Microbial production of dextran using pineapple waste extract: a two-step statistical optimization of submerged fermentation conditions and structural characterization

A two-step optimization protocol was attempted to optimize the condition for dextran production from pineapple waste using Leuconostoc mesenteroides NCIM-2198. Response surface methodology, in combination with numerical optimization technique, was explored for this purpose. In the first step, the initial medium pH (6.5–7.5), incubation temperature (25–35 °C), and time (12–60 h) were optimized from 45 full factorial runs. The maximum dextran yield was estimated as 1.46 g·[100 mL]⁻¹ while incubated at 29.2 °C for 57.2 h at an initial pH of 7.15. Further, sucrose concentration (2–10 g·[100 mL]⁻¹) and culture volume (3–7 mL·[100 mL]⁻¹) were optimized from 15 experimental runs. The maximum dextran yield (1.47 g·[100 mL]⁻¹) was obtained at 7.6 g·[100 mL]⁻¹ of sucrose with 3 mL·[100 mL]⁻¹ of culture volume at the previously optimized fermented broth. The response surface models were validated to explain the interaction between factors affecting dextran yield. The structural characteristics of the exopolysaccharide were analyzed. Fourier-transform infrared spectra showed that the exopolysaccharide contains similar spectral peaks as that of standard dextran. Nuclear magnetic resonance spectroscopy confirms the exopolysaccharide was dextran with mainly α-1-6 glycosidic bonds. Scanning electron microscopy explained its porous structure, which would be useful in retaining water and thus giving texturizing and viscosifying properties.