Step 1: Concept Overview:
The question asks us to identify defects in cheese caused by microbial activity. Microbial growth in cheese can be beneficial (e.g., starter cultures) or detrimental, leading to spoilage or defects.
Step 2: Detailed Analysis:
Analyzing each statement:
A. Mold Growth: While some molds are necessary for cheese production (e.g., Penicillium roqueforti in blue cheese), unwanted mold is a spoilage defect.
B. Yeast Growth: Uncontrolled yeast growth can cause off-flavors, gassiness, and discoloration, all considered defects.
C. Gassy defect in cheese: Excessive holes or splitting is caused by gas-producing microorganisms like coliforms, clostridia, or yeasts. This is a microbial defect called "early blowing" or "late blowing".
D. Discoloration in cheese: Pigmented bacteria, yeasts, or molds can cause unwanted colored spots (e.g., pink, black, brown), a quality defect.
All four statements describe microbially induced defects.
Step 3: Conclusion:
Mold Growth, Yeast Growth, Gassy defect, and Discoloration are all well-known microbial defects in cheese.