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The influence of glucose syrup on the retrogradation of cereal starches was investigated. Laboratory isolated starches from wheat (WS) and oats (OS – oat starch and ROS – residual oat starch) were used in this research. ROS was isolated from the flour left after the industrial separation of β-glucans. Gelatinization temperature of oat starches (63.82 °C and 64.01 °C for OS and ROS, respectively) was higher than for WS (62.26 °C), whereas gelatinization enthalpy for oat starches (8.87 J/g and 9.09 J/g for OS and ROS, respectively) was lower than for WS (9.99 J/g). Moreover, retrogradation percentage (%R) was similar for both oat starches (29.76% and 27.72% for OS and ROS, respectively), and was substantially lower than for WS (42.04%). The introduction of glucose syrup into system reduced the extent of the retrogradation. Rate of the process was suppressed for WS and ROS, whereas for OS it was increased. β-Glucan production process had no significant effect on the gelatinization and retrogradation of oat starch. [ABSTRACT FROM AUTHOR]

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 0.1 MPa). 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. [ABSTRACT FROM AUTHOR]

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). [ABSTRACT FROM AUTHOR]