I'm not jonb, but maybe I can fill in for a little while... Semen does contain some simple sugars, but usually not enough to be detected in the presence of stronger-flavored compounds.The starches are broken down into simple sugars, but proteins are broken down into amino acids, and usually recombined in other forms, but not sugars. Some of the main byproducts of protein metabolism are simpler proteins and (in the case of semen components) low-molecular-weight amines, especially spermine and spermidine. These two are how the body raises the pH of semen to counteract the acidity of the vagina. The human body manufactures acids easily, but bases are much more difficult. Spermine and spermidine both have very strong, distinctive odor and taste. Seafood and nori both contain quite a bit of iodine, which can also affect the smell and taste of ejaculates. Some compounds, too, leave the body entirely unmetabolized, so if those are present, would contribute some of their own characteristics.