Extraction Optimization and Antibacterial Property of Total Flavonoids from Zizania Latifolia Bracts and the Effect on Chilled Pork Preservation

: Zizania latifolia is a widely distributed aquatic vegetable, and its bracts are an agricultural waste with a large proportion. In this study, Total Flavonoids of Z. latifolia Bracts (TFZB) were extracted with Ultrasound-Assisted Enzymatic Extraction (UAEE) for the first time, and the extraction process was optimized using Response Surface Method (RSM), and compared with other methods. Then, the antibacterial activity of TFZB extracted with optimized UAEE was assessed and the effects on chilled pork preservation were investigated. The optimal UAEE conditions for TFZB were: Cellulase dosage of 0.7%, enzymolysis time of 60 min, ultrasonic power of 704 W, and ultrasonic time of 47 min. Under these conditions, the TFZB extraction rate was up to 1.92%, which was significantly higher than those of other methods. The Scanning Electron Microscope (SEM) observation verified that the cytoskeletons of bracts had been severely damaged, resulting in a large release of TFZB. The infrared spectrum confirmed that TFZB has the typical characteristics that belong to natural flavonoids. Moreover, the TFZB extracted with optimized UAEE exerts significant antibacterial activities against Escherichia coli and Staphylococcus aureus with Minimal Inhibitory Concentrations (MIC) of 2.5 and 1.25 mg/mL, respectively. Finally, the TFZB solutions were sprayed onto the surface of fresh pork, and the indexes of the sensory score, pH, Total Volatile Basic Nitrogen (TVB-N), Metmyoglobin (MetMb)%, and total count of bacterial colonies during the storage period of chilled pork were measured. The results indicated that TFZB at 1.0 mg/mL can significantly improve the sensory quality of chilled pork via inhibiting microbes, and better preserve the freshness of pork when compared with sodium benzoate at 5.0 mg/mL. The present investigation implied that the TFZB extracted with optimized UAEE can be used as a natural flavonoid alternative resource to produce environmental disinfection products and novel preserving agents for chilled pork preservation.