Functional Properties of Linseed Meal Fractions: Application as Nutraceutical Ingredient

Brown linseed (Linum ustatissimum) is pressed to produce oil, and the remaining linseed meal is rich in protein and soluble dietary fiber. To utilize the derivatives of linseed meal as food ingredients or additives, linseed meal was fractionated by controlling pH on a pilot plant scale. Chemical composition, functional properties and health related bioactivities, such as angiotensin converting enzyme (ACE) inhibition and antioxidant activities, of the fractions were then analyzed. The alkaline soluble protein had the highest content of secoisolariciresinol diglucoside (SDG) and showed good emulsification activity, comparable to that of whole egg. The acid soluble fraction showed the highest viscosity. ACE inhibition, antioxidant activities, and bile acid binding activity were observed in the soluble dietary fiber fraction. There was no correlation between SDG content and bioactivities. These findings indicate that the acid-soluble fraction is useful as a food ingredient to increase viscosity, while the soluble dietary fiber fraction has health-related features. (Authors abstract)

Many researchers attempted to utilize whole linseed by fractionation; however, these purification methods are time consuming, expensive or decompose useful compounds such as phenolic acids. The objectives of the present study were to determine the chemical composition and functional properties of linseed fractions as food ingredients, and to evaluate the health related efficacy of these linseed fractions using various in vitro methodologies.

After the fractionation process, the alkaline-soluble protein fraction contained 71.1percent protein, whereas the soluble dietary fiber fraction contained 32.3percent protein. The alkaline soluble protein fraction was well concentrated, and may thus be utilized as a protein source. The acid soluble fraction was a mixture of protein and carbohydrate, containing 53.2percent protein and 36.0percent carbohydrate.  The acid soluble fraction showed significantly higher contents of rhamnose and galactose than the soluble dietary fiber fraction, whereas the soluble dietary fiber fraction showed a significantly higher arabinose content than the acid-soluble fraction.

The acid soluble fraction contained significantly smaller amounts of SDG, coumaric acid and ferulic acid than the alkaline soluble protein. The alkaline soluble protein fraction contained significantly larger amounts of all three phenolic acids than the other fractions; the contents of SDG, coumaric acid, and ferulic acid.

The acid soluble fraction with a carbohydrate content of 36.0percent showed the highest viscosity among the fractions.  Soluble dietary fiber contained 57.3percent carbohydrate; however, it did not show a high viscosity.  The protein solubility of linseed alkaline-soluble protein was 48.0percent, and this was lower than egg (65.0percent) but similar to a commercial soy protein isolate (45.0percent). The water binding capacity of both insoluble dietary fiber fractions was highest. The oil binding capacity of insoluble dietary fiber was higher than that of the commercial soy protein isolate but the oil binding capacity of soluble dietary fiber was similar to that of the soy protein isolate.

ACE was inhibited only by the soluble dietary fiber fraction. Pepsin hydrolysate of the soluble dietary fiber fraction including 0.067 mg/g coumaric acid and 0.066 mg/g ferulic acid showed the highest ACE inhibition. These hydroxycinnamic acid contents were the highest among all the tested extracts.

No inhibition was observed with the original linseed fractions; however, enzymatic hydrolysis increased LOX inhibitory activity. LOX was inhibited by ascorbic acid with an IC50 of 0.056 μg ml. There was no relationship between LOX inhibitory activity and hydroxycinnamic acid content, as shown in Table 5. Therefore, this inhibitory effect may have been caused by other factors such as peptides or amino acids released from the protein part of the fraction. The fraction that effectively inhibited ACE did not effectively inhibit LOX. This suggests that the inhibition sites for ACE and LOX in these fractions are different.

In this study, DPPH radical scavenging and copper reduction were detected after pepsin or pancreatin hydrolysis, and their activities were not significantly different between pepsin and pancreatin hydrolysis. The difference between this study and previous studies indicate that both fractionation and hydrolysis methods affect antioxidant activity.

The fractionation and analysis results of this study led to the following conclusions: the acid soluble fraction is useful for increasing viscosity of food, and when making soybean
products with a certain viscosity, addition of the acid soluble fraction would be useful for obtaining the desired viscosity and enhancing the LOX inhibitory effect; using a pH controlled process, the soluble dietary fiber fraction produced antioxidative and antihypertensive compounds with reasonable foaming activity; and the alkaline-soluble protein fraction was a concentrate of SDG, coumaric acid, and ferulic acid, which may have been responsible for the observed antioxidative effects. (Editors comments)