月桂叶(Bay leaf,Laurus nobilis)

樟科(Lauraceae)月桂属(Laurus)

学名:Laurus nobilis

中文名:月桂叶

【生理活性】

整株地上部分来源的伊朗月桂精油,主要成分有桉叶油醇(1,8-Cineole,55.8%)、α-乙酸萜品酯(α-terpinyl acetate,15.14%)、品烯四醇(terpinen-4-ol,5.27%)、α-蒎烯(α-pinene,5.26%)、β-蒎烯(β-pinene,4.06%)、异丙基甲苯(p-cymene,2.7%)和芳樟醇(linalool,1.4%)#2。若再比较月桂生长、开花前、开花和结果期4种阶段采收所制精油彼此间差异,发现主成分含量仅稍有不同,差异并不明显#3。赛普勒斯北方的月桂叶精油也有相似的成分组成,主要是桉叶油醇(58.59%)、α-乙酸萜品酯(8.82%)和品烯四醇(4.25%)#4。

除了桉叶油醇和蒎烯类,花朵含量较高的挥发性成分有α-桉叶油醇(α-eudesmol)、β-榄烯(β-elemene)和β-石竹烯(β-caryophyllene),果实有(E)-β-罗勒烯((E)-β-ocimene)和双环大牻牛儿烯(bicyclogermacrene),花苞则是(E)-β-罗勒烯和大根香叶烯(germacrene D)#5。

其他在月桂叶有机溶剂萃取物中也发现多种黄酮糖苷和megastigmane糖苷类成分#6-7,例如:山奈酚-3-吡喃鼠李糖苷(kaempferol-3-rhamnopyranoside)、山奈酚-3,7-二吡喃鼠李糖苷(kaempferol-3,7-dirhamnopyranoside)和laurosides AE等物质。

民俗疗法

传统上使用月桂治疗风湿、皮肤和肠胃疾病,例如:胀气、消化不良、打嗝,在伊朗则用于癫痫治疗。土耳其人认为有缓解痔疮、风湿疗效,并可作为蛇毒解毒剂,因它能帮助利尿及舒缓腹痛。近期另外发现可能也有治疗糖尿病和预防偏头痛效果。#8-9

抗氧化

实验显示,月桂叶乙酸乙酯萃取物有最佳的清除自由基功效,除了对多种自由基来源见效外,也可有效减少油脂过氧化。另在小鼠试验,月桂叶萃取物可减少肝脏和血液内油脂的过氧化,达到保护作用,尽管有化学毒物存在,也同样有效。#10

抗菌

月桂的20%酒精萃取物,能抑制金黄色葡萄球菌,效力和四环霉素(tetracycline)相似#11。月桂叶精油于浓度3.185µL/cm 2暴露168小时下可完全杀死玉米害虫(玉米象,Sitophilus zeamais)并使虫卵灭绝#12。有研究比较生鲜和干燥月桂叶制成精油的抑菌差异,结果显示干燥来源精油表现较佳,能抑制大肠杆菌、绿脓杆菌、金黄色葡萄球菌、指状青霉和链格孢菌属,不过若和常用抗生素的抑菌力相比,仍是远远不及#13。

镇痛和抗发炎

小鼠和大鼠研究证明,月桂叶精油可镇痛且能抑制发炎引起的肿胀,另还有温和镇静功效。其镇痛和抗发炎表现与治疗用药吗啡(morphine)和匹洛西卡(piroxicam)效果相近#14。

抗癫痫

因药物(Pentylenetetrazol)诱发癫痫的小鼠,若于给予药物前先腹腔注射0.75-1 ml/kg的月桂叶精油,则可完全抑制癫痫的诱发#9。根据过去研究,月桂叶精油抗癫痫功效可能是多种成分合作发挥产生的结果,这些成分包含桉叶油醇、蒎烯、丁香酚(eugenol)、甲基丁香酚(methyl eugenol)和芳樟醇。

神经保护

在大鼠的帕金森氏症实验模型,多巴胺(dopamine)诱发神经细胞产生自由基并凋亡,6-羟基多巴胺(6-hydroxydopamine)同样能导致神经细胞死亡。月桂叶己烷萃取物在实验中,于浓度1.0μg/ml即能有效抑制多巴胺诱发的自由基,并减少细胞凋亡,保护神经细胞。萃取物主要的两种成分,木香烯内脂(costunolide)和去氢木香内酯(dehydrocostus lactone),与治疗巴金森氏症药物阿扑吗啡(apomorphine)的保护效果相比,似乎更为优异(IC 50=7.3、3.6,18.1μM)。#15

改善阿兹海默症

过去研究认为乙醯胆碱(acetylcholine)参与我们的认知和学习过程,乙醯胆碱酯酵素(acetylcholinesterase)负责水解完成工作的乙醯胆碱,因此抑制乙醯胆碱酵素有助保留更多乙醯胆碱,改善轻微或中度阿兹海默症。体外研究发现#16,月桂叶水萃物、酒萃物和精油皆有抑制乙醯胆碱酯酵素活性功效,其中以精油和酒萃物较明显。

改善糖尿病

α-淀粉酵素(α-amylase)和α-葡萄糖苷酵素(α-glucosidase)能将人体内碳水化合物分解成小分子糖,促进人体吸收,抑制这些酵素能减缓小分子糖进入血液造成餐后血糖上升,有助于改善第二型糖尿病。月桂叶精油经体外研究显示#17,具有抑制α-葡萄糖苷酵素活性功效,若能进一步纯化主要成分桉叶油醇(1,8-cineole)和R-(+)-柠烯(R-(+)-limonene),效果会更好。

护肝

月桂叶酒萃物在大鼠研究展现护肝功效。腹腔注射毒物的大鼠在36小时内会全数死亡,但在注射毒物和月桂叶酒萃物混合物的实验组,全数活过36小时,且肝损伤程度显著改善,在20天的观察期间,肝指数逐渐回复至未中毒前状态#18。

可能风险

丰年虾的毒性研究表示#19,月桂叶水萃物和酒萃物低毒性,但己烷萃取物高毒性,662.71 ppm即可使半数丰年虾致死。

【料理应用】

月桂原生于南欧地中海流域,是北美、欧洲和经典法式料理频繁使用的香草#8,15。将生鲜月桂叶干燥能提升香气,它耐煮,适合添加在蒸煮、炖肉、炖菜和汤品增添风味及去腥,但烹调后食用前应将月桂叶取出,因叶片似皮革、味如蜡、边缘尖锐、久煮生苦,不好吃也可能划伤喉咙或肠胃,这也是为什么要使用整片月桂叶的原因,为了方便取出#20-22。干燥月桂叶精油和压榨油常用于鱼、肉类和汤品料理调味,果实来源的油脂则可制皂#8,23。

月桂叶精油有助于托斯卡尼香肠的保存和安全,研究表示制造配方中添加浓度0.05-0.1 g/100 g精油可有效降低大肠杆菌群孳生、延长保存期限、减少油脂过氧化#24。饲料中添加月桂叶可影响肉质,虹鳟吃含有月桂叶的饲料后,重量降低,但蛋白质增加且带月桂香,感官评测上明显优于吃一般饲料的虹鳟#25。北非胡鲶(Clarias gariepinus)食用含月桂叶氯仿萃取物的饲料,可提高存活率、增加蛋白质和体重,有促进生长功能#26。

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