Penicillium is used in the production of

The correct option is Both (a) and (b).

Here is the step-by-step educational explanation of why this option is correct:

1. Production of Antibiotics:
Fungi belonging to the genus Penicillium are famous for producing the very first discovered antibiotic, penicillin. Specifically, species such as Penicillium chrysogenum (formerly known as Penicillium notatum) are cultured on an industrial scale to extract penicillin, which is used to treat various bacterial infections in humans and animals.

2. Cheese Fermentation and Ripening:
Certain species of Penicillium play an essential role in the dairy industry, particularly in cheese making. For example:
- Penicillium roqueforti is used in the production of blue cheeses (like Roquefort, Gorgonzola, and Stilton), where it gives the cheese its characteristic blue veins and sharp flavor.
- Penicillium camemberti is used to create the soft, white rind on cheeses such as Camembert and Brie.
During the fermentation and ripening processes, these molds secrete enzymes that break down proteins and fats, contributing to the unique texture, aroma, and flavor of the cheeses.

Conclusion:
Since Penicillium is actively used in both the production of antibiotics (a) and cheese fermentation (b), the correct choice is Both (a) and (b).