Screening of protease-producing lactic acid bacteria from Indonesian fermented fish products and its application in chitin extraction from vannamei shrimp (Litopenaeus vannamei) shell

Abstract

This study aimed to screen lactic acid bacteria (LAB) from traditional Indonesian fermented fish products, namely wadi and jambal, with high protease activity for chitin production from Litopenaeus vannamei shrimp shells. Twenty-eight colonies were successfully isolated and identified through biochemical tests such as catalase and Gram staining. Seven out of the twenty-eight colonies were identified as lactic acid bacteria based on their Gram-positive and catalase-negative results. These strains from wadi samples were named GWB 1.3, GWB 1.7, and GWB 2.5, while those from jambal samples were named GMJB 1.3, GMJB 1.6, GMJB 2.6, and GMJB 2.7. The protease activity of these strains was tested using the well-diffusion method on skim milk agar to assess their deproteinized activity. The diameter of the clear zone formed after 24, 48, and 72 hours of incubation was measured. GWB 1.7 and GMJB 2.6 showed the largest clear zone diameter with 21.3 mm and 22.5 mm, respectively, and were selected for the single step-fermentation of shrimp shells. The fermentation process was conducted in 6 days with different inoculum ranging from 0%, 5%, 10%, 15%, and 20% (v/v) as treatments. All treatments, including moisture, ash, and protein, were evaluated for proximate content in the final days. The results indicate that the 20% inoculum showed the highest deproteinization and demineralization for both bacterial strains. GWB 1.7 exhibited a demineralization of 43.7% and deproteinization of 25.2%, while GMJB 2.6 showed a demineralization of 39% and deproteinization of 16.1%. This study demonstrated that lactic acid bacteria from wadi and jambal samples could produce chitin from shrimp shells, a valuable biopolymer with various applications.