Tea saponin is a naturally active substance with wide application prospective, and its purity is the key factor limiting its application and value. In this study, the optimal conditions for ultrasonic-assisted two-phase extraction (UAATPE) of tea saponin from camellia meal were explored, and the possible extraction mechanism was discussed in order to develop an efficient, high-purity extraction technology, so as to provide a technical guidance for high-value utilization of camellia meal.

On the basis of the single factor experimental results, the key factors affecting the yield of tea saponin were screened by Plackett Burman design, and the extraction process was optimized by Box-Behnken design. The extraction efficiency of tea saponin using the UAATPE method was evaluated by comparing the extraction yield and purity to the traditional ethanol extraction method and water extraction method. Scanning electron microscopy (SEM) was employed to analyze the microstructure of camellia meal, and the possible mechanism of extraction by the UAATPE method was discussed.

The key factors affecting the yield of tea saponin were mass fraction of ethanol, mass fraction of ammonium sulfate, and ultrasonic time. The process parameters optimized by Box-Behnken design were as follows: an ethanol content of 27.50% (W/W), an ammonium sulfate content of 19.60% (W/W), a liquid-solid ratio of 50∶1, an ultrasonic time of 32 min, an ultrasonic power of 300 W and an extraction temperature of 60℃, and the yield of tea saponin at (26.21±0.54)% was achieved under the optimized conditions. Compared with the traditional method of ethanol extraction, the purity of tea saponin extracted by the UAATPE method increased by 6.57% (P<0.05), although the difference of the yield of tea saponin extracted by these two methods was not significant. Compared with the traditional method of water extraction, the yield and purity of tea saponin extracted using the UAATPE method were increased by 17.74% and 40.23%, respectively (P<0.01). The microstructure showed that owing to the effect of the camellia meal treated by the UAATPE method, the ultrasonic cavitation accelerated the tissue damage of the camellia meal, producing a large number of voids and strong surface shrinkage, which effectively promoted the release of tea saponin in the camellia meal. In the process of the UAATPE extraction, the tea saponin first entered the bottom phase with high electrical conductivity through solid-liquid extraction in the two-phase water system, and then moved to the top phase with high polarity through liquid-liquid extraction, achieving primary purification and improving the purity of tea saponin.

The UAATPE method could significantly improve the yield and purity of tea saponin, thus providing a new novel method for the efficient utilization of camellia meal.