Exploring the Role of Cereal Dietary Fiber in Digestion.

Increasing the dietary fiber of staple foods such as bread is an attractive way to promote healthy eating in a large part of the population, where dietary fiber consumption is reportedly below the recommended values. However, many consumers prefer white breads, which are typically low in dietary fiber. In this work, white bread was made from two wheat cultivars with differing fiber 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-fiber white bread compared to that in the control. Overall, this work demonstrates the potential to produce healthy, high-fiber white breads that are acceptable to consumers, with a reduced rate of starch digestion, by exploiting a genetic variation in the dietary fiber content of wheat cultivars.

Evaluation of dry heat treatment of soft wheat flour for the production of high ratio cakes.

An accurate method to heat treat flour samples has been used to quantify the effects of heat treatment on flour functionality. A variety of analytical methods has been used such as oscillatory rheology, rheomixer, solvent retention capacity tests, and Rapid Visco Analysis (RVA) in water and in aqueous solutions of sucrose, lactic acid, and sodium carbonate. This work supports the hypothesis that heat treatment facilitates the swelling of starch granules at elevated temperature. Results furthermore indicated improved swelling ability and increased interactions of flour polymers (in particular arabinoxylans) of heat treated flour at ambient conditions. The significant denaturation of the proteins was indicated by a lack of gluten network formation after severe heat treatments as shown by rheomixer traces. Results of these analyses were used to develop a possible cake flour specification. A method was developed using response surfaces of heat treated flour samples in the RVA using i) water and ii) 50% sucrose solution. This can uniquely characterise the heat treatment a flour sample has received and to establish a cake flour specification. This approach might be useful for the characterisation of processed samples, rather than by baking cakes. Hence, it may no longer be needed to bake a cake after flour heat treatment to assess the suitability of the flour for high ratio cake production, but 2 types of RVA tests suffice.

Digestion of starch in a dynamic small intestinal model.

PURPOSE: The rate and extent of starch digestion have been linked with important health aspects, such as control of obesity and type-2 diabetes. In vitro techniques are often used to study digestion and simulated nutrient absorption; however, the effect of gut motility is often disregarded. The present work aims at studying fundamentals of starch digestion, e.g. the effect of viscosity on digestibility, taking into account both biochemical and engineering (gut motility) parameters. METHODS: New small intestinal model (SIM) that realistically mimics gut motility (segmentation) was used to study digestibility and simulated oligosaccharide bio accessibility of (a) model starch solutions; (b) bread formulations. First, the model was compared with the rigorously mixed stirred tank reactor (STR). Then the effects of enzyme concentration/flow rate, starch concentration, and digesta viscosity (addition of guar gum) were evaluated. RESULTS: Compared to the STR, the SIM showed presence of lag phase when no digestive processes could be detected. The effects of enzyme concentration and flow rate appeared to be marginal in the region of mass transfer limited reactions. Addition of guar gum reduced simulated glucose absorption by up to 45 % in model starch solutions and by 35 % in bread formulations, indicating the importance of chyme rheology on nutrient bioaccessibility. CONCLUSIONS: Overall, the work highlights the significance of gut motility in digestive processes and offers a powerful tool in nutritional studies that, additionally to biochemical, considers engineering aspects of digestion. The potential to modulate food digestibility and nutrient bioaccessibility by altering food formulation is indicated.

Kinetic study of the thermal denaturation of a hyperthermostable extracellular α-amylase from Pyrococcus furiosus.

Hyperthermophilic enzymes are of industrial importance and interest, especially due to their denaturation kinetics at commercial sterilisation temperatures inside safety indicating time-temperature integrators (TTIs). The thermal stability and irreversible thermal inactivation of native extracellular Pyrococcus furiosus α-amylase were investigated using differential scanning calorimetry, circular dichroism and Fourier transform infrared spectroscopy. Denaturation of the amylase was irreversible above a Tm of approximately 106°C and could be described by a one-step irreversible model. The activation energy at 121°C was found to be 316kJ/mol. Using CD and FT-IR spectroscopy it was shown that folding and stability greatly increase with temperature. Under an isothermal holding temperature of 121°C, the structure of the PFA changes during denaturation from an α-helical structure, through a ß-sheet structure to an aggregated protein. Such data reinforces the use of P. furiosus α-amylase as a labile species in TTIs.

Mass transfer and nutrient absorption in a simulated model of small intestine.

There is an increasing need to understand how food formulations behave in vivo from both food and pharma industries. A number of models have been proposed for the stomach, but few are available for the other parts of the gastrointestinal tract. An experimental rig that simulates the segmentation motion occurring in the small intestine has been developed. The objective of developing such an experimental apparatus was to study mass transport phenomena occurring in the lumen and their potential effect on the concentration of species available for absorption. When segmentation motion was applied the mass transfer coefficient in the lumen side was increased up to a factor of 7. The viscosity of the lumen, as influenced by guar gum concentration, had a profound effect on the mass transfer coefficient. The experimental model was also used to demonstrate that glucose available for absorption, resulting from starch hydrolysis, can be significantly reduced by altering the lumen viscosity. Results suggest that absorption of nutrients could be controlled by mass transfer. Practical Application: To address health-related diseases such as obesity, novel foods that provide advanced functions are required. To achieve the full potential offered by the latest developments in the field of food material science, a fundamental understanding of the behavior of food structures in vivo is required. Using the developed gut model we have demonstrated that absorption of nutrients can be controlled by mass transfer limitations.

Predicting the thermal inactivation of bacteria in a solid matrix: simulation studies on the relative effects of microbial thermal resistance parameters and process conditions.

