The acid-alkali titration method of determination of degree of substitution(DS) for starch acetates has been improved by using acetone as solvent instead of ethanol. The saponification time could be reduced from 48 h or 72 h(using ethanol as solvent) to 1 h with acetone as solvent, and the RSD also decreased. The method has advantages of rapidity and high accuracy.
In this paper,calcium alginate gel beads were prepared through a homemade microcapsule preparation system with multi-nozzles under forced high-voltage electrostatic field.The effect of operation parameters on the large-scale preparation of gel beads was analyzed.The results showed that the air pressure of feed was the decisive factor affecting the size and yield of gel beads,and the size distribution was dependent on several factors including the distribution of electric field,pulse potential,air pressure of feed,pulse frequency,pulse width and threshold potential.The gel beads with good sphericity,smooth surface and low dispersivity(CV<20%)can be prepared by adjusting and optimizing above parameters.It is more important that the yield of gel beads by the microcapsule preparation system is 20—40 folds higher than the traditional electrostatic droplet generator,which makes it possible to realize the large-scale preparation of gel beads.
An intestinal bio-microreactor with potential application prospect as a drug delivery system was proposed and studied. It was designed to overcome the problems such as complexity of separation and purification, and subsequent high costs, which always exist in producing genetically engineered drugs. For example, the process of separation and purification can be omitted by oral administration of genetically engineered microbes entrapped in semi-permeable membrane of microcapsules. The microencapsulated cells can live, metabolize and secrete therapeutic proteins in intestinal tract. In this paper, Pichia pastoris GS115 was selected as the model microbe, alginate-chitosan (AC) microcapsules as the carrier, and the physicochemical performance of the intestinal bio-microreactor was studied. It was found that the encapsulation efficiency of living yeast cells during the preparation of microcapsules was about 80%. It was shown that all AC microcapsules with yeast cells were kept intact in simulated gastric solution and simulated intestinal solution, and the survival of microencapsulated cells in simulated gastrointestinal solutions was 200-times higher than that of free cells, which showed that AC microcapsules can protect the activity of yeast cells. Furthermore, when being orally administered in mice, AC microcapsules could go through stomach and adhere to the surface of small intestinal mucous membrane over 12 h. Therefore, it was concluded that AC microencapsulated yeast cells could be used as intestinal bio-microreactor to secret bio-drugs in vivo directly.
