Xingxun Liu

Developing gelatin-starch blends for use as capsule materials

Blends of gelatin with up to 50% hydroxypropylated high amylose (80%) corn starch were developed as capsule materials. Poly(ethylene glycol) (PEG) was used as both a plasticizer and a compatibilizer in the blends. In order to prepare hard capsules for pharmaceutical applications using the well-established method of dipping stainless steel mold pins into solution, solutions with higher solids concentrations (up to 30%) were developed. The solutions, films and capsules of the different gelatin-starch blends were characterized by viscosity, transparency, tensile testing, water contact angle and SEM. The linear microstructure of the high amylose starch, and the flexible and more hydrophilic hydroxylpropylene groups grafted onto the starch improved the compatibility between the gelatin and starch. SEM revealed a continuous phase of gelatin on the surface of films from all blends. The water contact angle of pure gelatin and the different blends were similar, indicating a continuous phase of gelatin. By optimizing temperature and incubation time to control viscosity, capsules of various blends were successfully developed. PEG increased the transparency and toughness of the various blends.

Thermal Decomposition of Corn Starch with Different Amylose/Amylopectin Ratios in Open and Sealed Systems

ABSTRACT Thermal decomposition of corn starches with different amylose to amylopectin ratios (0:100 waxy, 23:77 maize, 50:50 Gelose 50, 80:20 Gelose 80) were studied by thermogravimetric analysis (TGA) in an open system and differential scanning calorimetry (DSC) in a sealed system using stainless steel high-pressure pans with varying water content (9–75%). The initial water content did not affect the decomposition temperature in the open system because all water evaporated from samples before reaching the decomposition temperature. The sequence of decomposition temperature of different starches is waxy > maize > G50 > G80 in an open system. The moisture content in starch remains constant during the degradation process in a sealed system. Two decomposition temperatures were observed in the sealed system: the first at lower temperature represents long chain scission and the second at higher temperature involves decomposition of the glucose ring. The sequence of the first degradation is waxy > maize > G50 >...

Phase composition and interface of starch-gelatin blends studied by synchrotron FTIR micro-spectroscopy

The well recognized complex issue of compatibility between starch and gelatin was investigated based on their interface and phase composition using synchrotron FTIR micro-spectroscope. A high amylose (80%) corn starch grafted with flexible and hydrophilic hydroxpropyl groups and plasticized by poly(ethylene glycol) (PEG) was used in this work. The FTIR beam focused on a 5 μm×5 μm detection region and the micro-spectroscope was scanned across the gelatin-starch interface. It was found that there was about a 20 μm thickness layer where gelatin and starch were in co-existence, indicating that gelatin and starch are compatible to a certain degree in this system. The ratio of the areas of the saccharide CO bands (1180-953 cm(-1)) and the amide I and II bands (1750-1483 cm(-1)) was used to monitor the relative distributions of the two components of the blends. FTIR 2 and 3-dimensional maps indicated that gelatin constituted the continuous phase up to 80% of starch content. The PEG was homogeneously distributed in both gelatin and starch phases, and blurred the interface between gelatin and starch in the chemical maps, indicating that PEG acted not only as a plasticizer but as a compatibilizer for the gelatin-starch blends.

Developing hydroxypropyl methylcellulose/hydroxypropyl starch blends for use as capsule materials.

Blends of hydroxypropyl methylcellulose (HPMC) with up to 70% hydroxypropyl starch (HPS) were developed for use as hard capsule materials. Polyethylene glycol (PEG) was used as both a plasticizer and a compatibilizer in the blends. In order to prepare hard capsules for pharmaceutical application using the well-established method of dipping stainless steel mold pins into solution then drying at certain temperature, equilibrated solutions with higher solids concentration (20%) were investigated and developed. The solutions, films and capsules of the different HPMC/HPS blends were characterized by viscosity, transparency, tensile testing, water contact angle, SEM, as well as FTIR. The results showed that the blend system is immiscible but compatible in certain degree, especially after adding PEG. The hydroxypropylene groups grafted onto both cellulose and starch improved the compatibility between the HPMC and the modified starch. The higher viscosity of starch at lower temperature improved the viscosity balance of the system, which enlarged the operation window for the dipping-drying technique. The PEG increased the transparency and toughness of the various blends. By optimizing temperature and incubation time to control viscosity, capsules of various blends were successfully developed.

