a b s t r a c tFish muscle is rapidly degraded during post-mortem storage, due to proteolytic enzymes acting probably both on muscle cells and connective tissue. In this work we have developed a model system which may be used to study the enzymatic degradation occurring in intact post-mortem fish muscle. Degradation of myosin heavy chain (MHC) was monitored in muscle with pH adjusted to 6.05, 6.3 and 6.9 and in the presence of the enzyme inhibitors PMSF, EDTA, phenanthroline, pepstatin A, antipain, E-64 and the cysteine proteinase activator dithiothreithol (DTT). After storage, myofibrillar proteins were isolated and MHC-specific antibodies used to study the degradation in the different samples. MHC from muscle with pH 6.05 and 6.3 was degraded, while no severe degradation was observed at pH 6.9. Introduction of enzyme inhibitors into the muscle tissue clearly showed that mainly cysteine and aspartic proteinases are responsible for the in situ MHC degradation. This is supported by the severe breakdown of MHC in the muscle samples containing DTT.

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Oil extracted from the marine copepod Calanus finmarchicus contains the long chain omega-3 fatty acids eicosapentaenoic acid and DHA in addition to stearidonic acid (18:4n-3). Unlike other marine lipids, the fatty acids in this oil are esterified with long chain fatty alcohols as wax esters. The aim of this study was to examine the fate of the wax esters in oil from C. finmarchicus when given as a 2% supplement in a high fat diet to C57BL/6J mice for 11 weeks. The study confirmed that feeding mice a high fat diet supplemented with a small amount of oil containing wax esters reduced the body weight gain. During digestion, wax esters were hydrolyzed and the fatty acids absorbed since the fatty acid composition of the adipose tissue and liver reflected the enrichment with the Calanus oil. The composition of the liver lipids demonstrated elongation and desaturation of the C18 omega-3 fatty acids from the feed and accumulation of longer chained omega-3 fatty acids. Elevated levels of FFA and FAOH in the feces suggest that the absorption process, not the hydrolysis, could be a rate limiting step in utilization of small amounts of wax esters included in high fat diets in mice.Practical applications: The limited amount of available fish oil has led to extensive search for alternative sources of long-chain PUFA. One suggestion is to harvest at lower trophic levels, like small crustaceans, which may be abundantly present in the oceans. In this investigation, we have studied the effects of including the astaxanthin-rich oil from the marine copepod C. finmarchicus in a high fat diet in mice. This oil is different from other marine oils since most of the fatty acids are esterified to long-chain fatty alcohols, not in TAG, and that stearidonic acid is the major omega-3 fatty acid present. The results provide knowledge and understanding of aspects related to digestion and possible physiological effects of including small amounts of marine wax esters in diets.Abbreviations: ALA, alpha linolenic acid; þCal, inclusion of 2% calanus oil; DPA, docosapentaenoic acid; EE, ethyl ester; EPA, eicosapentaenoic acid; eWat, epididymal white adipose tissue; FAOH, fatty alcohol; FFA, free fatty acid; HFD, high fat diet; HPLC-ELSD, HPLC coupled with an evaporative light scattering detector; LC-PUFA, long-chain PUFA; pWat, perirenal white adipose tissue; SDA, stearidonic acid; WE, wax ester 1718Eur.

The consumption of seafood and the use of fish oil for the production of nutraceuticals and fish feed have increased over the past decades due the high content of long-chain polyunsaturated omega-3 fatty acids. This increase has put pressure on the sustainability of fisheries. One way to overcome the limited supply of fish oil is to harvest lower in the marine food web. Calanus finmarchicus, feeding on phytoplankton, is a small copepod constituting a considerable biomass in the North Atlantic and is a novel source of omega-3 fatty acids. The oil is, however, different from other commercial marine oils in terms of chemistry and, possibly, bioactivity since it contains wax esters. Wax esters are fatty acids that are esterified with alcohols. In addition to the long-chain polyunsaturated omega-3 fatty acids, eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the oil is also rich in stearidonic acid (SDA), long-chain monounsaturated fatty acids, and the long-chain fatty alcohols eicosenol and docosenol. Recent animal studies have indicated antiinflammatory and anti-obesogenic actions of this copepod oil beyond that provided by EPA and DHA. This review will discuss potential mechanisms behind these beneficial effects of the oil, focusing on the impact of the various components of the oil. The health effects of EPA and DHA are well recognized, whereas long-chain monounsaturated fatty acids and long-chain fatty alcohols have to a large degree been overlooked in relation to human health. Recently, however the fatty alcohols have received interest as potential targets for improved health via conversion to their corresponding fatty acids. Together, the different lipid components of the oil from C. finmarchicus may have potential as nutraceuticals for reducing obesity and obesity-related metabolic disorders.