Abstract:

Some enzymes produced during mold fermentation degrade the tissue structures of the residue left after the extraction of starch from Pueraria lobata tubers to facilitate total flavonoids extraction. On the basis of the fact, the development of a method for the extraction of total flavonoids from the residue left after starch extraction using mold fermentation and subsequent ultrasonic treatment was presented in this work. Aspergillus niger and Trichoderma koningii were separately cultured in Pueraria lobata tuber residue to degrade its tissue structures, and Aspergillus niger was the selected strain according to the release of total flavonoids. The parameters affecting Aspergillus niger fermentation, including oxygen condition, soybean meal amount in the fermentation medium, initial fermentation pH and fermentation temperature were investigated by single factor experiments. Additionally, the combined method was compared with sole Aspergillus niger fermentation and sole ultrasonic treatment. The best Aspergillus niger fermentation process was that Pueraria lobata tuber residue suspended in 20-fold volume of water with the addition of 1.0 g of soybean meal, which was adjusted to pH 5, was inoculated with 5% Aspergillus niger seed culture for 60h fermentation at 30 ℃, and the resulting concentration of total flavonoids in the fermentation broth was determined by HPLC to be 3.769μg/mL, which was increased to 5.204 μ g/mL after 5 min ultrasonic treatment. Subsequently, separation and distillation were sequentially done to obtain a crude product with a total flavonoids content of 2.974 mg/g.

Key words: microbial fermentation for cell disruption, total flavonoids from Pueraria lobata tubers, Pueraria lobata tuber residue left after the extraction of starch