Protein and lactose in skim milk and polyphenols, caffeine, and
fat in vegetable creamer added coffee are some possible components
that can interact with sweeteners chemically or at perceptual level.
Chemical interactions between stevia and other substances such as
water soluble vitamins, organic acids or sweeteners have not been observed
(Kroyer, 1999, 2010). The intrinsic bitterness of coffee or fat in
added creamer may have suppressed the sweetness of stevia more
than other sweeteners,