Ultrasonic-coupling Subcritical Water Extraction Of Polysaccharides From Lentinus

Lentinan polysaccharides(LP) showed a good effect in improving immunity, antivirus, antitumor, antioxidation et al. It deserved development and research. Hot water extraction(HWE) is the most commonly used method for the extraction of LP, but it limits extraction temperature, requires a long extraction time and possesses a slow extraction rate. So it is necessary to develop new and efficient extraction methods. Advantages with subcritical water extraction(SWE) include requiring simple equipment, a low process cost and the fact that it is pollution-free to the environment; therefore, it has been widely used in extracion and seperation field. Ultrasound technology showed unique advantage in extraction and has been widely combined with normal fluid extraction technology but rare with abnormal fluid. The paper introduced ultrasond to subcritical water extraction to improve polysaccharide yield.Under the condition of SWE and ultrasonic-coupling subcritical water extraction(USWE) considering the extraction temperature, extraction time, extraction pressure, ratio of solid to water and ultrasonic power to the influence of LP yield, the influence of temperature after vacuum degassing was also been discussed. The results were as follows: with the temperature rising, LP yield increased significantly, when the temperature exceeded 180℃, LP yield fell slightly.When extracting time growth, LP yield increased but decreased when the time surpassing 40 min. The influence of extraction pressure on the LP yield was not obvious. When the ratio of solid to water increased, the LP yield increasing then declining with 30 m L/g. With the augmentation of the ultrasonic power, the LP yield first increased then reduced, the most suitable ultrasonic power was 200 W. The LP yield extracted by USWE were higher than SWE, it demonstrated the exsistance of ultrasonic cavitation effect. The LP yield extracted by ultrasonic-coupling subcritical water extraction and vacuum(USWE+V) declined further illustrating the presence of ultrasonic cavitation effect, vacuum reduced the cavitation bubble nuclear in subcritical water, which affecting cavitation effect.The optimal extraction conditions obtained by response surface methodology(RSM) were as follows: an extraction temperature of 187℃, an extraction time of 40 min, a ratio of solid to water of 34 m L/g, and an ultrasonic power of 200W; the LP yield at these conditions was 34.024% 0.003(three trials). Extraction temperature is the most significant factor. Artificial neural network(ANN) was used to establish mathematical model of USWE. Firstly, using the network simulated the yield of LP on the condition of single factor by SWE and USWE, then predicted 30 optimization data and contrasted with the RSM. ANN has good fitting effect and prediction ability, the simulation effect was better than RSM in some extent.The scavenging effect of LP on ABTS radical was measured by rapid method of ABTS and the ferri iron reducing power was measured by FRAP method. These experiments were carried out on the condition of single factor(including extraction temperature, extraction time, ultrasonic power et al.). The results were: with the temperature rising, extracting time growing, ultrasonic power increasing, the scavenging on ABTS radicaland the ferri iron reducing power were strengthened, but was not the linear relationship with the extraction rate, the scavenging on ABTS radical and the ferri iron reducing power on the optimal condition were superior than others.For the nonideal state of water, the cavitation threshold value in subcritical water was higher than normal water, but collapse time was shorter. By establishing the cavitation bubble movement equation in subcritical water acquired the parameters to the influence of ultrasonic cavitation effect. From the view of mechanics obtained the acceleration of ultrasound in subcritical water was 6946 times of the gravitational acceleration. The ultrasonic cavitation effect and mechanical effect were the main reason to strengthen the subcritical water extraction.