PURPLE CARROT and PURPLE SWEET POTATO

In North America, carrots are orange and so are sweet potatoes.  But in other parts of the world, carrots come in a variety of colors and sizes, as do sweet potatoes.  Purple carrots and purple sweet potatoes are grown specifically for their high concentrations of anthocyanin molecules.  Anthocyanins are the molecules responsible for the red, blue, violet, and magenta colors found throughout the plant kingdom.

Interestingly, anthocyanins found in vegetables differ from the anthocyanins found in fruits.  Anthocyanins found in vegetables are more heat stable than anthocyanins found in fruits.  This is the “good news.”  The “bad news” is anthocyanins found in vegetables tend to taste like the underlying vegetable source … not good when using them to color food or beverage products with delicate flavors.

It should be noted that when plants create anthocyanin molecules, they do not create one, single anthocyanin molecule.  Rather, plants create a “soup” of anthocyanins and the unique mixture of these anthocyanin molecules gives a plant its distinct color.  The six (6) most common anthocyanin molecules found in plants are: pelargonidin, cyanidin, delphinidine, peonidin, petunidin, and malvidin.  If you can pronounce these molecular names, congratulations, you are now an organic chemist!  Of these six anthocyanin molecules, cyanidin is the most common of them all and its CAS #528-58-5 is often used to designate all the anthocyanin molecules together (even though each unique anthocyanin molecule has its own unique CAS number).

Preparation:

Anthocyanins are water soluble molecules; their extraction is straight forward.  Purple carrots or purple sweet potatoes are harvested, diced, and soaked in water containing up to 3000 ppm sulfur dioxide.  Sulfur dioxide greatly increases yield; however, it turns the anthocyanins colorless.  It is not until the sulfur dioxide is removed by evaporation, that a deep blue, highly viscous, concentrate is revealed. This concentrate is filtered to remove any remaining plant material and then acidified.  Once acidified, anthocyanins turn bright red.

This is a very special property of anthocyanins: anthocyanins are BLUE in solution at neutral pH (pH 6.0 – 7.0); and RED in solution at acidic pH (pH 2.5 – 4.0).

In a very real sense, anthocyanins are natural pH meters, responding to the pH of their environment by changing color from blue to red as their environment moves from neutral to acidic.

Application:

Anthocyanins may be used in foods generally throughout the world. They are frequently found in fruit drinks and other beverages, soft and hard candies, vinaigrettes, ice cream (where they are purple, not red, because of the high pH of ice cream), cereals, and pet foods.  Anthocyanins are used in nutritional bars, tablets, and powdered drink mixes.  It is important when using anthocyanins to make sure a food or beverage processor has complete control over the pH of the final product.  Small variations in pH will result in large variations in final product color.