In the present study, the potential of the microalga Pavlova viridis (=Diacronema viridis) as an n-3 polyunsaturated fatty acid (PUFA) source was evaluated and compared to Nannochloropsis sp. in diets for juvenile European sea bass (Dicentrarchus labrax L.) (initial weight~12.8±1.7 g) in an 8-week feeding trial. Six different isoenergetic and isonitrogenous test diets were used: (1) fish oil diet (FO), major lipid source fish oil (100 %), (2) basal diet, 40 % fish oil and 60 % plant oil (in equal parts rapeseed, sunflower, and linseed oil), (3) Pavlova 50 % (P50), 50 % of the fish oil of the basal diet was substituted by lipid content of P. viridis meal, (4) Pavlova 100 % (P100), 100 % of the fish oil of the basal diet was substituted by lipid content of P. viridis meal, (5) Nannochloropsis 50 % (N50), 50 % of the fish oil of the basal diet was substituted by lipid content of Nannochloropsis sp. meal, and (6) Nannochloropsis 100 % (N100), 100 % of the fish oil of the basal diet was substituted by lipid content of Nannochloropsis sp. meal. The specific growth rate was highest and feed conversion ratio was lowest in the P100 group (SGR 1.77±0.10 % day −1 ; FCR 1.17±0.01), although not significantly different to the results for the FO and the other algae-groups. Furthermore, the sum of PUFA was also highest in the P100 group, followed by the P50, N100, N50, and B group (mainly due to the high content of linoleic and linolenic acids coming from plant oils and microalgal products) with the lowest levels in the FO group. The highest amounts of docosahexaenoic acid (DHA) of total fatty acids were found in the FO and B group, although not significantly higher than in groups P50 and P100. The significantly highest amount of eicosapentaenoic acid (EPA, % of total fatty acids) was in the P100 samples and the lowest amount was in samples of the basal group. The histological analyses of liver and intestine samples did not reveal any negative effects caused by the experimental treatments. Based on the basal diet, a 50 % fish oil replacement by Nannochloropsis sp. meal and a total replacement by P. viridis meal were possible without negative effects on the growth performance and nutrient utilization of juvenile sea bass.

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Lipid‐containing extrudates are highly susceptible to lipid oxidation because of their porous structure and high specific surface area. The objective of this study is to investigate the effect of a low‐oxidizable medium‐chain triglycerides (MCT) coating on the oxidative stability. Therefore, cornmeal is extrusion cooked with commercial vegetable oil and various water contents (10–18% on dry matter) and partially coated with 5% w/w MCT oil. Lipid oxidation in the extrudates is examined during storage at +40 °C by measuring hydroperoxide concentrations in different lipid fractions (surface, inner‐surface, and matrix‐incorporated lipids). Hexanal is analyzed using headspace‐gas chromatography. Coating allocation is studied by fatty acid profiles of the lipid fractions, by fluorescence microscopy, and computerized microtomography. Application of an MCT coating leads to lower hydroperoxide concentrations and significantly reduces hexanal formation during storage. In particular, the surface lipids are stabilized. MCT oil diffuse only to small extent inside the extrudates and its effect on lipid oxidation can be attributed to differenct effects: filling surface microcracks, reducing the release of volatiles, and dilution of oxidizable lipids. This effect is strongest in porous extrudates with low feed‐water content.Practical applications: Inhibition of lipid oxidation of fatty extrudates is of great importance for producers as well as consumers. In this study, we examine whether it is possible to improve the oxidative stability of extrudates by application of a lipid‐based coating. The results of this study suggest that it will be possible in the future to produce extrudates that are protected from oxidation by a thin natural oil film. We expect that especially products such as kibbles could benefit from treatment with a low‐oxidizable lipid‐based coating. In these products, fats are already used in combination with other functional ingredients. The combination of an MCT coating with a palatant or antioxidant is, therefore, an obvious alternative and of high relevance for manufacturers.

Lipid oxidation is a major cause of quality deterioration during the production and storage of fat containing extrudates, which is a result of the high‐specific surface of the matrix with increased oxygen access. During the extrusion process, corn starch gelatinizes and forms an amorphous matrix that incorporates lipids. To estimate the effect of incorporation on oxidative stability of lipids a model extrudate of corn meal, water, and a mixture of sunflower‐ and rapeseed oil is developed. The extrusion process is conducted on a laboratory twin screw extruder with varying moisture contents, affecting in turn process parameters such as the specific mechanical energy. A fractionated extraction protocol serves to obtain surface lipids, inner surface lipids, and lipids incorporated in the starch matrix. Oxidation is analyzed at different points in time during storage at 40 °C in the three lipid fractions. Furthermore, the microstructure of the extrudates is analyzed by computerized microtomography (µCT). The results show that increasing fat inclusion decreases the rate of lipid oxidation. A compact structure with low expansion is achieved by high‐water contents. These extrudates in turn exhibit an increased amount of incorporated lipids less susceptible to oxidation. Practical Applications: The presented work investigates extrusion technology, widely used by industry. Lipid oxidation covers an important topic, as stable products are necessary in order to avoid waste. The stabilization of lipids in extrudates against oxidation is therefore of great interest. With the model extrudate used in this study and a newly developed lipid fraction extraction protocol, it is possible to define the regions in terms of oxidation status. The results of this study provide the basis for products with an enhanced stability against lipid oxidation because of their structural characteristics considering the principles of green chemistry. The aim of the present study is to investigate the relationship between the microstructure and lipid oxidation in corn extrudates. Therefore, a new fractionated lipid extraction protocol is developed. Increasing feed water extrudates expand less and thicker cell walls are formed. Increasing the degree of lipid inclusion results in lower degree of oxidation.