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

Abstract

Gibberellic acid (GA₃) 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 GA₃ 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-NH₄NO₃-(nitrogen source, between 0 and 5 g·L^-1) on GA₃ 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 NH₄NO₃ favor the GA₃ formation for intermediate values of glucose content (40 g·L^-1). Finally, a kinetic investigation showed an increasing behavior in the GA₃ production (10.1 g·kg of substrate^-1 was obtained), with a peak on the seventh day and subsequent tendency to stabilization.

Keywords: Agroindustrial residue; GA3; Gibberella fujikuroi; Solid-state fermentation; Waste management.