Isorhamnetin, Hispidulin, and Cirsimaritin Identified in Tamarix ramosissima Barks from Southern Xinjiang and Their Antioxidant and Antimicrobial Activities

As a natural potential resource, Tamarix ramosissima has been widely used as barbecue skewers for a good taste and unique flavor. The polyphenolics in the branch bark play a key role in the quality improvement. The purposes of the present work were to explore the polyphenolic composition of T. ramosissima bark extract and assess their potential antioxidant and antimicrobial activities. Hispidulin and cirsimaritin from T. ramosissima bark extract were first identified in the Tamarix genus reported with UPLC-MS analysis. Isorhamnetin (36.91 μg/mg extract), hispidulin (28.79 μg/mg extract) and cirsimaritin (13.35 μg/mg extract) are rich in the bark extract. The extract exhibited promising antioxidant activity with IC(50) values of 117.05 μg/mL for 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 151.57 μg/mL for hydroxyl radical scavenging activities, as well as excellent reducing power with an EC(50) of 93.77 μg/mL. The bark extract showed appreciable antibacterial properties against foodborne pathogens. Listeria monocytogenes was the most sensitive microorganism with the lowest minimum inhibitory concentration (MIC) value of 5 mg/mL and minimum bactericidal concentration (MBC) value of 10 mg/mL followed by S. castellani and S. aureus among the tested bacteria. The T. ramosissima bark extract showed significantly stronger inhibitory activity against Gram-positive than Gram-negative bacteria. Nevertheless, this extract failed to show any activity against tested fungi. Overall, these results suggested that T. ramosissima shows potential in improving food quality due to its highly efficacious antioxidant and antibacterial properties.