A simplified modification of the AOAC official method for determination of total dietary fiber using newly developed enzymes.

Since 1985, AOAC Method 985.29 has been globally adopted as a standard method for determination of total dietary fiber in foods. Nevertheless, an aspect of AOAC Method 985.29 that needs to be improved is the laborious process to treat 3 enzymes separately at their individual proper pH, which is quite time-consuming. Several examinations have been carried out to resolve this problem. The characteristics of newly developed thermostable alpha-amylase, neutral protease, and amyloglucosidase were evaluated based on the pH-activity profile and the property of starch hydrolysis in comparison with those of the conventional enzyme reagents. These 3 developed enzymes were found to work under the same pH condition and to accomplish sufficient digestion for the typical 3 starches: soluble starch, corn starch, and wheat starch. The experimental results revealed that the dietary fiber determination in foods could be performed without pH adjustment in the enzymatic digestion process. The modified method will be greatly helpful in determining the total dietary fiber contents in food materials with less laborious work and with an accuracy equivalent to that of AOAC Method 985.29.

A simplified modification of the AOAC official method for determination of total dietary fiber using newly developed enzymes: preliminary interlaboratory study.

A preliminary interlaboratory study was conducted to evaluate the validity of the modified AOAC method for determination of total dietary fiber by Tada and Innami, in which the 3-step enzymatic digestion process in AOAC Method 991.43 is modified to a 2-step process without pH adjustment. Total dietary fiber contents in 8 representative foodstuffs were measured using both the original AOAC Method 991.43 and the modified method in 6 research facilities in Japan. Repeatability relative standard deviations, reproducibility relative standard deviations, and Horwitz ratio values from the modified method were equivalent to those from AOAC Method 991.43, except in the rice sample. However, this exceptional case shown in the modified method was entirely dissolved by the addition of alpha-amylase stabilizing agents. The modified method, which shortens the process of enzymatic digestion from 3 to 2 steps and in which only reaction temperature is adjusted under the same pH, was found not only to give accurate values comparable to the original method, but also to substantially reduce the labor required by the laboratory staff in the process of routine analysis. This study revealed that the validity of the modified method was further ensured by adding alpha-amylase stabilizing agents to the reaction system.

Jew's mellow leaves (Corchorus olitorius) suppress elevation of postprandial blood glucose levels in rats and humans.

The study was performed to explore the suppressive effect of Jew's mellow leaves (JML) on postprandial blood glucose levels in rats and humans. A soluble dietary fiber (SDF) was extracted from the freeze-dried JML powder. An elevation of the postprandial blood glucose level in rats given 1% or 2% JML-SDF solution orally together with 20% glucose solution was significantly suppressed as compared with that observed in the control rats given only glucose solution. When seven healthy young male adults ingested 225 mL of JML mixed juice containing 15 g of freeze-dried powder with 75 g of glucose in the fasting state in the morning, the elevation of the postprandial blood glucose level was significantly suppressed as compared with the control subjects. The diffusion rate of glucose and the permeation rate of glucose in the cultured Caco-2 cells were both significantly reduced by the addition of appropriate amounts of JML-SDF when compared to the controls. These results indicate that the effective substance in JML for suppressing blood glucose elevation is a kind of mucilaginous SDF. The mechanism by which this suppression occurs may be largely attributable to the delayed absorption of glucose from the intestinal membrane in the upper digestive tract by viscous SDF.

Dietary fiber suppresses elevation of uric acid and urea nitrogen concentrations in serum of rats with renal dysfunction induced by dietary adenine.

This study was conducted to examine the effects of several kinds of dietary fiber (DF) with different physical properties on the elevation of uric acid and urea nitrogen concentrations in serum of rats induced by dietary adenine. DF decreased an uptake of 14C-labeled adenine in the rat jejunum in vitro, but the reduction varied with the physical property of DF. Male Wistar rats (3 weeks old) were fed a diet with or without a 0.4% adenine and a 5% DF (cellulose, chitin, chitosan, or xanthan gum) for 20 days. Feeding of adenine in the fiber-free group elevated the concentrations of uric acid, creatinine, and urea nitrogen in serum, but decreased the excretions of these compounds into urine and increased the amounts of 2,8-dihydroxyadenine (2,8-DHA) in kidney and urine. The test DF was found to suppress the elevation of uric acid, creatinine, and urea nitrogen concentrations in serum induced by dietary adenine, and to mitigate the decreased excretions of these compounds into urine and the increased retention of 2,8-DHA in kidney and urine. This phenomenon was remarkable in the xanthan gum group. These results suggest that DF suppresses the elevation of uric acid and urea nitrogen concentrations in serum by attenuating the absorption of dietary adenine.

Suppressive effect of viscous dietary fiber on elevations of uric acid in serum and urine induced by dietary RNA in rats is associated with strength of viscosity.

