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Abstract
The swelling of tomato pectin and isolated tomato pericarp cell wall material was investigated in aqueous media under different ionic conditions, pH, and external osmotic stress. Conditions were chosen to include those that would be encountered in vivo. Swelling in these systems was strongly influenced by the polyelectrolyte nature of the polymer and the extent of cross-linking with divalent counterions.
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Affiliation(s)
- A J MacDougall
- Food Biopolymer Section, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, U.K.
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2
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Leong CW, Newton JM, Basit AW, Podczeck F, Cummings JH, Ring SG. The formation of colonic digestible films of amylose and ethylcellulose from aqueous dispersions at temperatures below 37 degrees C. Eur J Pharm Biopharm 2002; 54:291-7. [PMID: 12445559 DOI: 10.1016/s0939-6411(02)00121-2] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The film forming properties of a commercial aqueous ethylcellulose dispersion (Surelease) mixed with a range of ratios of an amylose/butanol complex in the presence of a range of concentrations of a plasticiser has been studied by measuring the minimum film forming temperature (MFFT). Contrary to what was to be anticipated from the literature, it was found that an additional 4% of the plasticiser (dibutyl sebacate), normally present in the standard formulation of the ethyl cellulose dispersion, was sufficient to lower the MFFT to allow the formation of films at 35 degrees C. This was confirmed by assessment of the glass transition temperature of free films prepared by casting and drying at 35 degrees C by the application of dynamic mechanical analysis. This technique also demonstrated that the ethylycellulose and the amylose were not miscible. The ability of faecal slurry to digest the films formed at low temperatures was confirmed by the use of a batch fermenter. The extent of digestion was directly related to the amylose content of the films, ensuring the potential to provide films, which could function as colon specific coatings.
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Affiliation(s)
- C W Leong
- School of Pharmacy, University of London, London, UK
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Craig ID, Parker R, Rigby NM, Cairns P, Ring SG. Maillard reaction kinetics in model preservation systems in the vicinity of the glass transition: experiment and theory. J Agric Food Chem 2001; 49:4706-4712. [PMID: 11600011 DOI: 10.1021/jf0100752] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
Rates of reactant consumption for the Maillard reaction between lysine and glucose were measured for a noncrystallizing trehalose-sucrose-water matrix in the glass transition region. At temperatures above the glass transition temperature (T(g)), the consumption rates showed Arrhenius temperature dependence with activation energies of 135 and 140 kJ mol(-1) for lysine and glucose, respectively. Finite reaction rates were observed for glassy samples that were faster than that of one of the nonglassy samples. A comparison of experimental results with predicted diffusion-controlled reaction rate constants indicated that the reaction was reaction-controlled at temperatures above T(g) and approached the diffusion-influenced regime in the glassy state. The needs for further research on reactant diffusivity, the theory of the orientation dependence of reactivity, and a detailed understanding of the reaction mechanism and kinetics were identified.
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Affiliation(s)
- I D Craig
- Food Materials Science Division, Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK
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6
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MacDougall AJ, Brett GM, Morris VJ, Rigby NM, Ridout MJ, Ring SG. The effect of peptide-pectin interactions on the gelation behaviour of a plant cell wall pectin. Carbohydr Res 2001; 335:115-26. [PMID: 11567642 DOI: 10.1016/s0008-6215(01)00221-x] [Citation(s) in RCA: 35] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The effect of basic peptides on the gelation of a pectin from the cell wall of tomato was examined through the determination of gel stiffness, and swelling behaviour of the gel in water. Poly-L-lysine, poly-L-arginine, and a synthetic peptide, designed to mimic a sequence of basic amino acids found in a plant cell wall extensin, act as crosslinking agents. Circular dichroism studies on the interaction of synthetic extensin peptides with sodium polygalacturonate demonstrated that a conformational change was induced as a result of their complexation. In addition to their effect as crosslinking agents, the polycationic peptides reduced the swelling of the pectin network in water.
