Anthocyanins: Butterfly Pea Flower and extraction

I mentioned in my previous post about using a natural blue food colour for my cake decoration. You may be familiar with this pea flower plant. Not only is this a source of natural food colour, there may be health benefits in taking this flower as it is a rich source of antioxidants. It is used as a food ingredient especially in South East Asia. The juice of the flower is famous for making the Nyonya kuih called pulut tai tai in Malaysia. It is also used in making kerabu rice. This was recently featured in Gordon Ramsay’s programme where he travelled to Malaysia. I had such a laugh as the Malay lady in the programme non-chalantly called this vine ‘clitorial bush’, to much of Ramsay’s ‘surprise’. Well, the taxonomist is to blame really! Anyway, unlike the rice featured in that programme, Kelantan’s nasi kerabu is very blue. Here’s my mum’s version of kerabu.

 Yums! Nasi Kerabu with dry beef rendang, fish crackers and a whole lot of condiments. Goes well with some beer, and of course, a bit of budu (not pictured, sorry).

The Mumakil has several vines growing in the garden, but for us living in a KL apartment, having our own ‘clitorial bush’ is not an easy one. So when I went back to Kelantan, I picked some of the flowers and tried to make an extraction. First, I did some studying on how best to extract the colour and keep it. Anthocyanins are the pigments in plants and are the reason that give this flower its distinctive blue colouration.  They are also water-soluble, which meant they can be easily extracted from the plant cells with a solvent such as ethanol (this part is removed because of error, see below for explanation). Here’s how I made my extraction:

  1. After rinsing and letting the petals dry a little, sterilise a small jar/bottle by heating it in hot water (I used a chicken essence bottle).
  2. Stuff all the flowers collected into the bottle and add a little alcohol such as vodka (You can use water if you don’t want alcohol, but you will have a little less pigment) (same error, see below).
  3. Using the handle of a clean spoon, squish the flowers until they are bruised and submerged in the liquid.
  4. (Optional step) Cover the bottle with some cling film and leave it in the fridge for a week to maximise extraction.
  5. Strain out the flower using a fine sieve (tea strainer is good).
To make a syrup, just add a whole lot of sugar to the extract. In Thailand, the flower is used to make a drink. Inspired by this, I made a cocktail out of it.
Butterfly Pea Blue Vodka Fizz
Add blue flower extract and two shots of flavoured vodka to a tall glass with ice. Add soda water or tonic. Stir. Simple.
I used a flavoured vodka because the butterly pea flower doesn’t really have much taste to it.
Now to play with the colours…
 As anthocyanin is pH sensitive. Not only pH plays a part in the colouration, it can also degrade the colour a little. You can read more about it in this paper or on wiki if you are biochemistry inclined. So to keep the blue colour, the liquid of the extract must be on the alkaline side. I decided to play around to see the range of colours I can make.
Erm, Pinkydoodles has a few (by a few, I meant 10) test tubes in the apartment. Perfect for my little experiment. The middle test tube in the picture above shows the colour after extraction. On the left is what happened when I added lemon juice to the extract to make it acidic. A nice reddish-purple colour.  The right test tube shows what happened when I added sodium bicarbonate to make it neutral (I think? tell me if I’m wrong). It turned a greenish blue. I don’t have anything very alkaline in the house unfortunately, but the colour should still be blue. Heh, talk about your very own litmus test.
Here’s another look. You can see that it is purple at the zone between alkaline and acidic.
So, if you are looking for a substitute for blue food colouring that is not artificial, you could try this. Won’t work obviously if your food is going to be sour, that is the disadvantage of natural food colours sometimes.
-M.
p.s: Today’s post is made to coincide with the anniversary of the formation of our country. Happy Malaysia Day!
An error: Thanks to a reader, who pointed out a flaw in my statement “They are also water-soluble, which meant they can be easily extracted from the plant cells with a solvent such as ethanol”. Much thanks and my apologies for the error. Ethanol IS NOT water so does not equate to water soluble. That means the solvent one should use here IS water. My bad.
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9 comments on “Anthocyanins: Butterfly Pea Flower and extraction

  1. Quay Po says:

    It is so good to know this flower can be used for food coloring. Now the hard part is where to find them:D

    • teambudu says:

      Haha, that’s true. The trouble is to find that plant, which is becoming rather scarce. It’s a shame, because it’s such a pretty vine with flowers and beans that you can eat. I do sometime come across them in PJ/KL houses though…
      -M.

  2. Autumn Belle says:

    Do you boil the blue solution first before drinking and can we just drink the raw juice?

    • teambudu says:

      Hi, Autumn Belle.

      You can take the flower raw. You can also boil it. The colour will fade a bit though if you boil the flowers. Hope that answers your question.
      -M.

  3. With all due respect: While it’s obvious you make a fine, colorfully-blue extract, your chemistry info is incorrect when you say:

    “They are also water-soluble, which meant they can be easily extracted from the plant cells with a solvent such as ethanol. ”

    Being “water-soluble” does not automatically mean they are soluble in ethanol. In fact, the opposite is true. Most water-soluble substances are not soluble in ethanol. However, a few substances are both water soluble and alcohol soluble … but they are the exception.

    BTW, I’m presently in my Bangkok apartment enjoying a delicious boxed Butterfly Pea Flower drink … and while it also contains 3% lemon juice … the color of the drink is a vivid blue … not red.

    • teambudu says:

      Yes, I stand to be corrected.
      Because my “ethanol” here means vodka (40% and not 100% ethanol), it was soluble. Actually I found out that anthocyanins are less soluble in alcohol.

      I’m not sure what is a “boxed Butterfly Pea Flower drink” but my raw extraction does responds to low pH like many anthocyanins. Maybe something has made the anthocyanins stabilised (assuming that your 3% lemon juice does mean low pH of course)?

      Would be great to know how to stabilise the colour so I can use a natural blue dye (independent of pH)!

      -M

      • By “boxed” I meant the small box-like, one-serving containers that are also used to package milk and various fruit juices.

        Also, I have a correction to my last post …. I took a better look at the juice in sunlight, and indeed the color is more reddish that I originally thought. Anyway I’m happy to have discovered a ready-supply of good quality Butterfly Pea flower juice and it’s become a daily beverage.

  4. how can butterfly pea flower’s dye be used as natural indicator?????

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