Paul Cairns

Physicochemical studies using amylose as an in vitro model for resistant starch

Abstract The effects of hydrolysing amylose gels and films with porcine pancreatic alpha -amylase were studied in order to construct an in vitro model of resistant starch. Both gels and films proved to be partially resistant to hydrolysis, their susceptibility decreasing with increasing substrate concentration. Storage of gels for 1 day resulted in levels of crystallinity from 6 to 12%. Hydrolysis of these gels produced significant increases (from 272 to 557%) in crystallinity in all cases. The amount of resistant material remaining after hydrolysis increased (from 33% to 50%) with increasing gel concentration. Storage of amylose gels for 7 days resulted in levels of crystallinity of 28 to 35%. Hydrolysis of these gels led to increases in crystallinity, but to a lesser extent (from 148 to 175%) than before. The amount of resistant material remaining after hydrolysis increased (from 41 to 50%) with increasing gel concentration. Size-exclusion chromatography of resistant material from hydrolysed films indicated the presence of a high molecular weight component corresponding to undigested amylose, in addition to a low molecular weight component corresponding to partially digested amylose. Chromatograms of resistant material from both gels stored for 1 day and those stored for 7 days were almost identical and contained only a low molecular weight component with no sign of undigested amylose. X-ray line-broadening analysis showed the average sizes of the crystallites in the resistant material produced by hydrolysis of gels stored for both 1 day and 7 days to be approximately equal. The ability of the enzyme to diffuse into its substrate played a major part in the resistance to hydrolysis of amylose films, but had a much less important role in the resistance of gels. Not only crystalline, but also amorphous portions of amylose gels, were found to be resistant to enzymic hydrolysis. The resistant portion of amylose gels was modelled in vitro with a view to explaining the structure of resistant starch in vivo .

Physical Properties of Extruded Wheat Starch-Additive Mixtures

ABSTRACT The effects of the addition of fatty acids, monoglycerides (MG), and wheat germ oil (WGO) on the level of crystallinity and the crystalline structure of extrusion-cooked wheat starch have been studied using twin-screw extruders. Measurements of water solubility and water absorption indices were made on the extrudates, together with specific mechanical energy (SME) consumption and die pressure for the extruder. MG and the fatty acids added to a level of 4% caused an increase in Vhydrate type crystallinity. WGO addition to a level of 8% caused no change in crystallinity, although the Ehydrate type was favored at lower moisture contents. All additives caused a decrease in SME and an increase or maximum in die pressure. WGO behaved differently than MG and fatty acids in that its addition caused the water solubility index and expansion to increase, as previously observed for other oils added to flours.

CRYSTALLINITY OF LYOPHILISED CARROT CELL WALL COMPONENTS

The aim of this work was to investigate the effect of removal of cell wall components on the crystallinity of cell walls using X-ray diffraction. Various insoluble cell wall residues were prepared following a sequential extraction of carrot cell wall material. X-ray diffraction patterns were typical of cellulose although there was a possible contribution of pectic polysaccharides to the crystallinity. As more amorphous material was removed to produce a cellulose rich residue, the crystallinity index increased from 12 to 16%, larger than that estimated from cellulose alone. For the last residue treated with 4M KOH, a lower value of crystallinity was found (14%) which resulted from the change of some crystalline domains of cellulose into amorphous regions. Pressing conditions (temperature, water content) have been investigated and did not alter the crystallinity index significantly.

Evidence for intermolecular binding between deacetylated acetan and the glucomannan konjac mannan

Binary mixtures of deacetylated acetan and konjac mannan form thermoreversible gels under conditions for which the individual components do not gel. Such synergistic behaviour is normally attributed to intermolecular binding between the two polysaccharides. X-ray diffraction data obtained from oriented fibres prepared from deacetylated acetan-konjac mannan gels provides direct evidence for intermolecular binding between the two polysaccharides. The novel heterotypic junction zones appear to be six-fold helices with a pitch of 5.6 +/- 0.1 nm.

Physicochemical Characterization of Barley Carbohydrates Resistant to Digestion in a Human Ileostomate

ABSTRACT Physicochemical techniques, monosaccharide, and linkage analysis, have been used to investigate the digestibility of different forms of cooked barley starch in an ileostomist model. An ileostomate volunteer consumed a flapjack-type biscuit containing either barley flake, flour, or starch. Both starch and mucin were identified in the effluent and were found to make a significant contribution to the potentially fermentable substrate available to the large intestine. Chemical analysis of the effluents showed that the content of resistant starch in the effluent varied with presence and form of nonstarch polysaccharide and after consumption of barley flake and flour was 10.1 and 5.9% of the starch ingested, respectively. Wide-angle X-ray diffraction showed the excreted starch to be A-type only, indicating that the starch consumed in all three flapjack types was ungelatinized. These data demonstrate the potential of physicochemical techniques in the analysis of physiological samples.

Physicochemical characterization of an acetan variant secreted by Acetobacter xylinum strain CR1/4

Chemical mutagenesis has been used to produce mutants of Acetobacter xylinum NRRL B42 that are cellulose-negative and that produce variants of the acetan structure deficient in the side-chain sugar residues. The product of A. xylinum strain CR1/4 has been shown to possess a tetrasaccharide repeat unit with the side chain terminating in glucuronic acid. X-ray diffraction studies of oriented fibres suggest that the polysaccharide CR1/4 forms a fivefold helix with a pitch of 4.8 nm. Light-scattering studies on CR1/4 solutions suggest a molecular weight of 1.2 x 10(6) with radii of gyration values of 86 nm (aqueous solution) and 67 nm (0.1 M NaCl solution). The magnitude of the measured radii of gyration and the shape of the Holtzer plots suggest that CR1/4 can be described as a stiff coil. Preliminary differential scanning calorimetry data show melting behaviour consistent with order-disorder transitions of a charged helical structure. Rheological studies have revealed new synergistic interactions of CR1/4 with locust bean gum. Comparative studies of acetan and CR1/4 show that decreasing the length of the side chain enhances the solution viscosity.

Observations on the crystallization and melting of maltopentaose hydrate

Abstract The crystallization of maltopentaose from concentrated aqueous mixtures was studied by differential scanning calorimetry, X-ray diffraction and polarised light microscopy. Under the conditions of study it was observed that maltopentaose crystallized as a hydrate, with single crystals assembling into spherulitic structures. The crystalline hydrate melted at 78 °C with an enthalpy of fusion of 53 Jg−1.

Observations on the crystallization of oligogalacturonates.

Oligogalacturonates were produced by the limited enzymic hydrolysis of polygalacturonic acid and purified by ion-exchange chromatography. The fractions obtained were of limited polydispersity, determined by analytical ion-exchange chromatography. Oligomers with an average degree of polymerization of 10-15 were readily crystallized from aqueous salt solutions at neutral pH as single crystals. Crystal morphology of the salts examined, Na+, K+ and Ca2+ were characteristic of the salt. The wide-angle X-ray diffraction patterns obtained for the sodium salt were consistent with published fibre diffraction data of this salt form.