Different substrates and methane producing status affect short-chain fatty acid profiles produced by In vitro fermentation of human feces. (57/1890)

Five different substrates, i.e., lactulose, rhamnose, cornstarch, guar and ileostomy effluent, were used to determine whether methane producing status alters the production of short-chain fatty acids (SCFA) in methane producers (MP; n = 6) and nonproducers (MNP; n = 5). Fecal samples from MP and MNP were fermented with the five substrates using an in vitro fermentation method. Subjects with a mean breath methane concentration > 0.045 micromol/L above ambient air were classified as MP. Fermentation was stopped and samples were obtained at 3, 5 and 24 h. An HPLC method was used to measure the SCFA, acetate, propionate, isobutyrate, butyrate, valerate and isocaproate. A significant interaction between methane producing status and time for acetate production from lactulose was observed. There were no differences in fermentation of the four remaining substrates between MP and MNP, but there were significant differences among substrates in the two groups combined. Acetate production from lactulose was significantly greater than from the four other substrates, whereas that from ileostomy effluent was significantly less than the four other substrates. The amount of propionate produced from rhamnose was significantly higher than from the other substrates. The amount of butyrate produced from lactulose and cornstarch was significantly higher than from the other substrates. We conclude that differences exist in the fermentation patterns of lactulose, rhamnose, cornstarch, guar and ileostomy effluent. Methane producing status may influence fermentation patterns only of substrates that are largely fermented to acetate and not others.  (+info)

Fermentation of resistant rice starch produces propionate reducing serum and hepatic cholesterol in rats. (58/1890)

This study was designed to investigate the effects of different proportions of rice starch and cornstarch on lipid metabolism in rats fed high dietary cholesterol. Male Wistar rats were fed a 10 g/100 g fat diet containing 1 g/100 g cholesterol with 0 (control diet), 15, 30, 45 or 63 g/100 g rice starch with an enzyme resistant starch concentration of 1.26, 1.39, 1.52, 1.65 or 1.80 g/100 g, respectively, for 4 wk. Groups fed diets with < 63 g/100 g rice starch were supplemented with cornstarch to 63 g/100 g. The two kinds of starch had different structures as seen using scanning electron microscopy (SEM). The rice starch was an aggregation (n = 20-60) of smaller granules (3-8 microm in diameter), whereas the cornstarch was composed of larger (5-15 microm in diameter), single granules. The compound rice starch (0.99 kg/L) was larger in size and denser in structure than cornstarch (0.63 kg/L). Serum total cholesterol concentrations in rats fed both the 45 and 63 g/100 g rice starch diets were significantly lower than in all other groups (P < 0.05). The serum propionate concentration in the rats fed 63 g/100 g rice starch diets was significantly higher than that of other groups. Hepatic triglyceride and total cholesterol concentrations in rats fed 63 g/100 g rice starch diets were significantly lower than in the control group. These results suggest that, because the compound rice starch was an aggregation of smaller granules, larger in size and denser in structure than cornstarch, it was digested more slowly and altered lipid metabolism. Resistant rice starch may be fermented to produce propionate, which reduces serum and hepatic cholesterol.  (+info)

Inhibition of enzymic digestion of amylose by free fatty acids in vitro contributes to resistant starch formation. (59/1890)

The effect of lipids on the enzymic breakdown of starch was investigated using an in vitro assay system. Mixtures of potato amylose, amylopectin and starch and various lipids were incubated at 37 degrees C for 10 min and subjected to digestion by alpha-amylase (EC 3.2.1.1) and amyloglucosidase (EC 3.2.1.33). Lauric, myristic, palmitic and oleic acids and lysolecithin inhibited enzymic hydrolysis of amylose by approximately 35% (P < 0.05). Stearic acid and cholesterol had no effect on the enzymic breakdown of amylose. Retrograded amylose was hydrolyzed less readily (P < 0.05) than solubilized amylose, but the breakdown was not further inhibited in the presence of lauric acid. Fatty acids had no effect on the enzymic hydrolysis of amylopectin, whereas inhibition by fatty acids of the breakdown of whole starch was consistent with only the amylose fraction being affected. The possibility that interactions between starch and fatty acids in the digestive tract could contribute to the formation of resistant starch is considered.  (+info)