Insights into molecular structure and digestion rate of oat starch

The in vitro digestibility of oat starch and its relationship with starch molecular structure was investigated. The in vitro digestion results showed that the first-order kinetic constant (k) of oat starches (OS-1 and OS-2) was lower than that of rice starch. The size of amylose chains, amylose content and degree of branching (DB) of amylopectin in oat starch were significantly higher than the corresponding parameters in rice starch. The larger molecular size of oat starch may account for its lower digestion rate. The fine structure of amylopectin showed that oat starch had less chains of DP 6-12 and DP>36, which may explain the small difference in digestion rate between oat and rice starch. The biosynthesis model from oat amylopectin fine structure data suggested a lower starch branching enzyme (SBE) activity and/or a higher starch synthase (SS) activity, which may decrease the DB of oat starch and increase its digestion rate.

Understanding how the aggregation structure of starch affects its gastrointestinal digestion rate and extent.

Regulating the starch gastrointestinal digestion rate by control of its aggregation structure is an effective way, but the mechanism is still not clear. Multi-scale structure of waxy and normal wheat starches were studied by confocal laser scanning and scanning electron microscopes, as well as wide-angle and small-angle X-ray techniques in this study. In vitro digestion kinetics of those two starches and structure-digestion relationship were also discussed. Both waxy and normal starches show A-type diffraction pattern, but waxy variety shows a slightly higher crystallinity. Small-angle X-ray scattering results show that waxy wheat starch has higher scattering peak intensity (Imax) and a larger crystallinity lamellar repeat distance (Lp) compared with the normal wheat starch. We suggested that the higher digestion rate of waxy starch at initial stage is mainly due to more small-size particles, but the higher crystallinity and the larger crystalline lamellar size limit the digestion extent.

Morphology and phase composition of gelatin-starch blends

Morphology and phase compositions of different starch-gelatin blends were investigated by various microscopes: optical, SEM and synchrotron FTIR microscopy. A high amylose (80%) corn starch, grafted with hydroxypropyl to enhance flexibilty and hydrophilicity, and plasticized by poly(ethylene glycol) (PEG), was used in this work. SEM revealed that the surface became smoother after adding PEG. Optical microscopy observation revealed that compatibility between gelatin and starch was improved by adding PEG. An FTIR beam focused on a 5 μm × 5 μm detection area by the micro-spectroscope was used to map chemical composition. The ratio of areas of the saccharide bands (1180-953 cm−1) and the amide I and II bands (1750-1483 cm−1) was used to monitor the relative distributions of the two components in the blends. The FTIR maps indicated that gelatin constituted the continuous phase up to 80% of starch content. All of the FTIR spectra showed contributions from both starch and gelatin absorptions, therefore indicating that complete demixing with pure starch and gelatin domains did not occur. The PEG improved the compatibility of the gelatin-starch blends.

Starch Based Blends, Composites and Nanocomposites

The development and production of biodegradable starch-based materials has attracted more and more attention in recent years due to the depletion in the world’s oil resources and the growing interest in easing the environmental burden from petrochemically derived polymers. Furthermore, the unique microstructures of different starches can be used as an outstanding model system to illustrate the conceptual approach to understanding the relationship between the structures and properties in polymers.

Structure and digestion of hybrid Indica rice starch and its biosynthesis

The fine structure (including contents, size and chains length distribution) of amylose and amylopectin of Hybrid Indica Rice starch have an impact on digestion properties of Indica Rice. Indica Rice starches with different amylose contents were chosen as model materials in this study. The amylose and amylopectin size were characterized using size-exclusion chromatography (SEC), the fine structure of amylopectin were studied by flurophore-assisted carbohydrate electrophoresis (FACE) and parameterized by amylopectin biosynthesis model to identify associations with starch digestibility. The digestograms of all starches fit first-order kinetics. All results show that the hybrid Indica rice starch with higher amylose content has a slower digestion rate. SEC results show that there is no obviously in chains length distribution (CLD) for amylopectin, but a significantly sharp difference in amylose. No difference in amylopectin was also observed from FACE result. The amylose starch controlled by GBSSI enzyme may be the key parameter to influence starch digestion.

Phase Transition of Waxy and Normal Wheat Starch Granules during Gelatinization

The phase transition of waxy and normal wheat starches was systematically studied by light microscopy (LM) with a hot-stage, confocal laser scanning microscopy (CLSM) and differential scanning calorimetry (DSC). While being heated in water, waxy wheat starch showed a higher gelatinization enthalpy than that for the normal starch, which was also verified by the changes in birefringence. As confirmed by LM and CLSM, starch granules displayed an increased swelling degree with temperature increasing, and the gelatinization initially occurred at the hilum (botanical center) of the granules and then spread rapidly to the periphery. While the temperature range of birefringence was narrower than that of granule size change, the crystalline structure was melted at lower temperatures than those for the molecular orders. These results indicate that starch gelatinization was a complex process rather than a simple order-to-disorder granule transition.