Effect of dietary fiber on the induction of colorectal tumors and fecal beta-glucuronidase activity in the rat.

The purpose of the present study was to investigate whether three different types of dietary fiber, wheat bran, carrot fiber, and citrus pectin, influenced the induction of colorectal tumors produced by 1,2-dimethylhydrazine in rats. In all groups, the tumor yield was high (87 to 97%). In the wheat bran and carrot fiber groups, the incidence of colorectal tumors was not significantly different from that of the group fed on the fiber-free basic diet. The citrus pectin group, however, had a significantly higher incidence of colorectal tumors (p less than 0.001). An increased number of auditory duct tumors was also noted in this group. In a separate experiment, dietary pectin induced a 10-fold increase in fecal beta-glucuronidase activity but did not alter this activity in the bowel wall. It has been suggested that dietary fiber protects against the induction of colorectal tumors, but this was not the case in the experiment. It is possible that the high tumor yield made the demonstration of a weak protective effect of wheat bran impossible. The reason for the increased occurrence of tumors in the citrus pectin group is obscure and will be subjected to further investigation. Fecal beta-glucuronidase activity might be one factor of importance in the activation of the carcinogen.

Effect of two kinds of pectin and guar gum on 1,2-dimethylhydrazine initiation of colon tumors and on fecal beta-glucuronidase activity in the rat.

The effect of 5% low-methoxylated pectin, high-methoxylated pectin, and guar gum on 1,2-dimethylhydrazine initiation of colon cancer was investigated using groups of 30 rats. The growth of the rats in the different groups was very similar to that of control group fed a fiber-free diet. Both kinds of pectin increased the multiplicity of color tumors, whereas guar gum did not significantly influence carcinogenesis. Bacterial beta-glucuronidase activity in feces and colonic content was the same in pectin-fed rats and controls but significantly lower in the guar gum group. Thus, it was not related to the number of tumors in each group.

Digestibility of processed food protein.

An overview is given on the effects of food processing on the protein digestibility. Beneficial effects of food processing are primarily observed in a range of plant foods containing toxic substances and/or anti-nutrients (legumes, cereals, some seed food). Digestibilities improve by heating, soaking, germination and fermentation. These processing steps reduce the amount of active enzyme inhibitors through extraction, inactivation by heat or microorganisms, or by compositional modification through germination. Reduced protein digestibility is primarily associated with excessive heat, exemplified by the comparatively low digestibility of ready-to-eat breakfast cereals. Experiments with model systems indicate that some caution should be observed with the use of alkalis in food processing, and with products prone to the Maillard reaction.

Oats (Avena sativa) reduce atherogenesis in LDL-receptor-deficient mice.

AIM: The cholesterol-lowering properties of oats, largely ascribed to its contents of soluble fibers, beta-glucans, are well established, whereas effects on atherogenesis are less well elucidated. Oats also contains components with reported antioxidant and anti-inflammatory effects that may affect atherogenesis. In this work we examined effects of oat bran on plasma cholesterol, markers of inflammation, eNOS expression and development of atherosclerosis in LDL-receptor-deficient (LDLr(-/-)) mice. METHODS AND RESULTS: Female LDLr(-/-) mice were fed Western diet+/-oat bran. Two concentrations of oat bran (40 and 27%) were compared regarding effects on plasma lipids. There was a dose-dependent reduction of plasma cholesterol by 42 and 20% with 40 and 27% oat bran, respectively. Both concentrations also lowered plasma triglycerides (by 45 and 33%) and relative levels of plasma LDL+VLDL. The reduction of plasma lipids was accompanied by increased faecal excretion of cholesterol and bile acids. Oat bran (40%) efficiently reduced atherosclerotic lesion area in the descending aorta (-77%) and aortic root (-33%). Plasma levels of fibrinogen and soluble vascular cell adhesion molecule-1 (VCAM-1) were significantly lower, and immunofluorescence of aortic sections revealed a 75% lower expression of VCAM-1 in oat-fed mice. The expression of eNOS protein in the aortic wall was increased in mice fed oat bran. CONCLUSIONS: Oat bran supplemented to a Western diet lowers plasma cholesterol, reduces levels of some inflammatory markers, increases eNOS expression and inhibits atherosclerotic lesion development in LDLr(-/-) mice. It remains to be investigated which components in oats contribute to these effects.

