Softer sea baits, esp sardines, get freezer burn very easily.
If you buy them in bulk, they don't come vacuum packed, so they "burn" and start drying out within a few weeks.
They also seem to lose some of the oils "fresh" sardines have in the process.
Glazing them stops this happening and also stops them sticking together.
Andy mentioned doing it the other day but I couldn't remember how he said he did it.