Influence of Harvest Season and Drying Method on the Antioxidant Activity and Active Compounds of Two Bamboo Grass Leaves

Changes of the antioxidant activity and active compounds content from two bamboo grass leaves, namely, Pleioblastus kongosanensis f. aureostriatus and Shibataea chinensis, as affected by different harvest season and drying methods were investigated and the main compounds that influence the antioxidant activity of two bamboo grasses were analyzed by principal component analysis. The content of total flavonoids, phenolics, triterpenoids and eight active compounds, i.e., orientin, isoorientin, vitexin, homovitexin and p-coumaric acid, chlorogenic acid, caffeic acid, ferulic acid were determined by UV-spectrophotometer and reverse phase high performance liquid chromatography synchronously, respectively, while antioxidant activity was measured using diphenyl-2-picryl- hydrazyl and ferric reducing antioxidant power methods. Both bamboo grasses leaves showed the highest level of total active components and antioxidant activity in winter. Different drying methods also affected the active compounds. Lyophilization, followed by vacuum drying and microwave oven drying, was the most suitable method for keeping active components, yet considering the energy consuming, microwave oven drying was recommended for bamboo grass leaves. Practical Applications Bamboo leaves, with excellent free radical scavenging, antioxidation, antibacterial, antiviral, enhancing immunity and other biological effectiveness, have been used for over 1,000 years in Asia as health food material and folk medicine. Bamboo grasses leaves, with advantages of rapid growth, lush foliage and easy collection, were a kind of new potential leafy bamboo grove. In order to improve the comprehensive utilization of leaves and exploit them more scientifically and efficiently, the present study investigated the changes of total phenolics, flavonoids, triterpenoid and eight active compounds content as well as antioxidant actives in leaves in accordance with seasonal variation and different drying methods. The results showed the optimum season for bamboo grass leaves harvest is at winter, and microwave oven drying was finally suggested for postharvest handling. It may provide a theoretical basis for further suitable exploitation and utilization of the leaf resources of the bamboo grasses.