Characterization of the effects of chia gels on wheat doughand bread rheology as well as the optimization of breadroll production with the Nelder-Mead simplex method

摘要

Chia (Salvia hispanica L.) is becoming increasingly popular as ingredient for baked goods. The aim of the first part of this thesis was to investigate the influence of gel from ground chia on the rheology of different wheat dough systems and the resulting baked goods. The evaluated products were wheat bread and sweet pan bread.The effects of chia incorporated as gel in wheat bread dough as hydrocolloid were characterized using empirical and fundamental rheological methods and differential scanning calorimetry. To avoid competition of starch and ground chia with respect to the water uptake, chia was incorporated as gel. The gel was prepared of ground chia with 5 g/g and 10 g/g water, respectively. The doughs were prepared with 1-3 % chia related to the amount of wheat flour. The effects of gel from ground chia were studied also as fat replacer in sweet pan breads. The main focus of the work was to study the effects of the fat substitution on the dough rheology. The dough rheology was characterized using a rotational rheometer and a Rheofermentometer. The end products were evaluated with a texture analyser and two samples were additionally evaluated with respect to their fatty acid profile. The substitution was secondly addressed to reduce the total amount of fat in the product and to improve the nutritional value of the products regarding the fatty acid composition. The fat was replaced in four steps, and the ratio among the ingredients was held constant to ensure a better comparability.Within this thesis it was shown that addition of gel from ground chia can affect wheat doughs and the resulting baked products in a positive way. The approach of using ground chia as gel seems to be fruitful to avoid competition between starch and chia with respect to the water uptake while the crumb formation during the baking process takes place. The evaluation of the pasting profiles of wheat flour suspensions with chia gel addition reinforced this assumption. The gel from ground chia affected the pasting properties in a way that the viscosities decreased with increasing amount of chia. The rheological properties of the doughs were affected in negative ways with respect to further processing by the addition of too high amounts of chia gel. The dough stability was reduced and the resulting baked products were less and irregular porous and therefore compact. All doughs showed weakening regarding the rheometer measurements, however the linear viscoelastic region was not affected. The frequency sweep measurements showed for all doughs a decrease with increasing content of gel from ground chia. The creep-recovery tests of the sweet pan bread doughs revealed that the zero viscosity η0 decreased and the creep compliance J0 increased with increasing chia gel content. The weakening of the doughs may not absolutely be caused by the incorporated chia, but by the additional water. There seems to be a kind of interaction between ground chia particles, wheat flour constituents and water, because nearly the same results were achieved for 2 % and 1 % of ground chia with 5 g/g and 10 g/g water, respectively. These experiments lead also to the best results for incorporating gel from ground chia to wheat breads. The best results for sweet pan breads were obtained with 25 % fat replacement through gel from ground chia. This gel was prepared of 2.3 g ground chia with 5 g/g water.Summarizing the incorporation of defined amounts of gel from ground chia has a positive effect on the rheology and the resulting baked products. The retrogradation of the baked products was decreased over storage and the dietary fibre content was increased. Thus chia acts like a hydrocolloid. The nutritional values of the evaluated baked products, wheat bread and sweet pan bread, were increased. For the sweet pan breads an increase of omega-3 fatty acids was determined. The resulting best sweet pan bread exhibited an amount of 5 % linolenic acid. Gel from ground chia can therefore be incorporated into bakery products as hydrocolloid and for improving the nutritional values regarding the dietary fibre and omega-3 fatty acid contents. Another part of the work was the optimization of the production parameters, proofing time and baking temperature, for bread rolls. The optimization was performed with the Nelder-Mead simplex method. The optimization was necessary for a new oven type, where the oven walls were coated with a ceramic, that increased the infrared radiation during the baking process. The quality criterion for the optimization were the specific volume, the baking loss, the colour saturation, crumb firmness as well as the elasticity of the bread rolls. Within 11 experiments the optimal baking result defined by the results of a conventional oven was obtained. The optimal processing parameters for the bread rolls were a proofing time at 117 minutes and a baking temperature of 215 °C for 16 minutes.