Coalescence, cracking, and crack healing in drying dispersion
Kooij, H.M. van der; Kool, R.H.M. de; Gucht, J. van der; Sprakel, J.H.B. - \ 2015
Langmuir 31 (2015)15. - ISSN 0743-7463 - p. 4419 - 4428.
latex film formation - glass-transition temperature - polymer diffusion - deformation - polystyrene - interfaces - coatings - surface - modes - bulk
The formation of a uniform film from a polymer dispersion is a complex phenomenon involving the interplay of many processes: evaporation and resulting fluid flows through confined geometries, particle packing and deformation, coalescence, and cracking. Understanding this multidimensional problem has proven challenging, precluding a clear understanding of film formation to date. This is especially true for drying dispersion droplets, where the particular geometry introduces additional complexity such as lateral flow toward the droplet periphery. We study the drying of these droplets using a simplified approach in which we systematically vary a single parameter: the glass transition temperature (Tg) of the polymer. We combine optical with scanning electron microscopy to elucidate these processes from the macroscopic down to the single-particle level, both qualitatively and quantitatively, over times ranging from seconds to days. Our results indicate that the polymer Tg has a marked influence on the time evolution of particle deformation and coalescence, giving rise to a distinct and sudden cracking transition. Moreover, in cracked droplets it affects the frequently overlooked time scale of crack healing, giving rise to a second transition from self-healing to permanently cracked droplets. These findings are in line with the classical Routh–Russel model for film formation yet extend its scope from particle-level dynamics to long-range polymer flow.
Interactions between formulation and spray drying conditions related to survival of Lactobacillus plantarum WCFS1
Perdana, J.A. ; Fox, M.B. ; Siwei, C. ; Boom, R.M. ; Schutyser, M.A.I. - \ 2014
Food Research International 56 (2014). - ISSN 0963-9969 - p. 9 - 17.
glass-transition temperature - membrane phase-behavior - lactic-acid bacteria - flow-cytometry - industrial applications - dairy ingredients - osmotic-stress - water activity - rhamnosus gg - gel phase
Protective solid carriers are commonly added to probiotic cultures prior to drying. Their formulation is not trivial and depends on the drying conditions applied. In this study, we systematically investigated the influence of formulation parameters on the survival of Lactobacillus plantarum WCFS1 after drying. Low molecular weight carbohydrates (less than 2 kDa) with high glass transition temperatures provided the highest level of protection at both low (25 degrees C) and high (50 degrees C or higher) drying temperatures. Low molecular weight carbohydrates may provide stabilization by closely interacting with the lipid bilayer of the cell membranes. Meanwhile, carbohydrates with high glass transition temperatures probably provide stabilization via fixation of the cells in a glassy powder. Furthermore, adequate amounts of solid carrier are required to sufficiently stabilize the cells during drying. During drying, crystallization of solid carriers may occur. Depending on the crystal geometry, crystallization can be either beneficial (e.g. with mannitol or sorbitol) or detrimental (e.g. with lactose) to cell survival. Finally, the effect of formulation on cell viability during storage was studied. A decimal reduction time of approximately 300 days was observed when spray dried L. plantarum WCFS1 was stored at temperatures below 40 degrees C. The outcome of this study was used as a basis to construct a generalized diagram to indicate the combinations of formulation and drying conditions to maximally retain viability and operate dryers at high efficiency. (C) 2013 Elsevier Ltd. All rights reserved.
Measuring and modelling of diffusivities in carbohydrate-rich matrices during thin film drying
Perdana, J.A. ; Sman, R.G.M. van der; Fox, M.B. ; Boom, R.M. ; Schutyser, M.A.I. - \ 2014
Journal of Food Engineering 122 (2014). - ISSN 0260-8774 - p. 38 - 47.
glass-transition temperature - free-volume theory - lactobacillus-plantarum - diffusion-coefficients - sucrose solutions - moisture-content - solvent systems - sugar solutions - water - droplet
Knowledge about moisture diffusivity in solid matrices is a key for understanding drying behaviour of for example probiotic or enzymatic formulations. This paper presents an experimental procedure to determine moisture diffusivity on the basis of thin film drying and gravimetric analysis in a Dynamic Vapour Sorption (DVS) system. The extraction of moisture diffusivity is based on the “regular regime approach”. The method was explored and verified for its assumptions. It provided insight in the effect of moisture content and temperature on moisture diffusivity. Moreover, it was found that moisture diffusivity in different carbohydrate systems was similar and decreased with moisture content. The latter was explained by similar molecular interactions in carbohydrate systems and formation of a percolating network at low moisture content that affects water mobility. Subsequently, measured moisture diffusivities were compared to model predictions based on the generalised Darken relation. It was found that predicted moisture diffusivities were in fair agreement with these, including the effect of moisture content and temperature on moisture diffusivity. At low moisture content the model overestimated the sensitivity of moisture diffusivity towards temperature. This was explained by the fact that the different water–solid interactions at lower moisture content (including relaxation behaviour in the glassy state) are not considered in the modelling. Finally, the methodology was successfully evaluated to other solid matrices such as glycerol, skimmed milk and casein, providing different moisture diffusivities as function of moisture content.
