Optimizing Exopolysaccharide Production by Bacillus subtilis Using Spoiled Fig and Grape

Abstract

The study aimed to enhance exopolysaccharides (EPSs) production by the bacterial strain Bacillus subtilis ES (OR501464) isolated from sugar cane juice. Spoiled grape and fig extract were utilized as cost-effective substrates for EPS synthesis by B. subtilis ES (OR501464), and the impact of nutritional factors on EPS synthesis was assessed. Among nineteen bacterial isolates evaluated for EPS production, the isolate with the highest EPS yield was identified through a combination of phenotypic and genotypic analyses. The optimization process revealed that the highest EPS yield of 4.7 g/L was achieved in a production medium containing 4% sucrose, 0.1% NaNO₃, 0.002% Na₂SO4, and 2% NaCl at 30 °C and pH 9. Additionally, the study explored EPS generation by B. subtilis ES (OR501464) using spoiled grape and fig extract as substrates. The addition of 2% NaCl to spoiled grape extract increased EPS production to 4.357 mg/mL compared to 3.977 mg/mL with grape alone. However, 2% NaCl did not enhance EPSs production in fig waste. Supplementing spoiled fig or grape extract with 0.2 g/L Na₂SO₄ and 1 g/L NaNO₃ increased EPS production by B. subtilis ES (OR501464). The EPS was analyzed using GC-MS and FTIR spectroscopy for partial characterization. The study found that spoiled figs and grapes can be used as effective substrates for EPS production. The highest yield was achieved by adding 0.2 g/L Na₂SO₄ and 1 g/L NaNO₃. This study highlights the use of spoiled figs and grapes to produce valuable biopolymers, promoting sustainable and eco-friendly bioprocessing technologies.