Comparative characterization of complete and truncated forms of Lactobacillus amylovorus alpha-amylase and role of the C-terminal direct repeats in raw-starch binding. (60/1890)

Two constructs derived from the alpha-amylase gene (amyA) of Lactobacillus amylovorus were expressed in Lactobacillus plantarum, and their expression products were purified, characterized, and compared. These products correspond to the complete (AmyA) and truncated (AmyADelta) forms of alpha-amylase; AmyADelta lacks the 66-kDa carboxyl-terminal direct-repeating-unit region. AmyA and AmyADelta exhibit similar amylase activities towards a range of soluble substrates (amylose, amylopectin and alpha-cyclodextrin, and soluble starch). The specific activities of the enzymes towards soluble starch are similar, but the K(M) and V(max) values of AmyADelta were slightly higher than those of AmyA, whereas the thermal stability of AmyADelta was lower than that of AmyA. In contrast to AmyA, AmyADelta is unable to bind to beta-cyclodextrin and is only weakly active towards glycogen. More striking is the fact that AmyADelta cannot bind or hydrolyze raw starch, demonstrating that the carboxyl-terminal repeating-unit domain of AmyA is required for raw-starch binding activity.  (+info)

Digestion of so-called resistant starch sources in the human small intestine. (61/1890)

BACKGROUND: Resistant starch sources, which are only partially digested in the small intestine, can be used to increase colonic availability of short-chain fatty acids. OBJECTIVE: To study the characteristics of the fermentation of resistant starch, the digestion of resistant starch in the small intestine has to be quantified. We compared the metabolic fates of highly digestible cornstarch (DCS), Hylon VII (type 2 resistant starch), and Novelose 330 (type 3 resistant starch), which are of corn origin and, therefore, naturally enriched in (13)C. DESIGN: After administration of 40 g starch or glucose to 7 healthy volunteers, glucose and exogenous glucose concentrations in serum and (13)CO(2) excretion in breath were analyzed for 6 h. (13)C abundance in carbon dioxide was analyzed by isotope ratio mass spectrometry (IRMS) and (13)C abundance in glucose by gas chromatography-combustion IRMS. RESULTS: By comparing the area under the curve (2 h) of exogenous glucose concentration in serum ((13)C glycemic index) after intake of starch or glucose, (13)C glycemic indexes for DCS, Hylon VII, and Novelose 330 were calculated to be 82 +/- 23%, 44 +/- 16%, and 43 +/- 15%, respectively. Comparison of 6-h cumulative percentage dose recovery in breath showed that 119 +/- 28% of DCS, 55 +/- 23% of Hylon VII, and 50 +/- 26% of Novelose 330 was digested in the small intestine. CONCLUSION: The exogenous glucose response in serum and the (13)CO(2) excretion in breath can be used to estimate small intestinal digestion of resistant starch, which amounts to approximately 50%.  (+info)

Ontogenetic changes of potato plants during acclimation to elevated carbon dioxide. (62/1890)

