Production of Gibberellic Acid by Solid-State Fermentation Using Wastes from Rice Processing and Brewing Industry

Gibberellic acid (GA 3 ) is a natural hormone present in some plants used in agricultural formulations as a growth regulator. Currently, its production on an industrial scale is performed by submerged fermentation using the fungus Gibberella fujikuroi , which is associated with low yields, leaving the purification stages with high costs. An alternative is solid-state fermentation (SSF), which makes it possible to obtain higher concentrations of product using low-cost substrates, such as agroindustrial by-products. This research investigated the use of raw rice bran (RRB) and barley malt residue (BMR) as substrates for GA 3 production by the fungus Gibberella fujikuroi . Through two statistical designs, the effect of moisture (50 to 70 wt.%) and medium composition (RRB content between 30 and 70 wt.% to a mass ratio between RRB and BMR) was first evaluated. Using the best conditions previously obtained, the effect of adding glucose (carbon source, between 0 and 80 g·L −1 ) and ammonium nitrate—NH 4 NO 3 —(nitrogen source, between 0 and 5 g·L −1 ) on GA 3 productivity was analyzed. The best yield was obtained using 30 wt.% RRB and 70 wt.% BMR for a medium with 70 wt.% of moisture after 7 days of process. It was also found that higher concentrations of NH 4 NO 3 favor the GA 3 formation for intermediate values of glucose content (40 g·L −1 ). Finally, a kinetic investigation showed an increasing behavior in the GA 3 production (10.1 g·kg of substrate −1 was obtained), with a peak on the seventh day and subsequent tendency to stabilization.