Countable vs. Noncountable
The food/non-food distinction is just a symptom of a larger phenomenon.
What you are actually playing with in this question is the use of a noun in its countable sense vs. its mass-noun sense.
In English, when we speak generally about something stative or habitual, then, if there is an object, the object is pluralized:
I like apples.
However, some nouns have no plural because they are non-countable (i.e. mass nouns), like milk:
I like milk. (You would never say "I like milks".)
Now, the distinction you are noticing is that, for many countable nouns, there is also a mass noun counterpart. This mass noun form (should it exist) occurs when the countable object has, in some way, been split into pieces, mashed, ground up, liquified, or otherwise been rendered into a form where its discrete qualities are absent/irrelevant.
So if I am eating a cookie I would say:
This is a good cookie.
But if some crumbs end up on my shirt, I might say:
I got (some) cookie all over my shirt. (not "a cookie" or "some cookies")
When we refer to animals that we can eat, they are countable as long as they retain their discrete properties (usually while they are still alive):
I like chickens. (still countable)
But when the chicken is cut up into pieces and sitting on your plate, there is no exact piece of chicken that constitutes "a chicken". So, instead, you would say:
- I am eating chicken.
- I like chicken.
However, if you bought an entire chicken, baked it whole, and your family ate it at dinner, then you could grammatically say:
Our family had a chicken for dinner last night.
As well as:
Our family had chicken for dinner last night.
The only difference is that the latter sentence is ambiguous as to whether you had a whole chicken or, say, a bunch of chicken breasts.
In the case of your orange examples, you interpret the oranges sentence as whole oranges. If you like "oranges", it means you like more than just orange flavoring; "oranges" evokes the idea that you like taking a whole orange and eating it.
When you say "I like orange", it can mean two things:
It can mean that you like orange flavoring — the taste of orange. If you are talking about cooking, maybe you like orange in certain foods.
It can mean that you like the color orange. This one is a slightly different variation on the "uncountable" idea. The color orange, like happiness and exhaustion, is a universal concept that there can only be one of in the universe (when the word is used in its general sense). So, these concepts are uncountable because we only have one universe (that we can observe). Happiness is a single thing that you either have or don't have — if two people are happy, they haven't found "happinesses", just "happiness". (Sometimes universal concepts have have secondary meanings that are countable, e.g. "one of the many joys", but such meanings are not talking about the universal concept.)