The recovery of protein hydrolysate during enzymatic isolation of chitin from shrimp Crangon crangon processing discards

Shell waste from shrimp Crangon crangon processing is a good source of chitin and proteins, contained on a dry basis of the offals in amounts 17.8% and 40.6%, respectively. The digestion of the shells with proteolytic enzymes allow to recovery of the chitin and nutritionally valuable protein hydrolysate. These products were prepared from the shells preliminarily demineralized with 10% HCl solution at 20°C for 30 min using commercially available Alcalase at 55°C and pH 8.5. Recovered protein hydrolysate contained, on a dry basis, 64.3% of protein (N×6.25), 6.24% lipids and 23.4% of sodium chloride and had, at pH 4.0, a minimum solubility, and 81.7% of total nitrogen in the product. The PER value of the obtained product was 2.99 as compared with that for hydrolysates from capelin (2.64) and beef longissimus dorsi muscle proteins (2.81). The charcoal decolorization of the product decreased the PER and amino acid index (EAA) values from 2.99 and 125.4 up to 2.74 and 123.2, respectively. The total amount of residual small peptides and amino acids directly attached to chitin molecules and resistant to enzymatic hydrolysis depends on degree of hydrolysis (DH) and was about 4.4% at DH value of 30%. Such purity of chitin is sufficient for many purposes.