The E-numbers system is a European system to abbreviate various substances included in food products, and appears on the packaging. It seems like people are naturally suspicious of these codes, probably because they appear to indicate something very artificial and we would rather trust something that's more natural. For some, it's more than just a suspicion, which offers an opportunity to market products as being 'Free from E-numbers'.
I suppose the original purpose of E-numbers was to actually allow product manufacturers to use less printing space on their packaging to list the ingredients, and to eliminate ambiguity. This is particularly useful when printing information on small or multi-lingual packaging. Unfortunately it seems like this effort to help the consumer be more informed has backfired.
E-numbers are intended to be used to list any ingredient that has an E-number, but commonly used to list additives with long chemical names. Some of these can indeed be harmful, while some people are allergic to others, but many, or even most, are not only perfectly safe, but something you should actually want. The E-numbers in the range E200-E299 are preservatives, including sulphur Dioxide (E220) and carbon dioxide (E290). The range E300-E399 are antioxidants, including Vitamin-C (E300) and Vitamin-E (E306) and so on. These are chemicals found in many natural sources like fruit and herbs.
In other words, all sparking mineral water contains E290. In fact, a sparkling drink with vitamin-C would contain both E290 and E300. Many organic food products contain E-numbers, it's just never listed like that. In organic products, the full name of the plant material is used, even though the plant can contain dosens of substances which have their own E-numbers. Many natural ingredients derived from natural processes like fermentation have an E-number (e.g. xanthan gum). Even many of the popular food colours, like beta-carotene (E160a), are also sold as beneficial supplements to maintain and improve your health, or occurs naturally in carrots.
The substances that are normally obtained in a synthesized form, are usually based on something we used to extract from natural plant materials. The synthetic process is cheaper, and contrary to popular irrationality, a cheaper process means it's more efficient and has less of an impact on the environment. In other words we don't have to grow and destroy loads of styrax trees to obtain benzoic acid any more, just like we don't have to harvest many willow trees to eat the bark, instead of using simpler raw materials to produce aspirin.
Many people believe, mistakenly, that foods, medicines and supplements that are naturally produced are somehow potentially less harmful to their health than something synthetically produced. Having some unnatural sounding numbers for these substances make it seem even worse. However, all of this shows a clear lack of understanding what the E-numbers really are, and a general lack of understanding of food chemistry, and just general irrationality.
Most of the time decisions about what we eat are not based on logic, or even on being rational. It's a very emotional thing. We base our food decisions on knowledge, but knowledge that we select emotionally. If we care about our health, and most of us for the environment too, we are influenced by information presented to us that reminds us, emotionally, of wholesomeness. Cold, hard chemicals would appear to be the opposite to us.
It would be perfectly normal to list freshly squeezed organic orange juice to contain E300. However you will probably find it hard to sell. Actually this resistance to E-numbers has gone quite far. I've just had a quick look through all the food I have at home, and so far I could only find two items listing E-numbers, and the one is probably very old stock. I only have one 'organic' product at home. Not even the Coca-Cola products list the E-numbers any more, and I remember these being the first products I noticed with these codes.
Consumer choice wins, even though consumer choice is not entirely rational, or at least not in line with my own choice. Personally I would have preferred that all the products that I'm actually allergic to list the E-numbers, instead of some leaving them out again since there is no space.