Fatty acid composition and molecular order of phospholipids from Euvotium chevalieri in response to changes in water activity

Abstract

Summary: 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 (τ) 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 °C. The lipid order parameter (S, describing molecular order) and the rotational correlation time (ϕ, describing molecular dynamics) were calculated from r s and τ 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 ϕ 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 °G. 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.