土肉桂葉子精油之安定性及其改善方法

Abstract

土肉桂（Cinnamomum osmophloeum Kaneh.）葉精油具有許多良好的生物活性，但其安定性不佳，影響土肉桂相關產品的品質，因此，本研究探討土肉桂葉粉、葉精油及其主成分反式肉桂醛（trans-Cinnamaldehyde）的貯存性，尋求適當的保存條件及改善其安定性之方法，並探討精油於不同條件貯存1年後其反式肉桂醛含量及生物活性之變化。本試驗共採集14個地區品系的土肉桂葉子，並挑選其中1種品系的葉子打成葉粉後進行貯存試驗，另外，將13種品系的葉子萃取精油後進行長期貯存試驗，並由13種品系中選5種品系精油進行熱安定性試驗。 葉粉之貯存溫度越高會使反式肉桂醛含量減少越快，空氣流通也會促使反式肉桂醛含量下降，然而，光線對葉粉的影響較不顯著。含有丁香酚（Eugenol）之土肉桂葉精油的熱安定性佳，但不含丁香酚之精油以100℃加熱4 h後反式肉桂醛留存率為25.1%。為改善精油及其成分之熱安定性，評估7種抗氧化劑對反式肉桂醛熱安定性之影響，試驗結果證實丁香酚的效果最佳，當丁香酚與反式肉桂醛及精油的混合比例分別為2.6%及0.6%（v/v）時，即可獲得良好之熱安定性。 13種土肉桂品系的葉精油於25℃避光環境貯存12個月後，反式肉桂醛留存率可維持約70%以上；另外，不含丁香酚的土肉桂葉精油以不同條件貯存，於25及40℃避光環境貯存12個月後的反式肉桂醛留存率分別為90.8%及36.7%；若將精油置於照光環境（25℃）貯存，12個月後反式肉桂醛留存率下降為62.3%，而空氣對反式肉桂醛含量無顯著影響，此外，於精油添加抗氧化劑丁香酚和沒食子酸丙酯（Propyl gallate），仍無法改善光安定性。 反式肉桂醛具有良好的抗病媒蚊幼蟲、抗腐朽菌及抗黴菌活性，但熱氧化後其生物活性皆顯著下降，添加4.76%的丁香酚可改善其熱安定性及維持良好生物活性；而精油於不同貯存條件下的活性有所差異，反式肉桂醛留存率與生物活性呈高度正相關，因此，精油於25℃且避光環境下貯存之活性最佳。適當保存或處理土肉桂葉精油及葉粉，可使相關產品的加工製造或利用更穩定，以提高土肉桂的經濟價值。

Leaf essential oil from Cinnamomum osmophloeum Kaneh. has many excellent bioactivities, but essential oil of C. osmophloeum leaf has poor stability, which influences the quality of related products. Therefore, the appropriate storage conditions for C. osmophloeum leaf powder, essential oil, and its main constituent trans-cinnamaldehyde (Cin) were investigated. The methods to improve the stabilities of essential oils and Cin were also established. In addition, essential oils were stored at various conditions for one year and its Cin content and bioactivities were researched. In this study, 14 geographical provenances of C. osmophloeum were selected. Leaves from one provenance were ground into powder for storage experiment, and leaves from the other provenances were extracted by hydrodistillation to obtain the essential oil for storage experiment. Futhermore, 5 provenances of C. osmophloeum were selected from them for processing the thermal stability test. Content of Cin in leaf powder decreased significantly when it was stored with high temperature and in ventilated conditions, whereas the influence of light was slight. In addition, essential oils containing eugenol exhibited excellent thermal stability, but the retention of Cin decreased to 25.1% when essential oil without eugenol was heated at 100℃ for 4 h. Seven antioxidants were selected for improving the thermal stability of essential oil and Cin. Among them, eugenol provided the best thermal stability to Cin, and essential oil and Cin had excellent thermal stabilities when 0.62% (v/v) and 2.60% eugenol were added, respectively. 13 geographical provenances of C. osmophloeum leaf essential oils were preserved in dark condition at 25℃ for 12 months, and the retention of Cin was more than 70%. In addition, the essential oil of C. osmophloeum leaf without eugenol was preserved in various storage conditions. When it was stored at 25 and 40℃ for 12 months, the retention of Cin was 90.8% and 36.7%. Besides, the retention of Cin decreased to 62.3% when it was stored at 25℃ in lighted condition. However, the content of Cin in essential oil was not affected by air. Althought antioxidants including eugenol and propyl gallate were added into the essential oil, its stability could not be improved. Cin has excellent larvicidal, antifungal and antimildew activities, but these bioactivities all decreased after thermal oxidation. The thermal stability and bioactivities could be improved by the addition of 4.76% eugenol. Bioactivities varied when the essential oil was stored at various conditions and high correlations between retention of Cin and bioactivities were observed. Therefore, the essential oil showed the best bioactivities when it was stored at 25℃ in dark condition. The stability of C. osmophloeum related products could be improved when they were stored or treated properly, and consequently the economic value of C. osmophloeum might be increased.