red cabbage experiment three glasses

How Red Cabbage Changes Color – The Science of Blue, Pink and pH

Want to give your red cabbage salad a nice vibrant pinkish color? 只要撒上一点酸橙汁,原来是紫色的卷心菜就会变成粉红色! Or, to lighten up your cooked cabbage, 煮的时候加几片苹果,颜色会变浅.

想知道为什么会这样? It’s a great combination of complex molecules, pH, and our eyes. And it’s not even unique to red cabbage. 自然界中很多产品会根据所处环境的不同而改变颜色!

What gives red cabbage its color?

十大网赌排行榜周围到处都是颜色. They’re so common that you might think they’re simple as well. However, that’s not the case. Color and how we perceive color is a fascinating (but complex) topic. Colors can change depending on how and w在这里 you look at them (e.g. 在哪种光线下). 这取决于光线如何从颜色表面反射并进入十大网赌排行榜的眼睛. 使颜色可见, 某些波长的光必须经过反射和吸收才能到达十大网赌排行榜的眼睛.

这种反射和吸收通常是由具有相当特定结构的复杂分子完成的. 以红甘蓝为例, 这种颜色源于一种叫做花青素的分子. 这只是一组可以使食物呈红色的分子 更多的.

红甘蓝切片
红甘蓝横截面

花青素

花青素是一大类具有相同基本结构的分子, containing three rings of atoms (see below). 每一种花青素都含有相同的核心结构,这对吸收和反射光线产生颜色至关重要. 具体的工作原理对于本文来说太详细了(十大网赌排行榜建议阅读下面的参考资料). 简而言之, 这种特殊的结构允许分子将电荷(正电荷或负电荷)扩散到几个原子上.

在下面的结构中,每个花青素类型的r -基团都有不同的配置. 有些可能非常简单,只在这些位置包含氢原子. Others may contain larger complex structures. 这些不同的构型会改变分子与光的相互作用方式,从而改变分子的确切颜色. 也就是说,所有的花青素都有红/黑/紫/蓝的颜色.

anthocyanin structure, source 维基百科
The basic anthocyanin structure under acidic conditions. All anthocyanins share the core structure, but differ in the R-groups. 来源: 维基百科.

花青素的混合物

Red cabbage doesn’t just contain one type of anthocyanin molecule. Instead, it contains over 15 different ones!

花青素 are quite common in fruits and 蔬菜. 蓝莓、黑莓和某些红葡萄都含有花青素. 没有一种只含有一种花青素分子,它总是一种混合物. 正是这些分子的混合赋予了每种产品独特的颜色和行为.

花青素 are responsible for most reds/purples in plants. T在这里 are a few notable exceptions: 西红柿 (番茄红素) & 红甜菜(甜菜苷)!

Why does red cabbage change color?

因此,花青素的化学结构和配位决定了它们的颜色. 这种结构对周围环境的酸性非常敏感. It influences how it organizes the electrons within the molecule.

An acidic environment contains a lot of protons (H+). This results in the anthocyanin structure we shared above (with the O+). However, under less acidic conditions, this O+-基团失去正电荷,导致其他结构变化. 这些结构变化导致分子与光的相互作用不同,从而产生不同的颜色. Some anthocyanins can even completely lose color due to these changes.

The measure for acidity is the pH-value. A value between 0-7 is acidic, from 7-14 it’s alkaline. We’ve discussed acid base reactions in more detail 在这里.

切成薄片的红卷心菜加一些酸橙汁,使它变成粉红色而不是紫色
The red cabbage salad we discussed at the start, see that pinkish line? That’s w在这里 酸橙汁 has been sprinkled.

红甘蓝变色

花青素的类型决定了它们将如何应对环境ph值的变化. 以红甘蓝为例 the color roughly changes as follows (from: 斯坦福大学):

  • pH≈2:红色/亮粉色, 酸橙汁(十大网赌排行榜撒在沙拉上)会使酸碱度降低,使卷心菜变红
  • pH≈4:浅紫色
  • pH ≈ 6: violet (aka dark purple), this is approximately the color of your ‘native’ red cabbage, 如何购买
  • pH≈8:蓝色

在更高的pH值下, the red cabbage can even turn green/yellowish, 然而, you won’t generally encounter this when prepping red cabbage.

blueberry panna cotta with and without acid
Blueberries also contain pH-sensitive anthocyanins. These are two blueberry pannacottas, 唯一的区别就是右边的意式炖肉加了一些柠檬汁. Notice what a different those few drops make!

