Carly, instead of the lemon juice, personally, I would use vinegar. Either apple cider or distilled white. They are readily available at your grocery store and have a standardized 5% acetic acid value (which means the other 95% is water. that's really important). This is an amazing thread to read and learn how to use vinegar in your soaps. I know, because Top of Murray Hill "held my hand" and walked me through the math and science. (Honestly, this is the most amazing group of people I have ever had the good fortune to find!!) Believe me, if I can figure this out (and I am NOT joking when I say I suck at math!!), then anyone can figure this out. The only reason I can imagine using lemon juice in soap is for the acetic acid, which would mix with the NaOH and convert to sodium acetate and make a nice hard bar. However, that's exactly what the vinegar does and it is a controlled substance instead of a variable like lemons and lemon juice. I have a bottle of GV 100% lemon juice in my refrigerator that does not have the acetic acid content anywhere on the bottle's label. It just says it's made from lemon juice from concentrate, has some preservatives in it and lemon oil. It's fine for water and marinades, but I wouldn't soap with it. I just thought of this, I've got Natural Rice Vinegar in the cupboard. I wonder how that would work in soap? Hmmm.. I feel another experiment coming on. The acidity on that is only 4.2% so the math will be a bit more complicated for me.
http://www.soapmakingforum.com/showthread.php?t=59148