FATTY-ACID COMPOSITION AND MOLECULAR ORDER OF PHOSPHOLIPIDS FROM EUROTIUM-CHEVALIERI IN RESPONSE TO CHANGES IN WATER ACTIVITY

The mycelial growth of Eurotium chevalieri was examined at different water activities (a(w)) using glycerol as the osmoticum. Growth was optimal at 0.90 a(w) and restricted at 0.995 a(w) highlighting the xerophilic behaviour of E. chevalieri. Decreased a(w) produced an increase in the proportion of oleic acid (C18:1) at the expense of the proportion of linoleic acid (C18:2) of cellular phospholipids. The degree of unsaturation of phospholipid fatty acids showed a 20% decrease between 0.995 and 0.80 a(w) of growth. Steady-state fluorescence anisotropy (r(s)) and fluorescence lifetime (tau) measurements for liposomes prepared from cellular phospholipids of E. chevalieri and labelled with DPH (1,6-diphenyl-1,3,5-hexatriene) were made at 25-degrees-C. The lipid order parameter (S, describing molecular order) and the rotational correlation time (rho, describing molecular dynamics) were calculated from r(s) and tau data. Except at 0.995 a(w), a decrease in a(w) was accompanied by increasing r(s) and S values, indicating a rigidification of membranes, while rho values were not significantly different. Plots of order parameters and their first derivatives as a function of temperature exhibited break areas in the temperature range 20-48-degrees-C. These large temperature ranges for lipid transitions could correspond to chain melting of complex lipid systems which made up the liposomes prepared from phospholipids of E. chevalieri. However, as a(w) decreased, the transition temperatures increased globally, between 0.97 and 0.90 a(w).