Voges-Proskauer B (VP – B)

Voges–Proskauer Reagent B (VP‑B) is a strong alkaline solution, typically composed of potassium hydroxide (KOH), used as the second reagent in the Voges–Proskauer test for detecting acetoin in bacterial cultures.

🏭⚗️ Production
VP‑B is prepared by dissolving potassium hydroxide pellets in distilled water, often at a concentration of 40% (w/v). Some formulations may include creatine to enhance the color reaction. The solution is stored in a tightly closed container and used freshly for accurate test performance.

🔬 Properties
This reagent appears as a clear, colorless solution with a slippery feel due to its strong alkalinity. It has a high pH and is highly reactive in the presence of oxygen and organic compounds. When combined with VP-A (α-naphthol solution), it promotes oxidation of acetoin to diacetyl, which then reacts to produce a red complex.

🧪 Applications
VP‑B is used in the second step of the Voges–Proskauer test. After adding VP‑A to a glucose-phosphate broth culture, VP‑B is added to initiate the chemical reaction. In the presence of acetoin, a red to pink color develops within 15–30 minutes, indicating a positive result for organisms capable of 2,3-butanediol fermentation.

⚠️ Safety
Due to its high alkalinity, VP‑B is corrosive and can cause burns upon contact with skin or eyes. Use gloves, eye protection, and handle with care in a well-ventilated area. Store tightly sealed at room temperature and away from acids or incompatible substances.