This is a question almost the same as:
What happens if you swallow a mandarin seed?

This is my answer:

If you were able to chew the lemon seed and turn it like an applesauce consistency (fluid-like consistency) before you swallow it, it will be absorb in your gut and you get the nutrient.

But if you swallow it directly without chewing, you will excrete it from your body as undigested substances together with your feces.

A green juice will not undergo digestion, it goes directly to blood and you get the nutrient.

Lesson:
That’s why it’s very important to chew your food well. Our digestive organs won’t absorb the nutrients from the food that we eat unless it becomes a liquid.