Abstract: A method for preventing greening due to chlorophyll formation in raw unpeeled cold-stored potato tubers exposed to light prior to and including retail sale which comprises spraying or dipping the tubers in an aqueous emulsion containing a single surfactant so as to form a thin continuous film in and on the surface of the tuber which is relatively impermeable to carbon dioxide thereby ensuring an atmosphere containing at least 15% CO.sub.2 within the film and in the tuber. The surfactant preferably contains long chain fatty acid moieties and polyoxyalkylene or polyhydroxy moieties, and has an HLB rating below about 15. A modified process involves the addition of an organic acid, selected from aliphatic mono- and polycarboxylic acids having from 2-6 carbon atoms and at least one hydroxy or oxo group, and lactones thereof, excepting those dicarboxylic acids which readily form internal anhydrides, to the surfactant mixture in order to "tighten" the surfactant film formed on the tubers under treatment.