The US-EU trade talks are running into trouble on a number of fronts, but predictably agriculture is proving to be a particularly difficult issue. The farm lobbies on both sides of the Atlantic are active and influential and the EU feels a need to respond to the concerns of its citizens on such subjects as GM crops and hormone-raised beef. For its part, the US sees this as protectionism under another guise.
Food safety is an area where there is a particular gap with the EU sticking to the 'precautionary principle' which can justify intervention in the absence of much in the way of hard scientific evidence while the US has a more lenient 'risk assessment model' which only bans products if there is a known risk. The EU is about to approve a GM strain of corn/maize, but that is after a decade of debate and six scientific studies. It remains to be seen how much is actually planted.
The fundamental problem is that the public in the two entities have different attitudes on issues of this kind and these are difficult to overcome, particularly when the EU is engaged in a constant search for democratic legitimacy and popular support. Standing up to big US corporations marketing allegedly dangerous products and processes is one way of doing that.