With many foods today containing chemicals, agents and preservatives etc... What biological criteria must a new food and its constituent components satisfy biologically, to be defined as edible?
For example do they look at the chronic/acute affects of chemicals in the body?
This question is just limited to chemicals, if a new fruit was discovered, how would it be decided if it was edible or not?
As far as I know, edibility (wow, I'm surprised that passes the spell checker!) is not a strictly defined term, biologically or otherwise. Humans have been around eating and drinking stuff long before the scientific method was around to study this question rigorously, and before there were regulatory agencies charged with approving new products as "safe." As one might imagine, knowledge of what is and is not edible was likely passed down by oral tradition and personal experience.
Honestly, I'm not even sure designating a food (or a substance) as edible or inedible really makes much sense. Let's consider wild fruit, as mentioned in your question. If ingesting 5 or more berries of hypothetical fruit X causes your body to have a nasty reaction, then we could probably agree that fruit X is toxic and inedible (even if eating only 1 or 2 berries might not elicit the same reaction). On the other hand, ingesting berries of hypothetical fruit Y causes no reaction unless consumed in much larger quantities (maybe 100 or more berries). Although fruit Y does cause a reaction when ingested in excessive amounts, it would be a stretch to call it inedible. This principle applies to many foods that we typically consider edible but can be unhealthy or even dangerous when taken in excess.
So where do we draw the line? How much of a substance do you have to ingest without an adverse reaction to deem it edible? I don't think there is an objective answer to this question. It is complicated further by the vast amounts of variation in the human population: food allergies, differences in tolerance to certain substances, etc.
Much like Daniel Standage suggests, I think "edible" is more inferried than defined, sort of like looking at a black hole - its absence is defined by the activity around it. Human bodies are capable of metabolizing lots of compounds that become poisonous pass some threshold.
In medical terms there are LDmin and MLD and LD50: miminum Lethal Dose, Median Lethal Dose, Lethal Dose for 50% of the Population respectively.
There are also compounds that aren't lethal, but are definitely harmful. Trans-Fats are one, where the FDA hasn't determined any safe levels of Trans-Fats in foods; they're always dangerous and harm your system.
Then there are materials or chemicals that will simply pass through your system without being absorbed or interferring with anything. Cellulose (refined wood pulp) is a popular additive in pre-made diet foods because it adds mass and texture while being completely indigestable since humans do not produce cellulase. The same can be said for silicone dioxide (sand), which is also very unreactive and passes through your digestive system benignly.
So I'd say as long as whatever is eaten is below the LDmin and/or can benignly pass through your system without damage, it is 'edible.'
This is more a legal question, so I'll quote from what is lex in the EU:
Regulation (EC) No 178/2002 of the European Parliament and of the Council of 28 January 2002 laying down the general principles and requirements of food law, establishing the European Food Safety Authority and laying down procedures in matters of food safety
Article 2
Definition of "food"
For the purposes of this Regulation, "food" (or "foodstuff") means any substance or product, whether processed, partially processed or unprocessed, intended to be, or reasonably expected to be ingested by humans.
"Food" includes drink, chewing gum and any substance, including water, intentionally incorporated into the food during its manufacture, preparation or treatment. It includes water after the point of compliance as defined in Article 6 of Directive 98/83/EC and without prejudice to the requirements of Directives 80/778/EEC and 98/83/EC.
"Food" shall not include:
(a) feed;
(b) live animals unless they are prepared for placing on the market for human consumption;
(c) plants prior to harvesting;
(d) medicinal products within the meaning of Council Directives 65/65/EEC(21) and 92/73/EEC(22);
(e) cosmetics within the meaning of Council Directive 76/768/EEC(23);
(f) tobacco and tobacco products within the meaning of Council Directive 89/622/EEC(24);
(g) narcotic or psychotropic substances within the meaning of the United Nations Single Convention on Narcotic Drugs, 1961, and the United Nations Convention on Psychotropic Substances, 1971;
(h) residues and contaminants.
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CELEX:32002R0178:EN:NOT