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Affiliation(s)
- A J MacDougall
- Division of Food Materials Science, Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
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Needs PW, Rigby NM, Ring SG, MacDougall AJ. Specific degradation of pectins via a carbodiimide-mediated Lossen rearrangement of methyl esterified galacturonic acid residues. Carbohydr Res 2001; 333:47-58. [PMID: 11423110 DOI: 10.1016/s0008-6215(01)00120-3] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
A specific, chemical degradation of the methyl esterified galacturonic acid residues of pectins is described. These residues are converted, with hydroxylamine, to hydroxamic acids, and then, with a carbodiimide, to isoureas; the latter undergo a Lossen rearrangement on alkaline hydrolysis. The isocyanates formed are hydrolysed to 5-aminoarabinopyranose derivatives, which spontaneously ring open to give 1,5-dialdehydes. The latter are reduced, in situ, to avoid peeling reactions, with sodium borohydride to give substituted arabitol residues. Thus, overall, partially esterified pectins are specifically cleaved to generate a series of oligogalacturonic acids bearing an arabitol residue as aglycone. Analysis of oligomers so generated discloses the pattern of contiguous nonesterification in a variety of pectins of differing degrees of esterification. Other potential applications are described.
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Affiliation(s)
- P W Needs
- Nutrition, Health, and Consumer Science Division, Institute of Food Research, Norwich Research Park, Colney Lane, Norwich NR4 7UA, UK.
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Round AN, Rigby NM, MacDougall AJ, Ring SG, Morris VJ. Investigating the nature of branching in pectin by atomic force microscopy and carbohydrate analysis. Carbohydr Res 2001; 331:337-42. [PMID: 11383904 DOI: 10.1016/s0008-6215(01)00039-8] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Atomic force microscopy (AFM) has been used to investigate the nature of the long branches attached to pectin which were described in a previous report [Round, A. N.; MacDougall, A. J.; Ring, S. G.; Morris, V. J. Carbohydr. Res. 1997, 303, 251-253]. Analysis of the AFM images and comparison with neutral sugar and linkage analyses of the two pectin fractions suggest that the distribution and total amount of branches observed do not correspond with the pattern of neutral sugar distribution. It is thus postulated that the long chains consist of polygalacturonic acid, attached via an as yet undetermined linkage to the pectin backbone, with the neutral sugars present as short, undetected branches. This explanation would have important implications for the nature of 'in situ' pectin networks within plant cell walls and models of gelation in commercial extracted pectin, and the existence of significant branching will markedly influence the viscosity of extracted pectins.
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Affiliation(s)
- A N Round
- Institute of Food Research, Norwich Research Park, Colney, UK.
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9
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Abstract
The hydration and swelling of pectic polysaccharides was examined at different pHs and ionic strengths as a function of osmotic stress. For weakly charged pectic polysaccharides at low concentrations of a monovalent salt (20 mM), the main driving force for swelling originates from a polyelectrolyte effect due to the translational entropy of ions within the film. Swelling is reduced at higher salt concentrations and lower pHs. Polyelectrolyte collapse and minimal swelling is observed for more highly charged pectic polysaccharides. Replacement of the Na(+) counterion with Ca(2+) results in minimal swelling and the formation of network structures even for the weakly charged pectic polysaccharides.
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Affiliation(s)
- P Ryden
- Food Biopolymer Section, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
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Noel TR, Parker R, Ring SG. Effect of molecular structure and water content on the dielectric relaxation behaviour of amorphous low molecular weight carbohydrates above and below their glass transition. Carbohydr Res 2000; 329:839-45. [PMID: 11125826 DOI: 10.1016/s0008-6215(00)00227-5] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
The dielectric relaxation behaviour of several amorphous low molecular weight carbohydrates and their 10% w/w water mixtures has been studied in the supercooled liquid and glassy regions in the frequency range 100 Hz to 100 kHz. The dry carbohydrates show a primary alpha-relaxation (activation energy 250-405 kJ mol(-1)) at temperatures above the calorimetric glass transition temperature, Tg, and, in most cases, a secondary beta-relaxation (activation energy 42-55 kJ mol(-1)) at sub-Tg temperatures. Whilst D-mannose showed a beta-relaxation similar in strength to D-glucose, its deoxy sugar, L-rhamnose showed a relatively weak beta-relaxation. This indicates that the hydroxymethyl group influences relaxation in carbohydrate glasses. Addition of water shifted the alpha-relaxations to lower temperatures and increased the strength of the beta-relaxations. In glucitol this resulted in a merging of the alpha- and beta-relaxations. The beta-relaxation increased in strength and decreased in temperature for the series of water mixtures: D-glucose, maltose, and maltotriose.
