Advances in Betalain Biosynthesis and Metabolic Engineering for Sustainable Natural Pigment Production

Betalains are water-soluble pigments containing nitrogen, and they exist naturally in the plants of the order Caryophyllales. They have gained increasing attention in recent years because of their intense colours, antioxidant activity, and safety, thus making them suitable replacements for artificial dyes. The increasing interest in natural pigments has led to intensified research on betalain biosynthesis and optimization of pigment production. Nonetheless, their application in industry faces limitations, such as their low natural occurrence, sensitivity to environmental conditions, and instability during manufacturing and storage. Unlike previous reviews that primarily focused on betalain chemistry, biosynthesis pathways, or biological activity, the present review highlights recent developments in the engineering of the biosynthesis pathways, synthetic biology, elicitation approaches, omics-based pathway identification, and nanobiotechnology for betalain pigments. Special attention is paid to the comparison of plant, plant cell, yeast, and bacterial production systems, as well as recent advancements towards industrial production of betalain pigments and bottlenecks in the commercialization of sustainable betalain bio-factories.