Moisture sorption in mixtures of biopolymer, disaccharides and water
Sman, R.G.M. van der - \ 2013
Food Hydrocolloids 32 (2013)1. - ISSN 0268-005X - p. 186 - 194.
glass-transition temperature - frozen state transitions - vapor sorption - poly(ethylene glycol) - amorphous mixtures - sucrose - behavior - prediction - polymers - crystallization
The moisture sorption of ternary mixtures of biopolymer, sugar and water is investigated by means of the Free-Volume-Flory-Huggins (FVFH) theory. The earlier FVFH theory developed for binary mixtures of biopolymer/water and sugar/water has to be modified to account for two effects: 1) the change in the glass temperature due to the non-ideal mixing of biopolymer and 2) inhibition of self-association of the polymer if the mixture is quenched very fast into the glassy state. The modified FVFH theory forms a good basis for predicting moisture sorption for quaternary mixtures of biopolymers, di-, mono-saccharides and water - which can be viewed as a model for vegetables and fruits. (c) 2013 Elsevier Ltd. All rights reserved.
Structuring of expanded snacks based on patato ingredients : a review
Sman, R.G.M. van der; Broeze, J. - \ 2013
Journal of Food Engineering 114 (2013)4. - ISSN 0260-8774 - p. 413 - 425.
glass-transition temperature - damaged starch granules - physical-properties - extruded products - bubble-growth - semicrystalline polymers - rheological properties - extrusion behavior - sodium-chloride - foaming process
In this paper we review the current knowledge on the structuring via bubble expansion of starchy snacks, which are formulated on the basis of potato ingredients. These snacks are rarely discussed in scientific literature, but there are a scant number of patents dealing with various formulations and process descriptions. The general trends in the snack processing, we have described in a formal way using the Complex Dispersed Systems notation, augmented with a depiction of the processing pathway in the supplemented state diagram of starch. With this general framework in mind, we have compared the information given in the patents with scientific literature on cereal-based snacks. Based on this comparison we have formulated hypotheses about the functionality of the various ingredients with respect to the structuring of the potato snacks.
Single droplet drying for optimal spray drying of enzymes and probiotics
Schutyser, M.A.I. ; Perdana, J.A. ; Boom, R.M. - \ 2012
Trends in Food Science and Technology 27 (2012)2. - ISSN 0924-2244 - p. 73 - 82.
acid starter cultures - glass-transition temperature - inactivation kinetics - enthalpy relaxation - water activity - milk droplets - foods - state - mechanisms - stability
Spray drying is a mild and cost-effective convective drying method. It can be applied to stabilise heat sensitive ingredients, such as enzymes and probiotic bacteria, albeit in industrial practice for example freeze drying or freezing are often preferred. The reason is that optimum drying conditions and tailored matrix formulations are required to avoid severe heat damage leading to loss in enzyme activity or reduced survival of bacteria. An overview is provided on the use of protective carbohydrate-rich formulations in the spray drying of enzymes and probiotics. Subsequently, single droplet drying experimentation methods are reviewed for mapping drying trajectories of individual droplets. The advantage of these is to provide insight in inactivation kinetics of enzymes and probiotics and thus contribute to unravelling of stabilisation mechanisms. Finally, it is shown that detailed modelling of single droplet drying and insight in micro-structural changes during drying can be complementary to the experimental single droplet approaches.
Relations between sensorial crispness and molecular mobility of model bread crust and its main components as measured by PTA, DSC and NMR
Nieuwenhuijzen, N.H. van; Tromp, R.H. ; Mitchell, J.R. ; Primo-Martin, C. ; Hamer, R.J. ; Vliet, T. van - \ 2010
Food Research International 43 (2010)1. - ISSN 0963-9969 - p. 342 - 349.
glass-transition temperature - wheat-starch - fracture-behavior - pulsed h-1-nmr - water-content - gluten - foods - state
Consumer appreciation of brittle cellular foods, like bread crusts, depends on textural properties such as crispness. This crispy character is lost above a certain water activity. It is not known what exactly is happening in these crusts when water enters. So is it unclear whether it is the change in the starch or the gluten that initiates the loss of crispness with ageing time. In this paper the effect of water on the glass transition of model bread crusts was studied using two complementary techniques: phase transition analysis (PTA) and temperature modulated differential scanning calorimetry (TMDSC). The mobility of water was studied with nuclear magnetic resonance (NMR). The results were compared with sensory data. Bread crusts prepared with different types of flour were tested to evaluate the effect of flour composition on the crispness of model crusts equilibrated at different relative humidities. In addition the single flour components starch and gluten were studied. Sensory crispness scores decreased with increasing aw from 0.55 upwards. At aw 0.70 sensory crispness was completely lost. Both DSC and PTA showed a transition point at an aw of 0.70-0.75. NMR gave a transition point in the mobility of the protons of water at aw 0.58. This supports the hypothesis that loss of crispness starts as a result of processes at a molecular level, before the macroscopic glass transition. This also suggests that the presence of water that is not directly attached to the solid matrix causes the loss of crispness at low aw. At higher aw increased mobility of the macromolecules will start to play a role. NMR experiments with the separate flour components indicate that the T2 transition point in starch samples occurs at a lower RH than for gluten. This could imply that starch loses crispness at lower aw than gluten. Increased mobility of small components and side chains might induce increased energy dissipation upon deformation of the material resulting in less available energy for fracture propagation and with that in a less crispy product.