial context. The second part of this paper presents a critical review of the methods used to characterise caking to date.
The presence of amorphous material and other impurities must be assessed in crystalline lactose powders, as they can trigger amorphous and humidity caking. Particle size distribution is another key parameter requiring control as it can encourage caking through enhancement of particle interactions. In general, preventing caking in food powders can only be achieved by a thorough understanding of the production process and storage conditions. Moreover, the characterisation of caking remains a challenge as most methods published in the literature do not fit the needs of the food industry. The real demand is for a reliable method to predict caking which would be rapid and easy enough to be applied to each batch for quality control.
•The amorphous content in lactose powder has to be controlled to avoid caking.•Impurities and small particles encourage caking.•Mechanical pressure on the powder needs to be taken into account.•A universally applicable method to prevent caking is not feasible.
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•Numerical simulation of mixing in a human duodenum featuring circular folds.•Tracking evolving concentration and mixing level distributions under segmentation.•Mixing intensification ...by prominent vortices with high velocity and shear rate.•Promoting mixing by tall and slim folds with enlarged segmentation amplitude, frequency and wavelength.
The inner wall of the intestine has multiscale structures whose roles, beyond the increase of surface area for absorption, are yet to be discovered. In this study, the mixing process in a human duodenum with circular folds, driven by segmentation contraction, was simulated using a multiphysics model, making it possible to track the evolution of mixing level distributions and enabling quantitative evaluation of the structural role of folds in mixing intensification. It was found that, in a laminar flow regime, circular folds intensify both radial and axial mixing by synergistically offering prominent and long-lasting swirls/vortices, high fluid velocity and high shear rates. Tall and slim folds with enlarged segmentation amplitude, frequency and wavelength can enhance mixing. The maximum enhancement ratio can reach 6.18 under the investigated conditions. These findings will also be valuable for the improved design of biomimetic soft-elastic reactors for the chemical and pharmaceutical industries.
In casein micelle (CM), Ca is either precipitated in the colloidal calcium phosphate (CCP) stabilized by clusters of phosphoserine (SEP) residues, or is directly bound to SEP (or glutamic and ...aspartic acids) of caseins without inorganic phosphate. However, it is currently not possible to titrate separately the different micellar Ca forms, making it difficult to assess their respective importance for CM properties and behavior. Both Ca2+ and Mg2+ have the same binding constants with SEP. Moreover, MgHPO4 is more soluble than CaHPO4, and its natural concentration in milk is lower. Thus, upon addition of MgCl2, Mg is mainly exchanged with CM in the bound form, whereas upon addition of CaCl2, Ca is mainly exchanged in the precipitated form. Our objective was to assess the role of the 2 forms of micellar cations (bound and precipitated) during the enzymatic coagulation of cow milk. Magnesium chloride, CaCl2, or KCl (10 mM) were added to milk and pH was adjusted to 6.6 after overnight equilibration. The KCl-supplemented milk was a positive control to assess the effect of the increased ionic strength after MgCl2 and CaCl2 addition. Mineral partition between soluble and colloidal phases after salt addition was assessed both experimentally and by using computer simulation. Enzymatic coagulation was proceeded at 30°C. Hydrolysis of κ-casein was followed by the quantitative determination of caseinomacropeptide released by RP-HPLC, aggregation of para-κ-casein micelles was measured through the evolution of backscattering properties of milk and the gel time and gel firming kinetics were determined using a Chymograph (Chr. Hansen, Horsholm, Denmark). The KCl addition did not affect mineral partition. As expected, CaCl2 addition mainly increased the CCP content, whereas the addition of MgCl2 mainly increased the bound divalent cations content. The kinetics of κ-casein hydrolysis was slowed down after CaCl2 and MgCl2 addition, and was negatively correlated with the concentration of divalent cations in the soluble phase of milk. Aggregation and gel firming curves plotted versus the progress of κ-casein hydrolysis were similar for both CaCl2- and MgCl2-supplemented milk. In view of the dual-binding model for CM assembly, this means that both Ca forms reduce electronegative repulsions between para-micelles by specific charge shielding. Inclusion of 2 Ca forms in structural models for CM allows a more detailed comprehension of how mineral equilibria affect CM properties.
The evaporation of a colloidal dispersion is characterized by solute accumulation at the air-liquid interface, leading to the gradual formation of a gelled skin. The development of this layer, from ...preliminary colloid deposit to complete solidification, affects overall drying process and final sample morphology. Despite, progress in the last decades, the mechanisms governing skin formation in drying colloidal suspensions have not yet been fully clarified, especially in complex polydisperse systems. In this work, we investigate this open question in droplets consisting of the two main milk proteins, i.e. whey proteins and casein micelles. Using complementary experimental approaches, we evaluate skin rheological behavior during the different stages of the evaporation process, highlighting the specific role of each colloid. Our results are interpreted in the light of drying-induced protein stratification, whose evidence is provided by the direct observation of dry skin section structure. This study contributes to the understanding of the competitive drying mechanisms occurring in binary colloidal systems. Moreover, our outcomes are potentially valuable for the optimization of milk powder production in dairy industry.
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The concept of Metzner and Otto was initially developed for correlating power measurements in stirred vessels for shear-thinning fluids in the laminar regime with regard to those obtained for ...Newtonian liquids. To get this overlap, Metzner and Otto postulated and determined an “effective shear rate” which was proportional to the rotational speed of the impeller Although it was not based on a strong theoretical background, it was rapidly admitted as a practical engineering approach and was extended for seeking out a “Newtonian correspondence” with non-Newtonian results (i.e. different classes of fluids). This was applied in a variety of tank processes even for predicting heat transfer or mixing time, which stretches far away from the frame initially envisaged by Metzner and Otto themselves. This paper aimed to show how dimensional analysis offers a theoretically founded framework to address this issue without the experimental determination of effective quantities. This work also aimed to enlarge the underlying questions to any process in which a variable material property exists and impacts the process. For that purpose, the pending questions of Metzner and Otto concept were first reminded (i.e. dependence of the Metzner–Otto constant to rheological parameters, physical meaning of the effective shear rate, etc.). Then, the theoretical background underlying the dimensional analysis was described and applied to the case of variable material properties (including non-Newtonian fluids), by introducing in particular the concept of material similarity. Finally, two examples were proposed to demonstrate how the rigorous framework associated with the dimensional analysis is a powerful method to exceed the concept of Metzner and Otto and can be adapted beyond the Ostwald–de Waele power law model to a wide range of non-Newtonian fluids in various processes, without being restricted to batch reactor and laminar regime.
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•A simple, generic, and cost-effective method for mixing performance evaluation.•Tracking of global and localized mixing performance in a soft elastic reactor.•Mixing level ...characterized by the “distance” away from the ideally mixed state.•Quantification of mixing time, spatial and frequency distributions of mixing level.
An image analysis based method is developed in this work to quantitatively evaluate the mixing performance of a special soft-elastic reactor (SER), which promotes mixing through elastic wall movement. The source data collected are RGB values in each pixel of consecutive colour images taken by a CCD camera. The method can determine global indicators such as the average mixing level (i.e., the degree of homogeneity, uniquely characterized by the “distance” away from the ideally mixed state) and the mixing time. More importantly, it allows tracking of localized mixing performance throughout the entire mixing process by quantifying spatial and frequency-domain distributions of the mixing level. This simple, generic, and cost-effective method should be a powerful tool for mixing performance evaluation of most reactors with a variety of mixing mechanisms. It can be readily applied in the future to improved design and optimized operation of the SER.
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