Step 1: Understanding yogurt cultures.
Yogurt is produced through the fermentation of milk by specific bacterial cultures. The primary cultures used are Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus. These cultures work synergistically to produce the characteristic flavor and texture of yogurt.
Step 2: Analyzing the options.
- (A) Incorrect, Lactococcus lactis subsp. lactis is not used in the production of yogurt; it is involved in other dairy products like cheese.
- (B) Correct, Streptococcus thermophilus is a key starter culture in yogurt production.
- (C) Incorrect, while Leuconostoc mesenteroides is involved in some dairy fermentations, it is not typically used in yogurt production.
- (D) Correct, Lactobacillus delbrueckii subsp. bulgaricus is another essential culture for yogurt fermentation.
Step 3: Conclusion.
Thus, the correct answer is (B) Streptococcus thermophilus and (D) Lactobacillus delbrueckii subsp. bulgaricus.