Optimization of Process Conditions for Production of Succinic Acid and Lactic Acids from Cake Waste Using Response Surface Methodology

Food waste valorization into bio-based chemicals is an eco-friendly strategy to address environmental pollution and reduce reliance on fossil-based resources. This study explores the feasibility of bioconversion of cake waste into succinic acid (SA) and lactic acid (LA), through enzymatic hydrolysis and microbial fermentation. The compositional analysis revealed that, on a dry weight basis cake waste contains 572.0 mg g^-1 carbohydrates, 495.0 mg g^-1 starch, and 69.3 mg g^-1 protein, making it a nutritionally rich substrate for fermentation and then it was hydrolyzed using α-amylase, glucoamylase, and protease to release fermentable sugars and amino nitrogen. Enzymatic hydrolysis yielded 41.50 g L^-1 glucose and 4.56 g L^-1 free amino nitrogen. The enzymatic hydrolysate was subsequently fermented using Escherichia coli and Bacillus coagulans for SA and LA production, respectively. High performance liquid chromatography (HPLC) was used to quantify organic acid concentrations. Process optimization was performed using Box Behnken Design under response surface methodology (RSM), with three independent variables, namely, temperature, pH, and incubation time. The highest succinic acid yield (0.2194 g g^-1 cake waste) was obtained at a temperature of 40°C, pH of 7.5, and an incubation time of 144 h, while the maximum lactic acid yield (0.3178 g g^-1 cake waste) was recorded at a temperature of 47°C, pH of 5.6, and an incubation time of 94 h. Results demonstrate that cake waste can serve as a promising low-cost substrate for sustainable production of succinic and lactic acids, highlighting its potential for efficient food waste valorization through microbial bioprocessing.