For example, can the taste of pineapple be isolated to just a certain amount of "salty-taste-triggering-molecules" and "sweet-taste-triggering-molecules" etc.? Can our current understanding of the gustatory system predict the taste of a new substance (for example we could predict it tastes like chocolate) just based on the amount and ratios of these molecules?
The brain perceives taste or flavor as a combination of input from taste buds, the olfactory system, and even pain receptors (spicy foods). Other food contents, such as metal, spice, fat, pH, and even dissolved gas content seem to contribute.
While there are 5 types of taste receptor, there are some 2000 olfactory bulbs encoded by 1000s of gene. As such, it is not possible to predict how something will taste in a simplistic 5-taste combo. However, this is an area of active research, such that structural models are used to develop taste enhancers, artificial sweeteners etc.