Chemical and sensory evaluation of crude oil extracted from herring byproducts from different processing operations.

Fish oils extracted from marinated herring (frozen and unfrozen) byproducts and maatjes herring byproducts were evaluated on their chemical and sensory properties. The obtained crude oils had very low content of copper (<0.1 mg/kg oil), and iron values were 0.8, 0.1, and 0.03 mg/kg oil, respectively, for oil from maatjes and frozen and fresh byproducts. For the maatjes oil, a much lower value was found for alpha-tocopherol compared to the other oils. Storage stability results showed that the oils behave differently. Secondary oxidation products were measured for fresh oil, while for the maatjes and frozen byproducts' oil, tertiary oxidation products were detected. Over storage time, the maatjes and frozen byproducts' oils became more intense in odor, correlating positively at the end with sensory attributes of train-oil, acidic, marine and fishy. The best correlation between sensory and chemical analyses was found for FFA and fishy off-odor (r = 0.781).

Seasonal changes in crude and lipid composition of herring fillets, byproducts, and respective produced oils.

Crude and fatty acid composition analyses were performed on fillets, byproducts, and oil originating from herring (Clupea harengus) caught off the North Sea from June 1999 to January 2001. Monthly statistical differences were found in the fat content, the range of variation being larger in fillets than in byproducts. The most consistent change observed in fillets was an increase of unsaturation from May to September reflected in a reduced percentage of monounsaturated fatty acids, whereas for byproducts and oil this trend was not so well defined. The results indicated that the lowest values of the total amount of polyunsaturated fatty acids (PUFAs) in the oil were found from January to March (approximately 14%), coinciding with the postspawning and starvation period. In contrast, the highest values were found from June to August (approximately 23%). Thus, the herring byproducts are all year an adequate raw material for fish oil production; however, during the summer they are richer in PUFAs.

Composition and stability of herring oil recovered from sorted byproducts as compared to oil from mixed byproducts.

Herring oils produced from three different types of byproducts, only heads, mixed, and headless byproducts, were compared. Heads byproducts and its oil presented the highest oxidation levels and the lowest alpha-tocopherol content. Heads contained the lowest polyunsaturated fatty acids content and the highest amount of saturated fatty acids. No significant differences were found between the fatty acid composition of the mixed and the headless either in byproducts or in its oil. The oil was stored at two different temperatures (20 and 50 degrees C). Testing general linear models showed that oxidation was related to the peroxide value with a positive significant effect of the temperature, while the free fatty acids' model was more complex, with significant contribution of all of the effects studied. Fluorescence measurement was the one that correlated best with the oxidation progress.