Pieter Jacobs

Wheat (Triticum aestivum L.) Bran in Bread Making: A Critical Review

Wheat bran, a by-product of the industrial roller milling of wheat, is increasingly added to food products because of its nutritional profile and physiological effects. Epidemiological data and scientific studies have demonstrated the health benefits of consuming bran-rich or whole-grain food products. However, incorporation of wheat bran in cereal-based products negatively affects their production process. Furthermore, the organoleptic quality of the obtained products is mostly perceived as inferior to that of products based on refined wheat flour. This review summarizes the current knowledge on the impact of wheat bran on bread making, provides a comprehensive overview of the bran properties possibly involved, and discusses different strategies that have been evaluated up till now to counteract the detrimental effects of wheat bran on bread making.

Study of hydration properties of wheat bran as a function of particle size

New insights in the hydration properties of wheat bran as function of particle size were gained based on a novel water retention capacity test. Upon milling coarse bran with an average particle size of 1687 μm down to 77 μm, the specific surface increases by twofold, structural integrity was lost and water extractable arabinoxylan and damaged starch content were practically unaffected. A standard centrifugation-based water retention capacity, swelling capacity and Enslin-Neff absorption test showed up to threefold higher water absorption for large particles. During these hydration tests, bran is not (continuously) subjected to external forces which allows larger particles to hold more water in between bran particles and probably in micropores. In contrast, the water retention capacity as determined by a novel drainage centrifugation method, and Farinograph absorption were not affected by particle size. In these methods, continuous exposure of bran to external forces causes bran to retain only strongly bound water which is most likely bound in cell wall nanopores and through hydrogen bonding. These insights reconcile contradicting observations in literature with regard to this matter.

Wheat milling by-products and their impact on bread making

This study investigates the relationship between the properties of dietary fiber (DF) rich wheat milling by-products and their impact on bread making. From coarse bran over coarse and fine weatings to low grade flour, the content of starch and lipids increased, while that of DF and ash decreased. Enzyme activity levels differed strongly and were not related to other by-product properties. Average particle size of the by-products was positively correlated with DF and ash contents and their hydration properties. When meals from flour and by-products were composed on the same overall starch level to compensate for differences in endosperm contamination in the by-products, bread specific volume was more strongly depressed with fine weatings and low grade flour than with coarse bran and weatings. This suggests that the properties of the former were intrinsically more detrimental to bread making than those of the latter.

Harvesting yeast (Saccharomyces cerevisiae) at different physiological phases significantly affects its functionality in bread dough fermentation

Fermentation of sugars into CO2, ethanol and secondary metabolites by bakers yeast (Saccharomyces cerevisiae) during bread making leads to leavening of dough and changes in dough rheology. The aim of this study was to increase our understanding of the impact of yeast on dough related aspects by investigating the effect of harvesting yeast at seven different points of the growth profile on its fermentation performance, metabolite production, and the effect on critical dough fermentation parameters, such as gas retention potential. The yeast cells harvested during the diauxic shift and post-diauxic growth phase showed a higher fermentation rate and, consequently, higher maximum dough height than yeast cells harvested in the exponential or stationary growth phase. The results further demonstrate that the onset of CO2 loss from fermenting dough is correlated with the fermentation rate of yeast, but not with the amount of CO2 that accumulated up to the onset point. Analysis of the yeast metabolites produced in dough yielded a possible explanation for this observation, as they are produced in different levels depending on physiological phase and in concentrations that can influence dough matrix properties. Together, our results demonstrate a strong effect of yeast physiology at the time of harvest on subsequent dough fermentation performance, and hint at an important role of yeast metabolites on the subsequent gas holding capacity.

Torsional injuries of the lower limb: an analysis of the frictional torque between different types of football turf and the shoe outsole

Background Football turf is increasingly used in European soccer competition. Little is known on the rotational torque that players experience on these fields. High rotational torques between the shoe outsole and the sports surface has been correlated with torsional injuries of the lower limb and knee. Purpose To evaluate the effect of six parameters that could influence the rotational torque between the shoe outsole and the latest generation football turf. Study design Controlled laboratory study. Methods A testing apparatus was constructed to measure the peak torque generated during a controlled rotation of the foot. Six parameters that could potentially influence the frictional forces, were considered: (1) the sports surface, (2) the shoe outsole cleat design, (3) the weather conditions, (4) the weight, (5) the presence of an impact and (6) the direction of rotation. Results The football turf without infill showed significantly lower frictional torques than natural grass whereas a football turf with sand/rubber infill had significantly higher torques. Blades were associated with significantly higher torques than studs on natural grass and on one football turf with sand/rubber infill. Dry weather was associated with higher torques only for the football turf without infill. The torque increased linearly and significantly with an increasing vertical load. The rotational torque increased significantly following an impact. Torques on external rotational movements were significantly higher with blades. Conclusions Important differences in rotational torques are found and could be seen as potential risk factors for torsional injuries of the lower limb.

