Carbon source for glutamic acid fermentation: which substrate most commonly constitutes the main carbon feed in media for industrial glutamate (glutamic acid) production?

Introduction / Context:
The cost and composition of the carbon source strongly influence economics and yields in amino acid fermentations such as glutamate production with Corynebacterium glutamicum. Industrial media frequently rely on inexpensive, readily available feedstocks rather than pure sugars, provided process impurities are manageable.

Given Data / Assumptions:

• Industrial practice often substitutes pure glucose with agricultural by-products.
• Molasses (cane or beet) offers a cost-effective mixture of sugars and micronutrients after appropriate pretreatment.
• Process control (for example, biotin limitation, aeration) drives glutamate secretion independent of whether the carbon is supplied as pure glucose or molasses.

Concept / Approach:
Among the options, molasses is the classic “main” carbon feed in many large-scale glutamate processes due to price, availability, and acceptable performance after conditioning. While glucose and sucrose can also be used effectively, molasses remains the textbook industrial answer to “what the medium mainly consists of” in commercial practice.

Step-by-Step Solution:

Verification / Alternative check:
Industrial microbiology references for amino acid fermentations list molasses as a typical primary carbon source, with pretreatments to minimize inhibitors.

Why Other Options Are Wrong:

• Glucose/Sucrose: Effective but often costlier as primary industrial feeds.
• Lactose: Less common for glutamate; more associated with whey valorization.
• Starch hydrolysate: Possible, but molasses is the more classic, widely cited “main” component.

Common Pitfalls:
Equating laboratory media (pure glucose) with commercial media choices; ignoring pretreatment needs for molasses to mitigate trace metal inhibition.

Final Answer:
molasses