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Affiliation(s)
- T R Noel
- Institute of Food Research, Food Materials Science Division, Colney, Norwich, UK
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11
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Gunning YM, Parker R, Ring SG. Diffusion of short chain alcohols from amorphous maltose-water mixtures above and below their glass transition temperature. Carbohydr Res 2000; 329:377-85. [PMID: 11117321 DOI: 10.1016/s0008-6215(00)00203-2] [Citation(s) in RCA: 41] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
The apparent diffusion coefficient for short chain alcohols in undercooled maltose-water mixtures close to the calorimetric glass transition temperature, Tg, was measured by following desorption using headspace gas chromatography. The plasticising effect of the alcohols on Tg was characterised using differential scanning calorimetry. The initial appearance of alcohol in the headspace showed a linear dependence on the square root of time, allowing it to be modelled as a Fickian diffusive process. The diffusion coefficient decreased with increasing molecular size of alcohol and proximity to Tg. Close to the glass transition the variation of diffusion coefficient with temperature and composition does not follow that of viscosity and, for ethanol, divergence was observed at Tg/T> 0.88.
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Affiliation(s)
- Y M Gunning
- Institute of Food Research, Food Materials Science Division, Norwich Research Park, Colney, UK
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12
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Abstract
The hydration and swelling of pectic polysaccharides was examined at different pHs and ionic strengths as a function of osmotic stress. For weakly charged pectic polysaccharides at low concentrations of a monovalent salt (20 mM), the main driving force for swelling originates from a polyelectrolyte effect due to the translational entropy of ions within the film. Swelling is reduced at higher salt concentrations and lower pHs. Polyelectrolyte collapse and minimal swelling is observed for more highly charged pectic polysaccharides. Replacement of the Na(+) counterion with Ca(2+) results in minimal swelling and the formation of network structures even for the weakly charged pectic polysaccharides.
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Affiliation(s)
- P Ryden
- Food Biopolymer Section, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich NR4 7UA, UK.
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13
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Abstract
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.
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Affiliation(s)
- N M Rigby
- Food Quality and Materials Science, Institute of Food Research, Norwich Laboratory, Colney, UK.
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Gunning YM, Parker R, Ring SG, Rigby NM, Wegg B, Blake A. Phase behavior and component partitioning in low water content amorphous carbohydrates and their potential impact on encapsulation of flavors. J Agric Food Chem 2000; 48:395-399. [PMID: 10691646 DOI: 10.1021/jf9904158] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The compositions at which amorphous ethanol-maltose-water mixtures exhibit liquid-liquid separation have been determined in the temperature range from 20 to 80 degrees C. At water contents below approximately 20% w/w two phases were observed, with the maltose-rich phase slightly richer in water. Partition coefficients of organic nonelectrolytes ranging in hydrophobicity from 1, 2-ethanediol and 1,2-propanediol to benzyl alcohol and propyl acetate have been measured for octanol/sorbitol, benzyl alcohol/sorbitol, and 1-butanol/sorbitol mixtures. Linear correlations were found between the log partition coefficients in the various solvent systems. Replacing water with sorbitol results in more organic partitioning into the octanol. Replacing octanol with benzyl alcohol or 1-butanol also results in more organic partitioning into the hydrophobic phase. The results establish a relationship with partition coefficients for octanol/water mixtures, which are well studied experimentally and for which predictive approaches exist. The implications of these results for flavor retention and encapsulation are discussed.
