You don't need any additives to dissolve 120g/l of sugar into water. Wikipedia lists sucrose solubility as approximately 2000g/l at 25C, and HFCS has even highe

You don't need any additives to dissolve 120g/l of sugar into water. Wikipedia lists sucrose solubility as approximately 2000g/l at 25C, and HFCS has even higher solubility. The phosphoric acid is to make it taste better. 120g/l would taste unpleasantly sweet without the acidity.