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The aim of this research was to investigate the oxidation progress and pathways of krill and fish oil during 21 days of incubation at 40°C. The oxidative stability of the oils was investigated through: (i) classical methods such as peroxide value (PV), anisidine value (AV), thiobarbituric reactive substance (TBARS), conjugated dienes and trienes, and antioxidant content, and (ii) advanced methods such as determination of volatiles content by dynamic headspace (DHS)-GC/MS, lipid classes, and pyrrole content. In addition, the oxidative stability of the oils was evaluated under accelerated oxidation conditions using the Oxipres TM at 90°C. The results from analysis of PV, AV, TBARS, conjugated dienes and trienes, and the antioxidant content suggested that krill oil was more oxidatively stable than fish oil. However, the color or other constituents of the krill oil might affect the result of these classical methods. Nevertheless, the conclusion was supported by the results of the Oxipres TM measurements, which showed that the oxygen consumption was higher for fish oil. Furthermore, the level of most volatile lipid oxidation products was higher for fish oil. The development of Strecker degradation products and pyrroles formed as a result of non-enzymatic browning reactions could only be observed in krill oil. The presence of pyrroles might have contributed to the higher oxidative stability of krill oil. Krill oil also contained a higher level of tocopherol, astaxanthin and phospholipids than fish oil, which could have resulted in better protection against oxidation. The results demonstrated that the classical methods for measuring oxidative deterioration of lipids were not useful for krill oil.

The effect of activated carbon (AC) adsorption on the reduction of persistent organic pollutants (POP) in fish oil was studied based on response surface methodology at a 5-g/kg AC inclusion level. Pretreatment of the oil by alkali refining and bleaching increased the POP levels. The tested process variables (contact time and temperature) affected the AC adsorption rate and significant first-and second-order response models could be established. Polychlorinated dibenzo-pdioxins and dibenzofurans (PCDD/F) showed a very rapid adsorption behavior and the concentration and toxic equivalent (TEQ) level could be reduced by 99%. Adsorption of dioxin-like polychlorinated biphenyls (DL-PCB) was less effective and depended on ortho substitution, i.e. non-ortho PCB were adsorbed more effectively than mono-ortho PCB with a maximum of 87 and 21% reduction, respectively, corresponding to a DL-PCB-TEQ reduction of 73%. A common optimum for both PCDD/F and DL-PCB adsorption could not be identified. AC treatment had no effect on the level of polybrominated diphenyl ether flame retardants. The differences in adsorption patterns may be explained based on molecular conformation. No change in oil quality could be observed based on oxidation parameters. Compliance with present PCDD/F and DL-PCB legislation levels in fish oil can be achieved based on AC adsorption.

SummaryThe hydrolytic and cost effi ciencies of fi ve endopeptidases (Alcalase 2.4L, Corolase 7089, Neutrase 0.8L, Promod 671L and Protex 7L) to hydrolyze Atlantic salmon by-products were compared at standardized activity levels based on a casein assay. The substrate was characterized prior to the hydrolytic experiments (pH=6.5, t=50 °C) to obtain substrate--specifi c constants for nitrogen to protein mass (in g) ratio, i.e. conversion factor f N =5.23 and total amount of peptide bonds (h tot )=9.3 mmol per g of protein.At low enzyme activity to substrate ratio, all enzymes were equally effi cient in hydrolyzing the substrate. At highest enzyme activity to substrate ratio, Protex 7L, Alcalase 2.4L and Promod 671L gave higher degree of hydrolysis (DH=14.2-14.6 %) than Corolase 7089 (13.2 %) and Neutrase 0.8L (11.6 %) aft er 120 min of hydrolysis. No diff erences were observed in protein recovery (yield of solubilized protein) relative to DH. Determination of DH was followed by the pH-STAT and o-phthaldialdehyde methods. Based on pH-STAT data, response surface regression models were established based on the combined eff ects of hydrolysis time and enzyme activity to substrate ratio on DH and protein recovery. The modelling approach was combined with enzyme cost to identify the most cost-effi cient enzyme (Protex 7L).

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