Impact of Wheat Bran Hydration Properties As Affected by Toasting and Degree of Milling on Optimal Dough Development in Bread Making

The impact of the hydration capacity and hydration rate of wheat bran on optimal bread dough development and loaf volume was investigated using coarse bran, both native as well as after toasting, milling, presoaking, and combinations of the latter. It was found that toasting reduces brans hydration rate, which, during mixing, results in a temporary excess of water in which dough development takes place inefficiently and hence requires additional time. This mechanism was further substantiated by the observation that delayed dough development can be counteracted by the presoaking of bran. Milling of bran increases its hydration rate and results in faster optimal dough development. Presoaking of nonmilled bran, however, did not result in faster dough development. Smaller bran particles do lead to faster dough development, probably due to increased proper contacts between flour particles. Optimal loaf volumes did not change upon milling and toasting.

Dry heat treatment affects wheat bran surface properties and hydration kinetics

Heat stabilization of wheat bran aims at inactivation of enzymes which may cause rancidity and processability issues. Such treatments may however cause additional unanticipated phenomena which may affect wheat bran technological properties. In this work, the impact of toasting on wheat bran hydration capacity and hydration kinetics was studied. Hydration properties were assessed using the Enslin-Neff and drainage centrifugation water retention capacity methods, thermogravimetric analysis and contact angle goniometry, next to more traditional methods. While equilibrium hydration properties of bran were not affected by the heat treatment, the rate at which the heat treated bran hydrated was, however, very significantly reduced compared to the untreated bran. This phenomenon was found to originate from the formation of a lipid coating during the treatment rendering the bran surface hydrophobic. These insights help to understand and partially account for the modified processability of heat treated bran in food applications.

Study on the effects of wheat bran incorporation on water mobility and biopolymer behavior during bread making and storage using time-domain 1H NMR relaxometry

Water binding is suggested to be key in the deleterious effect of wheat bran on bread quality. This study investigates water mobility and biopolymer behavior during bran-rich bread making and storage, using 1H NMR. Coarse, ground, and pericarp-enriched bran were incorporated in bread dough, and their impact on freshly baked and stored bread properties was assessed. Compared to wheat flour control dough, bran incorporation resulted in a progressive immobilization of water during dough resting, which could be linked to changes in evolution of dough height during fermentation and oven rise. This, together with modified starch gelatinization behavior upon baking, can be related with the inferior quality of bran-rich breads. The impact was most pronounced with pericarp-enriched bran. Textural quality during storage was less affected for coarse or ground bran-rich bread compared to wheat flour bread, which could be principally attributed to retardation of amylopectin retrogradation in the presence of bran.

Study of the role of bran water binding and the steric hindrance by bran in straight dough bread making

This study investigates the effect of the physical presence and water binding of wheat bran during bread making, and the possible mechanisms behind this effect. Regular bran, pericarp-enriched bran and synthetic bran-like particles with different water binding capacities and particle sizes were used. Incorporation of regular and pericarp-enriched bran in dough (15% dm) led to a lower oven rise than the control dough. Bread volumes decreased with 11% and 30%, respectively. Dough with synthetic bran, having a low water binding capacity, displayed a near to normal leavening and oven rise and resulted in a bread volume decrease of only 5% compared to the control. Particle size reduction of regular bran and synthetic bran to an average size of 200 µm did not affect final bread quality. Results indicate that water binding by bran affects bread quality the most, whereas steric hindrance by physical presence of bran particles is less determinative.

Study of biopolymer mobility and water dynamics in wheat bran using time-domain 1 H NMR relaxometry

In this study, the molecular mobility of water and biopolymers in coarse, ground, and pericarp-enriched (PE) wheat bran and refined flour was investigated using time-domain proton nuclear magnetic resonance relaxometry, and related to their hydration properties. Several specific proton populations were present in the bran samples but not in flour. These populations were mainly assigned to protons of bran-related compounds such as arabinoxylan, cellulose, and lipids. All bran samples showed similar proton distributions at a 44% moisture level, although the chemical composition of coarse/ground bran and PE bran differed. When bran was further moistened up to 80%, an additional, more mobile water peak was noticed in coarse and PE bran, but not in ground bran. This can be explained by the fact that coarse and PE bran hold more weakly bound water than ground bran, which is most probably water entrapped in between bran particles.