What Gives Pepper Its Peppery Taste?

Millions spice up their meals by adding one or more forms of pepper¹ in various forms and amounts. Pepper livens up food by adding an aromatic hotness or spiciness to food. What substance or substances in pepper gives it its distinctive taste? It's a matter of chemistry. Let's examine how.

What's in a Name?

Plants that produce fruits called peppercorns used to season food belong to the family Piperaceae, genus Piper. This sort of pepper is not to be confused with certain other popular sorts, including chili peppers and bell peppers, which belong to the family Capsicum. This latter form of pepper derives many of its characteristics, including its hot taste, from compounds called capsaicinoids. Piperaceae piper peppers owe their flavor and their aroma to other compounds - many of which contain the letters p-i-p-e-r in their names.

Aromatics

The main contributor to the pungent taste of black pepper is the alkaloid piperine, although there are at least five other minor contributors, including: pipperettine, piperylin, piperolein A and B, and piperanine. The chemical structure of piperine is seen in the image associated with this article. Quite interesting from the chemist's perspective is the degree of conjugation found within the molecule. Conjugation is generally at least partly responsible for the color of natural occurring compounds. Doubtless it is also partly responsible for flavor, as well. What is conjugation?

Conjugation

In its simplest aspect, conjugation refers to the presence of alternating double bonds. The drawing reveals only two in piperine. A double bond is more than just two single bonds. A single bond lies between its two bonded atoms. A double bond includes such a bond type. However, the other component of a double bond is called a "pi bond." In a pi bond, electrons lie, not directly between atoms, but above and below them. Such bonded electrons are more readily subject to chemical attack by electron-loving or "electrophilic" reagents.

Obtaining the widest perspective of conjugation requires we consider other structures besides double bonds carbon atoms. One such structure found in piperine is carbonyl (‐C=O), in which carbon is double bonded to oxygen, plus atoms such as nitrogen and oxygen containing unbonded electrons. For such structures to be considered conjugated, their involved electrons must alternate as well. In the case of piperine, much of the structure is conjugated - including the six-carbon benzene ring (containing three alternating pi bonds) just to the right of the five-member di-ether ring at the far left in the drawing.

In Conclusion

Although color is directly measurable, and can conceivably be connected at some mathematical level with degree and type of conjugation, it would be facetious to say with certainty the same thing can be hoped for flavor. Nevertheless, there is such a thing as flavor chemistry, and the conjugation of the organic chemist will doubtless yield interesting and new flavors and aromas to tease, if not tempt, the palate.