Effect of Maillard reaction products on protein digestion.

A summary is given of experiments performed to study the effects of Maillard reaction products on protein digestion and uptake. A double-isotope technique was used to evaluate the impact of compounds formed in the Maillard reaction on the intestinal uptake of dietary proteins in rats. It was found that low-molecular weight compounds from a glucose-lysine reaction mixture reduced the plasma level of dietary protein-derived lysine. The reaction mixture inhibited in vitro carboxy-peptidase A (E.C. 3.4.17.1) and the brush border enzyme aminopeptidase N (E.C. 3.4.11.2). A glucose-lysine reaction compound, 2-formyl-5-(hydroxymethyl)pyrrole-1-norleucine was found to be a strong competitive inhibitor of aminopeptidase N (Ki = 0.2mM) in vitro. When given to rats (3 mg/g diet), it reduced the plasma level of lysine derived from both dietary free and protein-bound lysine. This compound also inhibited carboxypeptidase A, as did a number of substituted furans and pyrroles.

Effect of Maillard reaction products on protein digestion. In vivo studies on rats.

The effect of a glucose-lysine reaction mixture on protein digestion in rats was studied by using 3H-labeled free lysine, 14C- or 3H-labeled protein-bound lysine and 35S-labeled protein-bound cystine in the experimental diets. The low-molecular-weight part of the glucose-lysine reaction mixture (1.5% wt/wt in the diet) affected the utilization of dietary protein-derived amino acids, as revealed by the ratio and the levels of different labels in plasma after feeding. The browned crust from a heated minced-meat loaf was less well digested and had a lower biological value than the crumb in a nitrogen-balance study with rats. When the water-soluble fraction of the crust was removed, the biological value of the crust was restored to the value of the crumb but the digestibility remained low. The addition of the water-soluble fraction of the crust had only a slight effect on the digestibility of the crumb. It is concluded that compounds in the glucose-lysine reaction model affect the dietary protein utilization of rats but were not present or otherwise could not explain the reduced utilization of proteins in the crust of the heated meat product.

Effects of consumption of oat milk, soya milk, or cow's milk on plasma lipids and antioxidative capacity in healthy subjects.

A drink based on oats has been developed with new technology. In this study the effects of this oat milk, soya milk and cow's milk on plasma lipid, glucose, insulin, and antioxidant status (measured as the ability of serum to suppress the formation of the radical cation ABTS*+) were compared in 24 healthy men and women. Half of the subjects (group A) consumed 0.75-1 liters/day of oat milk and soya milk for 4 weeks each, and the other half (group B) consumed oat milk and cow's milk for two 4-week periods. In the combined groups A plus B the oat milk regimen resulted in decreased plasma cholesterol (4%) and low-density lipoprotein (LDL) cholesterol (9%) levels as compared with baseline, but no changes in high-density lipoprotein cholesterol (HDL) and triglyceride values were observed. Also soya milk consumption resulted in decreased LDL cholesterol concentrations. The only significant plasma lipid change observed during consumption of cow's milk was an increase in HDL cholesterol. No consistent changes in body weight, fasting blood glucose, serum insulin, and antioxidant status occurred after consumption of any milk regimen. A significant correlation between baseline antioxidant status and total plasma cholesterol was found (r = -0.56). It is proposed that the high content of beta-glucans in oat milk was responsible for the decreased plasma cholesterol and LDL cholesterol concentrations, but the effect could also be due to a replacement of saturated fat in the customary diet by unsaturated fat. It is concluded that oat milk can be used as an alternative to other milk drinks by subjects who would benefit from reduced LDL cholesterol values.

Cereal fructans: in vitro and in vivo studies on availability in rats and humans.

