In silico modelling of mass transfer & absorption in the human gut

AbstractAn in silico model has been developed to investigate the digestion and absorption of starch and glucose in the small intestine. The main question we are aiming to address is the relative effect of gastric empting time and luminal viscosity on the rate of glucose absorption. The results indicate that all factors have a significant effect on the amount of glucose absorbed. For low luminal viscosities (e.g. lower than 0.1 Pas) the rate of absorption is controlled by the gastric emptying time. For viscosities higher than 0.1 Pas a 10 fold increase in viscosity can result in a 4 fold decrease of glucose absorbed. Our model, with the simplifications used to develop it, indicate that for high viscosity luminal phases, gastric emptying rate is not the controlling mechanism for nutrient availability. Developing a mechanistic model could help elucidate the rate limiting steps that control the digestion process

Effect of freezing on microstructure and reconstitution of freeze-dried high solid hydrocolloid-based systems

Freeze-drying has been associated with high quality hydrocolloid-based products such as coffee. However, it is an expensive technique, and one way to reduce energy and water use is by drying concentrated systems. Controlling the ice crystal formation is important to produce final dried materials with desired microstructure and properties. This study presents the effect of freezing with and without temperature oscillations on the final microstructure and reconstitution of aerated and non-aerated freeze-dried concentrated (50 and 60% w/w) gum arabic and coffee systems. Samples were either frozen at -40 C or subjected to fluctuating temperatures between -40 and -20 C prior to drying. Thermal analysis of the systems showed lower nucleation and freezing temperatures for 50% compared to 60% solutions, as expected, and melting temperatures > -20 C. During drying, puffing of the material was observed, with appearance of a glass-like, puffed bottom layer, in particular for the 60% coffee frozen at -40 C. SEM micrographs revealed pores of dendritic, hexagonal, and circular shape, indicating voids produced by sublimation of ice crystals. Pore sizes were smaller (by 50%, of the order of 40ìm) for the 60%, than the 50% systems. Temperature fluctuations during freezing doubled the observed pore sizes and the apparent total porosity which effectively accelerated the dissolution kinetics. Aeration resulted in the appearance of air bubbles (diameter 200e1600 mm) that largely phase separated in gum arabic and resulted in faster rehydrating solids. This work demonstrates the potential of process design to control microstructural attributes and reconstitution properties of freeze-dried hydrocolloid-based products in systems with high solute concentrations

Microstructure and reconstitution of freeze-dried gum Arabic at a range of concentrations and primary drying temperatures

Freeze-drying is an energy intensive unit operation used for the production of dehydrated foods, such as instant coffee and dried fruits, and results in high sensorial, nutritional and reconstitution properties of the final products. Understanding the relationships between operating conditions and product quality is essential to design processes that are energy efficient, whilst producing high quality dried foods. In this work, the properties (microstructure and reconstitution) of freeze-dried gum arabic samples (with initial concentrations ranging between 20 and 60% solids by weight) were evaluated. The materials were dried at three different primary drying shelf temperatures, Ts (- 20, - 30 and - 40 ◦C). Sample temperatures recorded throughout freeze-drying were close to the pre-set Ts, with the exception of the 60% initial concentration system, where the sample was hotter than the shelf by 10–15 ◦C, in particular on increasing Ts. This was attributed to a combination of local temperature and pressure conditions that may have resulted in partial melting of the material. For the 20–50% systems, the properties of the freeze-dried materials were mainly affected by the initial concentration of the system, with increasing initial concentration generally resulting in lower porosities (ranging between 20 and 40%) and higher reconstitution times (ranging between 0.5 and 10min for 95% reconstitution). Pores were generally needle-shaped and <200 μm. Large (200–1800 μm), circular pores were observed in high initial concentration systems, and they were dominant in the microstructure of the freeze-dried 60% sample. The presence of these large bubbles was linked to the partial melting of the material, which enabled its expansion and puffing. For the 60% system, primary drying temperature had a profound effect on the properties of the freeze-dried solid, with samples dried at higher temperature showing higher porosity (e.g. 60–70% for Ts = -¬¬ 20◦C) and faster reconstitution rates (e.g. 3min for 95% reconstitution at Ts = - 20◦C). Overall, this study demonstrates the significance of formulation and shelf temperature on the porous structure of freeze-dried samples, which directly influences product performance

Crystallisation in concentrated systems:a modelling approach

AbstractWater crystallisation in concentrated systems has been studied using a combination of mathematical modelling and experimental work. Two different freezing models have been employed to describe primary and secondary mechanisms (i.e. non-seeded and seed-induced processes, respectively) in sucrose solutions up to 60% (w/w). Differential Scanning Calorimetry (DSC) has been employed to characterise the phase change of the binary water–sucrose system in primary processes, and the kinetic and thermodynamic parameters obtained were coupled to the heat transfer equation to obtain the product temperature distribution. A recently developed method has been also employed to measure crystal growth rates in seed-induced crystallisation systems. Simulated results for the secondary crystallisation mechanism were able to reproduce experimentally observed trends for growth rates. An evaluation of the energy consumption during freezing/crystallisation processes has been carried out to assess each mechanism performance (crystallisation will occur at temperatures approximately 20°C higher in seeded processes) considering different process conditions and product formulations (i.e. solids and air fractions)

Exploring the Role of Cereal Dietary Fiber in Digestion

Increasing the dietary fibre of staple foods such as bread is an attractive way to promote healthy eating in a large part of the population, where dietary fibre consumption is reportedly below the recommended values. However, many consumers prefer white breads, which are typically low in dietary fibre. In this work, white bread was made from two wheat cultivars with differing fibre contents. The resulting breads showed similar quality parameters (volume, specific volume, firmness, inner structure characteristics) with any differences maintained below 7%. Bread digestibility was evaluated using a novel dynamic in-vitro digestion model. Reduced digestion rates of 30% were estimated for the high-fibre white bread compared to the control. Overall, this work demonstrates the potential to produce healthy, high-fibre white breads, acceptable to consumers, and with reduced rate of starch digestion by exploiting genetic variation in dietary fibre content of wheat cultivars