Question

Identify which volatile compounds are primarily responsible for the distinctive aroma of coffee?

• A. Chlorogenic acid
• B. Caffeine
• C. Volatile aldehydes and ketones
• D. Polyphenols

Hint:

Aroma compounds must be "volatile" (capable of evaporating easily at room or drinking temperature) to reach olfactory receptors in the nasal cavity. Non-volatile compounds like caffeine and acids affect taste but not smell.

Answer 1

The Correct Option is C

Step 1: Understanding the Question:
The question asks to identify the class of chemical compounds primarily responsible for producing the characteristic, complex aroma of roasted coffee beans and brewed coffee.

Step 2: Detailed Explanation:

• Coffee Chemistry: Raw green coffee beans possess minimal aroma. The characteristic aroma of coffee is generated during high-temperature roasting.

• Chemical Reactions During Roasting: Roasting triggers thermal reactions such as the Maillard reaction, Strecker degradation, caramelization, and lipid pyrolysis. These reactions produce over $800$ volatile compounds that easily vaporize.

• Aroma-Active Volatiles: The major classes of highly volatile compounds responsible for aroma include volatile aldehydes (such as acetaldehyde and isovaleraldehyde) and ketones (such as diacetyl and acetoin), along with furans, pyrazines, and sulfur-containing compounds (thiols). These compounds provide roasted, sweet, nutty, and buttery aromatic notes.

• Why Other Options are Incorrect:

• Chlorogenic Acid: A non-volatile phenolic compound responsible for the acidity, astringency, and bitterness of coffee. It does not vaporize to produce aroma.

• Caffeine: A non-volatile purine alkaloid that contributes to bitterness and physiological stimulation but has no direct aroma.

• Polyphenols: Large, non-volatile antioxidant molecules that remain dissolved in the liquid phase and do not contribute to aroma.

Step 3: Final Answer:
Volatile aldehydes and ketones are the primary compounds responsible for the sensory aroma of coffee, making option (C) the correct choice.