Effects of Different Drying Methods on the Total Phenolic, Rosmarinic Acid and Essential Oil of Purple Perilla Leaves

The effects of different drying methods (shade, sun, oven at 50°C, mid-infrared drying at 50°C and freeze drying) on the color, the contents of total phenolic (TP) and rosmarinic acid (RA), and the chemical compositions of essential oil (EO) of purple perilla leaves were studied. Results showed that oven drying presented the lowest a*/b* (greenness/yellowness) and was therefore desirable to the final color of dried purple perilla leaves. Freeze drying achieved the highest TP and RA contents of 29.72 mg/g and 5.73 mg/ g, respectively. The highest EO yield of 0.45% (w/w) was obtained by oven drying and shade drying. Thirty-five compositions were determined in EO and the main compositions were 2-hexanoylfuran, caryophyllene, trans-α-bergamotene and linalool. The compositions of EO changed significantly with different drying methods. The present study demonstrated that freeze drying was suitable to retain high TP and RA contents, while oven drying was better to retain high EO yield.