Highly Efficient Extraction of Decanoyl Acetaldehyde from Houttuynia cordata by a Cryogenic Grinding Technique

Abstract

Regarded as the antibiotic of herbal medicine, Houttuynia cordata Thunb. (HCT) has been a time-honored traditional Chinese medicine (TCM) and widely employed for treating anaphylaxis, cough, cancer, and viral infection in China and other countries [1]. The medicinal properties claimed for the drug have been attributed to its volatile oil. Houttuynine (decanoyl acetaldehyde) is one of the key effective components in the essential oil of HCT. The content of decanoyl acetaldehyde in the volatile oil of HCT showed great differences. Qi M. et al 2 reported that the content of decanoyl acetaldehyde extracted by flash gas chromatography was only 0.60%. Zeng Z. et al 3 reported that the content of decanoyl acetaldehyde extracted by steam distillation (SD) was up to 5.1%. The maximum content of decanoyl acetaldehyde extracted by headspace solid-phase microextraction (HS-SPME) was 7.23% as reported by 4. Decanoyl acetaldehyde is unstable and easily oxidized into decanoyl acetic acid and then decomposed into 2-undecanone in the process of distillation and during storage 4. Thus, it is difficult to extract this component from HCT efficiently. Herein, we communicate the results of further research on the extraction of essential oil from HCT by the cryogenic grinding technique. The specimen was the fresh subterranean stems of HCT collected from Shanghai. The volatile components of HCT extracted by immersing the cryogenically ground HCT with ethyl acetate (ICG) was compared with two other methods of SD and solvent immersion at room temperature (IRT). An Agilent 6890 gas chromatograph equipped with a 5973N mass spectrometer was employed for analysis of the volatile components. Twenty-eight components extracted by SD, such as -pinene, -phellandrene, -pinene, -myrcene, limonene, 3-cyclohexen-1-ol, bornyl acetate, 2-undecanone, decanoyl acetaldehyde, etc., were obtained. The highest content among these components was 2-undecanone (26.56%), while the content of decanoyl acetaldehyde was only 0.03%. The volatile components extracted by IRT decreased remarkably, and only 14 compounds were obtained. The content of 2-undecanone among these components decreased from 26.56% to 0.63%, while the content of decanoyl acetaldehyde increased from 0.03% to 48.26%, in contrast to SD. The results showed that the oxidation of decanoyl acetaldehyde was inhibited effectively under lower extraction temperatures. Therefore, the content of decanoyl acetaldehyde in the volatile oil extracted by IRT was far higher than that extracted by SD, and it was also far higher than that obtained by HS-SPME (7.23%) 1. However, it was a time-consuming process, although the content of decanoyl acetaldehyde in the volatile oil obtained by IRT increased remarkably in contrast to SD and HS-SPME. On the other hand, decanoyl acetaldehyde was also oxidized slowly to produce more 2-undecanone, and the content of decanoyl acetaldehyde in the volatile oil extracted by IRT decreased slightly with increase in immersing time. A quick extraction method for the volatile components of HCT was developed, in which the extract was obtained by immersing the cryogenically ground HCT with ethyl acetate. The HCT was frozen by liquid nitrogen beforehand. Twelve volatile components as shown in Table 1 were obtained. The 2-undecanone was not detected, while the content of decanoyl acetaldehyde among these components reached as high as 62.54%. The results showed that the oxidation of decanoyl acetaldehyde was further restrained under extremely low temperatures. The extractability of the volatile oil by ICG increased up to 0.85%, in contrast to the two other methods SD (0.09%) and IRT (0.15%), while the extractability of decanoyl acetaldehyde increased to 0.53%. The results showed that the ICG extraction method was highly efficient for extraction of decanoyl acetaldehyde from HCT.