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Affiliation(s)
- Y M Gunning
- Food Materials Science Division, Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, United Kingdom
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15
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Gunning YM, Gunning PA, Kemsley EK, Parker R, Ring SG, Wilson RH, Blake A. Factors affecting the release of flavor encapsulated in carbohydrate matrixes. J Agric Food Chem 1999; 47:5198-5205. [PMID: 10606595 DOI: 10.1021/jf990039r] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The effects of water content and temperature variation on the release of flavor components into the headspace over flavors, encapsulated by an extrusion process, in low water content carbohydrate matrixes is studied. The largest amounts of release occurred when the matrix was above its glass transition temperature, whether this was due to increased water content or elevated temperature. Under these conditions up to 70% of the sucrose in the matrix crystallized over a period of 10 days, as quantified using Fourier transform Raman spectroscopy. Smaller amounts of headspace release occurred when the water content of the encapsulated flavor system was decreased from 3. 5 to 3.1% w/w. Small amounts of release occurred from the "as prepared" materials, which were associated with the presence of small amounts of unencapsulated flavor oil with direct access to the headspace. It was concluded that release due to matrix permeability was relatively slow as compared with the above mechanisms.
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Affiliation(s)
- Y M Gunning
- Food Quality and Materials Science, Institute of Food Research, Norwich Research Park, Colney, Norwich NR4 7UA, United Kingdom
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Femenia A, Selvendran RR, Ring SG, Robertson JA. Effects of heat treatment and dehydration on properties of cauliflower fiber. J Agric Food Chem 1999; 47:728-732. [PMID: 10563960 DOI: 10.1021/jf980462k] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/23/2023]
Abstract
The effects of heat treatment and dehydration on fiber structure and hydration properties, using cauliflower floret/curd and stem tissues, have been investigated. No major changes in fiber composition resulted from sample treatments, but the degree of esterification of pectic polysaccharides, approximately 60% in fresh cauliflower, decreased by approximately 12% in samples heated at temperatures >40 degrees C. Enzymic activity was considered to be responsible, through pectin methyl esterase activity. De-esterification was temperature and moisture sensitive. Hydration properties were also affected by processing conditions. The solubility of nonstarch polysaccharides in fresh, freeze-dried, and 40 degrees C dried samples was approximately 6% but increased to 12% in boiled samples and decreased in samples dried at 75 degrees C. Similar behavior occurred for swelling and water retention capacity (WRC), with swelling and WRC highest for boiled samples and lowest for samples dried at 75 degrees C. Hence, a decrease in de-esterification was not directly responsible for changes in hydration properties. The results demonstrate the importance of processing history on functional properties and on the preparation of fiber-rich ingredients for successful incorporation into foods.
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Affiliation(s)
- A Femenia
- Department of Biochemistry, Institute of Food Research, Norwich Research Park, Colney, United Kingdom
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Robertson JA, Majsak-Newman G, Ring SG. Release of mixed linkage (1-->3),(1-->4) beta-D-glucans from barley by protease activity and effects on ileal effluent. Int J Biol Macromol 1997; 21:57-60. [PMID: 9283016 DOI: 10.1016/s0141-8130(97)00041-x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The behaviour of barley beta-glucans in the upper gut has been assessed using ileal effluents recovered from a barley-based test meal. Results have been compared to in vitro treatments used to extract beta-glucans. In vitro, exposure to endogenous proteases led to a solubilisation of beta-glucan, ranging from 28% in the untreated to 83% following NSP isolation. In ileal effluent 60% of the beta-glucan was solubilised, similar to the in vitro treatment. However, the viscosity of the ileal effluent was low, comparable to a mucin standard. Although beta-glucan can be solubilised in the upper gut its viscosity would appear to have only a limited potential to affect nutrient bioavailability.
