Effects and Mechanisms of Low-temperature Plasma Pretreatment on the Ultrasound-assisted Extraction Process of Total Flavonoids from Ginger Powder

Objective: Effects of low-temperature plasma pretreatment assisted by ultrasound on the extraction of total flavonoids from ginger powder were studied, and its mechanism was preliminary discussed, and provided a new method for the extraction of total flavonoids from ginger powder. Methods: The single-factor tests and three-factor three-level response surface optimization tests were carried out with the yield of total flavonoids in ginger powder as the index and discharge power, treatment time and air intake volume of low-temperature plasma as factors. Meanwhile, the contents of 21 kinds of polyphenols in ginger powder were determined by HPLC before and after low-temperature plasma treatment, and the structure of ginger powder were characterized by scanning electron microscope (SEM) and Fourier transform infrared spectroscopy (FTIR). Results: The optimum extraction conditions for total flavonoids from ginger powder were as follows: Vacuum degree less than 100 Pa, discharge power of 295 W, treatment time of 60 s, air intake volume of 150 cm³/min, and the yield of total flavonoids was 26.9 mg/g. Chromatographic results showed that 21 kinds of polyphenols were separated with high precision (relative standard deviation, RSD≤3.75%), good stability (RSD≤4.25%), good repeatability (RSD≤4.75%) and accurate and reliable recovery rate (average recovery rate of 84.11%~100.86%). After low-temperature plasma treatment, total flavonoids content in ginger was increased, and phenolic acids content was decreased. Etching effect of low-temperature plasma increased the surface roughness of starch particles and cell wall fragments in ginger powder and led to the decomposition of lignin, which increased the contact area between solvent and ginger powder, and it was conducive to solvent penetration. Conclusion: Ultrasound-assisted low-temperature plasma treatment is an effective method to extract total flavonoids from ginger powder.