Salmon by-product storage and oil extraction

Abstract

Oils extracted from wild salmon by-products are excellent sources of long chain omega-3 polyunsaturated fatty acids including eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). However, quality loss is expected if time delays are encountered before oil extraction. The free fatty acid levels (FFA), fatty acid profile and total fat soluble antioxidant activity in extracted oil from aging pink salmon heads and viscera stored at two temperatures (6 and 15 °C) for four days were determined. The FFA values in raw salmon heads and viscera increased with storage time and temperature. A significant difference (p < 0.05) from the starting material was noted at day 1 at both temperatures for FFA. Fatty acid composition data indicated no changes in the levels of long-chain omega-3 fatty acids with the respective temperature. The concentration of long-chain omega-3 fatty acids EPA ranged from 9.3 to 11.3 g/100 g of crude oil and DHA ranged from 12.3 to 13.1 g/100 g of crude oil. The antioxidant activity of the pink salmon oils at day 0 was 0.89 ± 0.15 μmole Trolox equivalent/g of crude oil. Significant decreases (p < 0.05) from the starting material were noted on day 2 for 15 °C samples and day 3 for 6 °C samples. After four days of storage antioxidant levels (Trolox equivalent/g of crude oil) were approximately 25% of initial values. Oil extracted from raw salmon heads and viscera remained a good source of long chain omega-3 fatty acids even after 4 days of raw material storage at 15 °C; however, fat soluble antioxidant activity was reduced and free fatty acid levels increased with increased raw material storage temperature and time.

Introduction

Marine lipids are receiving a lot of attention because of the health benefits associated with high levels of the long chain omega-3 polyunsaturated fatty acids (PUFA) eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Decreased rates of cardiovascular disease have been noted in populations with high fish consumption, such as Alaskan Natives (Middaugh, 1990, Newman et al., 1993) and the omega-3 fatty acids are believed to be associated with these health benefits (Shahidi & Miraliakbari, 2004). High levels of DHA are found in brain tissue and DHA is essential during brain development and retina formation of infants (Hoffman & Uauy, 1992). Even with the plethora of scientific evidence on beneficial effects, the consumption of omega-3 PUFA in western diet is low and alternative ways of incorporating fish oil are being explored (Nielsen, Debnath, & Jacobsen, 2007).

In Alaska there was an estimated 110,000 Mt of by-products available for production from Alaska pacific salmon in 2005 (Bechtel, 2007). The two major by-products from the processing line of salmon in Alaska are heads and viscera, with the roe removed. Wild pink and red salmon are harvested in large quantities in Alaska and pink salmon by-products have been reported to contain 10.9% oil in heads and 2% oil in viscera (Bechtel, 2003). Alaska pink salmon by-products oils were evaluated by Oliveira and Bechtel (2005) and are a good source of omega-3 fatty acid. These salmon by-products are processed into oil and meals at some location; however much of the by-products is not utilised and there are issues associated with acquiring and processing them. The ability to process salmon by-products or refrigerate large volumes of by-product are absent, especially at small remote processing plants and this problem often results in the by-products being discarded. Another problem is the during peak production by-product processing capacity can not keep up with by-product accumulation and the raw material could remain unrefrigerated for days before processing. When storage time is prolonged and temperature increased, the raw by-product quality and freshness is decreased. Degradation of by-product proceeds rapidly due to the presence of enzymes and bacteria (Ashie, Smith, & Simpson, 1996). There is no literature evaluating the storage of salmon by-products or the oil extracted from salmon by-products.

In addition to the omega-3 PUFA, fish oil also contained natural fat soluble antioxidants. While most of the focus has been on the omega-3 PUFA little information on antioxidant properties are available. Antioxidants are important because of there ability to scavenge free radicals, which can reduce oxidation and other damaging reactions in food and biological systems. Marine oils are highly unsaturated and very susceptible to oxidation during exposure to oxygen, light, and heat (Lytle, Lytle, Newmark, & Deschner, 1992). In addition, oxidative as well as hydrolytic stability can differ greatly among different fish species (Boran, Karacam, & Boran, 2006). Some of these differences are due to the level of protection from naturally occurring antioxidants. Vitamin E and carotenoids are antioxidants found in wild salmon oil (Johnston et al., 2006). Incorporation of synthetic antioxidant is routinely used to maintain oil quality from rendered animal products; however, the addition is accomplished after oil extraction.

There are many methods used to measure antioxidant activity including the measurement of total fat soluble antioxidant activity using a photochemiluminescence (PCL) method (Besco et al., 2007, Harrison and Were, 2007, Lee et al., 2004, Sacchetti et al., 2005). The PCL method generates photochemical superoxide anion and uses a chemiluminescent detection system in the measurement of antioxidant activity (Popov & Lewin, 1996). One of the advantages of using PCL is that it assesses the total antioxidant activities, thus synergistic effects are accounted for using this procedure.

The objective of this study was to evaluate the quality of the extracted crude oil from raw pink salmon by-products (heads and viscera) stored for 0, 1, 2, 3 and 4 days at two different temperatures (6 and 15 °C) by determining free fatty acid levels (FFA), fatty acid profile and total fat soluble antioxidant activities.