Evaluation of the effect of malt, wheat and barley extracts on the viability of potentially probiotic lactic acid bacteria under acidic conditions

In this work, the effect of cereal extracts, used as delivery vehicles for potentially probiotic lactic acid bacteria (LAB), on the acid tolerance of the cells was evaluated under conditions that simulate the gastric tract. More specifically, the effect of malt, barley and wheat extracts on the viability of Lactobacillus plantarum, Lactobacillus acidophilus and Lactobacillus reuteri during exposure for 4 h in a phosphate buffer acidified at pH 2.5 was investigated. In the absence of cereal extracts all strains demonstrated a significant reduction in their cell population, particularly L. plantarum. The viability of L. plantarum was improved by approximately 4 log10 cycles in the presence of malt and 3 log10 cycles in the presence of wheat and barley. The survival of L. acidophilus and L. reuteri was increased by more than 1.5 and 0.7 log10 cycle, respectively, upon addition of cereal extracts. In order to evaluate the contribution of the cereal constituents on cell survival, the individual effect of glucose, maltose and free amino nitrogen (FAN), which were added at concentrations that correlated to the reducing sugar and FAN content of the cereal extracts, was examined. The viability of L. plantarum was progressively improved as the maltose or glucose concentration increased; an increase by approximately 2 log10 cycles was observed in the presence of 8.33 g/l sugar. The survival of L. acidophilus increased by more than 1 log10 cycle, even at very low concentrations of maltose and glucose (e.g., 0.67 g/l), while L. reuteri stability was enhanced in the presence of maltose but no appreciable effect was demonstrated in the presence of glucose. Sugar analysis indicated that glycolysis was inhibited in all cases. Addition of tryptone and yeast extract, used as sources of FAN, enhanced L. acidophilus acid tolerance, but did not affect L. reuteri and L. plantarum. The results presented in this study indicate that malt, wheat and barley extracts exhibit a significant protective effect on the viability of L. plantarum, L. acidophilus and L. reuteri under acidic conditions, which could be mainly attributed to the amount of sugar present in the cereal extracts

Effect of fat level, mixing pressure and temperature on dough expansion capacity during proving

In this work the effect of fat content on dough aeration during proving was investigated using dynamic dough density measurements. Doughs of three different fat levels (0%, 0.04% and 0.2% flour basis) were mixed under various pressures using a Tweedy mixer and proved at five different temperatures (30, 35, 40, 45 and 50 °C) in the dynamic dough density system. The dough expansion capacity and the time of the gas loss of each dough sample were measured and related to fat level, mixing pressure and proving temperature. The time of gas loss decreased with increasing proving temperature for all fat levels, as expected due to increasing yeast activity and reduced carbon dioxide solubility. The final gas capacity of dough is affected by the mixing pressure and the temperature. Fat content had no significant effect on the time of the loss of gas retention or the dough's final expansion capacity. However, fat affected the pattern of gas loss towards the end of proving; thus in doughs with fat, the gas loss rate occurred smoothly and gradually, in contrast to the doughs with no fat that exhibited sudden gas loss. The findings demonstrated that the dynamic dough density method is a sensitive, straightforward technique for the investigation of factors affecting gas retention in bread doughs

Discrete particle motion on sieves—a numerical study using the DEM simulation

This paper presents a mathematical investigation of particulate motion on an inclined screening chute using the Discrete Element Method (DEM). Special attention has been paid to the implementation of an apertured boundary and the algorithm for allowing particles to pass through apertures or to rebound when approaching the screen surface. Computational experiments have been conducted to examine the undersize particle motion across the material layer and through the apertures for bimodal mixtures comprising two different sizes of spherical polyethylene pellets. Discrete particle motion at different regions along the screen has been discussed in relation to the physical mechanisms inherent in the solids separation process and their determinative role on screening efficiency. Simulations have demonstrated the negative effect of near-mesh size particles and the positive role of relatively large particles on screening operations and the crucial effect of particle segregation in material layers. Comparison of screening rate along the screen with experiments has demonstrated adequate agreement. This computational study has shown the advantages of using DEM to understand the complex solids separation process. Further works are envisaged to focus on the development of advanced experimental techniques and the implementation of DEM for sieving processes involving moving screens

Effect of storage temperature and media composition on the survivability of Bifidobacterium breve NCIMB 702257 in a malt hydrolisate

The aim of this study was to evaluate the survivability of Bifidobacterium breve NCIMB 702257 in a three malt-based media supplemented with cysteine and yeast extract, and to determine the protective effect of these growth factors. A number of parameterised mathematical models were used to predict of kinetics of viability and total acidity during storage at different temperatures. Results demonstrated a good fit to the experimental mathematical model. The Arrhenius equations showed only reasonable fits and the polynomial plots contained a large area without data between 4 and 25 degrees C. In addition, it was shown that cysteine promotes growth and acid production by bifidobacteria, but does not extend survivability. On the other hand, increasing the yeast extract content of the fermentation media enhances the survivability of B. breve. To our knowledge, this is the first study to address the modelling of the survivability of probiotic bacteria in a cereal based fermentation media at different temperatures, introducing a more quantitative approach to the study of the shelf-life of a probiotic product. (C) 2009 Elsevier B.V. All rights reserved

Solids deposition in low-velocity slug flow pneumatic conveying

Solids deposition in the horizontal pipeline of a pneumatic conveying system was studied both mathematically and experimentally. Mathematically modelled results using the coupled discrete element method (DEM) and computational fluid dynamics (CFD) approach have demonstrated an intensive exchange of particles between the stationary layer (deposited particles) and the moving slug and a variation of solids concentration and pressure and velocity distributions across the slug. Slug flows were also visualised experimentally through a glass section and analysed by a high-speed video camera. The amount of particle deposition in the pipeline after a conveying was calculated by controlling the solids feeding rate using a rotary valve and by monitoring the solids flow out of the system using dynamic load cells. Experimentally generated data have quantitatively shown a tendency of more solids deposition with lower gas mass flow rate in slug flows except that, below a certain amount of solids mass flow rate, the deposition becomes independent of gas flow rate

A Numerical Simulation of Separation of Crop Seeds by Screening—Effect of Particle Bed Depth

Effective separation and grading of cereal grains and crop seeds are of importance in the production of quality cereal foods. This paper presents a two-dimensional numerical study of the separation process of crop seeds by screening, using the Discrete Element Method (DEM) modelling technique. Computational experiments have been conducted for the separation of two common crop seeds, soybeans and mustard seeds, using a vibrating screen. The screening rate and the required screen length at different feeding rates are discussed in relation to the discrete particle motion on the screen. This study has demonstrated the crucial effect of particle bed depth on screening efficiency. For a screening system involving granular materials, the critical feeding rate for the most effective screening operation can be determined via conducting the DEM simulation