Ultrastructure of Chicken Eggshell Observed by Scanning Electron Microscopy (2)
扫描电镜法观察鸡蛋壳超微结构形貌
王绍清，曹 红，曹宝森
(国家食品质量安全监督检验中心，北京
100094)
摘?要：通过扫描电子显微镜，对鸡蛋壳的各部分固态结构，如鸡蛋壳的壳膜、椎体层、柱状层、表面晶体层和表皮的超微结构的形貌进行观察，获得相邻柱状单晶在表面结晶层表现的不同结晶方向的特点、未成熟的椎体雏形结构及椎体横断面的径向结晶方向等特殊结构的超微形貌特征。综合这些能够表征鸡蛋壳基本结构及特殊结构超微形貌特征的系统照片资料，建立一个典型的鸡蛋壳基本超微结构模式，可应用于鸡蛋壳生长机理研究、真假鸡蛋鉴别等。关键词：鸡蛋壳；蛋壳膜；椎体层；柱状层；表面结晶层；表皮
Ultrastructure of Chicken Eggshell Observed by Scanning Electron Microscopy
WANG Shao-qing ，CAO Hong ，CAO Bao-sen
(China National Food Quality and Safety Supervision and Inspection Center, Beijing
100094, China)
Abstract ：Morphology characteristics of eggshell, such as cuticle layer, prismatic crystal layer, column layer, cone layer, and outer and inner eggshell membranes were investigated with scanning electron microscopy. In addtion, some new ultrastructural features were also observed such as different crystallization direction of adjacent columnar monocrystals on the outer surface of prismatic crystal layer, the immature cones, and the radial crystallization on the cross-section of cones. These ultrastructural characteristics of eggshell could be adopted as a typical model of eggshell ultrastructures for understanding of the eggshell formation process, egg authenticity determination and other related research work.
Key words ：chicken eggshell ；eggshell membrane ；cone layer ；column layer ；prismatic crystal layer ；cuticle layer 中图分类号：TS201.2 文献标志码：A 文章编号：1002-6630(2013)13-0110-05
doi:10.7506/spkx1002-6630-201313024
收稿日期：2012-04-11
作者简介：王绍清(1972—)，男，高级工程师，博士，研究方向为食品分析与掺假鉴别。E-mail ：wwwshq@https://www.360docs.net/doc/7613321984.html,
