DSC enthalpic transitions during starch gelatinization in excess water, dilute sodium chloride, and dilute sucrose solutions

Background: Starch phase transition characteristics were studied by pre-treating starch samples in excess water, dilute sodium chloride and dilute sucrose solutions and subjecting them to differential scanning calorimetry (DSC). Unmodified maize, wheat and potato starches were held at specific temperatures between 30 and 90 °C for 30 min and promptly cooled to 25 °C. Treated samples were then analyzed in situ by DSC. Results: It was found that the progression of the phase transition behavior differed among the three starches and was dependent on the solvent. It was also revealed that phase transition-related enthalpic changes started to occur at low temperatures and that this process involved a continuous sequence of structural changes, resulting in progressive differences in endothermic patterns from low to high temperatures. Conclusion: These findings are in agreement with recent evidence suggesting that starch gelatinization occurs over a wider temperature range rather than as a sudden order–disorder transition taking place within a narrow temperature range. The phase transition mechanism is determined by starch type and solvent combination

DSC enthalpic transitions during starch gelatinization in excess water, dilute sodium chloride, and dilute sucrose solutions

Background: Starch phase transition characteristics were studied by pre-treating starch samples in excess water, dilute sodium chloride and dilute sucrose solutions and subjecting them to differential scanning calorimetry (DSC). Unmodified maize, wheat and potato starches were held at specific temperatures between 30 and 90 °C for 30 min and promptly cooled to 25 °C. Treated samples were then analyzed in situ by DSC. Results: It was found that the progression of the phase transition behavior differed among the three starches and was dependent on the solvent. It was also revealed that phase transition-related enthalpic changes started to occur at low temperatures and that this process involved a continuous sequence of structural changes, resulting in progressive differences in endothermic patterns from low to high temperatures. Conclusion: These findings are in agreement with recent evidence suggesting that starch gelatinization occurs over a wider temperature range rather than as a sudden order–disorder transition taking place within a narrow temperature range. The phase transition mechanism is determined by starch type and solvent combination

Chemically leavened gluten free sorghum bread

Master of ScienceDepartment of Grain Science and IndustryRebecca A. ReganSorghum is unique in terms of its resistance to drought and heat and is grown and consumed around the globe. Moreover, sorghum does not contain gluten and has potential in the gluten-free market. A blend of non-wheat flour, starch and hydrocolloid typically provide the structure of gluten-free products. Most research on sorghum bread uses a yeast leavened process, HPMC gum, rice flour and corn, potato, or tapioca starch. Little is known about the functionality or interactions of different starches and hydrocolloids in sorghum batter. The objectives of this study were to examine starch-hydrocolloid interaction in chemically leavened gluten free sorghum bread; to evaluate the effects of different ingredients on gluten free bread quality made with sorghum flour: starch (tapioca starch, rice flour and potato starch): hydrocolloid (HPMC, locust bean gum and xanthan) and to develop a chemically leavened gluten free sorghum bread method. Bread was baked as pup loaves. Volume index was measured using the AACCI Method 10-91.01 template, crumb grain was evaluated using the C-Cell Imaging System and texture was determined with the TA.XT Plus Texture Analyzer. The base formula was commercial sorghum flour, water, starch, hydrocolloid, sugar, salt, shortening and double acting baking powder. Sorghum flour: starch (tapioca starch, rice flour and potato starch) ratios of 70:30, 80:20 and 90:10 were tested. Loaves containing all levels of rice flour had the same volume index (~165) as 100% sorghum flour (168) while all levels of tapioca starch and potato starch produced significantly smaller loaves (~150). The ratio of 90% sorghum flour and 10% starch (tapioca starch, rice flour and potato starch) was selected. The type and level of hydrocolloid significantly impacted loaf volume, grain and texture. Starch-hydrocolloid combinations which produced the best loaves were tapioca starch + 3% HPMC, rice flour + 3% xanthan and potato starch + 4% xanthan. Following initial optimization experiment, egg ingredients, fat, baking powder and water were added and evaluated individually to develop an optimized formulation. In general, addition of egg ingredients, shortening and oil did not improve the overall quality of sorghum based bread and were not added to the formula. However, emulsified shortening was effective. The best level of emulsified shortening was determined to be 3% for the breads with sorghum flour: tapioca starch or sorghum flour: potato starch and 5% for bread made with sorghum flour: rice flour. The best baking powder (SALP and MCP) levels were 5, 8 and 5% for sorghum flour: tapioca starch bread, sorghum flour: rice flour bread and sorghum flour: potato starch bread, respectively. Optimum levels of water for sorghum flour: tapioca starch bread, sorghum flour: rice flour bread, and sorghum flour: potato starch bread were 120, 110 and 120%, respectively. This research showed that different starch sources have different interactions with other ingredients in chemically leavened sorghum based gluten free bread

