A. Hakansson

Hydrodynamic radius determination with asymmetrical flow field-flow fractionation using decaying cross-flows. Part I. A theoretical approach

Direct determination of hydrodynamic radius from retention time is an advantage of the field-flow fractionation techniques. However, this is not always completely straight forward since non-idealities exist and assumptions have been made in deriving the retention equations. In this study we investigate the effect on accuracy from two factors: (1) level of sophistication of the equations used to determine channel height from a calibration experiment and (2) the influence of secondary relaxation on the accuracy of hydrodynamic radius determination. A new improved technique for estimating the channel height from calibration experiments is suggested. It is concluded that severe systematic error can arise if the most common channel height equations are used and an alternative more rigorous approach is described. For secondary relaxation it is concluded that this effect increases with the cross-flow decay rate. The secondary relaxation effect is quantified for different conditions. This is part one of two. In the second part the determination of hydrodynamic radius are evaluated experimentally under similar conditions.

Revealing the Size, Conformation, and Shape of Casein Micelles and Aggregates with Asymmetrical Flow Field-Flow Fractionation and Multiangle Light Scattering

Casein (CN) micelles are naturally occurring colloidal protein aggregates present in a dispersed state in milk. In this paper we aim to obtain a detailed description of physicochemical properties of CN micelles over the entire size distribution using asymmetrical flow field-flow fractionation (AsFlFFF) connected to multiangle light scattering (MALS) and refractive index (RI) detection. Conclusions are drawn on the colloidal level regarding shape and conformation by comparison with models of colloidal particles. By using AsFlFFF-MALS-RI, it is concluded that the CN micelles are highly polydisperse with an average rms radius and hydrodynamic radius of 177 and 116 nm, respectively. The results show that the majority of CN micelles have a spherical shape, whereas a low concentration exists of larger and elongated aggregates. By comparison with models of aggregates of colloidal particles, the aggregates are shown to be anisotropic, e.g., aggregating linearly (threadlike) or in a sheet, rather than forming randomly spherical clusters. The results show that the characterization of colloidal dispersions with AsFlFFF-MALS-RI and the comparison with theoretical models are of a general character and, thus, of fundamental importance for colloidal dispersions.

Hydrodynamic radius determination with asymmetrical flow field-flow fractionation using decaying cross-flows. Part II. Experimental evaluation

In this study we investigate the effect of programmed cross-flows on the error in the hydrodynamic radii (r(h)) determination with asymmetrical flow field-flow fractionation (AsFlFFF). Three different standard polystyrene particles (nominal radii of 30 and 40 and 50 nm) are fractionated with exponentially and linearly decaying cross-flows with different decay rates. Hydrodynamic radii are calculated according to retention theory including steric effects. Rapid decay is expected to give rise to systematic deviations in r(h) determination. The error in r(h) was found to be small when decay rates with half-lives longer than 6 min were used, whereas steeper decays could give rise to errors as high as 16% of the particle size. The error is often explained in terms of secondary relaxation. However, comparisons show that experimental errors are significantly larger than what would be expected due to secondary relaxation, suggesting that other factors also have to be considered in order to fully understand deviations for rapidly decaying cross-flow.

From diets to foods: using linear programming to formulate a nutritious, minimum-cost porridge mix for children aged 1 to 2 years.

Background Linear programming has been used extensively as a tool for nutritional recommendations. Extending the methodology to food formulation presents new challenges, since not all combinations of nutritious ingredients will produce an acceptable food. Furthermore, it would help in implementation and in ensuring the feasibility of the suggested recommendations. Objective To extend the previously used linear programming methodology from diet optimization to food formulation using consistency constraints. In addition, to exemplify usability using the case of a porridge mix formulation for emergency situations in rural Mozambique. Methods The linear programming method was extended with a consistency constraint based on previously published empirical studies on swelling of starch in soft porridges. The new method was exemplified using the formulation of a nutritious, minimum-cost porridge mix for children aged 1 to 2 years for use as a complete relief food, based primarily on local ingredients, in rural Mozambique. Results A nutritious porridge fulfilling the consistency constraints was found; however, the minimum cost was unfeasible with local ingredients only. This illustrates the challenges in formulating nutritious yet economically feasible foods from local ingredients. The high cost was caused by the high cost of mineral-rich foods. A nutritious, low-cost porridge that fulfills the consistency constraints was obtained by including supplements of zinc and calcium salts as ingredients. Conclusions The optimizations were successful in fulfilling all constraints and provided a feasible porridge, showing that the extended constrained linear programming methodology provides a systematic tool for designing nutritious foods.