到目前为止，国内外对鸡蛋的整体宏观构成，在大量研究成果的基础上，已经有了一致的认识。但在对鸡蛋壳超微结构形貌方面，虽然应特定研究的需要，相关研究资料里也给出了部分鸡蛋壳超微结构形貌照片，但依然缺乏足够详细的基础照片资料，并缺少系统研究成果的报道，因而无法建立一个基本的鸡蛋壳超微结构模式，也很难为鸡蛋壳生长机理、真假鸡蛋鉴别及其他相关研究工作提供参照。
在对鸡蛋的宏观整体结构研究方面，食品研究人员通过各种实验手段揭示了鸡蛋的基本结构如图1所示。鸡蛋由内向外主要由蛋黄、蛋白和蛋壳3个主要部分组成。整个鸡蛋被一层0.2～0.4mm 厚，黄白色或棕色不等的有孔石灰质蛋壳包裹着。蛋壳内侧衬着紧紧贴在一起的里外两层膜。这两层膜在鸡蛋粗端分开，并形成一个直径约为5mm 左右的气室。蛋白是一种水相的淡黄色胶状的液体，由黏度不同的3部分组成，紧贴蛋黄表面的蛋白层薄但黏性很强，其两端各形成一根系带，把蛋黄固定在
蛋壳的中心位置[1]。生鸡蛋里，蛋黄和蛋白都是液态，只有蛋壳和蛋膜是固态的，所以对鸡蛋的超微结构形貌的研究主要针对鸡蛋的蛋壳和蛋膜的超微结构进行观察。在对鸟类卵壳的超微结构研究方面，国内外研究者通过扫描电子显微镜对多种鸟类卵壳的超微结构形貌进行了观察，给出了大量的照片资料[2-4]。国内此方面相关研究主要从20世纪90年代初开始[5-9]。但这些研究多数主要注重于所研究的某稀有鸟类的卵壳与其生活环境、饲养条件或保存条件的关系，及其与其他鸟类卵壳的区别等，并没有从建立某种鸟类的卵壳超微结构模式的角度，给出详尽的照片资料。国内佘德伟[10]研究员，在对多种鸟类蛋壳超微结构进行详细研究的基础上，分析对照国内外前期研究经验和案例，给出了详尽的鸟类卵壳各部分结构的名称定义和解释。本研究将主要参照佘德伟研究中定义的鸟类卵壳各部分超微结构命名，参考国内外对各种鸟类卵壳研究的经验，通过扫描电镜，对鸡蛋蛋壳特有的固态结构，如蛋壳的壳膜、椎体层、柱状层、表
面结晶层和表皮等各部分超微结构的形貌进行观察，以建立一种典型的鸡蛋壳超微结构模式，为鸡蛋壳生长机理研究、真假鸡蛋鉴别及其他相关工作提供参照。
7
1.胚盘；
2.蛋黄膜；
3.卵黄心；
4.系带；
5.稀蛋白；
6.稠蛋白；
7.蛋孔；
8.气室；9.蛋壳外膜；10.蛋壳内膜；11.蛋壳(石灰质层)；12.蛋壳表皮[1]。
图 1 鸡蛋的横截面示意图
Fig.1 Cross-section of a chicken egg
1 材料与方法
1.1材料与试剂
所用鸡蛋采购于北京超市。
所用化学试剂均为分析纯，购自北京化工试剂公司。
1.2仪器与设备
S3400N型扫描电子显微镜日本日立高新技术有限公司。
1.3方法
1.3.1鸡蛋壳样品处理
将采购的新鲜鸡蛋敲碎，倒掉鸡蛋清和鸡蛋黄，先用自来水后用去离子水冲洗干净，然后置于红外灯下烤干备用。
1.3.2鸡蛋壳样品酸化处理
将制备好的鸡蛋壳或蛋壳膜样品置于体积分数4%甲酸溶液中浸泡20～40s不等，然后再用去离子水浸泡冲洗3～5次，最后置于红外灯下烤干备用。
1.3.3扫描电镜制样和观察
将制备好的鸡蛋壳小块样品，或平放，或垂直用导电胶带黏于样品台上。对于蛋壳膜样品可以直接平铺开，通过导电胶带黏于样品台上。黏好的样品喷金之后，置于电镜样品仓中，在高真空下，对样品各个部位，在不同倍率下分别进行观察拍照。
2 结果与分析
2.1鸡蛋壳
蛋壳是包裹在鸡蛋最外围的一层坚硬的结构，它象一个容器，承载着鸡蛋所有的液态组织如蛋黄和蛋白等，又象一道屏障，将鸡蛋所有的液态组织与外界隔离开来，保护着鸡蛋内部生态系统的独立性和完整性。鸡蛋的蛋壳由外向内主要由四部分组成：表皮层、表面结晶层、柱状层和椎体层。
2.1.1 鸡蛋壳的表皮层
a b
c d
e f
a.新鲜蛋壳外表面(×200)；
b.新鲜蛋壳外表面(×3000)；
c.经稀酸溶
液轻微溶蚀过的鸡蛋壳外表面(×200)；d.经稀酸溶液轻微溶蚀过的鸡蛋壳外表面(×3000)；e.经稀酸溶液溶掉表皮层后的鸡蛋壳外表面(×200)；f.经稀酸溶液溶掉表皮层后的鸡蛋壳外表面(×2000)。
图 2 鸡蛋蛋壳外表面电镜图
Fig.2 SEM images of the outer surface of chicken eggshell
