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Development of Economical Methods to Extract Salmon Head Oil for Use by Small Alaska Processors

Investigator

Subramaniam SathivelFood Science Department
Louisiana State University Agricultural Center

Students

Synopsis

Approximately 60,000 metric tons of salmon heads are made available each year as a byproduct of pink and red salmon processing in Alaska. Much of the oil in a salmon is found in the head, which contains 11 to 18 percent lipids. Salmon oil is an excellent source of the omega-3 polyunsaturated fatty acids, eicosapentaenoic acid and docosahexaenoic acid. This project seeks to compare salmon head oil extraction techniques and devise methods for use by small salmon processors.

Overview

The issue

Approximately 60,000 metric tons of salmon heads are made available each year as a byproduct of pink and red salmon processing in Alaska. Much of the oil in a salmon is found in the head, which contains 11 to 18 percent lipids. Salmon oil is an excellent source of the omega-3 polyunsaturated fatty acids, eicosapentaenoic acid and docosahexaenoic acid. This project seeks to compare salmon head oil extraction techniques and devise methods for use by small salmon processors, as a way to provide more opportunity for small processors to derive value from the processing. Making dry powders containing salmon oil will provide new and potential opportunities for utilization of salmon oil.

Why is this an Alaska Sea Grant project?

Alaska Sea Grant's Strategic Plan 2004–2010, theme 5, Seafood Science and Technology, has as one of its goals to "increase the economic value and enhance the reputation of Alaska's fisheries and seafood resources," with an objective to "improve the quality of seafood products."

How will researchers conduct their study?

Salmon oils will be extracted from red and pink salmon heads using a variety of techniques. The two best oil extraction techniques will be identified, and the extracted oil will be purified using adsorption technology. Purified salmon oils will be analyzed for nutritional, chemical, and physical properties and then microencapsulated and evaluated for shelf-life stability, sensory quality, nutritional properties, product acceptance, and market potential.

Specific tasks include (1) extract salmon oils using a variety of techniques, (2) the two best extraction techniques will be identified and the processes will be optimized for use in small salmon processing plants, (3) salmon oils will be purified using adsorption technology, and (4) purified salmon oils will be microencapsulated.

Research collaborators

The Kodiak Fishmeal Company and Green Pastures Products, LLC, and other small processors in Alaska are industrial partners. Dr. Peter J. Bechtel, USDA scientist and FITC affiliate professor, is a collaborator.

Results

What researchers learned

Based on our preliminary study, we selected the following four salmon extraction methods: RS1 involved a mixture of ground red salmon heads and water, no heat treatment, and centrifugation; RS2 involved ground red salmon heads (no water added), heat treatment, and centrifugation; RS3 involved a mixture of ground red salmon heads and water, heat treatment, and centrifugation; RS4 involved ground red salmon heads, enzymatic hydrolysis, and enzyme inactivation by heat and centrifugation. Triplicate experiments were conducted. Data were statistically analyzed (α = 0.05). The four extracted oil samples were evaluated for chemical, thermal, and rheological physical properties.

This study demonstrated the effect of the extraction methods on chemical, nutritional, thermal, and rheological properties of red salmon oil, which is useful for designing the purification process of the oil.

1. The enzymatic extraction process (RS4) recovered the highest amount (8.46%) of crude oil from red salmon heads compared to other extraction methods, but the oil had higher PV (8.78 meq/kg of oil). The RS3 process recovered a lower amount (4.07%) of crude oil from red salmon heads, while the peroxide value (4.72 meq/kg of oil) was lower than the other oils. The RS4 oil contained the highest percent of FFA (0.57 ± 0.02%) of all four methods. All red salmon oils had higher percents of FFA than acceptable, which indicates that further purification is needed. RS3 had higher water activity (0.94) than other oils, which may be caused by the cooking process of the red salmon heads with water. Color in salmon oil is associated with fat-soluble pigments; the RS4 process had more pigments, with a* = 10.94 and b* = 33.41, than the other oils. These data clearly demonstrated that extraction methods affected recovery of the crude oil from red salmon heads, peroxide value, percent FFA, and amount of pigments in the oil.

2. Total omega-3 fatty acids in the RS1, RS2, RS3, and RS4 were 25.8%, 25.15%, 26.1%, and 26.4%, respectively. All oil samples had only minor differences in fatty acid composition, which demonstrated that extraction procedures did not greatly affect fatty acid composition.

