In the present study, 77 samples of soy foods and feeds
commercially available in the Turkish retail market were obtained
in 2015. As reported in our previous work, successful GMO
screening of food products by PCR depends on selection of the
appropriate DNA isolation method (Turkec et al., 2015). Accordingly, in this study DNA from less processed materials (soya feeds,
flour, mince, tofu and soya-containing snacks & biscuits) was isolated using the Foodproof GMO Sample Preparation kit, giving
excellent yield and purity (A260/280 ratio > 1.8) for these samples.
However, this method gave low DNA yields with highly processed
and oily samples (soy sauce, soya milk, infant formula, and chocolate), for which the established CTAB precipitation method was
preferred. Among modifications tested to optimize the procedure
for these samples, using Edwards' buffer instead of 2% (w/v) CTAB
buffer in the initial lysis step was empirically found to improve the
DNA yield and/or purity. This suggests that the negatively charged
SDS detergent included in Edwards' buffer is more effective than
positively charged CTAB at separating soya gDNA from the other
components of these foodstuffs.