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Affiliation(s)
- J A Robertson
- Department of Biochemistry, Institute of Food Research, Norwich Research Park, Colney, UK
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19
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MacDougall AJ, Rigby NM, Ring SG. Phase Separation of Plant Cell Wall Polysaccharides and Its Implications for Cell Wall Assembly. Plant Physiol 1997; 114:353-362. [PMID: 12223708 PMCID: PMC158311 DOI: 10.1104/pp.114.1.353] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/18/2023]
Abstract
Concentrated binary mixtures of polymers in solution commonly exhibit immiscibility, resolving into two separate phases each of which is enriched in one polymer. The plant cell wall is a concentrated polymer assembly, and phase separation of the constituent polymers could make an important contribution to its structural organization and functional properties. However, to our knowledge, there have been no published reports of the phase behavior of cell wall polymers, and this phenomenon is not included in current cell wall models. We fractionated cell walls purified from the pericarp of unripe tomatoes (Lycopersicon esculentum) by extraction with cyclohexane diamine tetraacetic acid (CDTA), Na2CO3, and KOH and examined the behavior of concentrated mixtures. Several different combinations of fractions exhibited phase separation. Analysis of coexisting phases demonstrated the immiscibility of the esterified, relatively unbranched pectic polysaccharide extracted by CDTA and a highly branched, de-esterified pectic polysaccharide present in the 0.5 N KOH extract. Some evidence for phase separation of the CDTA extract and hemicellulosic polymers was also found. We believe that phase separation is likely to be a factor in the assembly of pectic polysaccharides in the cell wall and could, for example, provide the basis for explaining the formation of the middle lamella.
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Affiliation(s)
- A. J. MacDougall
- Department of Biochemistry, Institute of Food Research, Norwich Laboratory, Norwich Research Park, Colney, Norwich, NR4 7UA, United Kingdom
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Botham RL, Cairns P, Faulks RM, Livesey G, Morris VJ, Noel TR, Ring SG. Physicochemical Characterization of Barley Carbohydrates Resistant to Digestion in a Human Ileostomate. Cereal Chem 1997. [DOI: 10.1094/cchem.1997.74.1.29] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Affiliation(s)
- R. L. Botham
- Institute of Food Research, Norwich Research Park, Colney, Norwich, NR4 7UA, UK. Corresponding author. E-mail:
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21
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Abstract
The glass-transition behaviour of four hydrated wheat gluten proteins (alpha-gliadin, gamma-gliadin, omega-gliadin and high-molecular-weight (HMW) subunits of glutenin) was studied using differential scanning calorimetry (DSC). By fitting the data to the Gordon-Taylor equation, which has previously been used to describe the plasticization of polymers by diluents, the glass-transition temperatures (Tg) for the dry proteins were found by extrapolation. The values for Tg were within the range 397-418 K. Values for the heat capacity increment delta Cp at Tg for the plasticized proteins were also determined and ranged from 0.29-0.47 J g-1 K-1 with no dependence on water content. The differences in glass-transition behaviour of the proteins are discussed in relation to their secondary structure.
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Affiliation(s)
- T R Noel
- Institute of Food Research, Norwich Laboratory, Norwich Research Park, UK
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Affiliation(s)
- Y M Newman
- AFRC Institute of Food Research, Norwich, UK
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Williamson G, Belshaw NJ, Noel TR, Ring SG, Williamson MP. O-glycosylation and stability. Unfolding of glucoamylase induced by heat and guanidine hydrochloride. Eur J Biochem 1992; 207:661-70. [PMID: 1633817 DOI: 10.1111/j.1432-1033.1992.tb17093.x] [Citation(s) in RCA: 56] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
We have examined the stabilities of the catalytic and binding domains of glucoamylase 1 from Aspergillus niger and how these stabilities are affected by the O-glycosylated linker glycopeptide which separates the domains. On heating, the catalytic domain unfolds irreversibly, whereas the binding domain unfolds reversibly as shown by differential scanning calorimetry and by 1H NMR. The stability of three functional peptides, derived from glucoamylase 1, containing the binding domain alone and with 10 or 38 residues of the linker glycopeptide [Williamson, G., Belshaw, N.J. and Williamson, M. (1992) Biochem. J. 282, 423-428] was examined. Refolding in each case was reversible after thermal or chemical denaturation. beta-Cyclodextrin stabilised the binding domain by the same amount when it was part of glucoamylase 1 or an isolated domain. The thermal stability of the catalytic domain was not affected by the binding domain; however, the catalytic domain increased the melting temperature of the binding domain. Furthermore, the linker glycopeptide stabilised the binding domain against reversible thermal and chemical denaturation by about 10 kJ/mol, but only a portion of the O-glycosylated residues were required for stabilisation. On a simple molecular mass basis, the linker glycopeptide does not contribute as much as expected to the denaturational enthalpy of glucoamylase 1 and, in addition, shows only a small conformational change on chemical or thermal denaturation; this supports an extended structure for the linker. The results demonstrate that the unfolding pathway of glucoamylase 1 depends on the concentration of beta-cyclodextrin and that the presence of the catalytic domain and/or the linker glycopeptide stabilises the binding domain.
