Scale criteria for fungal renin production by solid-state fermentation

Renin, a milk-coagulating enzyme, is used to elaborate cheese. Traditionally, enzymes of animal origin have been used. However, fungal renin has evidenced high specificity in its coagulating activity as, for example, that obtained from Mucor bacilliformis culture on solid substrate. Solid state fermentation (SSF) is defined as the growth of microorganisms in solid substrate in the absence of free water For the scale-up production of fungal renin by using solid state fermentation some difficulties have been encountered, such as control of the fermentation, heat and mass transfer problems (limited capacity for dissipation of metabolic heat generated during culture), limited development of models and of scale criteria for reactors. In this paper it was established a scale-up criterium for the production of fungal renin using Mucor bacilliformis in a SSF. The process variables studied were the amount of initial substrate, the length-diameter ratio of the reactor (L/D) and the airflow rare, using as response variable the enzyme production. The best results were obtained using low L/D ratios (0.25) and an air flow rate of 3.3 ml/min per gram of dry substrate, yielding around 20000 UE per gram of dry substrate.