A high fructose diet induces insulin resistance in rats, although the exact molecular mechanism involved is unknown. In this study, we used immunoprecipitation and immunoblotting to examine the levels and phosphorylation status of the insulin receptor (IR) and insulin receptor substrate-1 (IRS-1), as well as the association of the IRS-1 with phosphatidylinositol 3-kinase (PI 3-kinase), and phosphotyrosine phosphatase (SHP2) in the liver and muscle of rats fed a control or high fructose diet for 28 d. There were no differences in IR and the IRS-1 protein levels in the liver and muscle of rats fed the control and high fructose diets. However, tyrosine-phosphorylation of the insulin receptor after insulin stimulation was reduced to 71 +/- 2% (P < 0.05) of control in the liver of the fructose-fed rats. In samples previously immunoprecipitated with anti-IRS-1 antibody and blotted with antiphosphotyrosine antibody, the insulin-stimulated IRS-1 phosphorylation levels in the liver and muscle of the fructose-fed group were only 70 +/- 6% (P < 0.05) and 76 +/- 5% (P < 0.05) of those of control rats, respectively. The insulin-stimulated IRS-1 association with PI 3-kinase was reduced to 84 +/- 3% (P < 0.05) in the liver and to 84 +/- 4% (P < 0.05) in the muscle of the fructose-fed group compared with control rats. Insulin-stimulated IRS-1 association with SHP2 was reduced to 79 +/- 5% (P < 0.05) in liver of the fructose-fed rats. These data suggest that changes in the early steps of insulin signal transduction may have an important role in the insulin resistance observed in these rats.

Normal and waxy corn starches were isolated, adjusted to different levels of moisture and heated at 100°C for 16h. The heat treated starches were hydrolysed with α‐amylase and amyloglucosidase. The starch samples were studied by determining their water‐binding capacity, pasting properties, X‐ray diffraction and by optical and scanning electron microscopy. The results showed that the heat‐moisture treatment produced an increase in the degree of crystallinity of normal and waxy corn starches at the level of 18% moisture. This result, in conjunction with a significant decrease in the enzymatic susceptibility, suggested a rearrangement of the starch molecules with strengthening of the linkages within the granules. On the other hand, the heat‐moisture treatment caused a rupture with further rearrangment of linkages within the granules for normal and waxy corn starches adjusted to the 27% moisture level. This produced a certain degree of starch degradation increasing the accessible regions of the granule to amylolysis.

Rats fed a high-fructose diet represent an animal model for insulin resistance and hypertension. We recently showed that a high-fructose diet containing vegetable oil but a normal sodium/potassium ratio induced mild insulin resistance with decreased insulin receptor substrate-1 tyrosine phosphorylation in the liver and muscle of normal rats. In the present study, we examined the mean blood pressure, serum lipid levels and insulin sensitivity by estimating in vivo insulin activity using the 15-min intravenous insulin tolerance test (ITT, 0.5 ml of 6 µg insulin, iv) followed by calculation of the rate constant for plasma glucose disappearance (K itt ) in male Wistar-Hannover rats (110-130 g) randomly divided into four diet groups: control,

The comprehension of the structure of starch granules is important for the understanding of its physicochemical properties. Native and sour cassava starches after being analyzed with respect to their pasting properties and baking expansion capacity, were treated with 2.2 N HCl at 38 °C for a maximum of nine days. The starch granules remaining after lintnerization were analyzed for amylose content and intrinsic viscosity, by X-ray diffraction, scanning electron microscopy and chromatographic analysis. The results indicated that the acid hydrolysis on all starches occurred in two steps. The first one, with high hydrolysis rate, was characterized by a quick degradation of the amorphous part of the granules whereas the second step, with lower hydrolysis rate, was characterized by a higher resistance of the organized areas of the granules to acid treatment. Most of the amylose chains were found in the amorphous areas of starch granules only a small percentage was involved in the crystalline regions. The microscopic and chromatographic analysis demonstrated that the acid hydrolysis was not able to disrupt the entire granular crystalline structure. Fermented starch showed amylose and/or amylopectin chain fractions resistant to pullulanase, probably due to structural alterations during fermentation.

The starch granules remaining after enzymatic hydrolysis were analyzed. Enzymatic corrosion efficiency was related to granule diameter. The intrinsic viscosity of enzymatically treated cassava and corn starches was gradually lowered by hydrolysis. X‐ray analysis and observation under a polarizing microscope suggested that enzymatic corrosion must occur in amorphous areas of the granules. Scanning electron microscopy showed that, for cassava granules, enzymatic corrosion occured mainly at the surface. Corn starch granules displayed considerable surface corrosion, as well as deep radial corrosion channels.

Insulin stimulates the tyrosine kinase activity of its receptor resulting in the tyrosine phosphorylation of pp185, which contains insulin receptor substrates IRS-1 and IRS-2. These early steps in insulin action are essential for the metabolic effects of insulin. Feeding animals a high-fructose diet results in insulin resistance. However, the exact molecular mechanism underlying this effect is unknown. In the present study, we determined the levels and phosphorylation status of the insulin receptor and pp185 (IRS-1/2) in liver and muscle of rats submitted to a high-fructose diet evaluated by immunoblotting with specific antibodies. Feeding fructose (28 days) induced a discrete insulin resistance, as demonstrated by the insulin tolerance test. Plasma glucose and serum insulin and cholesterol levels of the two groups of rats, fructose-fed and control, were similar, whereas plasma triacylglycerol concentration was significantly increased in the rats submitted to the fructose diet (P<0.05). There were no changes in insulin receptor concentration in the liver or muscle of either group. However, insulin-stimulated receptor autophosphorylation was reduced to 72 ± 4% (P<0.05) in the liver of high-fructose rats. The IRS-1 protein levels were similar in both liver and muscle of the two groups of rats. In contrast, there was a significant decrease in insulin-induced pp185 (IRS-1/2) phosphorylation, to 83 ± 5% (P<0.05) in liver and to 77 ± 4% (P<0.05) in muscle of the high-fructose rats. These data suggest that changes in the early steps of insulin signal transduction may have an important role in the insulin resistance induced by high-fructose feeding.

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This study evaluated the effect of pH on the microstructure of cream cheese and compared pH‐induced changes in its microstructure with concomitant changes in cheese firmness and meltability. On 4 different days, experimental batches of cultured hot pack cream cheese were manufactured and analyzed for initial chemical composition. The cheeses were then sectioned into samples that were randomly assigned to 7 different treatment groups. Three groups were exposed to ammonia vapor for 1, 3, and 5 min to increase the pH; 3 groups were exposed to acetic acid vapor for 30, 60, and 90 min to decrease the pH; and 1 unexposed group served as the control. After equilibration at 4 °C, samples were analyzed for pH, firmness, meltability, and microstructure by scanning electron microscopy. The effects of experimental treatments on cheese pH, firmness, and meltability were analyzed by randomized complete block analysis of variance (ANOVA). Relationships between cheese pH and firmness and meltability were evaluated by regression. Experimental treatments significantly affected cheese pH, firmness, and meltability. Cheese firmness decreased and meltability increased with increasing pH from about pH 4.2 to 6.8. Cheese microstructure also changed dramatically over the same approximate pH range. Specifically, the volume of the protein network surrounding the fat droplets increased markedly with increasing pH, presumably due to casein swelling. These data support the hypothesis that protein‐to‐water interactions increased as the cheese pH increased, which gave rise to progressive swelling of the casein network, softer texture, and increased meltability.