Step 1: Understanding the context.
The production of citric acid is a key industrial process, and there are various methods used for its commercial production. Batch fermentation is the traditional method for producing citric acid, in which microorganisms are grown in a fixed amount of substrate, and the fermentation process is completed in stages.
Step 2: Analyzing the options.
(1) Batch fermentation: Correct — Batch fermentation is the traditional method for the commercial production of citric acid. It involves fermenting a specific amount of medium and harvesting the product after a set period.
(2) Continuous fermentation: This method involves the continuous supply of substrate and removal of products, which is not the traditional method for citric acid production.
(3) Synchronous production: This is a general term for processes where all microorganisms are synchronized, but it is not a specific method for citric acid production.
(4) Solid state fermentation: This method uses solid substrates for microbial growth, but it is not typically used for the large-scale production of citric acid.
Step 3: Conclusion.
The correct answer is (1) Batch fermentation, as it is the traditional and widely used method for producing citric acid.