食品中膽固醇氧化物的分析，形成與抑制：綜論（第二部分）   全文下載

Analysis, Formation and Inhibition of Cholesterol Oxidation Products in Foods: An Overview (Part II)

膽固醇受熱或光照時會進行一系列自氧化或光氧化作用形成膽固醇氧化產物（cholesterol oxidation products, COPs）。許多研究指出，COPs 可能與許多生理不良反應有關，如細胞突變、致癌、血管腫瘤、細胞毒害、動脈硬化、細胞損傷及抑制膽固醇合成等。因此，COPs 的安全性已經是大眾所關切的問題之一。本文主要針對食品中COPs的分析方法及其生成與抑制作一綜合性的回顧及討論。食品中的COPs一般使用有機溶劑萃取，經皂化及固相萃取法純化濃縮後，再利用薄層層析（TLC）、高效率液相層析（HPLC）或氣相層析質譜儀（GC-MS）加以定性及定量。GC-MS測定COPs含量具有快速及靈敏度高的優點，但因高溫操作而可能產生其他異構物是其主要缺點。對HPLC而言，則無法分離某些幾何異構物及無法以紫外光偵測不含雙鍵的COPs，如5, 6- epoxide異構物及triol。許多因素會影響食品中膽固醇的氧化作用，如加熱、光照、貯存環境及食品組成等。食品中主要的COPs包含7α-OH、7β-OH、5, 6α-EP、5, 6β-EP、7-keto、20α-OH、25-OH及triol等。其中5, 6α-EP、5, 6β-EP、7-keto、20α-OH、25-OH為一級產物，而7α-OH、7β-OH及triol則為次級產物。部分抗氧化劑已被証實在適當濃度下具有抑制膽固醇氧化的效果。此外，適當的包裝亦可降低光和空氣對食品中膽固醇的氧化傷害，減少COPs的產生。更多的研究必須進行以瞭解如何有效抑制食品中COPs的生成。"

Cholesterol can undergo oxidation to form a large amount of COPs after heating at an elevated temperature for a certain period of time. Fioriti and Sim(66) heated the cholesterol solution at 82°C for 9 weeks and a total of 13 COPs was formed. The long heating period probably plays an important role for COPs formation because it has been reported that cholesterol is very stable at 100°C(68). Meanwhile, the application of different heating facilities may influence the production of COPs in various forms. The amount of COPs in the egg mix with direct heat treatment utilizing a gas fired oven to generate hot air, was found to be three times higher than the indirect heat treatment using a steam convection process(43). Of the various COPs, 7-keto, 5,6α-EP and 5,6β-EP were present in the highest amount. The ratio of 5,6α- EP/5,6β-EP was reported to be between 1 and 4(67). The reason that the direct heating treatment produced a higher amount of COPs can be attributed to the formation of nitrogen oxide, which is a by-product of organic combustion. Nitrogen oxide is known to be able to initiate the autoxidation of unsaturated fatty acids(43). Osada et al.(68) studied the stability of cholesterol during heating at 100, 120, 150 and 200°C for 24 hrs in an oven. Results showed that approximately 60% of cholesterol was destroyed after 150°C heating for 24 hrs, while the complete destruction of cholesterol was observed after 200°C heating for 6 hrs. Likewise, under this condition, all of the COPs formed were also degraded completely. Interestingly, no oxidized cholesterol was formed at 100°C for 24 hrs. In view of this result, certain cooking methods such as boiling and steaming are likely to limit the formation of COPs. A total of six COPs was generated, including 7α-OH, 7β-OH, 5,6α-EP, 5,6β- EP, 7-keto and triol in the heated cholesterol(68). 膽固醇受熱或光照時會進行一系列自氧化或光氧化作用形成膽固醇氧化產物（cholesterol oxidation products, COPs）。許多研究指出，COPs 可能與許多生理不良反應有關，如細胞突變、致癌、血管腫瘤、細胞毒害、動脈硬化、細胞損傷及抑制膽固醇合成等。因此，COPs 的安全性已經是大眾所關切的問題之一。本文主要針對食品中COPs的分析方法及其生成與抑制作一綜合性的回顧及討論。食品中的COPs一般使用有機溶劑萃取，經皂化及固相萃取法純化濃縮後，再利用薄層層析（TLC）、高效率液相層析（HPLC）或氣相層析質譜儀（GC-MS）加以定性及定量。GC-MS測定COPs含量具有快速及靈敏度高的優點，但因高溫操作而可能產生其他異構物是其主要缺點。對HPLC而言，則無法分離某些幾何異構物及無法以紫外光偵測不含雙鍵的COPs，如5, 6- epoxide異構物及triol。許多因素會影響食品中膽固醇的氧化作用，如加熱、光照、貯存環境及食品組成等。食品中主要的COPs包含7α-OH、7β-OH、5, 6α-EP、5, 6β-EP、7-keto、20α-OH、25-OH及triol等。其中5, 6α-EP、5, 6β-EP、7-keto、20α-OH、25-OH為一級產物，而7α-OH、7β-OH及triol則為次級產物。部分抗氧化劑已被証實在適當濃度下具有抑制膽固醇氧化的效果。此外，適當的包裝亦可降低光和空氣對食品中膽固醇的氧化傷害，減少COPs的產生。更多的研究必須進行以瞭解如何有效抑制食品中COPs的生成。