A method for estimating effective coalescence rates during emulsification from oil transfer experiments.

The Oil Transfer Technique (OTT) was developed by Taisne et al. [1] to measure coalescence during emulsification and has been applied since in several studies. One of the main drawbacks of this technique is that it only gives a qualitative measure of coalescence. This paper proposes a new evaluation method of OTT experimental results for estimating qualitative coalescence rates, e.g. for investigating the scaling of coalescence with emulsification parameters (such as homogenizing pressure, and emulsifier concentration). The method is based on comparison with simulated OTT experiments using bivariate Population Balance Equation models. Simulations have been performed under a wide variety of conditions in order to investigate the influence of assumptions on coalescence and fragmentation kernels. These investigations show that the scaling of coalescence rates could be determined accurately when the scaling of efficient residence time of drops in the active region of homogenization is known. The proposed evaluation method is also exemplified by analyzing OTT data from two previously published studies.

Has it become increasingly expensive to follow a nutritious diet? Insights from a new price index for nutritious diets in Sweden 1980-2012

Background Health-related illnesses such as obesity and diabetes continue to increase, particularly in groups of low socioeconomic status. The increasing cost of nutritious food has been suggested as an explanation. Objective To construct a price index describing the cost of a diet adhering to nutritional recommendations for a rational and knowledgeable consumer and, furthermore, to investigate which nutrients have become more expensive to obtain over time. Methods Linear programming and goal programming were used to calculate two optimal and nutritious diets for each year in the interval under different assumptions. The first model describes the rational choice of a cost-minimizing consumer; the second, the choice of a consumer trying to deviate as little as possible from average consumption. Shadow price analysis was used to investigate how nutrients contribute to the diet cost. Results The cost of a diet adhering to nutritional recommendations has not increased more than general food prices in Sweden between 1980 and 2012. However, following nutrient recommendations increases the diet cost even for a rational consumer, particularly for vitamin D, iron, and selenium. The cost of adhering to the vitamin D recommendation has increased faster than the general food prices. Conclusions Not adhering to recommendations (especially those for vitamin D) offers an opportunity for consumers to lower the diet cost. However, the cost of nutritious diets has not increased more than the cost of food in general between 1980 and 2012 in Sweden.

VELOCITY MEASUREMENTS OF TURBULENT TWO-PHASE FLOW IN A HIGH-PRESSURE HOMOGENIZER MODEL

The effect of disperse phase volume fraction on the turbulence in a scale model of a high-pressure homogenizer was studied experimentally. Velocity fields of the continuous phase were measured using particle image velocimetry. Refractive index matching combined with digital filtering enabled measurement with disperse phase present. Geometry and physical properties were carefully scaled in order to ensure turbulent flow and disperse phase modulation comparable to that of a technical high-pressure homogenizer. The results show a widening of the jet downstream of the gap and increased Reynolds stresses in the region of high turbulence intensity. This is consistent with previous experiments under similar conditions. Furthermore, the spectra of turbulent kinetic energy were investigated, indicating that the increase in turbulent kinetic energy is mainly due to an increase in energy of eddies of large length scales.

Fabrication of nanoemulsions by high-pressure valve homogenization

High-pressure valve homogenization is a standard technique for nanoemulsion formation in low-viscosity formulations. It is applied extensively in industrial applications and in academic research. T ...

General principles of nanoemulsion formation by high-energy mechanical methods

Emulsion formation is a challenging task. Breaking a large drop into smaller fragments gives rise to an increase in the total interfacial area and, consequently, in the interfacial energy. External ...

Home cooking trends and dietary illness: nutritional compliance of recipes in a Swedish food magazine 1970–2010

Aims: To investigate the trends in nutritional compliance of recipes from a Swedish food magazine to offer a perspective on the effects of home cooking on public health. Methods: The nutritional content of 654 recipes from magazine issues published in 1970, 1980, 2000, and 2010 were collected. The recipes were analyzed for macronutrient energy contribution, sodium content, and composition. Results: The recipes were in poor agreement with nutritional recommendations (excessive fat, protein, and sodium and insufficient carbohydrate and fiber content). Significant changes between 1970 and 2010 were the increased calorific contribution of fat (from 38 to 46%) and the reduced contribution of proteins (from 27 to 21%). The calorific contribution from spreads, cheese, bread, and fruit and vegetables have increased significantly, whereas the contribution from meat has decreased significantly. Conclusions: The poor nutritional compliance identified in this work indicates that consumers using the recipes as norms for home cooking risk following an unhealthy diet. This might have adverse effects on public health. However, the recipes have not become less compliant over time and therefore the data do not show an adverse trend in these norms.