Chitin extraction from shrimp (Litopenaeus vannamei) shells by successive two-step fermentation with Lactobacillus rhamnoides and Bacillus amyloliquefaciens

Abstract

Chitin was extracted from shrimp shells powders (SSP) by successive two-step fermentation. The best microorganisms Lactobacillus rhamnoides and Bacillus amyloliquefaciens (BA01) for demineralization (DM) and deproteinization (DP) were obtained and the optimal fermentation conditions for two-step fermentation were established. Firstly, we determined the cultured conditions (inoculum level 4%, initial pH 6.5, cultured temperature 37 °C, glucose concentration 5%, cultured time 48 h) of Lactobacillus rhamnoides and the organic acid quantities and types of fermentation broth of Lactobacillus rhamnoides. Under the conditions, the pH of fermentation broth was 3.4, the DM efficiency was 97.5% and the ash in the final residue was 1.2%, and the main organic acid was lactic acid. Secondly, the optimal cultured conditions of BA01 were inoculum level 6%, initial pH 6.5, cultured temperature 37 °C, glucose concentration 4%, and cultured time 84 h. Under the conditions, the protease activity of fermentation broth was 701.3 U/mL, the DP efficiency was 96.8%, the protein in the final residue was 1.5%, and the chitin yield was 19.6%. In addition, the chitin obtained by fermentation was compared with the commercial chitin using scanning Fourier transform infrared spectrometer (FT-IR), X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Solid-state 13C CP/MAS-NMR spectra, and Scanning electron microscope (SEM). The results showed the chitin obtained by fermentation maintains the excellent physicochemical and structural properties of commercial chitin. Moreover, in order to make full use of shrimp and crab shells resources, the amino acid composition of fermentation broth was detected. The results showed that the fermentation broth had high nutritional value and could be used as a health nutrient in animal feed, even food.