Browsing by Author "Gonapinuwala, Suchima Tharangi"

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    Commercially scalable fish collagen processing : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand
    (Massey University, 2023) Gonapinuwala, Suchima Tharangi
    Fish collagen has a potential for high-value applications in the biomedical industry due to its excellent biocompatibility, biodegradability and low antigenicity properties. It is also a viable alternative for mammalian collagen due to its high availability, having no risk of disease transmission or religious barriers and the low cost of raw material. However, its utilisation is limited due to the non-availability of industrial-scale processing methods. Maintaining the native triple-helical structure in collagen molecules and the native D-banding pattern in the collagen fibrils are the requisites for biomedical collagen, therefore the existing industrial fish collagen extraction methods for food or cosmetic applications cannot be used. Unlike mammalian-origin collagen, fish-origin collagen differs due to fish species differences, and it is not practical to develop by trial and error, collagen extraction methods for every individual fish species of interest. Therefore, this study was carried out to interpret how the fish skin structure and composition relate to the physico-chemical processes that occur during collagen extraction, to develop a biomedical collagen extraction method based on this understanding, and to present guidelines to use this method for other fish species at industrial-scale. This collagen extraction process was developed through three main steps: pretreatment, extraction, and fibrillogenesis, and important determinants at each step, in relation to the fish skin structure and composition were identified. The focus of the pretreatment step is to remove non-collagenous proteins and fats, and the swelling of the skin in the pretreatment medium was also found to be a critical aspect in this tissue due to the structure of fish skin. The focus of the extraction step is to solubilise collagen molecules into the extraction medium in its native triple-helical conformation. Using a hydrochloric acid medium at an initial pH of 2 was found to be important in preserving the native triple-helical structure of collagen molecules. In addition, four processing objectives were presented based on the underpinning knowledge, to apply this method to any fish species of interest: (i) an upper limit of pH 4 for the extraction solution; (ii) maximum swelling; (iii) a manageable viscosity of the extraction solution; and (iv) as few undissolved pieces of skin as possible. A second extraction was introduced as a pigment removal step to improve the purity and colour of collagen while still preserving the collagen native structure. The ultimate focus of the whole collagen extraction process is the formation of collagen fibrils with the native D-banding pattern, which is achieved in the fibrillogenesis step. An initial collagen concentration of 0.30% in 0.01 M hydrochloric acid solution, adding 0.1 M Sodium hydroxide until pH 9.3 with gentle mixing, and keeping undisturbed for 24 h at 4°C are recommended as processing conditions to obtain collagen fibrils with native D-banding pattern. The initial collagen concentration is critical for molecular availability and the mixing speed is critical for molecular mobility during fibrillogenesis. With this understanding of the behaviour of fish skin during the extraction process, and the knowledge on how it can be applied to any fish species of interest, the future processing of biomedical collagen from fish skin at the industrial level will be possible.