Microencapsulation of andrographolide using konjac glucomannan hydrolysate by spray drying technique

Abstract

This research aimed at developing a suitable coating material from konjac glucomannan (KGM) for encapsulating a plant bioactive compound, andrographolide, using spray drying. There are three steps of study. In the first step, a suitable process for modifying the rheological properties of KGM solution by enzymatic treatment was developed. Mannanase (1500 units of enzyme) per 9% (w/w) of KGM solution was used in the study. The concentration of KGM solution was varied from 9 to 18% (w/w). It was found that 12% (w/w) was the optimum KGM concentration to obtain the konjac glucomannan hydrolysate (KGMH) with the viscosity less than 100 mPa·s. High Performance Liquid Chromatography (HPLC) analysis of hydrolyzed KGM showed that more than 27% of DP4-DP7 oligosaccharides were obtained. The second step, the solution was then used as coating material in spray drying with inlet air temperature of 170 °C and outlet air temperature of 85±3 °C. It was found that KGMH which was prepared from 12% (w/w) KGM was suitable for coating 2% (w/w) andrographolide. Its efficiency of encapsulation was also higher than using KGMH combined with gamma-cyclodextrin or beta-cyclodextrin. To produce a bioactive microcapsule, effect of spray drying temperature (outlet air temperature, 75±3 °C and 85±3 °C and inlet air temperature 150 °C, 170 °C and 190 °C) and concentration of the KGM (9%, 12%, 15%, 18% and 21% (w/w)) on encapsulation efficiency and yield of andrographolide microcapsules was studied. In the third step, the results indicated that andrographolide microcapsules produced at outlet air temperature at 85±3 °C had significantly (p≤0.05) higher % encapsulation and % product yield than those at 75±3 °C. Increasing inlet air temperature to 170 °C and 190 °C resulted in a higher significantly (p≤0.05) % encapsulation yield than at 150 °C. Therefore, the effect of inlet air temperature and concentration of KGM can effect with encapsulation efficiency of microcapsules. The 18% and 21% (w/w) concentration of KGM can enhance the retention of andrographolide in the microcapsules more than those of 9%, 12%, 15% (w/w). It was found that increasing the concentration of KGM during enzymatic hydrolysis had the same effect as increasing the inlet temperature to 170 °C and 190 °C. Physical and chemical properties of the microcapsules did not differ significantly (p>0.05). The best condition is to use 21% (w/w) of KGM along with an inlet air temperature of 190 °C and outlet air temperature of 85±3 °C. It provided the best retention efficiency and yield of androprapholide. In vitro testing of release of andrographolide in a simulation model of piglet’s digestive system showed that more than 70% of andrographolide remained in the microcapsules and can be further released to the target site.