Optimization of β-carotene production from agro-industrial by-products by Serratia marcescens ATCC 27117 using Plackett–Burman design and central composite design

β-carotene is a widely known carotenoid molecule, commercially used as food and feed additive, cosmetic and pharmaceutical products. The current study investigates the usability of some agro-industrial by-products for β-carotene production by Serratia marcescens and optimizes the production process using Plackett–Burman Design (PBD) and central composite design (CCD).Rice bran, molasses and sugarcane bagasse were tested for their effects on β-carotene production by S. marcescens. Molasses was the high potent source for β-carotene production giving 1.1 mg/L after 2 days of incubation in the dark at 30 °C on a rotary shaker at 150 rpm.PBD was used to evaluate the effect of lactose, sucrose, beef extract, peptone, NaCl, MgSO4, KH2PO4, pH, inoculum size (ml/L) and agitation rate (rpm) on β-carotene production. Sucrose, lactose, peptone, beef extract, pH, inoculum size showed a positive sign of the effect on β-carotene production, while other factors showed a negative sign. The coefficient of determination, R2, was 0.9829, showing good fitness of the model.Factors screened by PBD were further optimized using CCD of Response Surface Methodology (RSM). Central composite rotatable design was used to determine the optimum levels of three independent variables (sucrose g/L, peptone g/L and pH) at five different levels, coded as – α, −1, 0, 1 and +α. Results of CCD were analyzed by standard ANOVA, and the quadratic regression equation was generated. The optimum production medium were composed of 2.5 g/L sucrose, 7.8 g/L peptone and pH 6.7 with a predicted value of 2.51 mg/L and actual value of 2.24 mg/L.