The stability of various formulations of mayonnaise stored in commercial glass jars, at 20C in the dark was studied. Dijon mayonnaise made with sunflower oil and containing mustard paste can be stored up to 10 months in closed jars without serious oxidative damage due to the presence of high amounts of natural tocopherols in the oil and limited oxygen availability. However, in the absence of mustard, the oxidative degradation was somewhat faster and the amount of conjugated dienes was increased more quickly and to a higher degree than that in the mustard containing sample. Supplying oxygen by opening one time the jars to air increased the rate of degradation, even when the mayonnaise was stored at 4C. Exposing of glass jars of mayonnaise alternatively to daylight and darkness for 1 month produced only little conjugated dienes while hexanal appeared in significant amounts. Addition of antioxidant (rosemary extract and EDTA) or emulsifier (DATEM) decreased the level ofphotooxidative volatiles in the headspace.