Why do apples bleed after soaking in boiling water for 10 seconds and what substance is it?

There are two types of wax on apples, both of them are from natural sources and are safe to eat. Occasionally other types of sprays are used on apples, including polyethylene (a type of plastic), which is derived from ethanol made from fermenting corn.

The first type of wax is produced by the apples themselves, and is called a bloom. These natural waxes are produced by the apple to protect it from drying out and from allowing fungal spores to penetrate and cause rot in the apple (this would damage the seeds and hence the chance of the plant reproducing successfully). The wax in blooms contain a bunch of chemicals (as one might expect), including ones found in petroleum.

Sometimes these waxes are removed from the apple by washing at the producer/growers after the apple is picked. In order to preserve the apple so that it appears on the shelf in a manner that most people like to eat, the apples are sprayed with the second type - a very fine wax coat which consists of about 3 milligrams of wax (3/1000ths of a gram, or 0.0001 oz) per apple. The waxes used here are from natural sources such as carnuba oil, candelilla wax or even shellac from the lac scale bug.

Boiling the apples as you did probably resulted in partial cooking of the apple (if the skin was loose at all, cooking is certain), this could result in releasing some of the fruit juice, much as you would when making apple sauce. As I am sure you know, apple sauce is sticky from the sugars in it, and this is likely the source of the sticky droplet - every time you picked up the apple or applied pressure to it, it squashed out some of the sticky sugar sauce.

Exactly what needs to be declared as a food additive is dependent on where in the world you are and often on the amount of additive added. It is quite likely that what you washed off the apple is a natural coating.

There is a basic description and some explanation of apple waxes at McGill University