STABILITY of SOIL FATTY ACID METHYL ESTERS (FAMEs) AFTER STORAGE as DRIED PELLETS or IN DISSOLVED FORM.

One problem after collecting soil samples is the extended processing time to run soil microbial analysis. Then, the problem arises how to store soil samples. Early studies have shown that soil microbial biomass and activities change with a change of environmental conditions i.e. with a change of temperature. Zelles et al. (1991) has shown that air-dried soils stored at 21 °C did not preserve biological activity compared with moist soil stored at cooler temperatures. Other (comparative) have shown that FAME concentrations in soil decrease dramatically (up to 50%) after cold storage (4 °C, -20 °C, -80 °C) (Lee et. al. 2006) compared to FAME concentrations in fresh soil. However, there are no reports on the effect of storage of fatty acid methyl esters (FAMEs) after their extraction from soil samples. To overcome the problem of extended soil storage, the objective of this study was to determine the stability of FAMEs during storage in -20 oC in two forms: dried or dissolved in a solvent. In the study we used soil that was sampled in Illinois farm, since this soil has high level of FAMEs. Two methods for extraction were used: EL-FAME and PLFA. In the first method lipids were extracted from the soil and converted to methyl-esters by alkaline methanolysis in a single step. In the second method lipids were extracted from soil with a single-phase mixture of chloroform, methanol and citrate buffer. The organic lipid-containing phase was collected and separated into neutral-, glycol- and phospholipids fractions by using silicic acid columns. The phospholipids were then converted to their methyl-esters by alkaline methanolysis and detected by GC. Our study showed that 80 – 100 % of individual FAME concentrations could be recovered in samples after storage in -20 °C in both, dried and dissolved forms.