Food-emulsions often have high volume fractions of dispersed phase and are thus expected to show coalescence during emulsification, however, food-emulsion coalescence is difficult to measure in homogenizer equipment. This study experimentally estimates the rates of fragmentation and coalescence in a high viscosity and high volume fraction model emulsion subjected to pilot-scale rotor-stator mixing in order to quantify the relative effect of coalescence and discuss the mechanism of coalescence during batch processing of high-fat emulsion foods. Rate constants of both processes are estimated using a previously suggested method relying on parameter fitting from the dynamic evolution of the total number of emulsion drops (Hounslow and Ni, 2004). The results show substantial coalescence taking place. Scaling of rates with respect to rotor tip speed suggests coalescence and fragmentation controlled by a turbulent viscous mechanism. (C) 2015 Elsevier Ltd. All rights reserved.
Although originally developed for fat globule disruption in dairy applications, high-pressure homogenizers are extensively used in other food processing applications. Two newer applications are in forming nanoemulsion for delivering supplemented nutrients and as a preservation technique, both using higher pressures than traditional applications. This has raised concern that friction heat created in the homogenizer causes thermal degradation to temperature sensitive molecules such as nutrients. This contribution uses a numerical model to give insight into temperature profiles for drops in a homogenizer valve and investigates when homogenization at elevated pressures is expected to cause thermal degradation. A fast method for estimating the extent of degradation for a given application is also proposed. It is concluded that no thermal degradation is expected inside the valve, almost regardless of operating conditions, due to the short residence time. Provided that cooling is applied after the homogenizer, degradation downstream of the valve can also be avoided.
Emulsification is a common process in the production in many non-solid foods. These food-emulsions often have high disperse phase volume fractions and slow emulsifier dynamics, giving rise to substantial coalescence during emulsification. Optimal design and operation of food-emulsification requires experimental methods to study how emulsification in general and coalescence in particular progresses under different conditions. Methods for coalescence quantification during emulsification has been suggested in literature but they are rarely used in food-emulsification research. This contribution offers a critical review of the different methods that have been suggested with special emphasis on their applicability to technical food-emulsification. The methods are critically compared in terms of design limitations, degree of quantification and applicability. A state-of-the-art in the form of two methods is identified and guidelines for their application are suggested. (C) 2016 Elsevier Ltd. All rights reserved.
The high-pressure homogenizer (HPH) is used extensively in the processing of non-solid foods. Food researchers and producers use HPHs of different scales, from laboratory-scale (∼10 L/h) to the largest production-scale machines (∼50 000 L/h). Hence, the process design and interpretation of academic findings regarding industrial condition requires an understanding of differences between scales. This contribution uses theoretical calculations to compare the hydrodynamics of the different scales and interpret differences in the mechanism of drop-breakup.
Results indicate substantial differences between HPHs of different scales. The laboratory-scale HPH operates in the laminar regime whereas the production-scale is in the fully turbulent regime. The smaller scale machines are also less prone to cavitation and differ in their pressure profiles. This suggest that the HPHs of different scales should be seen as principally different emulsification processes. Conclusions on the effect or functionality of a HPH can therefore not readily be translate between scales.
Cavitation is common in high-pressure homogenizers, and has severe negative effects such as noise and mechanical wear, but may also have a beneficial effect in promoting fragmentation. Greater knowledge concerning cavitation in the homogenizer valve is thus important in optimizing the design and utilization of emulsification equipment. The aim of this study was to locate the region of cavitation and to study its dependence on operating conditions. The cavitation in a model of a high-pressure homogenizer is examined in detail. A visualization technique, based on the scattering of light from cavitation bubbles in the flow, has been developed, tested and compared to acoustical measurements. Intense light scattering was observed in the gap of the valve, indicating cavitation bubble growth as well as collapse inside the gap. The scattering intensity increased with increasing inlet pressure and decreased with increasing back pressure.
The emulsification process is primarily determined by the rate of fragmentation and coalescence of emulsion drops. However, there is presently no fast, reliable method for measuring these rates for pilot and production scale high pressure homogenizers.
In this paper a method for simultaneous estimating fragmentation and coalescence is developed and tested based on the work of Hounslow and Ni (2004). Kernel type as well as rate extraction is performed based on the development of the total number of drops when recirculation an emulsion through a high-pressure homogenizer. The method has many advantages such as not requiring any specialty chemicals or complex analytical equipment. All measurements are made using laser diffraction equipment that is already standard for analyzing the effect of homogenization.
Experiments show fragmentation and coalescence rates close to that seen in previous studies and the scaling of coalescence rate and fragmentation with homogenizing pressure is in accordance with theory.