Magdalena Krystyjan

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).

Starch–metal complexes and their rheology

Abstract Changes in conductivity of 5 w/w% starch gels was studied on their titration with 0.1 M aqueous solutions of selected metal salts. Starch gels usually trapped around 10 mg metal ions per 1 g starch [Co(II), Cu(II), Fe(III), Ni(II)] and that value was only slightly dependent on starch origin (amaranthus, corn, potato, tapioca, waxy corn). Among salts studied (acetates, chlorides, nitrates) FeCl3 and NiCl2 were likely to be used because they hydrolyzed increasing conductivity of the solutions and formed micelles of corresponding hydroxides adhering to starch micelles and increasing amount of trapped metal. Addition of metal salts to starch gels had a devastating effect on pseudoplasticity and viscosity of starch gels and only potato starch gel was to a certain extent, exceptional in that respect.

Evaluation of the quality, nutritional value and antioxidant activity of gluten-free biscuits made from corn-acorn flour or corn-hemp flour composites

The aim of this study was to evaluate the effect of substituting 20–60% of corn flour with acorn or hemp flour on the quality, nutritional, pro-health value, and sensory properties of gluten-free biscuits. Partial replacement of corn flour with the mentioned above flours resulted in a significant reduction of biscuit volume and an increase of their hardness. The biscuits in the experiment were significantly darker than the control ones. Increasing the content of both studied flours resulted in a distinct trend of color variation from yellow toward red-purple. The protein content in biscuits with the addition of acorn flour did not differ significantly in comparison with the control biscuits, whereas biscuits with flour hemp contained 40–122% more protein in comparison with the control ones. The total dietary fiber content increased correspondingly with the addition of the investigated flours. The total polyphenols content (TPC) in biscuits with the acorn flour addition increased in the range of 308–801% in relation to the control, and the addition of hemp flour increased the TPC in the range of 41–143%. It was found that acorn flour contributed to higher growth (an average of 367%) of the antioxidant activity of the biscuits in relation to the control samples than the hemp flour (an average of 114%). The control biscuits obtained the highest sensory score, similarly biscuits with 20 and 40% acorn flour addition. The most favorable replacement should be that not more than a 40% substitute of corn flour with acorn flour.

Arabinoxylan-starch-protein interactions in specially modified rye dough during a simulated fermentation process

The purpose of the work was to determine which processes occur during fermentation of rye dough beside progressive hydrolysis of biopolymers and production of gases, and also to determine which compounds are most responsible for them. The study was conducted with a specially modified dough containing starch, arabinoxylan preparations (non-modified, hydrolysed and cross-linked) and protein obtained from rye wholemeal. Despite the same consistency of the dough samples, their viscosity and values of rheological parameters depended on the amount of arabinoxylan preparations and their molecular weight. Already at the stage of mixing the dough, high molecular complexes of arabinoxylan-protein and arabinoxylan-arabinoxylan were formed. Complex formation was confirmed in the modified dough preparation with rye starch including only arabinoxylan or rye protein as well as a combination of arabinoxylan and rye protein. The highest amount and molecular dimension of complexes were found in the sample composed of starch, cross-linked arabinoxylan and rye protein.

Physico-chemical and rheological properties of gelatinized/freeze-dried cereal starches

Abstract The influence of gelatinization and freeze-drying process on the physico-chemical and rheological properties of cereal starches was evaluated, and it was observed that modified starches revealed an increased water binding capacity and solubility when compared to dry starches, while exhibiting the same amylose and fat contents. The molecular weights of starches decreased after modification which resulted in the lower viscosity of dissolved modified samples in comparison to native starch pastes. As it was observed by scanning electron microscopy modified starches were characterized by an expanded surface, a uniform structure and high porosity.

Binary mixtures of two anionic polysaccharides simulating the rheological properties of oxidised starch

Abstract Modifications of starches are carried out to improve their industrial usefulness. However, the consumers prefer natural products. For this reason, various methods of starch properties modification are applied to replace those requiring the use of chemical reagents. The aim of this study was to determine whether it is possible to use binary pastes, containing normal potato starch and xanthan gum, as substitutes of chemically modified starches (with oxidised starch E 1404 pastes as an example). Flow curves with hysteresis loops, apparent viscosity at constant shear rate of 50 s−1 and in-shear structural recovery test with pre-shearing were applied to study the rheological properties of the pastes. It was found that two anionic hydrocolloids, potato starch and xanthan gum, can form binary systems with thickening properties, provided that their proportions are adequately adjusted. Some of the binary pastes under investigation exhibited rheological properties resembling pastes of starch oxidised with hypochlorite (E 1404). The way of tailoring the binary pastes properties is presented.

Retrogradacja skrobi z dodatkiem i bez dodatku nieskrobiowych hydrokoloidów polisacharydowych - metody pomiaru i ich zastosowanie

S t r e s z c z e n i e W pracy przedstawiono podzial metod pomiaru zjawiska retrogradacji skrobi z dodatkiem oraz bez dodatku nieskrobiowych hydrokoloidow polisacharydowych (NHP), wśrod ktorych wyrozniono techniki makroskopowe oraz molekularne. Scharakteryzowano metody makroskopowe, takie jak: skaningowa kalorymetria roznicowa (DSC), pomiary tekstury, badania oscylacyjne, turbidymetria oraz pomiary synerezy zeli, a takze podano przyklady dotychczasowego ich zastosowania. W grupie molekularnych technik pomiaru retrogradacji szczegolną uwage zwrocono na najcześciej stosowane metody, tzn. jądrowy rezonans magnetyczny (NMR) oraz rentgenografie proszkową. Ponadto podano ograniczenia zastosowania innych metod badania procesu retrogradacji skrobi. Slowa kluczowe: retrogradacja, skrobia, nieskrobiowe hydrokoloidy polisacharydowe, metody pomiaru retrogradacji skrobi, stabilnośc zeli skrobiowych