H YPOCHOLESTEROLEMIC –H YPOGLYCEMIC AND O THER E FFECTS

5.4.3 H YPOCHOLESTEROLEMIC –H YPOGLYCEMIC AND O THER E FFECTS

Alginates are polysaccharides with strong hypocholesterolemic effects. These biopolymers are resistant to gastrointestinal hydrolases in humans, and thus hardly digestible, unless they are depolymerized and fermented by microbial enzymes in the intestine. Research showed a reduction of plasma cholesterol in mice, following an alginate-rich diet (50 g/kg). This is likely to result from the interruption of enterohepatic circulation of bile acids, which leads to higher liver sterol output and bile acid excretion in the feces. 196

The effectiveness of alginate in reducing blood glucose has also been studied, and alginate products have been used to assist the treatment of patients suffering from diabetes. This probably occurs through the decreased diffusion of glucose in the gastrointestinal tract, due to the high viscosity and gelling properties of alginate. 98 Other important biological functions of alginate include the prevention of gastroe- sophageal influx and epigastric burning, management of dyspepsia, and treatment of gastritis and gastroduodenal ulcer. 98,197 Drugs and patented products are already in use for these purposes (Gaviscon, Algitec, Gastralgin). Apart from the antimicro- bial activity mentioned in Section 5.4.2, alginates mediate the normalization of esophageal and gastric pH, reduce acidic refluxes, facilitate the regeneration of mucus membrane in the stomach, and suppress gastrointestinal inflammation by forming a protective gel layer with the gastric juices, covering the mucus membrane (gastric dressing). 98,197 Additionally, sodium alginate is known for its antitoxic prop- erties, especially the ability to suppress bioabsorption of harmful heavy or radioactive metals, such as strondium and cadmium. 98,198 Also, a calcium alginate-containing bioactive food additive (Detoxal) is currently used for its antitoxic effects (e.g., against chemically induced hepatitis, where it helps to control lipid peroxidation and reduce lipid and glycogen content in the liver). 98

Xanthan was also shown to significantly reduce cholesterol levels in rats when supplemented at 1% (w/w) in a daily diet with a cholesterol content of 2% (w/w). 105

Nevertheless, as mentioned in Section 5.2.3, the effectiveness of xanthan in hyper-

Functional Food Carbohydrates

cholesterolemic humans is still uncertain, 106 and its characterization as a bioactive compound is still tentative.

Also, hypoglycemic effects of polysaccharides from Ganoderma lucidum fruit bodies have been reported. Although the mechanism of action is not well studied, it is possible that attachment of the polysaccharides to intestinal surfaces reduces and decelerates glucose absorption. 199

Another aspect of bioactive microbial polysaccharides is their antioxidative properties. Some mushrooms are known for antioxidative functions. Although these are primarily due to the phenol content of mushrooms, polysaccharides also con- tribute to antioxidant activity. 165,200 For instance, polysaccharide isolates (protein- bound or not) from liquid cultures of Antrodia camphorata were partly responsible for inhibition of lipid peroxidation. 200 Also, an antioxidative effect of yeast cell wall mannan isolates, namely, glucomannan from Candida utilis, mannan from S. cere- visiae , and mannan from Candida albicans, has been reported. 164 In addition, anti- oxidant properties against chemically induced DNA oxidative damage have been demonstrated by polysaccharides of Lentinus elodes, G. lucidum, and Coriolous versicolor . 201 Antioxidative action against hydroxy radicals was also shown by a sulfoethyl glucan derivative of S. cerevisiae. 169 These effects are mainly due to the scavenging ability of these biopolymers toward reactive oxygen species and other free radicals. 164,169,200,201

Lastly, other biological functions of microbial polysaccharides have been reported, such as antithrombotic effects (e.g., of curdlan sulfate or alginate) 98,202 or wound-healing properties (e.g., of PGG-glucans and alginate), 2,28,98 and probably merit further investigation.