It depends, if only you need a masking agent its possible to use MD (if your material is hydrophilic), but if you like to make a controlled delivery capsule plus masking effec, the problem is more complex
Possibly pineapple is causing pain and that is interfering with the perception of bitterness. I found this paper that possibly will be useful to you, from "Chemical Senses" journal: http://chemse.oxfordjournals.org/content/28/1/45.long (Stimulation of Bitterness by Capsaicin and Menthol: Differences Between Lingual Areas Innervated by the Glossopharyngeal and Chorda Tympani Nerves)
This paper concluded that not all people perceive both sensory characteristics in the same way. You should make some sensory analysis with your added pineapple samples to be sure what is happening with your product.