Actually, most bottled or other containerized lemon juices are reconstituted lemon juice. It's made by adding lemon oil to lemon juice concentrate from which most of the water has been taken. To keep the taste standardized, more or less of the lemon oil must be added. In addition, since much of the acidicity of the original lemon has been "watered down", most bottled types contain preservatives to maintain color and freshness, which usually include sodium bisulfate and sodium benzoate.
Admittedly, I, being from the U.S., am not familiar with the Jif brand. Fresh lemons have none of these of course... If you're interested and can find a copy, read Dr. A.F. Beddoe's book Biological Ionization in Human Nutrition concerning the health benefits of hot water and lemon juice.