在蛋壳的最外层有一层特别薄(3～5μm)，由输卵管腺体分泌的透明黏质蛋白质形成的，以白垩有机物或香脂类为主的护膜，此护膜即蛋壳的表皮层。此护膜不仅使蛋壳表面润滑有光泽，同时起封闭气孔，防止水分丧失和细菌侵袭的作用。在电镜下，蛋壳外表面凹凸不平(图2a)。在这些凸包之间交界处，可以清晰看到孔径较大的蛋孔，如图2a、c、e中的白色箭头所示。这些蛋孔与椎体层椎体之间凹处的孔洞相通。在高倍电镜下观察凸包的凸面上，可以看到孔径更微小的蛋孔(图2b)，通常由于运输或放置中碰撞破坏和空气中的干燥作用，蛋壳的表皮层也会破损，从而可以开启部分原本被表皮层覆盖的蛋孔。如果将蛋壳短时间浸泡在稀酸溶液(4%的甲酸溶液)中，溶掉部分表皮层后，在低倍电镜下可以看出蛋壳表皮的粗糙程度不一样，凸包的凸面变得更加粗糙，凹陷的边界处变化不明显(图2c)。在高倍电镜下，清楚看到凸包的凸面的表皮层已经被严重破坏，众多细微蛋孔被打开(图2d)。经稀酸溶液充分浸泡后，蛋壳的表皮层被完全溶掉，露出蛋壳表面结晶层(图2e)。从结晶层表面上看(图2e)，蛋壳的表面结晶层并不是一个整体，而是由一
个个无固定形状封闭界线围成的独立区域拼接而成。这些无定形界线的形状与柱状结晶层的一个个柱状单晶的外沿线(即椎体层中一个个椎体之间凹槽，图3g)的形状大致相同。而且这些相邻独立区域的结晶生长方向各不相同。如图2f所示，白色箭头表示各自所在区域的结晶生长方向，三个相邻区域结晶生长方向各不一样。同样可以推测，图2a 中的一团团无固定形状的凸包应该与表皮下的一个个柱状单晶相对应。由于在鸡蛋壳形成时，蛋壳的每个柱状单晶从其中心到周边，结晶生长停止的时间不一致，即柱状单晶周边的结晶生长先停止，中心的结晶生长最后停止，最终造成柱状单晶的外端面中心凸，边界凹的现象。
2.1.2鸡蛋壳的横截面结构
a b
c d
e f
g h
a.横截面全图(×230)；
b.表皮和表面结晶层(×2500)；
c.椎体侧面(×1000)；
d.柱状层(×2000)；
e.椎体层内侧(×500)；
f.椎体结点处(×2000)；
g.酸洗后椎体层内侧(×200)；
h.酸洗后椎体结点(×1000)。
图 3 鸡蛋壳横截面电镜图
Fig.3 SEM images of cross-section and cones of chicken eggshell
鸡蛋壳的四部分主要结构：表皮层、表面晶体层、柱状层和锥体层可以从鸡蛋壳横断面的照片上清晰辨别出(图3a)。鸡蛋壳的表皮层如上所述，是附着于鸡蛋壳最外围的一层油脂状物质，如图3b中最上方的薄层。紧靠表皮层下方的是表面结晶层，此部分主要由方解石结晶构成(图3b中最上方薄层下面的结晶体)，结构致密，厚度约为20μm。
表面结晶层的下方就是占据蛋壳2/3厚度的柱状结晶层，厚度约为200μm。它既是鸡蛋壳强度的主要贡献者，也是鸡卵生长时的主要钙源。柱状结晶层的典型特征是横断截面上分布众多纵横交错并相通的微小气孔通道(图3d)，这些气孔通道使得蛋壳的此部分结构呈现出海绵一样的结构。与表面结晶层相比较，柱状结晶层的气孔通道数目增加明显。
柱状结晶层的下方即为椎体层(图3a、c)，椎体层是由一个个半球型锥状突起构成，外侧与柱状结晶层相接，内侧通过锥状突起顶端的结点(图3c)与蛋壳外膜相衔接。在鸡蛋壳开始形成时，椎体由结点向上延续生长，不断扩大成半球状，同时压缩相邻椎体之间的空隙，直至相邻椎体靠到一起，在相互挤压作用下结晶继续向上生长，形成由一个个柱状单晶紧密排列而成的柱状结晶层，所以椎体层与柱状结晶层的界线并不明显，近似为椎体的根部。在高倍电镜下，可以看到椎体层表面由无数球形突起构成，还有许多微小的气孔。从椎体的纵断面(图3b)看，椎体中也有着纵横交错的气孔通道，数量比柱状结晶层略少。椎体之间的凹陷处有着孔径较大的孔洞，这些孔洞与开口于鸡蛋壳表面凸包之间凹陷处的蛋孔相通。无论是椎体表面的微小蛋孔还是椎体之间的孔径较大的蛋孔，都承担着椎体之间空隙与外界交换气体的重要作用。
