Extraction and characterisation of proteins from by-products from the shellfish processing industry.

The fish and shellfish industry processes 851,984 tonnes of fish per year
worldwide. However, only 43% of that is consumed, and valuable proteins are processed
as waste. Protein hydrolysates are widely used in food technology for their nutritional and
functional properties. The goal of this project is to extract protein from whelk by-products
derived from the shellfish processing industry and create protein hydrolysates that have
marketable value. The by-products were divided into two types: raw (R) and cooked byproduct (C). The proteins were extracted using the pH shift method and quantified using
the Bradford assay. It was possible to extract a maximum of 455 mg/g at a neutral pH, for
which R had the highest protein yield. Proteins were also qualified using reverse phase
high-performance liquid chromatography (RP-HPLC) that showed that R has more
hydrophilic proteins while the C extracted protein showed more peaks in the hydrophobic
phase. The Fourier-transform infrared spectroscopy (FTIR) indicated the presence of
glutamine, tyrosine, and serine in the extracted proteins. Extracted proteins were then
hydrolyzed using Alcalase and α-Chymotrypsin. It was possible to obtain higher degrees
of hydrolysis (DH) using Alcalase. The hydrolysates were tested for antioxidant activity
using the DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) free radical antioxidant assay.
Alcalase hydrolysates showed to have overall lower IC50 for stabilization of the DPPH
radical than α-Chymotrypsin, the lowest one being 13.92±1.57 µg/mL for the Alcalase
hydrolyzed neutral proteins. The IC50 results obtained are significantly lower than the
ones described in other studies using the same enzymes or other marine species. This can
indicate that more heterogenous mixtures of by-product can originate extracted proteins
that when hydrolyzed lead to higher radical scavenging activity, thus making shellfish
industry by-product a sustainable and valuable source of antioxidant peptides.