Oyster farming represents one of the most developed aquaculture activities, producing delicacies unfortunately related to a direct accumulation of waste shells. Facing what is becoming an environmental issue, chemists are currently developing solutions to add value to this wild source of raw material in line with the principles of sustainable chemistry. An argumentative overview of this question is proposed here with a focus on recent data. Starting with a presentation of the environmental impact of oyster farming, existing and promising applications are then classified according to the type of raw materials derived from the oyster shell, namely the natural oyster shell (NOS), the calcined natural oyster shell (CNOS), and biomolecules of the organic matrix extracted from the oyster shell. Their relevance is discussed in regard to their scalability, originality, and sustainability. This review constitutes the first critical compilation on oyster shell applications, with the aim to provide essential elements to better comprehend the recycling of waste oyster shells.
The colour of oyster shells is a very diverse characteristic morphotype, forming intriguing vivid patterns both on the inside and outside of the shell. In the present study, we have identified for the first time, the presence of several porphyrins as constituents of the shell pigmentation of the Crassostrea gigas oyster consumed worldwide. The precise molecular structures of halochromic, fluorescent and acid-soluble porphyrins, such as uroporphyrin and turacin, are unambiguously determined by reverse phase liquid chromatography combined with high resolution mass spectrometry. their presence account for the purple colouration of shells but also for the dark colouration of adductor muscle scars. We have also defined the endogenous origin of these porphyrins, specifically secreted or accumulated by the shell forming tissue. These findings are pioneering analytical proofs of the existence of the haem pathway in the edible oyster Crassostrea gigas, evidenced by the chemical identification of haem side-products and supported by the recent publication of the corresponding oyster genome. Shells are the armour of many molluscs. Their diversities of shape, ornamentation and colour have always attracted humans throughout the ages. In bivalves, related to the requirements of the pearl farming industry, shell morphotypes and colours of pearl oysters (e.g. Pinctada margaritifera) have been extensively studied compared to their edible cousins (e.g. Crassostrea gigas) 1. Prized by gourmets, the aesthetic appeal of shellfish as a gastronomic showcase is arousing growing interest. However, the accumulation of wasted shells becomes a real environmental problem, predominantly in oyster farming or tourist areas 1. At a time when sustainable and intelligent uses of renewable aquatic resources are needed, the transformation of this calcareous by-product into a value-added material is a relevant challenge to be taken up. While the use or transformation of calcium carbonate or its organic matrix is the first-line source for recycling edible oyster shell, its colouration is still unwell understood and therefore little valued 1. Despite the functional roles of shell colours in camouflage, thermoregulation or immunity, the molecular mechanisms related to shell colouration remain poorly documented 2. This gap of knowledge is partly due to the lack of elucidation of the chemical nature of shell pigments, particularly in the Crassostrea genus. By combining the identification of shell pigments with corresponding biosynthetic pathways and associated genes, key information on the relation between shell colouration, mineralization or other molecular mechanisms can be obtained as previously reported in marine snails 3. Therefore, the identification of shell pigments appears to be a possible gateway to the recovery of natural dyes from wasted oyster shells for a broad range of applications in health or material science, helping to contribute to a sustainable future for shellfish farming industry 1. In the Pteriomorphia group, including edible and pe...
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