Highly efficient shrimp shell recovery by solid-state fermentation with Streptomyces sp. SCUT-3

Owing to the rising global production of crustaceans, chitinous waste is being increasingly produced but poorly recycled. The development of new sustainable biorefinery methods is of urgent necessity for replacing traditional chemical recycling methods. A newly isolated Streptomyces sp. SCUT-3 strain, with robust protease secretion and chitin utilization abilities, was used for recycling shrimp shell waste (SSW) in this study. Under optimized conditions, 92.6 % of SSW protein was recovered by 5 d of solid-state fermentation (SSF), of which two-thirds was harvested as free amino acids (FAAs), and one-third as oligopeptides. The deproteinized SSW residue from SSF was easily subjected to calcium extraction, and 92.0 % of calcium was recovered in 30 min using lactic acid. The remaining residue was recovered as chitin products with high purity, a high acetylation rate of 90.5 %, and a low degree of crystallization. Altogether, the Streptomyces SSF-plus-lactic-acid method developed in this study can convert 100 g SSW into 33.6 g FAAs, 16.7 g oligopeptides, 7.4 g calcium (in the form of calcium lactate), and 19.5 g chitin. Analyses of the economic benefits and environmental impact revealed that this method has a low cost (20 %), high profit (10-fold), and a low environmental footprint (1.08 %) compared to traditional-chemical methods, and is superior to other newly developed physicochemical, enzymatic, and biofermentation methods. Higher protease production and constitutive chitinase expression SCUT-3 strains are under-constructed. The possibility of the enhanced super shell degradation strains to realize higher protein yields, synchronous protein, and chitin degradation, or sequential protein and chitin degradation for chitinous waste recycling is discussed. This green sustainable method developed in the study will light the way for the future shell waste recycling industry.