Currently, melanosis is prevented by increasing cooking time, which results in reduced weight recoveries. At present, cooked weight recoveries average between 93-95% of landed beach weight. An average increase of 1% over the entire industry would result in an increased return of $1-2 million per season (see B2: Background). Thus there is significant scope for improvement. In addition, prevention of melanosis would result in further savings of approximately $1 million per season (see B2: Background).
For the industry to consistently achieve maximum cooked weight recoveries, whilst reliably controlling melanosis, a systematic investigation of the impact of processing on these factors is essential. The information generated by this study will be used to define best processing practices in order to increase overall quality of the product and profitability of the industry.
Final report
Each year 4-5,000 tonnes of western rock lobster are cooked and exported to countries such as Japan and Taiwan. When existing cooking methods are used a proportion of cooked western rock lobster go black, this results in a product that is unacceptable to the customer
The blackening of the flesh is known as melanosis and is caused by an enzyme called polyphenoloxidase (PPO). Melanosis is a major problem for the western rock lobster industry and it has been estimated that it costs the industry over $1 million per year. Finding a solution to the problem of melanosis by stopping PPO activity is therefore necessary. Currently, cooking is the most common method used in food processing to stop enzyme activity. However, as the PPO enzyme is evidently still active after export lobsters have been cooked it was important to first understand what was happening to the enzyme when it was heated.
This study showed that when lobsters were heated to an internal temperature between 60 and 80°C there was a large increase in enzyme activity. It was not until after temperatures reached 90°C, or more, the enzyme activity stopped. Overall it was found that for 50% of the cooking time, temperatures only reached between 60-80°C. Therefore they did not get high enough to kill the enzyme; rather, current cooking methods actually increase the enzyme ‘s activity.
