it turns red[first it was purple
It is called denaturation
Lemon juice!
It's possible that the asparagus juice contains an indicator chemical which is reacting to the acid in the lemon juice. (Note that I don't know exactly which indicator is involved, or even if this actually happens; I'm just offering an explanation for the phenomenon you say you've observed.)
Citric acid in the lemon. Sugars in the lemon juice as it dehydrates.
It turns into a scientific yellow substance called "urine".
it turns red[first it was purple
It gets wet.
Salty lemon juice.
Salt turns blue when added to lemon juice because it has iodine inside it. When lemon juice is added to iodine, it changes colour.
water
if its pure lemon juice with no added sugar then it has no sugar in it. and most lemon juice are like that. its in lemon soft drinks and lemon cordials that add the sugars.
it dies
It is called denaturation
Possible formation of sodium citrate.
Because the chef added it to enhance the taste.
happpens
it fomes