A Study Of Mung Bean Starch Extraction With Protease And Its Ultrasonic Modification

Mung beans were planted widely; especially in the area of Yellow River and Huai River. Because of the special property of mung bean starch, it was used in the production and procession of bean vermicelli. The wet process was used to product the mung bean starch, but during the soaking, the SO2 was added into the solution which could pollute the environment and increase the cost. The effects of hydrolysis temperature, hydrolysis time, alkaline protease concentration and solid-liquid ratio were investigated, and the extraction process of starch with orthogonal experiment was studied. Results indicated that the optimal hydrolysis conditions were hydrolysis temperature of 46℃, hydrolysis time of 4.5h, and alkaline protease concentration of 700U/g and solid-liquid ratio of 1:3. The purity of prepared starch reached up to 93.97%.Different frequency ultrasound combined with amylase was applied into the treatment of mung bean starch. Compared to the single frequency ultrasonic treatment, the effects of the dual-frequency ultrasonic treatment on the properties and structure were studied. The research was aimed to provide reference datas for the production of mung bean starch modified. Determination of the degree of hydrolysis, retrogradation, solubility and peak viscosity were used to measure the effects of ultrasound on the properties of mung bean starch. Both the single frequency and dual-frequency ultrasonic treatment could promote amylase to hydrolyze mung bean starch. Compared to the single frequency treatment, the effect of dual-ultrasound was significant. Compared with the peak viscosity of native starch, the peak viscosity of starch treated by single frequency declined in various degrees. The peak viscosity of starch treated by dual-frequency ultrasound decreased 90% or more. The native starch grain diameter was 27.76μm, while it decreased 1μm after treated by single frequency ultrasound combined with amylase, and it declined to about 25.20μm after dual-frequency ultrasonic treatment. After the treatment, both the retrogradation and the solubility were changed. Short time ultrasonic treatment could delay starch degradation, and long time treatment could promote starch degradation obviously. Differernt frequency ultrasonic treatment combined with amylase could increase starch solubility. The solubility increased with increasing of the treatment time and the frequency. Compared to the single frequency ultrasonic treatment, dual-frequency treatment could increase the solubility significantly.Scanning electrical microscope, X diffractmeter and infrared spectrometer were applied to measure the effects on the structures. Holes or channels could be seen on the surface after the single-frequency ultrasonic treatment; there are more, deeper hole after treated by dual-frequency ultrasound treatment. The analysis of X-ray diffraction and infrared spectrum showed that the characteristic diffraction peak intensity was significantly reduced, diffuse diffraction features gradually increased without any damage in crystal of native starch. It means that crystal lattice ordering degree of starch was reduced.