Table 1 Comparison of the yield and purity attributes of chemical and biological platforms for indigo synthesis, and a representative summary of key dye product features, that suppliers commonly test for dye standardization

Process Attributes

Chemical Platforms

Biological Platforms

Process yield

Difficult to reliably assess; industrial performance of multi-step Pfleger–Heumann indigo synthesis processes is kept as trade secrets (“Chemical synthesis of indigo” section)

Good titers often range 0.3 mg/L–1 g/L, with 18 g/L reported as highest (“Upstream processing (USP) considerations” section)

Product purity

From 96 to 97% for standard processes, to > 99% if additional purification steps would be employed (Kolhaupt et al. 1991; Kolhaupt and Bergmann 1993)

Small-scale studies suggest a potential to match the purity of commercial synthetic indigo (O'Connor et al. 1997). For example, Dai et al. (2019) biologically synthesized indigo of 96% purity, while 94–99% was obtained by Lončar et al. (2019)

Chosen exemplary key dye product features

Color shade and levelness, fastness, solubility in water, solution stability, dispersion properties, tinting strength and organic impurities content (ISO 2022; Jasper and Günay 2014; Motschi 2003; Park 2013; Park and Shore 2007)