锥状突起的顶端通过结点与蛋壳外膜相衔接(图3c)。图3e～h分别给出在低倍和高倍电镜下观察到的，去除蛋壳膜后的椎体顶端在酸洗前后的照片。从图3e、f可以看出，部分蛋壳膜纤维与椎体结点顶端的突起深深相互嵌在一起，蛋壳的椎体和柱状单晶就是从这些结点开始依次生成的[11]。通过稀酸溶液溶去蛋壳外膜的蛋白纤维后，可以清晰看到椎体层的椎体排列是无序的(图3g)，这说明蛋壳的椎体从蛋壳外膜上的哪一点开始结晶生长是随机的，但随着椎体的生长，椎体的直径逐渐膨大，相邻椎体的外沿也逐步靠近，这在空间上压缩了后来生成的新结点的成长空间，而且此时在充满椎体层空隙的高浓度的骨桥蛋白[12-13]作用下，小的和新的结点会停止生长。最终错落无序排列的椎体层在相互挤压作用下继续向外结晶生长形成由一个个柱状单晶构成的柱状晶体层(图3a、g)。在图4a～d中，给出了酸洗前后，在蛋壳外膜剥离时，随蛋壳外膜一起剥离下来的椎体断头横断面照片。由此同样可以看出，椎体的排列是无序的，并且椎体形成时，结晶是沿辐射方向生长的。稀酸溶液浸泡后，椎体中心部分首先软化，部分被溶去，椎体外围结构相对较坚固，耐受稀酸溶液腐蚀的能力较强(图4c、d)，这可能与结晶的成熟度有关。
a b
c d
e f
g h
i j
a～b.酸洗前附着于蛋壳外膜外侧面上横断椎体及其断裂面
(a.×200，b.×2000)；c～d.酸洗后附着于蛋壳外膜外侧面上横断
椎体及其断裂面(c.×500，d.×1500)；e.酸洗前蛋壳内膜外侧面
(×2000)；f.酸洗后蛋壳内膜外侧面(×2000)；g.酸洗前蛋壳内膜
内侧面(×1000)；h.酸洗后蛋壳内膜内侧面(×1000)；i.蛋壳内膜
内侧纤维层(×2000)；j.酸洗的蛋壳内膜内侧纤维层(×2000)。
图 4 鸡蛋壳的蛋壳膜各部分结构的扫描电镜图
Fig.4 SEM images of shell membranes of chicken eggs
2.2蛋壳膜
紧贴在鸡蛋壳内侧的蛋壳膜，由内外两层纤维膜组成。与鸡蛋壳椎体层相衔接的是蛋壳外膜，内侧包裹鸡蛋清的是蛋壳内膜。两层膜都是由多层蛋白黏多糖纤维交织而成的网重叠构成。围绕鸡蛋壳内侧，两层膜紧紧贴在一起，只在鸡蛋粗端的气室处才分开。按照由外向内的顺序依次对外膜外侧即与蛋壳椎体层相衔接的一侧、外膜内侧、内膜外侧和内膜内侧，分别通过电镜进行观察，结果如图4所示。蛋壳外膜的外侧直接与椎体层相衔接，由于膜纤维与椎体顶部结点互相嵌在一起，进行外膜剥离时，部分椎体头也随外膜一起断裂下来，这为实验提供了一个很好的椎体头横断面研究实例。稀酸浸泡对断裂的椎体头结构影响明显，对外膜外侧的纤维结构影响不大。蛋壳外膜内侧和蛋壳内膜外侧，无论从二者分离的气室部分取样还是从二者贴合的其他部分取样，在电镜下观察发现二者都是由纵横交错的蛋白多糖纤维组成，并且纤维上有许多黏多糖的瘤状突起(图4e～j)。在用稀酸溶液浸泡后，蛋白纤维并没有发生任何变化，蛋白纤维上附着的瘤状突起的数目减少了。在蛋壳内膜内侧(图4g、h)上附着一层很薄的膜，这层膜覆盖在纵横交错，凹凸不平，结有无数瘤状突起的纤维上，好像在树枝条上蒙一块绸缎。1995年，佘德伟在研究非洲鸵鸟蛋壳膜时，有学者[7]在研究家鸡蛋壳膜时发现了类似的光滑内膜结构。但国内佘德伟[10]学者在研究家鸡蛋壳膜时，却没有发现此膜结构，只看到和内、外膜相贴面一样的纤维层结构。膜覆盖下的蛋白纤维上，依然结有无数瘤状突起(图4i)，与其他部分纤维层一样，这些瘤状突起在经稀酸溶液浸泡后，数量减少(图4j)。另外，在观察随外膜剥离而断裂开来的椎体头时，还发现在蛋壳外膜外侧上具有多种未成熟的椎体雏形结构(图5)。这些未成熟的椎体雏形结构，由于较晚才开始生长，当椎体层成型后，椎体间隙中的骨桥蛋白浓度增高，抑制了这些椎体雏形结构的继续生长。
a b
c d
e f
a～f.分别放大2000、3000、2500、2000、2500、4000倍。
图 5 鸡蛋壳椎体层的各种不正常椎体雏形的超微结构的扫描电镜图Fig.5 SEM images of some immature cones in the cone layer of chicken
