Extraction, identification and physical-chemical stability of anthocyanins from two Hydrangea varieties

To explain the reason for different flower color adjustabilities of Hydrangea macrophylla, non-adjustable color ‘Tijana’ and adjustable color ‘Ravi Brent’ of Hydrangea macrophylla were used as experimental materials. The extraction conditions were optimized and the components of H. macrophylla anthocyanins were measured. Their physical-chemical stabilities were also explored, aiming to explore the mechanism of flower color adjustability. The optimal extraction conditions of Hydrangea anthocyanins by the ultrasonic method were determined through L9（33）orthogonal experiments. The anthocyanin components were separated and identified by UPLC-Q-TOF-MS. And the effects of temperature, light, metal ions and sugars on the physical-chemical stabilities of H. macrophylla anthocyanins were also explored in vitro conditions. The results were as follows: (1) The optimal conditions for extraction of H. macrophylla anthocyanins were that the ethanol concentration for ‘Tijana’ and ‘Ravi Brent’ were 70% and 80% respectively; the ratio of plant material to extraction solution was both 1∶20; and the extraction time was both 20 m. (2) The main anthocyanin component of the two varieties was both Delphinidin 3-O-glucoside. (3) H. macrophylla anthocyanins were more stable when stored below 70℃ and in the dark. (4) Both Cu2+ and Al3+ change the color of the anthocyanin solution, and Cu2+ specifically improved the stability of the anthocyanin of ‘Tijana’. 10-90 mmol·L-1 Ca2+, Al3+ and 90 mmol·L-1 Mg2+ had significant effects on the stability of anthocyanin of both varieties. Glucose, maltose, sucrose, galactose and 8%-10% concentration of rhamnose increased the stability of the non-adjustable color ‘Tijana’ Hydrangea macrophlla anthocyanins. While 4%-10% concentration of rhamnose promoted the stability of adjustable color ‘Ravi Brent’ Hydrangea macrophylla anthocyanins. The non-adjustable color ‘Tijana’ of H. macrophylla anthocyanins were more stable to light, sugars and most metal ions, compared with the adjustable color ‘Ravi Brent’. Only the anthocyanins of the adjustable color ‘Ravi Brent’ of H. macrophylla turned from pink to blue, and its stability increased after adding low medium concentration (10-30 mmol·L-1) of Al3+. However, the non-adjustable color ‘Tijana’ of H. macrophylla did not have this kind of color change, indicating that the difference in color adjustability of H. flowers is related to its physical-chemical stability. These results provide the theoretical reference for the extraction and observation of H. macrophlla anthocyanins, flower color improvement and dry flower color protection.