Esterification of Endosperm Lutein with Fatty Acids during the Storage of Wheat Seeds

Abstract

The structural changes in lutein, one of the major carotenoid pigments of wheat endosperm, during the storage of seeds were investigated. Wheat seeds were stored for up to 120 days at 30°C under a relative humidity of 75, 56, 32, or 8%. The wheat seeds were then milled, and carotenoid pigments were extracted from the flour with water-saturated butanol. The HPLC analysis revealed that the hydroxyl groups of lutein had been gradually esterified with fatty acids during storage. Esterification proceeded faster as the relative humidity was reduced. It seems that the rate of esterification was increased when the water generated by esterification evaporated from the seeds at low relative humidity. The amounts of free fatty acids, substrates for the esterification of lutein, in the flour increased during storage, the increase in free fatty acids proceeding faster as the relative humidity was increased. When the seeds were heated in an autoclave at 120°C for 20 min before storage, neither the esterification of lutein nor an increase in free fatty acids occurred. These results indicate that both reactions proceeded enzymatically. We speculate that the esterification of lutein occurred due to catalysis by lipase (triacylglycerol acylhydrolase), which produced free fatty acids from glycerides, or by other acylhydrolases which have similar kinetic properties to those of lipase.