The aim of this paper was the study of the rheological instability (thixotropy and/or antithixotropy) of normal potato starch (NPS) pastes depending on their concentration (2-5%) and degree of pasting. Flow curves with hysteresis loops, apparent viscosity at constant shear rate and in-shear structural recovery tests were carried out. Granule size profiles, the pasting characteristic of corresponding starch suspensions and the transmittance of the pastes, the molecular weights and polydispersity of granular starch and its pastes prepared at 80, 95 and 121°C were also studied. The degree of pasting was dependent on the temperature and the concentration and influenced strongly the rheological behavior of the pastes. All pastes belonged to the non-Newtonian liquids thinned by shear and were rheologically unstable to the various extent. Thixotropic properties were connected to the size and the number of the starch granules in the pastes as well as depended on the measuring method used. In the 2 and 3% samples pasted at 80°C the swelling of the granules prevailed their destruction (thixotropy was observed). In the other samples the destruction predominated the swelling (antithixotropy observed).
The aim of this paper was to investigate the influence of dietary fibers from oat (OF) and apple (AF) (concentration 0.2%) on the pasting properties, rheological (including thixotropic and anti-thixotropic) and textural properties of 3% and 4% (w/w) waxy potato starch pastes. The samples were characterized by their pasting characteristics, the hysteresis loop test, and textural properties measured during storage. It was found that the breakdown viscosity values of the blends, including oat fibers, were lower than those of the others (waxy potato starch (WPS), WPS-AF), which suggests that these samples would have higher resistance to retrogradation and therefore would form a more stable paste. The pattern of flow curves showed that the investigated waxy potato starch and starch-fiber pastes were non-Newtonian fluids, thinned by shear. Areas of the hysteresis loops indicated that pastes with fibers had anti-thixotropic or mixed thixotropic/anti-thixotropic character. The greatest areas of the anti-thixotropy hysteresis loops were characteristic for WPS, while its mixtures with AF and OF caused a decrease in the value of these areas. It can indicate that starch-fiber blends were more stable during shearing. Fiber-type and starch concentration strongly affected the textural parameters of the starch-fiber gels.
The aim of this study was to develop a concept of production for wheat bread enriched with chia seeds and to examine selected physicochemical properties. The examined product was wheat-flour bread made by a single-phase method, using yeast. The production concept assumed the modification of the recipe by replacing part of the wheat flour (1 or 5% w/w) with whole (CHw) or ground chia seeds (CHg). Bread quality was determined by calculating: dough yield, bread yield, baking loss, total baking loss and loaf volumes. Color was determined using the CIE L*a*b* system. In the texture analysis, the following texture parameters were measured: hardness, cohesion, chewiness and elasticity. The contents of crude fat, crude fiber, total protein, total ash and the total content of polyphenols were assessed to characterize the nutritive value of the bread. The breads with 1% addition of chia (1%CHw, 1%CHg) were characterized by the highest volume of loaves, which increased by at least 8.6% compared to the control bread (C), while in the case of 5% chia, the loaf volume depended on the form of seeds (better results were obtained with whole seeds). Substituting wheat flour with 1% chia seeds (whole or ground) resulted in a significant increase in nutritional value. For potential bread manufacturers, from a technological and economic point of view, replacing wheat flour with whole chia seeds at 1% (w/w) is most advantageous, compared to 5% (w/w).
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