Decarboxylation Of Palm And Groundnut Oils In Medium Uv Irradiation

INTRODUCTION Vegetable oils undergo appreciable deterioration during processing and storage. The residual free fatty acid (FFA) concentration of vegetable oils is a function of the processing and storage conditions. Vegetable oils spoilage, usually defined as rancidity, is the result of fatty acid moity has been recognized as the point of attack in peroxide formation Peroxide-forming reactions are known to involve free residual 3, 4 and studies have also shown singlet oxygen to be involved 5, . Dyes and pigments have also been shown to sensitize the formation of peroxides. 7, 8 A new dimension in vegetable oils deterioration different from the familiar and well studied reaction such as acid/base hydrolysis, and cleavage resulting from peroxide formation appears to be the case in ultraviolet (UV) irradiation of these oils. The principal focus of our earlier studies was the decarboxylation phase of these reactions, in which, through monitoring of the CO2 evolution, the reaction rate was determined to be first order with respect to the oil concentration. In the present studies, we have been Conventional palm and groundnut cooking oils have been photolysed using a medium UV photochemical lamp. Room temperature photolysis of crude palm oil led principally to decarboxylation of the residual free fatty acid. H2O treated palm oil, however, produced mainly additional fatty acid on photolysis. Decarboxylation of untreated palm oil achieved a 95% reduction in baseline free fatty acid value within the first 10 minutes. This was followed by a gradual and linear drop in the acid value below the baseline value. Decarboxylation was also the major reaction in the acetone-sensitised crude palm oil photolysis. The decarboxylation rate was, however, slightly lower than the unsensitised reaction. In the case of groundnut oil, unsensitised and acetone-sensitised system showed similar behaviour within the first 10 minutes. For the unsensitised system, a substantial rise in acid value above baseline value was followed by decarboxylation to an acid value well below baseline in 60 minutes. For the sensitized system, the acid value remained constant at about 59% above baseline value in the 10 to 30 minutes reaction interval. Beyond 30 minutes, it rose by as much as 155% above baseline. The rise then slowed down somewhat after 45 minutes of reaction.