Isolation, purification, identification, and stability of anthocyanins from Lycium ruthenicum Murr

Response surface methodology was used to investigate the ultrasonic-assisted extraction of anthocyanins from Lycium ruthenicum Murr. A Box-Behnken design of three-level-three-factor was used to optimize extractive factors, including ethanol concentration (A), ultrasonic extraction time (B), and liquid-solid ratio (C) and to achieve high extraction yield of the anthocyanins. The three parameters were optimized at 70% (v/v), 28min, 33: 1 (mL/g), respectively, the best extraction yield of anthocyanins was 7.12 ± 0.093%. The AB-8 resin was further to be chosen for purification the anthocyanins. Anthocyanin composition was analyzed by HPLC-MS2, the possible structures can be speculated as petunidin-3-O-(glucosyl-p-coumaroyl)-rutinoside-5-O-glucoside, pentuidin-3-O-(caffeoyl)-rutinoside-5-O-glucoside, delphinidin-3-O-(p-coumaroyl)-rutinoside-5-O-glucoside, petunidin-3-O-(p-coumaroyl)-rutinoside-5-O-glucoside, malvidin-3-O-(p-coumaroyl)-rutinoside-5-O-glucoside, cyanidin-3-O-rutinoside, and petunidin-3-O-(p-coumaroyl)-rutinoside. The thermal stability indicated the high purity of anthocyanins, and purified anthocyanins combined with whey protein isolate (WPI) can enhance the thermal stability of anthocyanins. The thermal stability of the purified anthocyanins was higher than that of the unpurified anthocyanins; whereas the thermal stability of the purified anthocyanin-WPI synthesis was greater than that of the purified anthocyanins. The thermal stable anthocyanins and anthocyanin-protein synthesis has the potential application in the functional food industry.