A combined mathematical model for predicting heat penetration and microbial inactivation in a solid body heated by conduction was tested experimentally by inoculating agar cylinders with Salmonella typhimurium or Enterococcus faecium and heating in a water bath. Regions of growth where bacteria had survived after heating were measured by image analysis and compared with model predictions. Visualisation of the regions of growth was improved by incorporating chromogenic metabolic indicators into the agar. Preliminary tests established that the model performed satisfactorily with both test organisms and with cylinders of different diameter. The model was then used in simulation studies in which the parameters D, z, inoculum size, cylinder diameter and heating temperature were systematically varied. These simulations showed that the biological variables D, z and inoculum size had a relatively small effect on the time needed to eliminate bacteria at the cylinder axis in comparison with the physical variables heating temperature and cylinder diameter, which had a much greater relative effect.

Growth and enumeration of the meat spoilage bacterium Brochothrix thermosphacta.

Brochothrix thermosphacta is a common meat spoilage bacterium. The morphology of this bacterium changes from coccobacilli and short rods to chains during growth, which may give a false estimation in numbers using some enumeration techniques. Methods for the quantification of this bacterium have been compared. Turbidimetric readings showed good agreement with cell dry weight indicating that the former provides a good measure of the change in cell mass during growth. The turbidimetric method also correlated well with bacterial numbers determined by plate counts, flow cytometry and manual counts (by microscope) over a limited range of 10(7)-10(9) cells/ml. Flow cytometry and manual counts gave a linear relationship over a wider range of 10(5)-10(9) cells/ml. The sensitivity of analysis, growth rates and lag time attained using these methods were also compared. As a consequence of changes in bacterial cell size during growth, turbidimetry over-estimated the growth rate. The plate count method proved unable to detect the difference between bacteria existing as chains or single cells. The sensitivity of analysis and the calculated growth related parameters were similar for flow cytometry and manual counts. This suggests that flow cytometry is capable of counting individual cells in a chain. Further investigation showed that passage of B. thermosphacta cells through the flow cytometer resulted in the breakage of chains into single cells. The reliability, low error and rapidity of this technique make it attractive for bacterial enumeration, something which has been demonstrated using B. thermosphacta, a bacterium which exhibits complex morphologies.

Visualization and modelling of the thermal inactivation of bacteria in a model food.

A large number of incidents of food poisoning have been linked to undercooked meat products. The use of mathematical modelling to describe heat transfer within foods, combined with data describing bacterial thermal inactivation, may prove useful in developing safer food products while minimizing thermal overprocessing. To examine this approach, cylindrical agar blocks containing immobilized bacteria (Salmonella typhimurium and Brochothrix thermosphacta) were used as a model system in this study. The agar cylinders were subjected to external conduction heating by immersion in a water bath. They were then incubated, sliced open, and examined by image analysis techniques for regions of no bacterial growth. A finite-difference scheme was used to model thermal conduction and the consequent bacterial inactivation. Bacterial inactivation rates were modelled with values for the time required to reduce bacterial number by 90% (D) and the temperature increase required to reduce D by 90% taken from the literature. Model simulation results agreed well with experimental results for both bacteria, demonstrating the utility of the technique.

Magnetic resonance imaging studies of diffusion in polymers.

For a number of polymer/penetrant systems, for example fatty foods in direct contact with plastic wrapping, the migration of substances from the polymer is governed by the amount of penetrant entering the polymer. For food packaging this means that the rate of migration of substances into the food can be governed by the uptake of food into the packaging itself. To develop predictive models of migration under various conditions there is therefore a need to understand the mechanism of the penetration of the food into the packaging. In this paper a summary of recent Magnetic Resonance Imaging (MRI) studies is reported. Uptake of simulant, as measured by MRI, is quantitative and agrees well with gravimetric uptake data. Data are shown for a comparison of olive oil and isooctane penetration into low density polyethylene at various temperatures. Further, the rate of ingress of isooctane into a variety of commercial polyethylene plaques has been shown to differ widely. These data also allow us to probe the molecular interactions between polymer and penetrant. Finally MRI is combined with a Pulsed Gradient Spin Echo (PGSE) technique to provide spatially resolved measurements of penetrant diffusivity within a polymer. Diffusivity as a function of volume fraction of penetrant can also be measured. These data provide invaluable insights into diffusion in polymers which will aid development of more accurate models of polymer/penetrant interactions and small molecule mobility.

The measurement of insoluble proteins using a modified Bradford assay.

A technique for determining the amount of thermally denatured, insoluble protein is described. The assay has been validated using four globular proteins, bovine serum albumin, beta-lactoglobulin, lysozyme, and ovalbumin. It consists of a resolubilization protocol, using 8 M urea and 5% 2-mercaptoethanol, linked to the Bradford dye binding assay. The resolubilization protocol was carried out at 100 degrees C to enable complete recovery of all insoluble proteins. Beta-Lactoglobulin resolubilization was completed after heating for 1 min, whereas samples of bovine serum albumin, lysozyme, and ovalbumin required heating for 1.5 min. The assay can measure protein concentrations as small as 10 micrograms, typically with standard deviations of 3%, thus comparing favorably with the standard Bradford assay. Other types of denaturation, such as chemical denaturation causing subsequent insolubility, may be studied with this technique providing that there is no interference with the Bradford assay.

Suggestions for the operation of radial flow cells in cell adhesion and biofouling studies.

An analysis of the radial flow cell is presented to show that the assumption of creeping laminar flow should be used cautiously. Simple models which account for the influence of fluid inertial forces over most of the width of the plate are reviewed. A modified Reynolds number is introduced which may be used to test the validity of the creeping flow solution.