Crystal structure solution of hydrogen bonded systems : a validation and an investigation using historical methodologies followed by a review of crystal structure prediction methodologies to date

There are many chemicals that crystallize into more than one form. This phenomenon is called polymorphism. In each form or polymorph, inter and intra-molecular binding differ to varying degrees. As a result of this structural variation, the physical properties of the solid phases may also differ. Even the smallest of changes at the molecular level can result in a significant change in the final adopted crystal structure. Polymorphism in crystal structures allows studies of structure-property relationships since it is only the packing motifs that differ between polymorphs. In this thesis, a ‘computationally assisted’ approach to crystal structure solution was taken. X-ray powder diffraction was used to generate unit cell dimensions and space groups while historical in-house molecular modelling methods were used to generate possible trial structures that would be the starting point for refinement. Finally, a review of the latest methodologies for crystal structure prediction and consideration of polymorphism within the pharmaceutical industry completes this work

Relationship between α-amylase degradation and the structure and physicochemical properties of legume starches

Starches from different cultivars of black beans, pinto beans, smooth peas, lentils and wrinkled peas were isolated and their composition, physicochemical properties and susceptibility towards porcine pancreatic a-amylase were determined. -- The yield of starch ranged from 16.4 to 34.1% on a whole seed basis. The shape of the granules in black bean, pinto bean, smooth pea and lentil varied from round to oval to irregular, while compounds in rounded rosette were observed for wrinkled pea starch. Bound and total lipids ranged from 0.26 to 0.80% and 0.35 to 0.84%, respectively. The total amylose content of black bean, pinto bean, smooth pea and lentil were in the range of 30.5-39.3%, whereas that of wrinkled pea was much higher (78.4%). The percentage of lipid-complexed amylose in native starches ranged from 10.3 to 12.2%. The X-ray diffraction pattern was of the 'B' type in wrinkled pea starch and of the 'C' type in the other starches. The relative crystallinity and the 'B' polymorphic content ranged from 17.7 to 33.4% and 27.1 to 92.2%, respectively. Wrinkled pea starch exhibited the lowest relative crystallinity (17.7%) and the highest 'B' polymorphic content (92.2%). -- The swelling factor (SF) and the extent of amylose leaching (AML) of native starches were in the range of 3.4-17.7 and 11.0-17.8%, respectively. The gelatinization temperatures (To , Tp, Tc) and enthalpy (ΔH) of native starches (with the exception of wrinkled pea starch) were in the range of 60.0-65.7°C, 66.0-76.5°C, 76.4-88.8°C, and 14.6-20.1mJ/mg, respectively. Differences in SF, AML, To , Tp, Tc, and ΔH between cultivars of the same species were more pronounced in black bean and lentil starches. Wrinkled pea starch did not show an endothermic peak indicating that starch chain interactions within the amorphous domains were more extensive in wrinkled pea starch. -- All starches exhibited a biphasic hydrolysis pattern, i.e. a relatively rapid rate initially followed by a progressively decreasing rate thereafter. Wrinkled pea starch exhibited a much higher initial hydrolysis velocity than did the other starches. Cultivars of black bean and lentil showed significant differences in their initial velocities. However, differences in initial velocity between cultivars of smooth pea and pinto bean were not significant. Black bean, lentil and wrinkled pea starches showed a plateau at 93, 85 and 65% hydrolysis, respectively. The time taken for the appearance of the plateau was identical for the black bean cultivars, but was different for the lentil cultivars. Pinto bean and smooth pea cultivars showed no plateau. At the end of the assay period (120h), cultivars of each legume species were hydrolyzed to the same extent, and the extent of hydrolysis among the legume species followed the order: black bean > lentil > smooth pea > pinto bean > wrinkled pea. Scanning electron micrographs showed that starches were slightly eroded during the initial hydrolysis stage (<20% hydrolysis), but the integrity of most of the granules was well maintained. However, roughened surfaces and disc like depressions were obvious for all starches, except for lentil starch. No morphological differences were observed between cultivars from the same species for both native and hydrolyzed starches. The X-ray diffraction pattern and the 'B' polymorphic content of all starches remained unchanged upon hydrolysis. However, the relative crystallinity increased in wrinkled pea, but remained unchanged in the other starches. On hydrolysis, the apparent amylose content decreased in all starches. The extent of this decrease was most pronounced in wrinkled pea. In all starches, the enthalpy of gelatinization decreased, and the gelatinization transition temperatures increased slightly, on hydrolysis. -- This study demonstrated that differences in the composition and physicochemical properties of starch between cultivars from the same species were marginal. The rate and extent of hydrolysis were influenced mainly by structural organization and interactions of the starch chains within the native granule, as well as by the extent of association between hydrolyzed amylose chains