檸檬精油儲存於檸檬果皮的油胞皮層內，其中約90%為單萜烯類，主要成分為d-檸檬烯 (d-limonene)，其次為β-蒎烯 (β-pinene)以及γ-松油烯 (γ-terpinene)，故選擇以上三個成分作為HPLC定量分析精油的目標物。檸檬的用途，以食用為主，在壓榨成汁後，所剩殘渣與果皮占整顆檸檬重量的一半，因此近年來廢棄果皮再利用的議題受到重視，果皮內含有豐富的果膠、精油以及生物活性物質 (bioactive compounds)，而精油除了芳香療法及香味添加的應用外，其主要成分d-檸檬烯具有預防癌症的功效，包括皮膚癌及乳癌，此外，精油為良好的抑菌劑，如：真菌、桿菌等，由於抗癌、抗菌與抗氧化等功效，使精油在食品及醫藥營養方面有其重要性。故本實驗期能在安全且環保的前提下提升精油的萃取效率與產量，並且探討精油的抑菌效果。
本實驗以食品級界面活性劑萃取檸檬精油。以食品級與生物相容性為優先考量，並且以雲點溫度、精油溶解度、粒徑分布及穩定性與臨界微胞濃度作為篩選指標，得到最佳配方－P123與T80混合比例1：4。混合界面活性劑水溶液萃取結果顯示，P123/T80 (1：4)的萃取能力亦為最佳，並且隨著濃度與時間增加而上升，萃取新鮮與廢氣檸檬皮的最大量為每克的皮可萃取出5.92與2.08 mg的精油量，約占實際含量之59.21與50.21%。精油的抑菌活性實驗結果顯示，精油對三種細菌之抑制效果為B. cereus最佳，E. coli BL21 (DE3) 其次，P. hauseri ZMd44最差，且比較萃取的精油與增濃的精油對抑菌的結果可知，增濃技術能使抑菌效果有所提升。以界面活性劑增濃檸檬精油實驗結果顯示，精油的初始濃度對增濃效果沒有影響，而添加鹽類，會造成雲點溫度大幅下降，以6 wt% P123/T80具有最佳的增濃效果，其增濃因子約為20倍。

In this study, lemon essential oils (LEOs) were extracted from lemon peels by using nonionic microemulsions which could avoid the problem of residual organic solvent and large energy consumption. At first, the stability of the microemulsion formulations, including P123/Tween80 (in 1/4 mass ratio), P123/PE 64 (in 1/4 mass ratio) and P123/T20 (in 1/2.5 mass ratio), was examined by size measurements with the dynamic light scattering (DLS). Our results showed that P123/Tween 80 was the most stable one during a test duration of 21 days. With the good storage stability, the P123/Tween80 system could satisfactorily form microemulsions and extract LEOs from peels. Effects of various parameters including the mixed ratios of surfactants, the dosage of surfactants and the concentrations of micellar solutions, as well as the procedures of the dynamic extraction, were all investigated in attempt to optimize the extraction condition. The results of LEOs extraction obtained by using 6 wt% P123/Tween80 after 24 h indicated an LEO extraction efficiency of 59.2% and 50.2% for fresh and waste peels, respectively. Moreover, the preconcentration technique was well used with sodium sulfate added to dramatically decrease the cloud point of the three formulations. Under the optimal condition, the preconcentration factor of P123/Tween80 was more than 20 and the most in all mixed surfactants used in this work. On the other hand, the antibacterial activity was determined against bacteria using growth curve and disc diffusion method under in vitro conditions. The commercial LEOs and extracted LEOs had fairly better activity against Bacillus cereus, compared with Escherichia coli BL21(DE3) and Proteus hauseri ZMd44. It is also found that the antibacterial effect of LEOs could be further improved by using preconcentration technique, leading to the higher concentration of LEOs present.

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