A reddish cast on a dill pickle spells almost certain gastronomic distress, but the same bacteria that’s responsible for the spoilage could help clean up dyes in textile-industry wastewater, according to a new study by the U.S. Department of Agriculture’s Agricultural Research Service. Certain species of lactic-acid bacteria produce a red coloration when combined with tartrazine, a yellow food-coloring agent—commonly known as FD&C Yellow No. 5—that belongs to a class of synthetic chemicals known AZO dyes. During testing, ARS researchers noticed that several Lactobacilli also modified other AZO dyes, including those used and discharged by the textile industry into wastewater streams.

pickles, Ilenys Pérez-Díaz, U.S. Department of Agriculture, AZO dyes, pollution, wastewater


How a bunch of food scientists stumbled upon a food-grade method of treating textile effluent was a matter of serendipity. Commercial dill pickle makers use either tartrazine or turmeric to give the brine its traditional yellowish tint. When ARS microbiologist Ilenys Pérez-Díaz and her co-workers inoculated unspoiled jars of hamburger dill pickles with Lactobacilli from spoiled jars, they discovered that pickles immersed in tartrazine-colored brines developed the red hue on their skins, but those that were exposed to turmeric or had no added coloring did not. When the perfect bacterial-growth-supporting conditions were attained—a pH between 3.9 and 3.5 does the trick—the tartrazine disappeared to result in the red-colored spoilage.

AZO dyes imbue fabric with vibrant colors and although most are nontoxic, several are known to be mutagenic.

In textiles, AZO dyes imbue fabric with warm, vibrant colors such as red, orange, and yellow, and although most are nontoxic, several are known to have mutagenic properties. The implications of the research, therefore, are nothing to scoff at. “Considerable effort has been made to identify microorganisms capable of degrading AZO dyes in wastewater streams from the textile industry,” says Pérez-Díaz. “If food-grade Lactobacilli capable of degrading a range of AZO dyes were identified, they might be organisms of choice for waste-treatment applications.”

+ Press release+ USDA Agricultural Research Service