Statistical optimization of cultural parameters for the optimized production of alginic acid using apple (Malus domestica) peels through solid-state fermentation

The industrially significant biopolymer, alginic acid, is mainly obtained from farmed brown seaweeds. Owing to differences in structural composition of alginate isolated from various species, the bacterial alginate has gained significant importance. Pakistan meets the industrial demand of alginate by importing it from developed countries. The current research was planned to assess the potential of apple peels (Malus domestica) for alginate production by using Azotobacter vinelandii through solid-state fermentation. Various cultural parameters were optimized using CCD of response surface methodology (RSM) like incubation days, pH, temperature and inoculum volume. Maximum yield of alginate (180.64 mg/gds) was achieved by fermentation of apple peels at substrate water ratio of 1:3 for 2 days with 3 mL volume of inoculum at pH 7.5 and 37.5 °C. Statistical analysis showed the F value and p value as 10.93 and 0.00 that indicates that the proposed model was highly significant. The goodness of fit of the model was determined by a coefficient of determination (R²) having a value of 90.5% indicating the accuracy of the model. Alginate produced was quantified by HPLC method and was found to be 97% pure in contrast to standard (100% pure of Sigma-Aldrich). The results indicated that alginate can be efficiently produced through solid-state fermentation by utilizing cheap fruit by-product as the substrate.