How to keep fresh lemon juice for a week without a change in its taste?
I do not think that there is a better way they not to squeeze the lemon until you need them :D

Regardless, if you want to do testing and are concerned about the bitter notes that develop , I recommend  doing the research with grapefruit instead as it turns bitter is a matter of minutes and has a much stronger bitter flavor then the lemons do. 
That way you at least have a shorter turn around time.