Iodophors

Brief Description:

Iodophor is an iodine containing solution with a solubilizing agent such as a surfactant or providone. Iodophor is widely used in the brewing and dairy industries as a sanitizer. The iodine is usually complexed with a high molecular weight carrier typically a polymer (Palmer 1999). The most common iodophor is 1-vinyl-2-pyrrolidinone complexed with between 9% and 12% iodine (Gottardi 2001). The polymer serves three functions. First it increases the solubility of the iodine. Second, the polymer complexes with iodine, creating a reservoir of free iodine as the equilibrium of free and bound iodine shifts.  Third, the polymer maintains a low but lethal level of free iodine in the solution of around 15 ppm at pH less than 7. This concentration is controversial, however as Donnell (1977) recommends a solution of 25 ppm. Other forms of iodine based sanitizers involve ethyl alcohol, propyl alcohol, and glycerol.

Iodine is a very lethal agent that enters the cell and prevents protein synthesis. According to Palmer (1999), iodine oxidizes the hydrogen-sulfur bonds in the amino acid cysteine, preventing peptide synthesis and leading to cell death.  Further mechanisms of cell toxicity involve iodination of membrane lipids and oxidation of membrane proteins.

Iodophors can be difficult to use in industrial applications due to controversy about lethal concentrations. In a study of seven bactericidal solutions, including quaternary ammonia and phenolic compounds, the iodophor was the only ineffective solution at the manufacturer’s recommended concentration (Gottardi 2001). The effectiveness of the iodophor solution did not increase even after extended contact time.

Application in Wine Microbiology:

Iodophors and other iodine based preparations have not been popular in the wine industry. Iodine reacts with metals (Gottardi 2001), is inactivated by sulfur compounds (Palmer 1999), stains the skin, is an irritant, a poison, volatile, and is unstable in solution. The pH of the solution and to a lesser extent the temperature greatly affects the equilibrium concentration of iodine. Perhaps the greatest drawback to iodophors and iodine based sanitizers is the extremely complex chemistry. It is difficult to predict its reaction and efficacy in a complex solution. With water there exist nine different equilibria equations and at least ten iodide species (Gottardi 2001). Despite these problems, iodophors have been successfully employed for sanitizing bottling lines. An iodophor spray of 25 ppm performed hourly was successful in eliminating yeast from a bottling line (Donnelly 1977).

Despite unpopularity in the wine industry, iodophors are popular among homebrewers due to rapid sanitizing action, and because they quickly volatilize to leave the solution free of iodine. Certain homebrewers dislike the staining that iodine solutions impart after continuous use. Iodophors are also used in the dairy industry because of its solubility and efficacy at cold temperatures where other sanitizers would be impaired.

References:

  • Donnelly, David M. 1977 Elimination from Table Wines of Yeast Contamination by Filling Machines. Am. J. Enol. Vitic. 28:3
  • Palmer, John J.2006 How to Brew Brewers Publications Colorado.
  • W. Gottardi, "Iodine and Iodine Compounds." Disinfection, Sterilization and Preservation, 4th Edition, S. Block (Ed). Lea and Febiger Publishers, 2001, 152- 16.