Hydrolysate (sugars) at the concentration of 20 g/L is preferred for citric acid production.

OK thanks Selvaraju. But I was thinking that there was a particular volume of the hydrolysate to be used. If we can achieve the 20g/L, how much volume of the hydrolysate should be used. Secondly, how much volume of the medium should be used. Those are the two things I want to find out. In most papers people just say they used a mineral salt medium and hydrolysate for fermentation, but they don't state the volumes of both used.

I would imagine the emphasis for the fermentation would be on the concentrations of nutrients, hydrolysates, the fermenting organism, and end products more than the volume. In my studies and research, volumes are almost always treated as a secondary concern.  I would imagine you have an assay or other technique such as HPLC already to determine the sugar levels of your hydrolysate. With that info I would back calculate how much hydrolysate and a concentrate of the MSM would be needed to reach the desired levels of supplemental nutrients from the MSM and the hydrolyzed sugars.

In my lab, anything over 100 ml was considered a larger experiment. I ran mine at 20 ml or less. If you are trying to optimize, personal experience says that volumes under 100ml are the easiest to manage.

It would be easier to answer your question if I knew the concern you had related to volume and the goal of your experiments. I have attached links to a couple papers that discuss aspects of A. niger citric acid production related to your prior research and study. Best of luck.

http://www.sciencedirect.com/science/article/pii/S0960852499001078

http://www.sciencedirect.com/science/article/pii/S0960852406005943

http://www.ncbi.nlm.nih.gov/pubmed/947831

It depends on the sugar concentration.Sugar concn should be in the range of 10-30g /L of mineral medium. It can be assessed by application of response surface methodology.

Thank you every one for your kind suggestions.