3. Total α-tocopherol content in RS1 and RS2 were 0.17 mg/g, while RS3 and RS4 had less than 0.01 mg/g of α-tocopherol. Both RS3 and RS4 production processes involved heating, which might have contributed to the low α-tocopherol values.

4. Different extraction procedures resulted in different amounts of minerals in the oils. Phosphorus levels ranged from 10.04 ppm in RS1 to 44.90 ppm in RS4. The oil extracted in the RS2 process had a higher level of potassium than other processes, while RS3 oil contained higher amounts of magnesium. This study demonstrated that the level of minerals in the oil depended on the extraction methods.

5. Moisture contents were 0.23%, 0.81%, 0.98%, and 0.22% for RS1, RS2, RS3, and RS4, respectively. RS2 and RS3 samples, which were obtained from red salmon heads heated at higher temperatures, contained more moisture compared with RS1 and RS4 samples with no heating or lower temperature heating. This indicates that extracting temperature might be a factor affecting moisture content.

6. Contents of insoluble impurities were low, with the highest value of 0.1% for RS2. This study demonstrated that the extraction process affected the amount of impurities in the oil samples.

7. The thermal stabilities of the oil samples are as follows: RS2 > RS1 > RS3 > RS4. The weight loss at 500 degrees C was similar for RS2, RS1, RS3, and RS4 at 94.50, 94.58, 94.94, and 95.47%, respectively. This study also demonstrated that extraction procedures had an effect on percent thermal degradation of the red salmon oil from heads. Almost all (>99.96%) of the unrefined red salmon oil samples were decomposed at 550 degrees C.

8. RS4 exhibited the highest viscosity at –10°C. From 0 to 25°C, RS1 was more (P < 0.05) viscous than the other samples. The results indicated that the extraction methods affected the apparent viscosity and flow behavior properties of the red salmon oils from heads.

Research impacts

Information on chemical, thermal, and rheological properties from this study can be used for the design of a purification process to produce red salmon oil for human consumption.

Research outcomes

Optimization of salmon oil extraction and purification of salmon oil from salmon heads will provide more opportunity for small processors to derive value from the processing of their fish. Making dry powders containing salmon oil will provide new and potential opportunities for utilization of salmon oil.

Evaluation of this project will include a review of the products and processing methods by interested
nutraceutical and food ingredient companies, seafood processors, and Alaska fish meal plants. Results
will be available to the public through the University of Alaska Fairbanks Fishery Industrial Technology Center website, and a report will be submitted to the scientific literature.

A synopsis of the results generated in this project will be made available to other university researchers and the Alaska seafood Industry through publications, websites, and the many extension services within the university, including the University of Alaska Cooperative Extension Service, the Marine Advisory Program, and the University of Alaska Fairbanks Fishery Industrial Technology Center. Additionally, the results will be sent to the Alaska Sea Grant College Program Education Services, which disseminates this kind of information through publications, press releases, and radio shows. Workshops will be given in Alaska for small salmon processors and entrepreneurs wanting to become familiar with small-scale salmon oil processing, salmon oil quality considerations, and processing safety.

The researchers completed their study and published their results in the following journals:

Yin, H., K.M. Solval, J. Huang, P.J. Bechtel, and S. Sathivel. 2011. Effects of oil extraction methods on physical and chemical properties of red salmon oils (Oncorhynchus nerka). J. Am. Oil Chem. Soc. 88(10): 1641–1648. http://doi.org/10.1007/s11746-011-1824-x

Yin, H., Y. Wan, J. Huang, S. Sathivel, and P.J. Bechtel. 2009. Effect of different extraction processes on the chemical and physical properties of red salmon oil (Oncorhynchus nerka). Ann. Mtg. of the Institute of Food Technologists, Anaheim, CA, abstract no. 119-35, p.
139.

Yin, H., Y. Wan, J. Huang, S. Sathivel, and P.J. Bechtel. 2009. Effect of the extraction methods on chemical, nutritional, thermal, and rheological properties of red salmon oil (Oncorhynchus nerka). 60th Ann. Mtg. of the Pacific Fisheries Technologists, Portland, OR, p. 28.

Sathivel, S. 2010. Chapter 34: Fish oil extraction, purification, and its properties. In: Seafood Quality, Safety, and Health Effects, C. Alasalvar, K. Miyashita, F. Shahidi, and U. Wanasundara, eds. Blackwell Publishing LTD, Garsington Rd., Oxford, UK.