The bottom line is that food standards in some areas in the US are looser giving food manufacturers lower costs. Meanwhile, in the EU regulations are stricter particularly it would seem with regard to baby food.
The Independent’s article is part of growing campaign of fear highlighting the downside risks of Brexit. Whilst individually these risks might to necessarily be that large, collectively they will start to increasingly worry ordinary people.
The elephant in the room is that the British people were conned about Brexit, thinking that immigration would be slashed and the EU contributions would prop up the failing public health service. I expect that in the Autumn we shall see an increasing push-back against Brexit.