Capsella bursa-pastoris (cv. Banye) was soaked in 100 μmol/L melatonin solution for 10 min and then stored at 2 ℃. Its quality and antioxidant capacity were evaluated as a function of storage time, and changes in chloroplast ultrastructure in its leaves were observed. The results showed that treatment with 100 μmol/L melatonin significantly reduced the respiration rate, inhibited the degradation of chlorophyll, decreased the accumulation of reactive oxygen species (ROS), and increased the activity of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), and ascorbate peroxidase (APX) and the contents of antioxidants. After 18 days of storage, melatonin-treated Capsella bursa-pastoris showed a 17.3% reduction in respiration rate, a 1.18- and 2.23-fold increase in the contents of ascorbic acid (ASA) and reduced glutathione (GSH), respectively, and a significant increase in the activities of SOD and glutathione reductase (GR) compared with the distilled water-treated control. The ultrastructural observation showed that the shape of chloroplasts and the lamellar structure of chloroplast grana in Capsella bursa-pastoris leaves were maintained well after treatment with melatonin. Therefore, melatonin treatment is beneficial to inhibit the yellowing, maintain the quality of Capsella bursa-pastoris and the structure of chloroplasts, and improve the antioxidant capacity of Capsella bursa-pastoris.

To determine the effects of drying methods on the volatile compounds and explore the key aroma compounds in Chrysanthemum nankingense leaves, head-space solid phase micro-extraction combined with gas chromatography mass spectrometry (HS-SPME-GC-MS) was employed for quantitative and qualitative analysis of the volatile compounds in C. nankingense leaves dried by hot air drying, vacuum-freeze drying or microwave-hot air drying. The result showed that a total of 140 compounds belonging to six classes (terpenes, esters, aldehydes, alcohols, aromatic compounds and other substances) were identified in all samples. Of these, 112, 86, 83 and 85 were detected in fresh and dried C. nankingense obtained by hot air drying, microwave-hot air drying, and vacuum-freeze drying, respectively. Among these compounds, terpenes were the most abundant, with contents of 229474.33, 64629.68, 56469.88 and 70832.87 μg/kg in fresh, hot air dried, microwave-hot air dried, and vacuum-freeze dried samples, respectively. Compared with the other drying methods, vacuum-freeze drying gave better retention of the abundance of volatile compounds. Vacuum-freeze dried C. nankingense had similar flavor to fresh samples, showing camphor-like, turpentine-like, flowery and grassy aromas. GC-MS combined with odor activity values (OAVs) confirmed that β-ocimene, caryophyllene and trans-β-farnesene were the major aroma components. GC-MS combined with E-nose can represent an efficient nondestructive method for the detection of volatile compounds in C. nankingense leaves and allow the discrimination of dried C. nankingense obtained by different drying methods. These results provide a theoretical basis for choosing drying methods and understanding the difference in volatiles components in dried C. nankingense obtained by different drying methods.