um, try eating more fruits (no pun intended) - the fructose is used in your semen for the spermatozoa's food (so it can live in the vagina and make its way though . . . i'll stop there cause i don't anyone would appreciate it
)
But thats the reason why fruits would change the taste. If there is excess fructose in your body, it can be released through semen. Also different amounts of salt in your body would contribute to that too, if you wanted to give it a more salty taste - however you'll find most semen has that salty taste/texture to it anyways, with/without the extra sweetener.