Optimization of the Preparation of High-purity Konjac Glucomannan Using the Ultrasound-assisted Acid-ethanol Precipitation Method and Analysis of Its Physicochemical Properties
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Abstract:
High-purity white konjac glucomannan (KGM) was prepared using the ultrasound-assisted acid-ethanol precipitation method. The purity of KGM was used as the evaluation index, and single-factor experiments and the response surface methodology were used to optimize the process conditions. Furthermore, the physicochemical properties and structure of KGM were analyzed. According to the results, the optimum conditions for the preparation of KGM using the ultrasoundassisted acid-ethanol precipitation method are as follows: ultrasonic treatment duration, 28 min; solvent pH, 3.7; volume fraction of ethanol, 70%; solid-to-liquid ratio, 1:75; and ultrasonic treatment temperature, 60 ℃. Under these conditions, the purity of KGM reached 97.08%, which is significantly higher than that of products obtained using conventional ultrasoundassisted ethanol extraction. Compared with raw white konjac powder, the high-purity KGM possessed improved water holding capacity (51.39 g/g), swelling power (17.05 mL/g), viscosity (34 600 mPa•s), cation-exchange capacity, and chroma. In particular, its oil holding capacity (2.69 g/g) was approximately 1.5 times that of raw white konjac powder. Compared with the 95% KGM standard, the experimentally obtained KGM exhibited no significant difference in the abovementioned physical and chemical properties. The microstructure analysis indicated that the surface of KGM had few impurities and a large number of small pore structures, similar to a honeycomb. Fourier-transform infrared spectroscopy revealed that the molecular structure of KGM had characteristic absorption peaks of polysaccharides. Thermogravimetric analysis indicated that the extracted sample was of high purity and had good thermal stability. Therefore, KGM prepared using the proposed method has good physical and chemical properties. These results provide a reference for the further development and application of high-purity KGM.