eggshell
3 结论
本研究通过扫描电子显微镜，按照由外向内，依次对鸡蛋壳(包括表皮、表面结晶层、柱状层和椎体层)、蛋壳外膜和蛋壳内膜的外表面、纵截面和内表面，及膜纤维等各部分固态结构的超微形貌进行系统观察，总结了大量可以表征鸡蛋壳超微结构特征的照片资料。同时本研究还首次观察到相邻柱状单晶在表面结晶层表现的不同结晶方向的特点、未成熟的椎体雏形结构及椎体横断面的径向结晶方向等特殊结构的超微形貌特征。这些系统的鸡蛋壳各部分固态结构的照片资料和部分特殊结构的特征照片可以帮助我们建立一个典型的鸡蛋壳超微结构模式，为鸡蛋壳生长机理研究、真假鸡蛋鉴别及其他相关工作提供参考。
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good afternoon everybody! I’m very glad to stand here and give you a short speech about challenge and opportunity,双手交握微笑 So, what’s an opportunity? It’s a great chance to achieve dreams, it’s a platform to show ourselves.Just as now,I’m standing here showing myself,it's one of my dreams,also my opportunity. Then, what about challenge? Challenge is a new or difficult task which test our ability and skill. it is a fighter, a sense of courage, the fearless spirit towards all difficulties, Many people are afraid of being challenged, worrying about change and failure.I used to be a member of them，but now,I find that sth we haven’t done isn’t as difficult as it seems, fear always hindered our courage. Said so much,此刻我最想与你们分享的一句话就是： we should welcome being challenged,and try to enjoy it.它很可能是你进步的机会 Cruel competition isn 't the excuse for failure. No one is regularly on a winner or a loser. To the strong willed, competition is the spring of hope; To the weak minded, it means the winter of despair. So turning into opportunities means taking advantage of these challenges and benefiting from them.In this way,you can be the boss of your life.这句语法有没有错误？指着他，手势 That’s all, thank you!
关于坚持的英语演讲稿
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关于生活的英语演讲稿3篇
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