Measurement of effective diffusion coefficients in dairy powders by confocal microscopy and sorption kinetic profiles
Maidannyk, Valentyn ; Lutjes, Eva ; Montgomery, Sharon ; McCarthy, Noel ; Auty, Mark A.E. - \ 2019
Food Structure 20 (2019). - ISSN 2213-3291
Confocal - Diffusion - Food powders - Microscopy - Rehydration
A new method for the visualisation and determination of local diffusion coefficients in dairy powders is described based on real-time visualisation of penetration of fluorescent dyes into individual particles of spray-dried dairy powders including skim milk powder, milk protein concentrate and whey protein isolate. The rehydration process was controlled by adding polyethylene glycol (PEG) as a viscosity modifier to the aqueous phase in ratios of 1:0, 1:1, 1:3 and 1:4 aqueous rhodamine to PEG, respectively. Real-time effective diffusivity values were obtained from analysis of confocal laser scanning microscope images. Particle size was measured optically. Results indicated that for all dairy powders, rehydration rates were highly dependent on particle size. Effective diffusivity increased linearly with increasing particle size and average effective diffusivity of the liquid phase was calculated for all particle size distributions using this dependence. The Guggenheim-Anderson-de Boer (GAB) water sorption relationship was used to model water sorption isotherms over a broad range of water activities. Vapour phase systems had significantly higher effective diffusivity than liquid phase systems. The results obtained by this new method is broadly in agreement with previously published works, suggesting this new method may be used to measure the hydration of individual powder particles.
Effect of pore size distribution and particle size of porous metal oxides on phosphate adsorption capacity and kinetics
Suresh Kumar, Prashanth ; Korving, Leon ; Keesman, Karel J. ; Loosdrecht, Mark C.M. van; Witkamp, Geert Jan - \ 2019
Chemical Engineering Journal 358 (2019). - ISSN 1385-8947 - p. 160 - 169.
Adsorption kinetics - Diffusion - Particle size - Phosphate adsorption - Pore size distribution - Porous metal oxide
Phosphate is a vital nutrient but its presence in surface waters even at very low concentrations can lead to eutrophication. Adsorption is often suggested as a step for reducing phosphate down to very low concentrations. Porous metal oxides can be used as granular adsorbents that have a high surface area and hence a high adsorption capacity. But from a practical point of view, these adsorbents also need to have good adsorption kinetics. The surface area of such adsorbents comes from pores of varying pore size and the pore size distribution (PSD) of the adsorbents can affect the phosphate adsorption kinetics. In this study, the PSD of 4 different adsorbents was correlated with their phosphate adsorption kinetics. The adsorbents based on iron and aluminium (hydr)oxide were grinded and the adsorption performance was studied as a function of their particle size. This was done to identify diffusion limitations due to the PSD of the adsorbents. The phosphate adsorption kinetics were similar for small particles of all the adsorbents. For larger particles, the adsorbents having pores larger than 10 nm (FSP and DD6) showed faster adsorption than adsorbents with smaller pores (GEH and CFH). Even though micropores (pores < 2 nm) contributed to a higher portion of the adsorbent surface area, pores bigger than 10 nm were needed to increase the rate of adsorption.
Analysis and modeling of enhanced green fluorescent protein diffusivity in whey protein gels
Luo, Qi ; Sewalt, Erik ; Borst, Jan Willem ; Westphal, Adrie H. ; Boom, Remko M. ; Janssen, Anja E.M. - \ 2019
Food Research International 120 (2019). - ISSN 0963-9969 - p. 449 - 455.
Diffusion - FCS - Gastric digestion - GFP - Modeling - Pepsin - Whey protein gel
During gastric digestion, hydrolysis of proteins by pepsin contributes largely to the breakdown of protein-rich food. We hypothesized that the effect of pepsin is limited by its diffusivity, which is co-determined by the food structure and the local pH in the food during digestion. To investigate the principle mechanism of enzyme diffusion in food matrices, we used enhanced green fluorescent protein (EGFP) as probe to study the diffusivity of proteins in whey protein isolate gels, using fluorescence correlation spectroscopy (FCS). Gels made with different ionic strength showed distinctive elastic moduli but did not show differences in diffusivity of EGFP. Some models for diffusion in hydrogels yield good description of the obtained data, and can approximate the enzyme diffusion in diverse food matrices. However, the enzyme pepsin is more complicated than the probe EGFP, to yield more accurate predictions, electrostatic and enzyme-substrate interaction also need to be considered.
