Statistical sequential optimization of process parameters for inulinase production by Kluyveromyces marxianus ATCC 36907 in solid-state fermentation using beer residue

The biotechnological production of inulinase, a hydrolytic enzyme with important applications in the food and pharmaceutical industry, is presented as a possible route for the valorization of beer residues. The current study employs a sequential optimization strategy, based on statistical experimental designs, was employed to optimize inulinase production by Kluyveromyces marxianus ATCC 36907 in solid-state fermentation (SSF), including the Plackett-Burman (PB) design and the Central Composite Rotatable Design (CCRD). The most important variables selected of SSF using dried beer residue were the concentration of sugarcane molasses, concentration of yeast extract (additional source of nitrogen) and the incubation temperature. The CCRD, which through the response surface methodology (RSM), determined the optimal fermentation conditions for these three variables, which were 47.1% (w/w), 0.032 g gds & xfffd; 1 and 37.5 degrees C, respectively. It was found that the RSM model has a predicted R2 value of 0.9512 and adjusted R2 of 0.8884, and can significantly predict (p < 0.05) the response variables of enzyme activity. Under these optimal conditions, it was possible to obtain a maximum inulinase activity of 239.38 U gds & xfffd; 1 of dried beer residue and maximum productivity at 48 h of 3.69 U gds.h-1. While there is ample literature on inulinase production by solid-state fermentation using K. marxianus, this is the first report on the use of beer residue as a potential source for the production of this enzyme with significant high yield that is on par with the enzymatic activities reported so far using different substrates and different lineages of K. marxianus.