Wild-caught halibut is experiencing a rise in a quality related defect that affects its market reputation. Consumers will order expensive halibut from restaurants, and the fish sometimes comes out nearly inedible. Why? This is due to a problem with the meat itself. “Chalkiness” of the meat has increased in recent years and may be due to both warming waters and stress placed on the fish during capture.
Chalky halibut is a phenomenon where the protein inside the halibut becomes denatured. This results in a white, opaque appearance to the fillet, as opposed to the shininess consumers are used to. The meat itself often tastes tough and dry. However, it’s almost undetectable while undergoing processing and the ability to detect chalky halibut before it is served is difficult. Processors currently rely on pH tests, but the results can be inconsistent.
Christina Dewitt, Director of the Seafood Research and Education Center at Oregon State University (OSU), and Angee Hunt, Assistant Professor at OSU, are working on a project together that can potentially help detect chalky halibut before it gets to the consumer.
“I started looking into chalky halibut and began to understand the muscle chemistry of what was happening and why it was happening,” Dewitt said. “Chalky halibut might be caused by extreme stress—rapid lactic acid production. One of the ways that they detect chalky halibut is by measuring pH. There’s been some studies where they stress fish and they’ve demonstrated they can produce chalky halibut in those fish, and found that the pH of the meat is abnormally high as a result of that.”
Dewitt and Hunt’s work, however, centers around the technology of bioimpedance. Bioimpedance is a non-invasive, rapid tool that sends out electrical currents that can detect certain qualities within a body, in this case, a fish’s body. For example, the equipment can detect tissue composition and function.
“Typical bioimpedance is based on a technology that uses two different frequencies of electricity, and then they can use the resistance that occurs between those emitted frequencies to basically determine different things like the amount of fat content or the amount of degradation that’s occurring in the cell,” Dewitt said.
Both Dewitt and Hunt will be traveling to Kodiak, Alaska, this summer to scan wild halibut for chalkiness using a bioimpedance device. In this study, alongside the current technology of pH detection, Dewitt is hopeful bioimpedance will prove more reliable.
“We want to scan the fish [in Alaska] using our device,” Dewitt said. “We’ll probably scan it in a couple of different areas, and then they’re going to be collecting pH data on the fish. What we’re hoping is that when they pick it up using pH, we can definitely pick it up also [with bioimpedance]. We want to show that correlation, that the device can pick it up when it’s obvious.”
For Hunt, she is looking forward to working directly with fishers and processors in Alaska.
“This opportunity enables researchers to better understand the day-to-day challenges and identify opportunities for collaboration between industry and academia,” Hunt said.
Next, their studies in Alaska will involve collecting data to correlate with the data that shows muscle degradation. Multi-frequency bioimpedance sensors can make it possible to capture shifts in electrical properties across a spectrum and detect tissue changes over time. Current commercial grade bioimpedance technology uses just one frequency to estimate impedance. But their project will utilize a range of frequencies, from 1-200 kilohertz, to simultaneously evaluate quality changes.
“We’re going to be scanning 100 frequencies, instead of just two, and looking to see if there is a relationship that the regular device can’t pick up,” Dewitt said. “We’re going to use both the research grade device and the commercial device that we have right now and take measurements side by side. We’re also going to collect the data from the plant, and then hopefully collect a small sample of the muscle that we can take with us to do some lab analysis on. The first stage of this is really to understand the frequencies that detect changes in the muscle structure when there is chalky halibut.”
After the summer session in Alaska, there is still more to be done before the fish make it to the market. For Dewitt, there is an importance placed on gathering this data for statistical evaluation. By comparing these impedance values of frequencies, distinct patterns may emerge, allowing for a look into the physiological states or tissue responses across varying conditions.
“And the next stage would be thinking forward, once you know the frequencies that respond the best to chalky halibut, then you would go back and try to sort those based on those frequencies and see how they perform,” Dewitt said. “And then collect samples from fish that are being predicted as having chalky halibut and finally test them to see if they confirm what we are thinking is going to happen.”
It’s not just Alaska, either. Dewitt’s team is talking with local processors in Oregon and Washington. If there is chalky halibut coming in, they want to know about it and receive samples, if possible. The problem with chalky halibut that her team is trying to solve is ultimately stopping the fish from being received by the market. Dewitt and Hunt hope to improve its overall market competitiveness by catching it early with bioimpedance.
“The bad part about chalky halibut is sometimes it gets past the plant,” Dewitt said. “It gets past the distributor and only shows up once the consumer gets it, so it begins to give a bad reputation to halibut, [which usually] has a good reputation, but it loses its reputation each time it gets consumer complaints. There’s a lot more of it showing up, and it got past all these different players. Ideally, you would take some preventable steps. It shouldn’t get to the consumer.”
At all of these different levels of processing halibut, chalky halibut is a thorn in the side of halibut production. There is a huge need to detect it early. Dewitt and Hunt are on a mission to prove that bioimpedance could work for this.
“Using the bioimpedance machine we hope to be able to detect the quality differences between individual chalky and non-chalky halibut,” Hunt said. “Early detection will allow each type to be directed to the appropriate processing to maximize utilization, consumer experience, and economic value of halibut harvests.”
By Maia LeClair, SIRF intern