Anthocyanins, a class of natural dyes, as antioxidant molecules, stimulate visual acuity and reduce damage to the retina (1), decrease the expression of inflammatory biomarkers (2), decrease the risk ...

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Anthocyanins, a class of natural dyes, as antioxidant molecules, stimulate visual acuity and reduce damage to the retina (1), decrease the expression of inflammatory biomarkers (2), decrease the risk of type 2 diabetes mellitus (3) .
However, inserted into foods or beverages, they are subject to chemical degradation and color fading in the presence of vitamin C or ascorbic acid (4).

Anthocyanins are water-soluble colored pigments found in terrestrial plants and are responsible for the red, blue, and purple coloration of many flowers and fruits. In addition to the plethora of health benefits associated with anthocyanins (cardioprotective, anti-inflammatory, antioxidant, and antiaging properties), these compounds have attracted widespread attention due to their promising potential as natural food colorants. Previously, we reported the biotransformation of anthocyanin, specifically cyanidin 3-O-glucoside (C3G), from the substrate (+)-catechin in Escherichia coli. In the present work, we set out to systematically improve C3G titers by enhancing substrate and precursor availability, balancing gene expression level, and optimizing cultivation and induction parameters. We first identified E. coli transporter proteins that are responsible for the uptake of catechin and secretion of C3G. We then improved the expression of the heterologous pathway enzymes anthocyanidin synthase (ANS) and 3-O-glycosyltransferase (3GT) using a bicistronic expression cassette. Next, we augmented the intracellular availability of the critical precursor UDP-glucose, which has been known as the rate-limiting precursor to produce glucoside compounds. Further optimization of culture and induction conditions led to a final titer of 350 mg/liter of C3G. We also developed a convenient colorimetric assay for easy screening of C3G overproducers. The work reported here constitutes a promising foundation to develop a cost-effective process for large-scale production of plant-derived anthocyanin from recombinant microorganisms (5).

References_______________________________

(1) Straw berry as a health promoter: an evidence based review. Giampieri F., Forbes-Hernandez T. Y., Gasparrini M., Alvarez-Suarez J. M., Afrin S., Bompadre S., et al. (2015).  Food Funct. 6 1386–1398. 10.1039/c5fo00147a

(2) Samadi A. K., Bilsland A., Georgakilas A. G., Amedei A., Amin A., Bishayee A., et al. (2015). Amulti-targeted approach to suppress tumor-promoting inflammation. Semin. Cancer Biol. 35 151–184. 10.1016/j.semcancer.2015.03.006

(3) Guo H., Ling W. (2015). The update of anthocyanins on obesity and type 2 diabetes: experimental evidence and clinical perspectives. Rev. Endocr. Metab. Disord. 16 1–13. 10.1007/s11154-014-9302-z

(4) Stability improvement of natural food colors: Impact of amino acid and peptide addition on anthocyanin stability in model beverages.

Chung C, Rojanasasithara T, Mutilangi W, McClements DJ.

Food Chem. 2017 Mar 1;218:277-284. doi: 10.1016/j.foodchem.2016.09.087.

(5) Development of a Recombinant Escherichia coli Strain for Overproduction of the Plant Pigment Anthocyanin.

Lim CG, Wong L, Bhan N, Dvora H, Xu P, Venkiteswaran S, Koffas MA.

Appl Environ Microbiol. 2015 Sep;81(18):6276-84. doi: 10.1128/AEM.01448-15.

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