A new cyanine from oxidative coupling of chlorogenic acid with tryptophan: Assessment of the potential as red dye for food coloring

•A red dye from coupling of chlorogenic acid with tryptophan (CGA-TRP) was prepared.•A tryptophan linked benzochromeno[2,3-b]indole was identified as the major component.•CGA-TRP exhibited high pH and thermal stability compared to anthocyanins and betanin.•The sodium salt of CGA-TRP performed well as colorant of various food matrices.•The sodium salt of CGA-TRP was not toxic on hepatic and colonic cell lines.