Concentration dependence of recovery rates of an exogenous short linear DNA fragment from soya flour

Recovery rates of an exogenous short linear DNA fragment from soya flour by two methods for isolation of DNA-cetyltrimethylammonium bromide solubilization with liquid-liquid extraction (CTAB-LLE) and chaotropic solid-phase extraction (SPE)-were determined using quantitative real-time polymerase chain reaction. Recovery rates varied from 3 to 54% for CTAB-LLE and from 8 to 66% for chaotropic SPE in a concentration-dependent manner, the highest values being achieved only at high concentrations of the DNA fragment (400ng(100mg matrix for CTAB-LLE and =100ng(100mg matrix for chaotropic SPE). These results suggest that if an exogenous DNA fragment is intended to be used as an internal standard, its working concentrations have to be selected very carefully. Presented results also underline the fact that recovery rates of the currently used methods for DNA isolation from food are relatively low and represent an important problem in the development of quantitative DNA-based methods for food analysis.