A new freeze-dry method for salmon cubes that cuts processing time and energy consumption compared to current techniques, while retaining food quality, could be used on less appealing fish meat to add value, said US scientists.
Researchers from the US Department of Agriculture (USDA) said the salmon cubes produced using the technique could be used to create healthy snacks or as salad toppings or in ready-to-eat soups.
Time and temperature manipulation
The novel two-stage process initially involves freezing small pieces of salmon before subjecting them to freeze-drying to reduce moisture content. The cubes are then put into a dryer for a second time to remove any remaining moisture.
The key was to establish a process that would produce freeze-fried cubes with less than 10 per cent moisture, said the team made up of scientists from the University of Alaska-Fairbanks and the government’s Subartic Research Unit (SARU).
Focussing on the manipulation of time and temperature, the group developed a process that took only nine hours – against a traditional processing time of at least 20 hours. It also achieved a moisture reduction of 97 per cent from fillets of three common Alaskan Pacific salmon species – pink, sockeye and chum.
In experiments, an average of three frozen fillets that were partially thawed, cut into cubes, arranged into freeze-dry trays, and processed immediately. To reduce the time and remove moisture from the salmon cubes at a faster rate, the temperature during the freeze-drying process was raised from –40˚C to 0˚C.
“We took about 50 to 60 per cent of the time off the traditional drying process,” said Chuck Crapo, a seafood technologies with the UAF Marine Advisory Program.
The fish pieces also retained their original colour, shrank by only 12 per cent and rehydrated quickly – the latter being advantageous for dry soups, said the researchers.
USDA scientist Peter Bechtel said this swifter, more energy-efficient process could potentially be used with lower value fish meat that may otherwise remain unused.
“Sometimes when the salmon gets too close to spawning season, the roe is of high quality and value, but the muscle quality has deteriorated and often has limited uses,” he said. “Therefore, it’s considered a byproduct; but a freeze-dried product would be a way to use edible portions of meat and add value.”
Bechtel is also looking at nutritional quality characteristics of freeze-dried fish through analyses of amino acids and minerals. These findings will be used to identify food products that can be developed for health-conscious consumers, he said.