These detract from the visual quality and occur within five days of processing, thus precluding their transport to customer by sea and reducing their potential value.
An investigation of progression described the appearance of the staining over a five day period. An attempt to prevent the staining was carried out by packing the fillets in two forms of modified atmosphere, one where the fillets were maintained in standard boxes with the addition of carbon dioxide releasing pads, and one where the fillets were individually sealed in vacuum bags with carbon dioxide releasing pads.
It was found that the packaging prevented oxidation of lipids in the muscle but the visual and textural quality was greatly reduced. A further investigation monitored the appearance of stains in fish that had previously been bled at sea. It was found that the yellowish stains were less apparent in the bled fish compared to those that had not been bled.
In addition, the textural quality was again reduced suggesting this may be a most suitable method for improving the quality such that the fresh fillets may be transported by sea. It is proposed that the likely cause is related to the breakdown of iron-containing pigments such as haemoglobin and myoglobin.