Investigation of enzymatic hydrolysis process to valorize waste mussel shells

Nguyen, Thi-Hong-Xuan (2021) Investigation of enzymatic hydrolysis process to valorize waste mussel shells. Masters thesis, Memorial University of Newfoundland.

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Abstract

Blue mussels (Mytilus edulis) are the most common mussel harvested with high value nutritional compounds including proteins, vitamins ( C, A, and B12), and minerals (iron and calcium). Blue mussels are filter feeders eating plankton from the water. Mussel farming is more sustainable form of aquaculture as fish meal, chemicals (antibiotics and additives) are not required and the risk of pathogens escaping into the coastal ecosystems is minimal. The worldwide aquaculture and processing of mussels is rapidly increasing and blue mussels are Canada’s top shellfish aquaculture product produced in every province in Atlantic Canada, as well as in Quebec and British Columbia. By-products from mussel aquaculture and processing, such as processed mussel shells, unmarketable and broken mussels, make up a significant waste stream from this industry and are currently difficult to valorize. Waste mussel shells are a potential source of bio-calcium carbonate and proteins. Protein enzymatic hydrolysis, a process where protein macromolecules are hydrolyzed to amino acids and peptides of smaller size. The process is a simple, effective, and environmentally friendly means of valorizing waste mussel shells, producing two product streams: mussel shells without residual meat and non-toxic hydrolysate. This study includes a review of literature on valorizations of waste mussel shells for the source of bio-calcium carbonate and proteins. The review shows the lack of kinetic studies for enzymatic hydrolysis of mussels, required for any scale up to a commercial process. In this study, mussel meat is removed from whole mussels by using enzymatic hydrolysis technology. The process is carried out using a food grade enzyme, Multifect PR 6L, and tap water at neutral pH, with no pH control, and a temperature 50ﾟC. To determine the rate of hydrolysis, the degree of digested meat (DM) is used in this study instead of the degree of hydrolysis (DH). The enzyme and substrate concentrations were varied to determine the impact of these factors on the final digested meat and rate of reaction. The fraction of digested meat (or degree of shell cleaning) varied from 0.57 g/gₘₑₐₜ to 0.94 g/gₘₑₐₜ depending on the enzyme and substrate (meat) concentrations. Soluble protein concentration of the obtained hydrolysates was also analyzed. After evaluating a number of reaction rate mechanisms, the first-order model is suggested as the best model to describe the enzymatic hydrolysis of whole raw mussels. The soluble protein concentration in the resulting hydrolysate increases with the increases in the amount of digested meat.

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