i think that "des" in this case refers to a belongings. "La nourriture des jeunes elephants"-the meal of young elephants.
in a previous sentence the opposite was given i.e. de becomes des in front of an adjective (?)
Yes, but how do we know from pronunciation whether the speaker is referring to "some good strawberries" or "good strawberry" ?
No, "de la" is used with uncountable substances, like "de la soupe" and "de la" is necessarily singular.
strawberries are countable, so singular "une fraise", plural "des fraises"
now, if you add an adjective just after "des", it becomes "de"