The Use of Plant Pigments as Natural Food Colors in The Food and Beverage Industry

Colors, in general, have been utilized in food preparations for centuries. It was said to be in 2600 BC when natural dyes were found in China. In addition, Egyptians and settlers in the Indus Valley practiced dyeing. Among the dyes used in the early times are henna and saffron. Advancement of civilization included the use of dyes in architecture, grooming, textiles and food. Natural food color can be defined as a dye, pigment or compound produced by living things or minerals that are capable of coloring objects, animals and drugs, cosmetics, beverages and foods. Food pigments are compounds that enhance, change or restore food and beverage colors. In some cases, they help improve the taste. More so, one or more health benefits are reaped by consumers from consuming them.

Among the most widely used sources of natural colors are plants. The most obvious plant parts that produce colors are from the stem, root, bark, fruits and seeds. A specific example is Leucosceptrum canum. It is a plant found in China. A distinct yellow pigment can be extracted from its flowers. It is used on foods which range from candies, sauces, sausages, fruit drinks to carbonated drinks. There are different types of plant pigments. But in general, four basic groups can be distinguished. They are betalain pigments, flavonoid pigments, isoprenoid pigments and porphyrin pigments. They all have their distinct characteristics and issues or challenges. These issues affect the stability of food colors from plant sources. Some might fade in intensity due to heat. Some might change once exposed to acidic environments while some may have showed insolubility to certain substances. These being said, manufacturing companies have these obstacles to deal with. They proved to be inevitable because of consumer demands for natural products over manufacturing costs.

The Food and Drug Administration (FDA) also has a big part with the scope of using natural over synthetic food colorants. Betalain pigments are further subdivided into red betacyanins and yellow-orange betaxanthins. However, only red betacyanins are utilized as food pigments. The betalains range in color from yellow to red-purple, but are restricted to a single order of flowering plants, the Caryophyllales, which includes cacti, bougainvillea, carnations, some carnivorous plants and red and yellow beets.

Phytolacca americana L. is another source of betalains, but it has been banned as a food colorant due to the presence of toxic saponins and lectins. Unexpectedly, betalains are also found in some higher fungi such as Amanita muscaria (fly agaric). They are not soluble in oil but are soluble in water. The color of betalains is insensitive to pH in the range from acid to neutral.

The study and characterization of natural and artificial derivatives of betalains suffers from two important limitations. These are low solubility in non-aqueous media and hydrolytic instability in aqueous media. According to Slimen et al. 2017, Betalains are chemically labile in highly acidic aqueous media, or when the pH is less than 1, and alkaline hydrolysis occurs at a pH of more than 8. It restricts most studies in aqueous media to slightly acidic conditions. Even at pH 5, the thermal decomposition of most derivatives occurs in a few minutes at 100 °C. The highest stability, however, is observed at the pH 4-5 range. In addition, other factors concerning their stability are the amount of pigments used in a solution and the presence of iron ions, water activity, the occurrence of antioxidative properties and as mentioned earlier, temperature. Unfortunately, betalains are weakly resistant to light and temperature above 70°C. When exposed to high temperatures, the color may then change from red to yellow. For this reason, betalain compounds are applied only to fresh products.

At times, they are used to packaged foods but only when atmosphere is modified, or to products that are not processed thermally. They are used to give color to a variety of foods such as sauces, jams, jellies, candies, ice creams, frozen foods, yoghurts, powdered desserts and milk-based drinks. Flavonoid pigments have been among the most well-researched plant pigment. Anthocyanins are the best-known representative of the group due to resent discoveries in their health benefits. Approximately more than 500 compounds have been researched, so far. They are widespread in plants and are responsible for most of the red, blue and purple colors of fruits and flowers, in addition to some vegetables like purple carrots, purple potatoes, purple corn, beans, and red cabbage. Several plant leaves like purple trees, the red leaves that surround the small yellow flower of poinsettias, new foliage of many plant species and the red colors of autumn leaves. The pigments are water and ethanol soluble. However, they do not dissolve in oil. Anthocyanins belong to weakly stable compounds. Their stability is easily affected by temperature increase, prolonged heating and storage and the presence of oxygen. These conditions lead to formation of yellow or colorless chalcones and even browning.

Despite of these stability issues affecting the food and beverage manufacturing process, anthocyanins have numerous benefits to health and well-being. It became widely known to minimalize the activity of some enzymes and eliminate superoxide free radicals. The presence of anthocyanin has brought greater sales due to it being marketed as a superior antioxidant.

Products containing anthocyanin were said to cause the following: decreased problems with sclerosis, improved arterial hypertension, better metabolism, prevented tumorous activities, lessened allergies and showed to be a significant vitamin source. Anthocyanins have been shown to act as a ‘sunscreen’, protecting cells from photo-damage by absorbing blue–green light, thereby protecting the tissues from photoinhibition or high light stress. This antioxidant property is conserved even after consumption by another organism, which is another reason why fruits and vegetables with red skins and tissues are nutritious food sources.

Further researches are still conducted to show its promising influence in cardio-vascular disorders and eyesight. These properties prove how important it is for people to consume anthocyanins on a regular basis. Presently, application of the flavonoids group of pigments by the food industry is a common practice in the manufacture of alcoholic, non-alcoholic and fruit juices, sauces, cheeses, jellies, jams and candies.