Utilization of By-Products from Norwegian Spring Spawning Herring for Human Consumption
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There is an increasing demand for oils and proteins of marine origin for human consumption. Marine lipids are rich in the long chain omega-3 polyunsaturated fatty acids, especially eicosapentaenoic acid (EPA; C20:5 n-3) and docosahexaenoic acid (DHA; C22:6 n-3), that have documented beneficial health effects. Marine proteins contain all the essential amino acids and are an excellent protein source, and recent studies have shown that marine protein hydrolysates possess desirable bioactive properties. The main objective of this work was to utilize Norwegian spring spawning herring by-products for production of oil and protein for human consumption. The strategy was to carry out the studies on a semi-industrial scale in order to achieve more easy knowledge transfer between research and industrial implementation. Oil and protein fractions were produced in a mobile production plant by two different methods, thermal treatment (wet-rendering) or enzymatic hydrolysis. The focus of the trials has been on the influence of production method and processing conditions on the compostion, quality and stability of the oil, and on the quality and properties of proteins. Oxidation of marine lipids will occur during storage and processing of the by-products. Thus, different strategies were tested to try to minimize lipid oxidation. A better understanding of how hemoglobin promotes lipid oxidation will provide valuable information on how Hb-mediated lipid oxidation can be prevented. Another approach is addition of antioxidants to the by-products, prior to oil and protein production, in order to minimize oxidation during processing. The work in this thesis has shown that high quality oil and proteins can be produced from herring by-products. Both thermal treatment and enzymatic hydrolysis were well-suited processes for production of low oxidized herring oil, resulting in oils with low peroxide value (PV < 2.5 meq peroxides/kg lipid) and low anisidine value (AV > 1.2). Early addition of antioxidants to the by-products resulted in decreased oxidation during processing (up to 70 % reduction in total oxidation). In addition, higher oil stability was achieved because of added antioxidants present in the crude oil. The water soluble herring proteins (stick water and hydrolysate) contained all the essential amino acids required for a balanced diet in adults. Thus, herring by-products can be a valuable protein source for human consumption. The processing method affected the colour of the proteins, dried protein powders produced by thermal treatment were more lighter and less yellow compared to dried hydrolysates. Process conditions and enzymes played an important role in the formation of bitterness in the hydrolysates, and can be used as a tool for controlling bitter taste in the product.