The bioavailability of cereal fructans (fructooligosaccharides) was investigated both in vitro and in vivo. In vitro studies indicated very slow hydrolysis by human gastric juice and by homogenate of the intestinal mucosa (rat). After intubation of fructans into the stomachs of rats, the recovery of fructans in the small intestine and colon was approximately the same as that of an unabsorbed marker (polyethylene glycol), indicating no or very low disappearance of fructans in the small intestine. In vivo studies of the small intestine in rats showed that the rate of disappearance of fructans was lower than that of mannose, which is known to be absorbed through passive diffusion. In addition the cariogenic effect of cereal fructans was compared to that of glucose. Acid formation from low molecular-weight fructans was found in human dental plaque in vitro. A mouth rinse with unfractionated fructans, containing some quantities of sucrose, fructose and glucose, resulted in relatively low pH values in human plaque in vivo, even if the decrease in pH was somewhat less pronounced when compared with a mouth rinse with glucose.

Effect of preheating on potato texture.

Preheating potatoes at 50 to 80 degrees C has a firming effect on the cooked potato tissue. This effect is particularly pronounced at a preheating temperature of 60 to 70 degrees C followed by cooling. Several theories have been presented in the literature to explain this firming effect: retrogradation of starch, leaching of amylose, stabilization of the middle lamellae and cell walls by the activation of the pectin methylesterase (PME) enzyme, and by the release of calcium from gelatinized starch and the formation of calcium bridges between pectin molecules. Most probably, none of these theories alone can explain the phenomenon and more than one mechanism seems to be involved. Some of these mechanisms seem to be interdependent. As an example, calcium could be considered as a link all the way through release after starch gelatinization to cross-linking pectin substances in the cell wall and the middle lamellae, which has been demethylated by the PME enzyme. More research and "clear cut" experiments are needed in order to elucidate the role of each mechanism, especially which of them is the main contributor to the process of firming. Most probably, the calcium-pectin-PME mechanism plays a secondary role, that is, it only retards the collapse of the tissue structure that would otherwise occur during the final heating without preheating, and it is not the main factor of firmness.

A study of some important vitamins and antioxidants in a blackcurrant jam with low sugar content and without additives.

Blackcurrant (Ribes nigrum) jam was manufactured with the aim of producing a jam with a low sugar content, and without any additives. Four temperatures were investigated, namely 60 degrees C, 76 degrees C, 92 degrees C and 97 degrees C. Processing time varied between 1-20 min. After processing, the highest content of ascorbic acid was found in the jam processed at 97 degrees C for 1 min, which contained 63.3 +/- 2.6 mg ascorbic acid/100 g jam. At all combinations investigated more than 60% of the original amount of ascorbic acid was retained after manufacturing and packaging. The jam made at 92 degrees C was stored in a shelf-life study for 13 months. The jam was then stored at 8 degrees C, ambient temperature and at 37 degrees C. At ambient temperature the jam was stored both in dark and in daylight, at 8 degrees C and at 37 degrees C the jam was stored in dark. After 13 months of storage, at 8 degrees C, 60% of the amount of ascorbic acid and 29% of the amount of anthocyanins were retained. In the jam stored at higher temperatures less of both was retained. The beta-carotene in the jam was found to be stable throughout the whole shelf-life study. Exposure to light did not have any effect on any of the components studied. The degradation of anthocyanins was best described by a second-order reaction and the activation energy was determined to be 90 kJ/mol. A jam of blackcurrant may be considered as a good source of vitamins and antioxidants after one year, if certain precautions concerning manufacture and storage conditions are taken.

Wheat bran increases high-density-lipoprotein cholesterol in the rat.

