New method for bleeding and superchilling cod fillets could cut costs
The Norwegian research group made the claims as it unveiled details of its fish processing project that had examined the effects of immediate gutting and filleting of unbled fish, followed by rinsing of the fillet.
Lead researcher Bjorn Tore Rotabakk said the aim was to considerably shorten the processing time for cod without being left with more blood in the fillet. The technique had also investigated the effect of superchilling on quality. The new technique takes up to 20 minutes before the fillets are packaged and ready to be shipped and could cut processing time by an hour, he told FoodProductionDaily.com.
“I see a huge benefit for processors,” he said – citing labour and investment and space cost savings.
“And by using superchilling before packaging they don’t need equipment for ice production,” added Rotabakk. “In addition, less ice means less carbon dioxide emissions, and hopefully this improves the carbon footprint of the product – although we haven’t yet done any calculations on this.”
At present, farmed cod intended for the EU market is often processed in Denmark, France or Poland, said the group. But because there are no punitive duties on processed white fish in the EU and with the new method processing could be performed near fish farms and slaughterhouses in Norway.
Method
In a trial with pre-rigor white cod, one group of the farmed fish was bled in a traditional bleeding vessel, without movement. The fish were cut across the gills and laid in sea water for 30 minutes to bleed out before gutting and filleting. The other group of cod was not bled in the traditional way, but gutted and filleted directly after being killed. After filleting the fish was washed by sprinkling with fresh water for 10 minutes.
“The new method skips the live chilling and the bleeding step”, Rottaback said. “We have tried to directly process the fish after killing, and replaced the bleeding step by sprinkling the fillets with water. This helps remove the blood from the fillet, and gives a fillet with equal quality as traditional bleeding.”
Live chilling was replaced with superchilling of the fillet – whereby the fish is superchilled with nitrogen gas for around 3-4 minutes, he added.
Both groups were then divided into two subgroups for packing in different ways. One group was superchilled to about -1°C and packed in expanded polystyrene cases without ice. The other group was packed directly into expanded polystyrene cases and 3kg of ice was placed on top. After packing, the four groups were transported and stored at 0°C until the fillets were 6 days old. The cases were sent by refrigerated transport and arrived at their destination after about 48 hours.
“The temperature in the cases was logged during transport and storage. The equalisation temperature of the case of superchilled fish was -0.9°C, which corresponds very well with the theoretical equalisation temperature of cod, which is stated as being -1.0°C,” said Rotabakk.
Results
The team said drip loss was significantly reduced with the new superchilling method compared to traditional techniques – although it was not yet clear why. However, drip loss was greater than usual with its bleeding method –as the fillets were weighed after 10 minutes of rinsing. The rinsing led to water being absorbed into the surface of the fillets and temporarily bound to the muscle.
Using the new method resulted in no change of colour compared to traditional processing methods but the group found the surface texture of the fish was softer. Rotabakk said this could be regarded as an indication of fillet degradation but added that the issue was believed to be “solvable”. The overall results were described as “very promising”.
“Reducing the processing time brings many advantages. Because the whole process can be performed in one place, you save both time and energy, and there is less transporting. This gives both environmental and financial savings,” said Hogne Bleie, director of biology and biosafety at Atlantic Cod Farms AS. “Filleting directly after death and the use of superchilling remove the need for repacking in other places, which means a great deal of packaging material can also be saved.”