Controlling the color of red cabbage

通讯

Want to be updated on new food science articles? 订阅 to our weekly newsletter

In order to keep red cabbage in your preferred color, you have to control the acidity of the environment. 在大多数情况下,你可能会选择红色或紫色,而不是蓝色.

沙拉

As discussed at the top of this article, 在你的红卷心菜沙拉中加入一点酸橙汁或醋,让它呈现出明亮而有活力的颜色. These are all acidic ingredients that will keep the pH-value low.

烹饪红球甘蓝

If boiling red cabbage in water, 你可以在沸腾的液体中加入一点酸性物质,让它保持红色. 通常可以加苹果. 它们增加了一些酸味,以保持较低的酸碱度,但也为最后的菜肴增添了一丝甜蜜!

Note that, unlike a lot of other colors in fruits and 蔬菜 (e.g. 叶绿素), anthocyanins aren’t that sensitive to heat. 你可以安全地烹饪或煮你的红卷心菜,而不会失去所有的色素. Do try to keep the volume of boiling liquid low. A lot of anthocyanins will leach out of the red cabbage, in extreme cases you can even end up with pale red cabbage!

red cabbage experiment three glasses

Changing the Colour of Red Cabbage

Since red cabbage can be changed in color so easily, it's a great vegetable to use in a real scientific experiment on pH!  You can force the cabbage to change color by adding something acidic or something alkaline (with a pH>7). 你也可以用这个测试来判断某种液体是否比其他液体更酸. 让十大网赌排行榜看看会发生什么.

材料

  • Red cabbage leaves (4 large leaves are plenty)
  • 你想测试的酸, 例如:柠檬汁, 酸橙汁, 醋, 橙汁, 果汁, 苏打水! - take care to use regular food ingredients and no other chemicals, these might react a lot more strongly and vigorously.
  • 你想测试的碱性成分,例如:小苏打,肥皂

工具

  • 锅+炉子
  • Three clear glasses (take more if you want to test more liquids)
  • 搅拌器/汤匙

指令

    1. Take the red cabbage leaves and break them in slightly smaller pieces. 把它们放在锅里,盖上水,你可以加入大量的水(1-2升就可以了).
    2. Bring the cabbage to the boil and leave to boil for a few minutes, the water should have clearly changed color.
    3. 让卷心菜和水冷却,直到它凉到可以倒进玻璃杯里.
    4. Pour the 'red cabbage juice' in your glasses.
    5. 现在有趣的事情开始了! Add one of your test liquids to a glass of red cabbage water. 一开始只滴几滴, 在需要的地方搅拌,继续添加,直到你满意的颜色.
    6. !Be sure to be very careful when making acids and alkaline ingredients! These tend to react very intensely! 例如,小苏打和酸发生反应,会产生相当强烈的气泡.

笔记

这就是在红甘蓝汁中加入一点小苏打的结果, 注意蓝色?!

Red cabbage juice + baking soda, pH science

Adding a squirt of lemon juice turns it pink!

Adding lemon juice to red cabbage - effect of pH on colour

来源

Arapitsas, Panagiotis & Sjoberg,每 & 特纳,夏洛. (2008). 利用高分辨液相色谱-光电二极管阵列检测和电喷雾电离-线性离子阱质谱技术表征红甘蓝中的花青素. 食品化学. 109. 219-226. 10.1016/j.foodchem.2007.12.030.

Ummi Kalthum Ibrahim, Ida Idayu Muhammad and Ruzitah Mohd Salleh, 2011. The Effect of pH on Color Behavior of 芸苔属植物oleracea 花青素. Journal of Applied Sciences, 11: 2406-2410. link

Pericles Markakis,花青素作为食物颜色,Elsevier, 2012,第1章, link ; chapter 1 contains an extensive deep dive into the chemistry and the dependency on pH of anthocyanins

Pourjavaher, Simin; Almasi, Hadi; Meshkini, Saeed; Pirsa, Sajad; Parandi, •, 基于细菌纤维素纳米纤维和红甘蓝(甘蓝科)提取物的比色pH指示剂的研制, Carbohydrate Polymers 156 (2017) 193–201, http://doi.org/10.1016/J.CARBPOL.2016.09.027

《十大网赌排行榜》,白菜化学-寻找酸和碱,《十大网赌软件》,2012年1月26日, link

斯坦福大学, Red cabbage color indicator chart, 在这里.

新闻更新

Enter your email address below to subscribe to our weekly newsletter

留下一个回复

Your email address will not be published.

This site uses Akismet to reduce spam. Learn how your comment data is processed.

跳到指令