| Oat ?-glucan is a non-starch polysaccharide present in the cell wall with immuno-enhancement,hypoglycemic,anti-viral,anti-tumor,and other physiological functions.It has attracted people's increasingly interest and attention.In this paper,oat WeiDuYou 1st produced in Shanxi was used as materials for the extraction of?-glucan.Solution and gel properties of the extracted ?-glucan were studied.Freeze-thraw cycles were used to prepare oat ?-glucan cryogel for sustained-release of theophylline,and the sustained release characteristics were studied.The purity of the extracted ?-glucan was 88.4%,and the weight-average molecular weight was 674.3 kDa,which was designated as OGO.Three other ?-glucan samples with different molecular weight were obtained by acid hydrolysis,namely OG30,OG60 and OG90 with the weight-average molecular weight 385.3,314.6 and 252.0 kDa.The four samples were mainly used in the follow-up study.Light scattering and intrinsic viscosity measurement showed ?-glucan molecules existed as random coils in aqueous solution.Rheological studies showed that intermolecular entanglement mainly presented in 4%?-glucan solutions and 1%?-glucan solutions with higher molecular weight,while there may be aggregates or weak network structure in 1%?-glucan solution with lower molecular weight.Study on low field NMR showed that 1%?-glucan solution,4%OGO and OG30 only had a single signal of T2,and the T2 changed a little whether the solution was refrigerated or stored at room temperature.Phase separation occurred in 4%OG60 and OG90 solution.In which T2s of the upper solution phase increased with the storage time,and the corresponding signal ratio A2s reduced gradually.T2g and A2g of the gel phase firstly increased and then reduced.Microstructure analysis indicated that fibrous and granular structures were the major component at low concentration.There were more granular structures in lower molecular weight ?-glucan solution.The lamellar structure became more compact in solution with increasing concentration and molecular weight of ?-glucan.Aggregates formed in lower molecular weight ?-glucan solution were smaller and had a larger number.The results showed that the prepared p-glucan solutions were difficult to form a gel quickly duiring storage.Then freeze-thaw method was used to prepare oat ?-glucan cryogel.From the result of water relaxation properties,rheological properties,and textural properties of the gel,it was found that ?-glucan solution was easier to form a gel with higher concentration and smaller molecular size during freeze-thaw cycles.The cryogel from higher concentration solution with larger ?-glucan molesules had better gel properties through more freeze-thaw cycles.Phase separation occurred in 1%?-glucan solution during freeze-thaw cycles.The structure of high molecular weight P-glucan gel was compact,while the low molecular weight gel presented loose structure.4%?-glucan solutions formed integral gels after certain freeze-thaw cycles.The network of low molecular weight ?-glucan gel was looser with larger mesh structure.The prepared cryogel was used as a carrier to release theophylline.The optimum preparation condition was:adding theophylline of 5%weight of ?-glucan to 4%OGO solution.The mixture was exposed to 8 freeze-thaw cycles and then lyophilized to obtain a dry gel.The mechanism of sustained release could be described by Peppas equation.Releasing of theophylline from ?-glucan gel was mainly Fick diffusion mechanism. |
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