Dysphagia thickeners in context of use: Changes in thickened drinks viscosity and thixotropy with temperature and time of consumption.

Dysphagia patients might need to thicken drinks. The viscosity of these thickened drinks varies among commercial thickeners and drinks compromising the ingesta safety. The aim of this study was to investigate how temperature and resting time affect the rheological properties of thickened drinks. Four commercial thickeners were used to thicken water, coffee, orange juice, and milk at two concentration levels used in dysphagia drinks (nectar and pudding). To study the effect of temperature, flow curves of thickened drinks at 10°C and 50°C were obtained and to study the effect of resting time, flow curves of thickened drinks at 25°C were obtained at different times (0, 30, and 60 min). All samples displayed shear-thinning and time-dependent behavior (thixotropy or antithixotropy). The effect of temperature on viscosity values and relative thixotropic area (RTA) depended on the thickener and the drink. Overall, apparent viscosity showed higher values at 50°C than 10°C, especially in thickeners containing starch and in drinks with higher soluble solids (milk and orange juice). This was attributed to the water absorption of pregelatinized starch granules favored by temperature. Antithixotropy was mainly observed at pudding concentration for the starch-containing thickeners, and decreased with temperature. The effect of resting time on apparent viscosity and RTA depended also on the drink and thickener. Mostly, apparent viscosity values increased with resting time and antithixotropic behavior decreased. Both effects, increase in viscosity and decrease of antithixotropy with time, indicated that thickening action was being developed over the resting time.

Influence of steam jet-cooking on the rheological properties of dry and wet cationized starch solutions.

Steam jet-cooking allows for efficient dissolution of cationic starch in paper production as it operates above the boiling point of water at elevated pressures. However, the processes involved during jet-cooking and its consequences on dissolution and finally paper properties have not been fully resolved so far. As cationic starch is the most important paper additive in the wet end, any energy or material savings during dissolution will enhance the ecologic and economic performance of a paper mill. Here, we address the topic of solubilization of four different industrially relevant cationic starches processed via steam jet-cooking. We showcase that rheology is a useful tool to assess the solubility state of starches. Some starches featured liquid-like rheological behavior (loss moduli, G", greater than storage moduli, G') in linear viscoelastic tests and anti-thixotropic behavior in hysteresis loop tests. In contrast, cationic corn starches exhibited gel-like behavior (G' > G″) and negligible hysteresis directly after cooking. HYPOTHESES: To evaluate the decisive factors for complete dissolution of industrial cationic starches using jet-cooking and to correlate them to rheological properties.

The Effect of the Addition of Dietary Fibers from Apple and Oat on the Rheological and Textural Properties of Waxy Potato Starch.

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.

Study of rheological properties of açai berry pulp: an analysis of its time-dependent behavior and the effect of temperature.

The industry of açai-based products has been growing in the last few years. Knowledge about the physical properties of açai pulp, including its rheology, is essential to the optimization of industrial processes. This work presents the rheological behavior of açai berry pulp in relation to the effects of shear rate, temperature, and time of shearing. The entire study was carried out in the temperature range of 10-70 °C. Açai pulp showed a non-Newtonian, pseudoplastic, and time-dependent behavior. Four upward and backward shear rate cycles were evaluated, resulting in complex hysteresis loops, in which thixotropy and anti-thixotropy zones were observed. Downward flow curves could be satisfactorily represented by the Power-Law rheological model. The stress profiles as a function of shear rate obtained in the first upward curves suggest a breakdown of the initial fluid structure at low shear rates. Tests were also carried out at a constant shear rate of 20 s-1 and, in this case, the Weltman model of thixotropy satisfactorily fit the experimental data. The activation energy, which was calculated by the Arrhenius equation, was 29.0 kJ/mol. The achievements of this work may be useful to further studies about açai pulp rheology and may contribute to process design in the açai industry.

Thixotropic properties of waxy potato starch depending on the degree of the granules pasting.

This paper presents the rheological instability (thixotropy/antithixotropy) of waxy potato starch (WPS) pastes depending on their concentration (1-5% w/w) and pasting temperature (80, 95 and autoclaved: 121°C, at 0.1MPa). The hysteresis loop, apparent viscosity at constant shear rate as well as the in-shear structural recovery tests with and without pre-shearing were applied. The pastes were also characterized by the granularity profile, molecular weight, polydispersity and optical transmittance. Differences in rheological properties of the pastes prepared at 80 and 95°C as well as autoclaved resulted from degree of granules pasting. At 121 °C dissolution of the granules occurred, while at the lower temperatures only the partial pasting of the granules took place. Pasting temperature of WPS significantly influenced rheological parameters of the resulted pastes which had thixotropic, antithixotropic or mixed thixotropic/antithixotropic behavior. Autoclaved pastes, regardless their concentration were antithixotropic as demonstrated by the areas of hysteresis loops derived from the flow curves signalized by the degree of structure recovery (DSR) which exceeded unity. The apparent viscosity of WPS pasted at 121°C strongly decreased as compared to the samples pasted at lower temperatures. Samples pasted at 80 and 95°C showed both thixotropic and antithixotropic behavior, with a predominance of the latter. The starch concentration played an important role in the formation of the rheological properties of the resulted pastes. Its influence was strongly connected with the degree of the granules pasting, therefore with the temperature of pastes preparation. For the pastes prepared at 80 and 95°C the values of thixotropy and apparent viscosity increased, while the values of DSR decreased with an increase of concentration. In the autoclaved pastes the antithixotropy, DSR and apparent viscosity increased with increasing starch concentration. It was also found that apart from the concentration and temperature also the shear rate influence the thixotropic behavior.

Thixotropic properties of normal potato starch depending on the degree of the granules pasting.

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).