Why is the Color Blue So Rare in Foods, and Why is This Important?
Corn is yellow, carrots are orange, celery is green, onions are white, tomatoes are red, wheat is brown, and pepper is black. In their natural state, all plant foods have a signature color. Noted author Michael Pollan is famously known for a simple-yet-profound quote: “Eat food. Not too much. Mostly plants.” When we follow this advice, we are likely eating plant foods of many colors. My close colleague and friend, Deanna Minich, PhD, is also an author as well as a talented artist, who has a distinctive personality and a widely admired interest in the color spectrum of food. Her 2018 book, The Rainbow Diet: A Holistic Approach to Radiant Health Through Foods and Supplements, describes and celebrates the variety of plant-derived nutrients we can benefit from when we eat a diet of vivid color and diversity.
Using color as a guideline for healthy eating is a wonderful approach. It’s an easy concept to grasp and it even comes with an element of fun. It would be challenging to look at an array of fresh and bright produce and not find beauty in nature’s bounty, wouldn’t you agree? But as you survey your options in that grocery store, or farmers market, or roadside stand, one color is less common than the rest: blue. Why is this and what does it have to do with the unique nutrients in specific plant foods?
In food, the colors red, orange, yellow, green, brown, black, and white all relate to the presence of specific families of plant pigments. Examples include beta-carotene in carrots, chlorophyll in kale, lycopene in tomatoes, tannins in tea, zeaxanthin in corn, betalains in beetroot, ellagic acid in berries, and curcumin in turmeric. The color blue in foods is another matter, entirely. The blue story tells us some very interesting things about the complex relationship between our diet and our health.
In the May 3, 2019 issue of Science magazine, author Kai Kupferschmidt wrote an excellent article titled “In Search of Blue.” This piece introduces the unique features of plants that have blue flowers or berries, and describes the work of Yoshikazu Tanaka, PhD, a research scientist at Suntory, a leading brewing and distilling company in Japan. Although Suntory is known as a major whiskey producer, a decision was made within the company to branch out into the profitable cut flower business. In a project that could euphemistically be described in many ways — a “blend,” a “mix,” a “cocktail” of scientific expertise — Dr. Tanaka’s team has undertaken a project that unexpectedly unites both worlds: to produce a blue rose. Why? To honor Scotland, the birthplace of whiskey, whose national flag is blue and white.
The quest to create a blue variety of rose is the stuff of legends. In 1913, the German chemist Richard Willstatter discovered that the blue pigment in corn flowers was an anthocyanidin; he named it cyanidin. Later, this same blue pigment was determined to be present in red roses. In 2005, x-ray crystallographic data revealed that cyanidin produces a blue color when it is combined in a plant with six molecules of a colorless copigment arranged around two metal ions. It produces a red color — as in the case of a red rose — when combined with other pigments made by the plant. Similar chemistry has been found in other types of blue flowers, albeit with a different anthocyanidin: delphinidin. With this information in hand, Dr. Tanaka and his team genetically engineered a rose that produced delphinidin, thereby creating the first known variety of a purplish-blue rose.
Genes that code for the production of anthocyanidins are very relevant to this question about the scarcity of blue foods. Richard van Breeman, a natural products chemist at Oregon State University, and Cathie Martin, at the John Innes Centre in Norwich, United Kingdom, have been collaboratively investigating blue plant pigments and — more specifically — they are interested in finding naturally derived blue colorants of the anthocyanidin family. It may surprise you to learn that presently there are only two blue food dyes approved for use in the United States and their origins may also raise eyebrows. Blue №1 was originally made from coal tar, while blue №2, or indigo carmine, is produced from synthetic indigo, a natural blue colorant derived from spirulina and approved for confectionery products by the FDA in 2014 (it is a very unstable ingredient, however).
The take away? Blue foods are rare and unique because anthocyanidin content is a rare and unique chemical feature in the plant world. This knowledge can elevate your next gourmet adventure to new levels. Consider the Malay rice specialty, nasi kerabu. The flowers of the butterfly pea give this dish its characteristic blue color, announcing to all who partake or just enjoy its visual presentation that anthocyanidins are a feature of the meal.
The Health Effects of Dietary Blue Anthocyanidins
Let’s keep things simple by starting with the most well-known and obvious blue (anthocyanidin-containing) food: the blueberry. In a recent scientific review of the health-promoting properties of blueberries, anthocyanidin content was determined to be a major contributor to the positive effects that blueberry consumption may impart. It has been suggested that anthocyanidins have anticancer, anti-obesity, anti-inflammation, and anti-diabetic properties, and may also be protective to vision and liver function. Because of the ways they can influence systemic health, the anthocyanidins in blueberries could be considered functional ingredients for the prevention chronic disease. In recent years, because of a growing body of scientific studies, the tiny-yet-mighty blueberry has achieved special status as an example of a fruit that can be uniquely beneficial to health.
Anthocyanidins are also present in coffee, whole grains, cherries, cranberries, and strawberries, all of which have been the subject of scientific health studies. There is even evidence that blue-purple edible flowers that are rich in anthocyanidins could have a role in the prevention of diabetes, obesity, and inflammation.
What about purple potatoes, purple carrots, and purple rice? All contain blue anthocyanidins. Blue, like yellow and red, is a primary color. But in a world full of beautiful blue things, it’s important to appreciate not only how rare blue is in food, but also why it is elusive. Now you know. To ensure that you are consuming all of the plant-derived nutrients in your diet, make the extra effort to add some blue to your culinary rainbow.