Abstract
Purple or black carrots (Daucus carota ssp. sativus var. atrorubens Alef) are characterized by their dark purple- to black-colored roots, owing their appearance to high anthocyanin concentrations. In recent years, there has been increasing interest in the use of black carrot anthocyanins as natural food dyes. Black carrot roots contain large quantities of mono-acylated anthocyanins, which impart a measure of heat-, light- and pH-stability, enhancing the color-stability of food products over their shelf-life. The genetic pathway controlling anthocyanin biosynthesis appears well conserved among land plants; however, different variants of anthocyanin-related genes between cultivars results in tissue-specific accumulations of purple pigments. Thus, broad genetic variations of anthocyanin profile, and tissue-specific distributions in carrot tissues and organs, can be observed, and the ratio of acylated to non-acylated anthocyanins varies significantly in the purple carrot germplasm. Additionally, anthocyanins synthesis can also be influenced by a wide range of external factors, such as abiotic stressors and/or chemical elicitors, directly affecting the anthocyanin yield and stability potential in food and beverage applications. In this study, we critically review and discuss the current knowledge on anthocyanin diversity, genetics and the molecular mechanisms controlling anthocyanin accumulation in carrots. We also provide a view of the current knowledge gaps and advancement needs as regards developing and applying innovative molecular tools to improve the yield, product performance and stability of carrot anthocyanin for use as a natural food colorant.
Highlights
Application and Potential of Carrot as a Source of Natural AnthocyaninsThe global market of natural colorants in the food industry was valued at USD 1.32 billion in 2015, and is expected to continue to grow over 7% annually between 2017 and 2022 [1]
There are no official statistics of worldwide purple carrot production, estimations by the food industry based on the annual need of 10,000 tons of carrot-derived anthocyanins place worldwide purple carrot production at approximately 100,000 ha [27]
Anthocyanin accumulation is determined by the activity of structural genes, which are divided into general phenylpropanoid metabolism genes and early and late biosynthesis genes (EBGs and LBGs, respectively) [61,62]) (Figure 3)
Summary
The global market of natural colorants in the food industry was valued at USD 1.32 billion in 2015, and is expected to continue to grow over 7% annually between 2017 and 2022 [1]. Anthocyanins are a class of flavonoid antioxidants, and they represent some of the most vivid colors in nature, varying amongst shades of red, purple and blue, and they are produced in various plant tissues, including the leaves, roots, flowers and fruits These natural pigments are generally unstable, and are susceptible to degradation driven by temperature, acidity and light exposure. A wide range of colors can be obtained from black carrot pigments, such as strawberry pink at low pH, versus purple and blue shades at higher pH [7,8] This versatility is useful for coloring fruit juices, soft drinks and other food products [7], and could be used as a replacement for synthetic colorants such as FD&C Red. 40 (allura red) [3,8,9]. There are no official statistics of worldwide purple carrot production, estimations by the food industry based on the annual need of 10,000 tons of carrot-derived anthocyanins place worldwide purple carrot production at approximately 100,000 ha [27]
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