This study was performed to clarify how dietary fiber (DF) with different viscosities would be associated with dietary RNA metabolism. Male Wistar strain rats, four weeks old, were fed diets containing a 3% (w/w) yeast RNA and a 5% (w/w) viscous DF for five days. Viscosity of DF samples used, in order of strength, were xanthan gum (XG) > guar gum (GG) > locust bean gum (LBG) > karaya gum (KG) > pectin (PE) = arabic gum (AG) > CM-cellulose (CMC) = inulin (IN). The serum uric acid concentration in the viscous DF groups significantly decreased as compared with that in the cellulose (CL) group. The urinary excretions of uric acid and allantoin in the respective groups given AG, GG, IN, KG, PE, and XG were significantly suppressed as compared with those in the CL group. The fecal RNA excretion was markedly increased in the IN, KG, PE, and XG groups in comparison to the CL group. The DF with high viscosity significantly suppressed RNA digestion by RNase A and decreased uptakes of 14C-labeled adenosine and adenosine 5'-monophosphate (5'-AMP) in rat jejunum. The results reveal that the suppressive effect of DF on elevation of serum uric acid concentration induced by dietary RNA in rats is associated with the strength of DF viscosity. The mechanism by which this is accomplished is suggested to be attributed to the inhibitions of digestion for dietary RNA and/or absorption of the hydrolyzed compounds.

Dietary fiber suppresses elevations of uric acid and allantoin in serum and urine induced by dietary RNA and increases its excretion to feces in rats.

This study was performed to examine the effects of several kinds of dietary fibers (DF) with different physical properties on dietary RNA metabolism. Male Wistar strain rats, 4 wk old, were fed diets with or without a 3% yeast RNA and a 5% DF (cellulose, chitin, chitosan, inulin, and xanthan gum) for 20 d (Experiment 1) or 5 d (Experiment 2). Feeding DF tested lowered the serum uric acid and allantoin concentrations and the urinary excretions of their compounds and increased the amount of RNA excreted into the feces compared with fiber-free. The water-holding capacity and nucleotide adsorption of chitin and chitosan in acidic solutions were higher than those of cellulose. The digestion rate of RNA by RNase A in vitro was found to be lower in the DF tested than in fiber-free. The decrease was remarkable in chitosan and xanthan gum. The uptakes of 14C-labeled adenosine and adenosine 5'-monophosphate (5'-AMP) in the rat jejunum were markedly decreased in regard to chitosan and xanthan gum in comparison with the fiber-free. These phenomena suggest that DF with high viscosity is more strongly associated with the suppression of RNA digestion by RNase A and the depression of the uptake of purine compounds to jejunum. The present results reveal that the elevation of serum uric acid concentration induced by dietary RNA can be suppressed by DF in rats.

Effects of a partially hydrolyzed curdlan on serum and hepatic cholesterol concentration, and cecal fermentation in rats.

A significant reduction was observed for serum and hepatic cholesterol concentrations in the rats fed diet containing a 5% partially hydrolyzed curdlan (PHCD), whereas only the hepatic cholesterol concentration was decreased in the curdlan (CD)-fed rats. The cecal contents in the CD group contained a significantly larger amount of short-chain fatty acids, but not those in the PHCD group. CD, but not PHCD, significantly increased the population of cecal bifidobacteria. From the in vitro fermentation test with cecal contents from cellulose powder (CP) and CD-fed rats, PHCD proved to be easily fermented by both cecal contents; incidentally CD was more susceptible to the cecal contents from CD-fed rats than to those from CP-fed rats. These results suggest that PHCD is involved in the modulation of lipid metabolism and intestinal microflora through a different manner from the native CD in rats.

Administration of beta-carotene suppresses lipid peroxidation in tissues and improves the glucose tolerance ability of streptozotocin-induced diabetic rats.

The present study attempted to examine the antioxidative effect of dietary beta-carotene (BC) on lipid peroxidation (LPO) in the streptozotocin (STZ)-induced diabetic rats. Male Sprague-Dawley (SD) rats were fed on the AIN76 standard diet with or without 0.1% BC. On the 21st day after introduction of these diets, STZ was intraperitoneally injected in half the subjects of both groups. All animals were sacrificed seven days after the STZ injection. Glucose tolerance and thiobarbituric acid reactive substance (TBARS) in the tissues or serum were measured. Body weight gain in the BC + STZ group was significantly higher than that in the STZ group (p < 0.05). Blood glucose and TBARS concentrations of the liver, pancreas, and serum in the BC + STZ group were significantly lower than those in the STZ group. The blood insulin concentration in the BC + STZ group was significantly higher than that in the STZ group. The hepatic and serum beta-carotene concentrations in the BC + STZ group were significantly lower than those in the BC group. Moreover, the synthesis and oxidation of glutathione (GSH) in the BC + STZ group were reduced when compared to the STZ group. These results suggest that the administration of beta-carotene suppresses the elevation of LPO and reduces the symptoms of diabetes mellitus (DM) in the STZ-induced diabetic rats.