Dietary soybean phospholipids increase the oxidative stability of lipids extracted from fish fillets.

We previously reported that the feeding of soybean phospholipids to fish increased the storage stability of n-3 polyunsaturated fatty acids (PUFA)-rich fish fillets. In this study, we examined the storage stability of lipids extracted from fish fed a diet containing soybean phospholipids and fish oil. Rainbow trout were divided into two groups, and were fed an either 2.5% soybean phospholipids (test) or no phospholipids (control) containing diet for 4 weeks. Lipids were extracted from fish fillets after the feeding period, and were subjected to an oxidation test. Lipids extracted from the fillets of fish in the test group exhibited lower values of oxygen absorption than those in the control group, and the degradation of docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA) was inhibited. Higher percentages of DHA and EPA were bound to phosphatidylcholine and phosphatidylethanolamine in the extracted lipids in the test group than in the control group. These results indicate that the oxidative stability of lipids extracted from fish fed soybean phospholipids is high, and that the higher percentages of DHA and EPA in PC and PE may have resulted in the higher stability of the lipids extracted from fish fillet.

Effect of dietary n-6/n-3 ratio on liver n-6/n-3 ratio and peroxisomal beta-oxidation activity in rats.

The optimal dietary n-6/n-3 ratio has not been fully elucidated. To investigate the influence of the dietary n-6/n-3 ratio on this ratio in the body and on liver beta-oxidation peroxisomal activity, rats were fed diets containing fat at an n-6/n-3 ratio of 1 to 16 for 4 weeks. To investigate whether elevation of the liver peroxisomal beta-oxidation activity increases the n-6/n-3 ratio in the body, rats were fed a diet containing a peroxisome-activating agent, bezafibrate, for 2 weeks, and its influence on the liver n-6/n-3 ratio was examined. The slope of the regression line between the dietary and liver total lipid n-6/n-3 ratios was significantly smaller when the dietary n-6/n-3 ratio was 4 or greater than when it was smaller than 4. Peroxisomal beta-oxidation and acyl CoA oxidase activities were significantly lower in rats fed a diet with an n-6/n-3 ratio of 16 than in those fed a diet with a ratio of 1. The peroxisomal beta-oxidation activity in the bezafibrate-supplemented group was significantly higher than that in the control group. The serum and liver total lipid n-6/n-3 ratios were significantly higher in the 0.015% bezafibrate-supplemented group than in the control group. These findings suggest that the liver n-6/n-3 ratio might be controlled via peroxisomal beta-oxidation in rats.

Alpha-linolenic acid-rich flaxseed oil ingestion increases plasma adiponectin level in rats.

Adiponectin, an adipose-specific secretory protein, exhibits antidiabetic and antiatherogenic properties. The effect of alpha-linolenic acid (ALA) on adiponectin has not been revealed. ALA is included abundantly in vegetable oils such as flaxseed oil. In this study, we attempted to clarify the effect of ALA-rich flaxseed oil (FSO) intake on the adiponectin level in rats. Seven-week-old male Sprague-Dawley rats were fed test diets containing high oleic safflower oil (HOSO) or FSO for 4 weeks. After the experimental period, the plasma adiponectin concentration in the FSO-fed group was higher than that in the HOSO-fed group. The adiponectin content of perirenal adipose tissue in the FSO-fed group was also significantly higher than that in the HOSO-fed group. However, the adiponectin mRNA level in the perirenal adipose tissue did not differ significantly between the HOSO-fed and FSO-fed groups. In this study, we clarified the effect of the ALA-rich FSO ingestion on the plasma adiponectin concentration in rats. It was suggested that the ALA-rich FSO intake might exhibit beneficial effects through an increase of the adiponectin level.