Transgenic potato plants (Solanum tuberosum cv. Desiree) with an antisense repression of the chloroplastic triosephosphate translocator were compared with wild-type plants. Plants were grown in chambers with either an atmosphere with ambient (400 mu bar) or elevated (1000 mu bar) CO2. After 7 weeks, the rate of CO2 assimilation between wild-type and transgenic plants in both CO2 concentrations was identical, but the tuber yield of both plant lines was increased by about 30%, when grown in elevated CO2. One explanation is that plants respond to the elevated CO2 only at a certain growth stage. Therefore, growth of wild-type plants was analysed between the second and the seventh week. Relative growth rate and CO2 assimilation were stimulated in elevated CO2 only in the second and the third weeks. During this period, the carbohydrate content of leaves grown with elevated CO2 was lower than that of leaves grown with ambient CO2. In plants grown in elevated CO2, the rate of CO2 assimilation started to decline after 5 weeks, and accumulation of carbohydrates began after 7 weeks. From this observation it was concluded that acclimation of potato plants to elevated CO2 is the result of accelerated development rather than of carbohydrate accumulation causing down-regulation of photosynthesis. For a detailed analysis for the cause of the stimulation of growth after 2 weeks, the contents of phosphorylated intermediates of wild-type plants and transgenics were measured. Stimulation of CO2 assimilation was accompanied by changes in the contents of phosphorylated intermediates, resulting in an increase in the amount of dihydroxyacetone phosphate, the metabolite which is exported from the chloroplast into the cytosol. An increase of dihydroxyacetone phosphate was found in wild-type plants in elevated CO2 when compared with ambient CO2 and in triosephosphate translocator antisense plants in ambient CO2, but not in the transgenic plants when grown in elevated CO2. These plants were not able to increase dihydroxyacetone phosphate further to cope with the increased CO2 supply. From these changes in phosphorylated intermediates in wild-type and transgenic plants it was concluded that starch and sucrose synthesis pathways can replace each other only at moderate carbon flux rates.  (+info)

Impact of elevated cytosolic and apoplastic invertase activity on carbon metabolism during potato tuber development. (63/1890)

During tuberization in Solanum tuberosum var. Desiree maximal catalytic activities of invertase(s) and sucrose synthase are inversely correlated. During the early stages, invertase activity is high and declines during maturation. The decrease in invertase activity is accompanied by a decrease in the hexose to sucrose ratio and an increase in sucrose synthase activity. This switch is paralleled by the onset of the storage phase as shown by the accumulation of starch and storage proteins. Biochemical and genetic evidence suggests that sucrose synthase activity is positively correlated with sink strength. To explore the possibility of enhancing sink strength in potato tubers by elevating the sucrolytic capacity, transgenic potato plants expressing either cytosolic or apoplastic yeast invertase in their tubers were made. Surprisingly, cytosolic invertase led to a decrease and apoplastic invertase to an increase in tuber yield. To understand the causes of the observed phenotypes, carbon metabolism in tubers of transgenic and control plants was analysed during different stages of tuber development. Both cytosolic and apoplastic invertase resulted in decreased sucrose and elevated glucose contents, indicating that sucrose is accessible in both compartments. Metabolic perturbation, however, was found to be compartment specific. Elevated cytosolic invertase activity led to increased carbon flux towards glycolysis and accumulation of phosphorylated intermediates. The phosphorylated intermediates were not used to build up starch. In contrast, apoplastic invertase does not lead to a significant increase in hexose phosphates compared to untransformed controls. Thus, hexoses originating in the apoplast are not efficiently phosphorylated during potato tuber development, which might be explained by an endocytotic uptake of sucrose and/or hexoses from the apoplast into the vacuole bypassing the cytosolic compartment.  (+info)

Water stress enhances beta-amylase activity in cucumber cotyledons. (64/1890)

Cotyledons detached from 4-d-old cucumber (Cucumis sativus L.) seedlings were subjected to water stress (air-drying or PEG-treatment) to examine the effects of the stress on carbohydrate metabolism. Amylolytic activity in the cotyledon was increased about 6-fold by water stress within 1 d. The substrate specificity and the action pattern indicated that beta-amylase is responsible for the activity. Activities of azocaseinase, malate dehydrogenase and triose-phosphate isomerase were not affected by water stress, indicating that the effect of the stress on beta-amylase is rather specific. Cycloheximide-treatment strongly reduced the enhancement of beta-amylase activity. The hypocotyl of cucumber seedlings also exhibited an increase in the enzyme activity when subjected to water stress. The major free sugars in cucumber cotyledons were glucose, fructose, maltose, and sucrose; sucrose being the most abundant. Sucrose content in excised, unstressed cotyledons increased markedly during the incubation. Changes in other free sugars were small compared with that of sucrose. Starch also accumulated in unstressed cotyledons. In stressed cotyledons more sucrose and less starch accumulated than in unstressed ones. Such results were discussed in relation to the enhancement of beta-amylase activity.  (+info)