1. Five groups of male Sprague Dawley rats were given for 6 months a diet with high protein and fat contents but a very low dietary fibre content (group B), and this diet mixed with (g/kg) 50 low-methoxyl pectin (group L), 50 high-methoxyl pectin (group H), 50 guar gum (group G) and 200 wheat bran (group WB, corresponding to 100 wheat fibre) respectively. 2. The weight increment was significantly lower in group G than in the other groups. Assuming no energy value of the dietary fibre, the weight increment (/kJ) was the same in groups B, L and H, lower in group G and higher in group WB, indicating that a proportion of the bran fibre might in fact be available as a source of energy. 3. Wheat bran increased total plasma cholesterol and high-density-lipoprotein cholesterol after 6, 12 and 26 weeks. Group G had significantly lowered plasma cholesterol after 12 weeks. Pectin on the other hand did not significantly influence total or HDL-cholesterol levels. It is therefore possible that the plasma cholesterol lowering effect of pectin previously demonstrated in the rat is dependent on the presence of significant amounts of dietary cholesterol as our diets did not contain added cholesterol. Plasma triglycerides decreased with age but were similar in all groups.

Consumption of oat milk for 5 weeks lowers serum cholesterol and LDL cholesterol in free-living men with moderate hypercholesterolemia.

The aim of this study was to investigate whether consumption of a newly developed oat milk deprived of insoluble fiber would result in lower serum cholesterol and low-density lipoprotein (LDL) cholesterol levels in men with moderate hypercholesterolemia. The study had a randomized, controlled double-blind design, and oat milk was compared with an identically flavored control drink. Sixty-six men were recruited from a screening program and were randomly assigned to two groups. Each group took either oat milk or a control drink (rice milk) for 5 weeks (0.75 liters/day) and then switched to the other drink regimen for another 5-week period with a 5-week washout period between the test periods. The oat milk contained more dietary fiber, especially beta-glucan (0.5 g/100 g), than the control drink (<0.02 g/100 g). Both drinks were well appreciated and got similar sensory evaluation, indicating that the double-blind design had been attained. In the final analysis 52 subjects remained. Compared with the control drink, intake of oat milk resulted in significantly lower serum total cholesterol (6%, p = 0.005) and LDL cholesterol (6%, p = 0.036) levels. The decrease in LDL cholesterol was more pronounced if the starting value was higher (r = -0.55, p < 0.001). The concentration of high-density lipoprotein cholesterol was not significantly different after consumption of the two drinks. Serum triglycerides did not change significantly after intake of oat milk, but a significant increase was observed after intake of the control drink (p = 0.003). It is concluded that also oat milk deprived of insoluble fiber has cholesterol-reducing properties.

Changes in plasma insulin, enterostatin, and lipoprotein levels during an energy-restricted dietary regimen including a new oat-based liquid food.

The changes in plasma insulin, enterostatin, lipid, and glucose levels during weight reduction were studied in 32 subjects having a body mass index of 25-35. The 31 subjects who completed the study followed for 23 weeks an energy-restricted dietary regimen which included a new oat-based soup as the main meal once or twice daily. The intake of energy decreased from 8.9 to 6.2 MJ/day from 0 to 22 weeks, the energy percentage from fat decreased from 35 to 30%, and the intake of dietary fiber increased from 21 to 25 g/10 MJ. The body weight decreased from 83 to 78 kg after 6 weeks and to 77 kg after 23 weeks. Plasma glucose had decreased significantly from 5.4 to 5.2 mmol/l, and plasma insulin from 122 to 98 pmol/l after 23 weeks. In contrast, the plasma enterostatin concentration did not vary significantly over five sampling times, the mean values ranging from 25 to 30 nmol/l. Plasma cholesterol declined from 5.6 to 5.2 mmol/l, low-density lipoprotein cholesterol from 3.8 to 3.3, and plasma triglycerides from 1.5 to 1.3 mmol/l from 0 to 23 weeks. High-density lipoprotein cholesterol increased from 1.1 to 1.3 mmol/l. It is concluded that an energy-restricted regimen leading to lower plasma insulin, triglyceride, and low-density lipoprotein cholesterol levels did not significantly affect the plasma enterostatin concentration in overweight subjects. A new oat-based liquid food as a part of the dietary regimen was well tolerated.