INS 440 on a label means pectin. INS 440 (E440 in Europe) covers pectins, including amidated pectin, which Codex lists as a gelling agent, thickener, stabilizer and emulsifier. Pectin is a natural part of plant cell walls; the commercial ingredient is extracted mainly from citrus peel and apple pomace, the leftovers of juice making.
Pectin is what makes jam set. The most common types need plenty of sugar and some acid to form a gel, which suits sweet fruit fillings, while low-methoxyl and amidated pectins set with calcium and less sugar. The gel is short and clean rather than rubbery, and it carries fruit flavour well.
In the Euro Choco Pie with marshmallow and raspberry jam, pectin is listed at just 0.3%, next to gelatin (INS 428) at 2.4% and citric acid. The pectin most likely sets the raspberry jam, while gelatin builds the marshmallow. Being plant-derived, pectin is a common choice when an animal-free gel is wanted.
