Biomedical subjects

Peter R Ellis

Publications and source records attributed to Peter R Ellis.

5 recordsLinked to original sources

PubMed2006

Almonds decrease postprandial glycemia, insulinemia, and oxidative damage in healthy individuals.

Strategies that decrease postprandial glucose excursions, including digestive enzyme inhibition, and low glycemic index diets result in lower diabetes incidence and coronary heart disease (CHD) risk, possibly through lower postprandial oxidative damage to lipids and proteins. We therefore assessed the effect of decreasing postprandial glucose excursions on measures of oxidative damage. Fifteen healthy subjects ate 2 bread control meals and 3 test meals: almonds and bread; parboiled rice; and instant mashed potatoes, balanced in carbohydrate, fat, and protein, using butter and cheese. We obtained blood samples at baseline and for 4 h postprandially. Glycemic indices for the rice (38 +/- 6) and almond meals (55 +/- 7) were less than for the potato meal (94 +/- 11) (P < 0.003), as were the postprandial areas under the insulin concentration time curve (P < 0.001). No postmeal treatment differences were seen in total antioxidant capacity. However, the serum protein thiol concentration increased following the almond meal (15 +/- 14 mmol/L), indicating less oxidative protein damage, and decreased after the control bread, rice, and potato meals (-10 +/- 8 mmol/L), when data from these 3 meals were pooled (P = 0.021). The change in protein thiols was also negatively related to the postprandial incremental peak glucose (r = -0.29, n = 60 observations, P = 0.026) and peak insulin responses (r = -0.26, n = 60 observations, P = 0.046). Therefore, lowering postprandial glucose excursions may decrease the risk of oxidative damage to proteins. Almonds are likely to lower this risk by decreasing the glycemic excursion and by providing antioxidants. These actions may relate to mechanisms by which nuts are associated with a decreased risk of CHD.

Adult↗

PubMed2005

A novel xyloglucan from seeds of Afzelia africana Se. Pers.--extraction, characterization, and conformational properties.

This paper is the first multi-scale characterization of the xyloglucan extracted from seeds of the African tree Afzelia africana Se. Pers. It describes the extraction and characterization of this polysaccharide in terms of both primary monosaccharide and oligosaccharide composition. It also includes a study of the seed morphology. Morphological characterization includes optical, transmission, and scanning electron microscopy. The polysaccharide exists in thickened cell walls of the cotyledonary cells, and the extracted xyloglucan is structurally quite similar to those from tamarind seed and detarium. Nevertheless there are some subtle differences in the fine structure, particularly in the oligomeric xyloglucan composition. The chain flexibility of the polysaccharide is also discussed in the light of our recent measurements reported elsewhere [Biomacromolecules2004, 5, 2384-2391].

Carbohydrate Conformation↗

PubMed2004

Role of cell walls in the bioaccessibility of lipids in almond seeds.

BACKGROUND: Certain nutrients and phytochemicals in almonds may confer protection against cardiovascular disease, but little is known about factors that influence their bioavailability. A crucial and relevant aspect is the amount of these dietary components available for absorption in the intestine, which is a concept referred to as bioaccessibility. OBJECTIVE: We investigated the role played by cell walls in influencing the bioaccessibility of intracellular lipid from almond seeds. DESIGN: Quantitative analyses of nonstarch polysaccharides (NSPs) and phenolic compounds of cell walls were performed by gas-liquid chromatography and HPLC, respectively. In a series of experiments, the effects of mechanical disruption, chewing, and digestion on almond seed microstructure and intracellular lipid release were determined. In the digestibility study, fecal samples were collected from healthy subjects who had consumed diets with or without almonds. Almond seeds and fecal samples were examined by microscopy to identify cell walls and intracellular lipid. RESULTS: Cell walls were found to be rich in NSPs, particularly arabinose-rich polysaccharides, with a high concentration of phenolic compounds detected in the seed coat cell wall. During disruption of almond tissue by mechanical methods or chewing, only the first layer of cells at the fractured surface was ruptured and able to release lipid. In fecal samples collected from subjects consuming the almond diet, we observed intact cotyledonary cells, in which the cell walls encapsulated intracellular lipid. This lipid appeared susceptible to colonic fermentation once the cotyledonary cell walls were breached by bacterial degradation. CONCLUSION: The cell walls of almond seeds reduce lipid bioaccessibility by hindering the release of lipid available for digestion.

Adult↗

PubMed2002

The effect of guar galactomannan and water availability during hydrothermal processing on the hydrolysis of starch catalysed by pancreatic alpha-amylase.

The effects of water-soluble nonstarch polysaccharides (sNSP) on human metabolism are considered to be beneficial because they decrease postprandial glycaemia and insulinaemia following ingestion of starch-rich foods. The mechanisms by which sNSP attenuate the postprandial rise in blood glucose are not well understood but their presence increases the viscosity of gastrointestinal contents, which affects physiological functions, e.g. gastric emptying and peristalsis. Increased viscosity and decreased water activity during hydrothermal treatment of starch could influence alpha-amylase action. Using guar galactomannan as a representative of sNSP, we found that galactomannan has a direct noncompetitive inhibitory effect on alpha-amylase with a K(i) value of approximately 0.5% (3.3 microM). The inhibition is not time dependent and studies suggest direct binding of the enzyme to galactomannan; the resulting galactomannan-amylase complex being inactive. Processing of starch at low water levels greatly affects the catalytic efficiency of alpha-amylase. The Km value for starch heat treated in limited water is raised and kcat is lowered relative to starch gelatinised in excess water. Since galactomannan has no effect on the Km of alpha-amylase, we conclude that the inhibitory action of the polymer is not secondary to a decrease in available water. Neither does it seem to be a consequence of impaired diffusion of enzyme, substrate and products because of an increase in viscosity of the medium.Thus, the effects of sNSP in lowering postprandial glycaemia not only involve modifications of gut physiology, but also include direct inhibition of the first stage in the biochemical degradation of starch.

Amylose↗

PubMedDate not supplied

Solution properties of the xyloglucan polymer from Afzelia africana.

In this paper we describe the solution properties of a new xyloglucan polysaccharide extracted from the African legume Afzelia africana Se. Pers. The polysaccharide is of high weight-average molecular weight (Mw), but application of the "pressure cell" method enabled a range of Mw fractions to be prepared. Results from the light scattering/intrinsic viscosity measurements on these fractions suggest that like other xyloglucans from tamarind and detarium it occurs in solution as a polymeric coil, with a small amount of excluded volume. Measurement of dilute and semidilute solution rheology suggests that, like these polymers, and the related galactomannan series, it forms viscous solutions at higher concentrations via entanglements.

Biocompatible Materials↗