Bioactive components and antibacterial activities of hydrolate extracts by optimization conditions from Paeonia ostii T. Hong ＆ J. X. Zhang

Tree peony is an economically important plant with nine wild species distributed in China. Among them, Paeonia ostii T. Hong ＆ J. X. Zhang is one of the most cultivated wild species for its ornamental, medicinal, and edible oil values. However, the biochemical composition and biological activities of hydrolate extracts from P. ostii are largely unknown. In this study, we investigated the potentials of various P. ostii organs for being used as antibacterial agents. The single-factor optimization and Box-Behnken Design (BBD) experiments were performed to determine the optimal hydrosol extraction conditions as follows: extraction duration of 4 h, temperature of 90 °C, pressure of 0.35 MPa, and ratio of 6:1. In total, 150 volatile chemicals were identified and quantified from P. ostii through gas chromatography-mass spectrometry (GC-MS). The antibacterial activities against eight Gram-positive and Gram-negative bacterial were examined. Among the volatile substances, mono-terpenoids (31.36–77.28 %) was of the highest content in P.ostii, followed by alcohols (17.69–26.82 %). The quantitative test demonstrated the P. ostii hydrosols being significantly effective against Staphylococcus aureus and Streptococcus hemolytis-β. In particular, the newly-grown leaf hydrosols displayed more pronounced antibacterial effects than those from other organ, with the inhibition zones and minimal inhibitory concentrations (MICs) being 10.65–17.5 mm and 0.78–12.5 mg/mL, respectively. The results indicate that the hydrolate extracts from P. ostii possessed remarkable antibacterial activities against some common skin-infecting and food-borne bacterial pathogens, implying that P. ostii could be a potential source for antibacterial agents for food, pharmaceutical, and cosmetics.