Executive Summary: Extraction and characterisation of proteins from mussel co-product streams

Summary of Project and Key Findings:
There is interest in isolating and identifying proteins extracted from mussel co-product streams. AgResearch undertook a proof-of-concept study to extract proteins from the co-product streams which mostly consisting of mussel foot, adductor muscles and mussel byssus. Mussel byssus is a mass of elastic threads and is composed of a mixture of three different categories of proteins. Depending on their function, the proteins can be classified as fibrous; which form load-bearing cables in the core of the threads, cuticular; that form a protective coat around the cables and adhesive; that connect the cables to the solid substrate. The fibrous proteins can be collagenous in nature whereas the cuticular proteins have a high content of lysine and exotic amino acids such as 3.4-dihydroxyphenyl-L-alanine (DOPA). Mussel foot proteins (MFps) allow mussels to adhere to various substrates underwater. This adhesive versatility is facilitated by adhesive proteins that contain DOPA allowing the formation of hydrogen bonds with hydrophilic substrates. Mussel byssus is a good source of collagens, but byssus collagens are unique in their sequence compared to other known sources of collagens.

Raw material supplied was subjected to a novel sequential extraction scheme starting with a mild acid extraction step, followed by an enzymatic extraction and finally an extended alkali extraction for solubilising the most resilient proteins. The sequential extraction process provided the opportunity to evaluate protein type and yield at each stage of extraction and enabled steps to reduce extraction of contaminants. It was expected that due to unique protein crosslinks present in these raw materials, the extraction efficiency using mild conditions will be low and hence an extended alkali procedure was used for the collagenous protein extraction. The mild acidic and enzymatic steps were used to mainly extract non-collagenous proteins.

This study was a step towards transforming these low value bio-resource streams into higher value ingredients.

The presence of unusual amino acids present in mussel co-product streams can be potentially targeted for pharmaceutical applications, the extractable adhesive proteins from the co-product streams have a huge potential in medical research and industrial applications. Depending on the nature of extractable proteins, there is potential for the development of future biological reagents, biomedical materials and/or food, nutraceutical products. There is on-going discussion re potential applications of these extracted proteins.