Lipase diffusion in oil-filled, alginate micro- and macrobeads
Leusden, P. van; Hartog, G.J.M. den; Bast, A. ; Postema, M. ; Linden, E. van der; Sagis, L.M.C. - \ 2018
Food Hydrocolloids 85 (2018). - ISSN 0268-005X - p. 242 - 247.
Oil digestion - Microbeads - Encapsulation - Diffusion - Maxwell-Cattaneo equation
Triglycerides, which are broken down in the lower part of the intestinal tract, give a stronger ileal brake feedback, resulting in a feeling of satiety and causing people to eat less. The digestion of triglycerides into fatty acids by lipase in the intestine can be delayed by encapsulating oil droplets. In this study the release of fatty acids and oil droplet breakdown in a simulated intestinal system was investigated, for oil droplets encapsulated in alginate micro- (10.7 μm) and macrobeads (1.77 mm). It was found that fatty acid release rate was greatly decreased by encapsulating the oil droplets into an alginate matrix compared to loose droplets. Microscopic imaging of the breakdown of the oil droplets showed a sharp front moving from the bead interface to the centre of the bead, and the change in position of the front scaled linear with time. The motion of the front is well described by combining the mass balance for lipase with a Maxwell-Cattaneo type equation, for the mass flux vector. The front in microbeads seemed to move slightly slower (0.15 (±0.04) μm per minute) than for the macrobeads (0.20 (±0.02) μm per minute). The release of free fatty acids in microbeads was faster than in macrobeads, despite the slower front movement, because of the larger amount of surface area available.
Pepsin diffusivity in whey protein gels and its effect on gastric digestion
Luo, Q. ; Borst, J.W. ; Westphal, A.H. ; Boom, R.M. ; Janssen, A.E.M. - \ 2017
Food Hydrocolloids 66 (2017). - ISSN 0268-005X - p. 318 - 325.
Pepsin - GFP - FCS - Diffusion - Whey protein gel - Gastric digestion
Protein is essential to human health, but its digestion kinetics in varied structures are not yet well understood. We previously found different kinetics of protein hydrolysis in solution and in gels, and we hypothesized that the difference stemmed from the steric hindrance of gel structure to the diffusion of pepsin and its hydrolysates. To better understand the pepsin diffusivity in food matrices and its effect on digestion, we determined the diffusivity of pepsin in water and in whey protein isolate (WPI) gels by fluorescence correlation spectroscopy (FCS). We estimated the pepsin concentration gradient during digestion based on the determined diffusivity, which showed that the pepsin is constrained within a thin layer from the gel surface. Gel composition analysis confirmed this constraint: peptides as protein fragments were observed only in the first 2 mm of the WPI gels after 6 h of in vitro gastric digestion. Scanning electron microscopy indicated that pepsin loosened the microstructure of whey protein gel surfaces, which may accelerate pepsin diffusion and consequently gel surface disintegration. We conclude that the mode of whey protein gel digestion is determined by the summed effect of diffusion limitation, hydrolysis rate and microstructure transformation.
Factors affecting adoption of economic management practices in beef cattle production in Rio Grande do Sul state, Brazil
Dill, Matheus Dhein ; Emvalomatis, Grigorios ; Saatkamp, Helmut ; Rossi, João Augusto ; Pereira, Gabriel Ribas ; Barcellos, Júlio Otávio Jardim - \ 2015
Journal of Rural Studies 42 (2015). - ISSN 0743-0167 - p. 21 - 28.
Administration - Diffusion - Innovation - Livestock - Rural development - Technology
Beef cattle production in the Rio Grande do Sul State, Brazil, faces serious challenges due to low profitability and competition for alternative land uses. Despite this, many farmers have not yet adopted economic management practices as a support tool to enhance the competitiveness of their farms, due to differences related to lifestyle, values, customs, traditions and personal goals. We interviewed 73 farmers in order to understand the factors affecting the adoption of such practices. A probit model was estimated to identify farmers' characteristics, access to information, and production and economic characteristics that affect the adoption of economic management practices. Farmers with large landholdings and diversified production are less likely to adopt such practices. On the other hand, a number of factors, such as Internet access, participation in farmer associations, receiving technical assistance, number of cows bred annually, weaning rate greater than 70%, and utilization of the birth to slaughter system, positively affect the probability of adoption. Considering that few workshops and training programs on farm management are offered to farmers, the information presented in this study might be useful to motivate the development of extension programs, which take into account farmers' characteristics and, thus, achieve better results in terms of dissemination of economic management techniques.