Kinetics and antimicrobial activity of gallic acid by novel bacterial co-culture system using Taguchi’s method and submerged fermentation

Abstract In this present study, a tannase positive Bacillus gottheilii M2S2 and Bacillus cereus M1GT were co-cultivated for the production of gallic acid by using tannic acid as the sole carbon source through submerged fermentation. Optimizing various factors is important for the improvement of coculture metabolite production. Taguchi orthogonal array (OA) of Design of experimental (DOE) methodology was used to estimate the influence and significance of five factors (tannic acid concentration, glucose concentration, agitation speed, and inoculum size) on the gallic acid production in shake flask. L16 OA with five factors in four levels was considered with an experimental matrix of 16 trials. Among all the factors, Agitation speed contributed the highest for gallic acid production (28.28%), followed by glucose concentration (21.59%), inoculum size (19.6%), tannic acid concentration (19.54%), and pH (11.09%). Validation experiments were executed at the found optimized conditions which resulted in a 6.36-fold increase in gallic acid yield compared to the unoptimized condition. Further, the kinetics of growth, tannic acid degradation, and gallic acid yield were evaluated at the optimized conditions. The kinetic parameters Yx/s, Yp/s, and Yp/x were determined as 0.292 mg of cells/mg of tannic acid, 22.2 µg of gallic acid/mg of tannic acid, and 70.76 µg of gallic acid/mg of cells with a growth rate of 0.273 h− 1 after 24 h of fermentation. Finally, antimicrobial activity of the product gallic acid was investigated against food-borne pathogenic E. coli, and Serriatia marcescens, Bacillus sp. and S. aureus using the agar disc diffusion technique. Gallic acid showed bacteriostatic against E. coli, S. aureus, and Serriatia marcescens with a zone of inhibition of 2 cm, 1.6 cm, and 1.3 cm respectively. Thus the cost-effective bioproduct gallic acid proved to be potentially effective to control food poisoning diseases and preserve foodstuff.