Biodegradation of shrimp biowaste by marine Exiguobacterium sp. CFR26M and concomitant production of extracellular protease and antioxidant materials: production and process optimization by response surface methodology.

Twelve marine bacterial cultures were screened for extracellular protease activity, and the bacterium CFR26M which exhibited the highest activity on caseinate agar plate was identified as an Exiguobacterium sp. Significant amount of extracellular protease (5.9 ± 0.3 U/ml) and antioxidant materials, measured as 2,2'-diphenyl picrylhydrazyl (DPPH) radical scavenging activity (44.4 ± 0.5 %), was produced by CFR26M in submerged fermentation using a shrimp biowaste medium. Response surface methodology (RSM) was employed to optimize the process variables for maximum production of protease and antioxidant materials by CFR26M. Among the seven variables screened by two-level 2**(7-2) fractional factorial design, the concentration of shrimp biowaste, sugar, and phosphate was found to be significant (p ≤ 0.05). The optimum levels of these variables were determined by employing the central composite design (CCD) of RSM. The coefficient of determination (R (2)) values of 0.9039 and 0.8924 for protease and antioxidant, respectively, indicates the accuracy of the CCD models. The optimum levels of shrimp biowaste, sugar, and phosphate were 21.2, 10.5, and 2.3 % (w/v) for production of protease and 28.8, 12, and 0.32 % (w/v) for production of antioxidant material, respectively. The concentration of shrimp biowaste, sugar, and phosphate had linear and quadratic effect on both protease and antioxidant productions. RSM optimization yielded 6.3-fold increases in protease activity and 1.6-fold in antioxidant material production. The crude protease of CFR26M had a maximum activity at 32 ± 2 °C with pH 7.6. This is the first report on the use of marine Exiguobacterium sp. for concomitant production of protease and antioxidant materials from shrimp biowaste.