F ENUGREEK G UM

4.2.4 F ENUGREEK G UM

4.2.4.1 Source

Fenugreek, Trigonella foenum-graecum, is a ca. 60-cm-tall annual leguminous plant native to southern Europe and western Asia and has a long history as a culinary and medicinal herb since ancient times. The plant is grown in northern Africa, the

Mediterranean, western Asia, northern India, and currently in Canada. 49 The fenugreek pod is about 3 to 10 cm long and 1 cm wide and contains 10 to 20 seeds with a size of about 2 to 3 mm. The seed has a strong aroma and is somewhat bitter in taste.

4.2.4.2 Method of Production

Fenugreek gum is extracted from the endosperm or ground whole seed with water or dilute alkali, and the yield varies from 13.6 to 38%, depending on the variety/cul-

tivar and extraction methods. 50 Commercial fenugreek gum products, such as Fenu- pure and Fenu-life, contain over 80% galactomannans with about 5% proteins. Laboratory preparation involving pronase (a nonspecific protease isolated from Streptomyces griseus ) treatments produces gum products of much higher purity with less than 0.6% protein contaminants. 49

4.2.4.3 Chemistry and Structural Features

The molar ratio of galactose to mannose of fenugreek gum is approximately 1:1. A reported value of the molecular weight is 1.4 million, compared to 1.3 and 1.2

million for commercial guar and locust bean gum, respectively. 49 The radius of gyration of fenugreek gum was 75 nm, which is in agreement with the range obtained by experiments and modeling for a gum with equal galactose and mannose contents and a molecular weight of 1.4 million. 9,51

4.2.4.4 Functional Properties and Applications

Solution properties of fenugreek gum are typical of a random coil polymer. 49 In steady-flow rheological tests, fenugreek gum solutions exhibit pseudoplastic behav-

ior at high shear rates. Mechanical spectra of locust bean, guar, and fenugreek gums with comparable molecular weights are similar in shape, but with slightly smaller moduli values for fenugreek gum. Fenugreek gum is a nongelling galactomannan and shows resistance against freeze–thaw treatments. In addition, little synergistic interaction was observed between fenugreek gum and other gums. 52

Polysaccharides are generally considered to be non-surface active, although in practice some surface activity of a gum specimen may be observed in experiments. Such apparent surface activity has been attributed to the presence of small amounts

of protein impurities. 53 Fenugreek gum was reported to possess substantial surface activity and be able to produce stable oil-in-water emulsions with moderately small droplet sizes (2 to 3 μm). 54–56 In addition, physical separation of protein residues

from the crude gum sample did not reduce the surface activity. 54 It is therefore

Functional Food Carbohydrates

tempting to assume that the surface activity is an intrinsic property of the polysac- charide. However, a protease-treated fenugreek gum sample containing less than 0.6% protein (calculated from nitrogen content) exhibited a reduced surface activ-

ity. 49 These conflicting results may solely indicate that the protease treatment is more effective in eliminating residual proteins. Protein components in fenugreek gum ingredients may be tightly associated with polysaccharide chains and capable of dominating some surface activity-related functional properties.

4.2.4.5 Physiological Properties and Health Benefits

The seed of fenugreek is a popular food ingredient in northern Africa and southern and western Asia, where it is consumed in various ways in ordinary daily diets. One of the most popular uses is as an appetite-stimulating spice in curries, while the testa of the fenugreek seed contains steroidal saponins that are amphiphilic, highly surface active agents and may find pharmaceutical applications. Fenugreek seed powders have been reported to have antidiabetic and hypocholesterolemic properties in

humans. 57 The galactomannan fiber appears to delay gastric emptying and contributes to antihyperglycemic effects. Hypocholesterolemic effects have been attributed to binding of cholesterol with both the saponins and galactomannan fibers in the digestive tract and subsequent excretion in the feces. The conversion of hepatic

cholesterol to bile salts may also increase. 57 Inhibitory effects of fenugreek seed powder on colon carcinogenesis have been reported and attributed to suppressed activities of a carcinogen-liberating enzyme, β-glucuronidase, and mucinase, which hydrolyzes the protective mucin and exposes the underlying intestine cells to carci- nogenic toxins. 58