Objective Using wild blueberries from Daxinganling Area, northeastern China as raw materials, the effects of organic solvent extraction, ultrasonic-assisted, microwave-assisted, and light-wave-assisted extraction methods on the extraction effects, chemical structure, and antioxidant function of proanthocyanidins and phenols from blueberries were studied.
Method The contents of proanthocyanidins, total phenols, total flavonoids and anthocyanins in the four kinds of extraction solution were determined by spectrophotometry. The structural changes of the four kinds of extraction solution were analyzed by infrared spectrum. The microstructure of the residues of blueberry treated by different ways was observed by scanning electron microscope. The total reducing capacity and the scavenging ability of DPPH, ABTS as well as hydroxyl radicals of the four kinds of extraction solution were also measured.
Result The maximum yield of proanthocyanidins extracted by microwave-assisted method was (15.72 ± 0.03) mg/g. The results showed that there was no obvious change in the chemical structure of proanthocyanidins extracted by four methods through infrared spectrum, and the pores and folds on the surface of the residue after microwave-assisted extraction were obvious by SEM (P < 0.05). When the blueberry proanthocyanidins extracted by the four methods was adjusted to the same concentration of 30 μg/mL, there was no significant difference in total reduction ability and DPPH free radical scavenging ability (P > 0.05). The free radical scavenging percentage of DPPH was above 97%. The order of scavenging capacity of hydroxyl radicals was general solvent extraction > microwave-assisted extraction > light wave assisted extraction > ultrasonic assisted extraction. The ultrasonic assisted method had the worst scavenging effect on ABTS radicals, and the solvent extraction method had the strongest.
Conclusion At the same concentration, the antioxidant activity of the solution from the solvent extraction is stronger, but the microwave-saaisted extraction method has the highest yield of proanthocysnins and the antioxidant activity is not significantly different from that of the solvent extraction method (P > 0.05). Microwave can promote the extraction of proanthocyanidins in a short time because of its strong ion polarization and dipole rotation, and there is no significant difference in the chemical structure and antioxidant function of proanthocyanidins after microwave treatment, so the microwave assisted method is more suitable for the extraction of proanthocyanidins from blueberry. By comparing the yields obtained when ultrasonic, microwave, and light wave treatments are performed separately and the yields after re-extraction after ultrasonic, microwave, and light wave treatments, it is found that ultrasonic, microwave, and light wave treatments dominate the extraction.