Functional and nutritional characteristics of protein recovered during isolation of chitin from shrimp waste

Shrimp shells are a good source of chitin when processed into chitosans. Only about 10% of the raw material dry matter is recovered as chitosan. The objective of this work is to isolate the protein (during de-proteinization of chitin) using nitric acid 30% (this designated as acidic protein) and 1 M sodium hydroxide (this designated as alkaline protein). The functional properties, amino acid contents and nutritional quality of both isolated protein were evaluated. The acidic protein had significantly (p < 0.05) higher emulsification activity (51.58), emulsification stability (48.15) and foam capacity compared to the alkaline protein. The acidic protein also exhibited a broader range of minimum solubility at pH range 4-6 (from 11.21% to 12.54%). Meanwhile, the minimum solubility (22.89%) of the alkaline shrimp waste protein was quite sharp at pH 4. The highest emulsification activities of acidic protein extract were observed at pH 2 (63.82) and pH 10 (68.76) while the lowest were observed at pH 6 (44.32). The same trend was noticed for the emulsification stability. The emulsification activity of the alkaline protein extract ranged from 31.25 (at pH 4) to 52 (at pH 10) and its stability ranged from 44.21 to 51.12 at the same pHs. The alkaline protein is rich in isoleucin and valine compared to the FAO/WHO reference pattern, while leucine and lysine are slightly deficient compared with the same reference. On the other hand, the acidic protein contains higher amounts of lysine, therionin and valine compared to the reference pattern. The alkaline protein had a higher chemical score and calculated protein efficiency ratio (51.46% and 1.94, respectively) compared to 42.10% and 1.75, respectively for acidic protein.