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Affiliation(s)
- G Williamson
- AFRC Institute of Food Research, Norwich Laboratory, Norwich Research Park, England
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Abstract
The melting behaviour of highly crystalline spherulites, of a short chain amylose DP-15 corresponding to both the A and B polymorphs of starch has been studied as a function of water content. At water contents greater than 40% w/w A-type spherulites melt at temperatures approximately 20 degrees C higher than B spherulites, whilst both crystal forms melt at lower temperatures in the presence of increasing amounts of water. Using the Flory-Huggins relationship for polymer crystal melting in the presence of a diluent, it is possible to predict a value for the ideal melting temperature of the dry crystals of 530 K.
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Affiliation(s)
- M A Whittam
- AFRC Institute of Food Research, Norwich, UK
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26
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Abstract
The glass transition temperature (Tg) values for carbohydrates alone and in binary mixtures have been determined using differential scanning calorimetry. The Tg of the carbohydrate depends strongly on molecular weight and less on structure. The Tg of the binary mixtures was dependent on composition and, in most instances, was linear with respect to mole fraction. The effect of water on depressing the Tg of the carbohydrates and their binary mixtures was also evaluated. The observed behaviour was compared with that predicted from a thermodynamic approach.
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Affiliation(s)
- P D Orford
- A.F.R.C. Institute of Food Research, Norwich Laboratory, Great Britain
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Whittam MA, Orford PD, Ring SG, Clark SA, Parker ML, Cairns P, Miles MJ. Aqueous dissolution of crystalline and amorphous amylose-alcohol complexes. Int J Biol Macromol 1989; 11:339-44. [PMID: 2489102 DOI: 10.1016/0141-8130(89)90005-6] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Complexes of amylose, the linear starch polysaccharide, with linear alcohols having chain lengths varying from 4 to 8 carbon atoms, were prepared. Either crystalline or amorphous complexes could be formed depending on preparation conditions. Crystalline complexes gave sharp X-ray diffraction patterns, characteristic of the VH form of amylose, whereas no observable pattern was obtained from the amorphous form. Thermal dissociation of the complexes occurred at increasing temperatures with increasing alcohol chain length. Crystalline complexes dissociated at temperatures approximately 23 degrees C higher than their amorphous counterparts and the enthalpy of dissociation was also greater for the crystalline samples. Enthalpy values were independent of alcohol chain length. Differences in thermal behaviour of the two types of complex may be described in terms of the polymer crystal lattice energy and may explain the variability of reported results for complex dissociation in the literature.
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Affiliation(s)
- M A Whittam
- AFRC Institute of Food Research, Norwich, UK
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28
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Orford PD, Parker R, Ring SG, Smith AC. Effect of water as a diluent on the glass transition behaviour of malto-oligosaccharides, amylose and amylopectin. Int J Biol Macromol 1989; 11:91-6. [PMID: 2489071 DOI: 10.1016/0141-8130(89)90048-2] [Citation(s) in RCA: 232] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
The glass transition behaviour of amorphous malto-oligomers from dimer to hexamer was investigated as a function of diluent (water) concentration using differential scanning calorimetry. The glass transition temperatures of the pure compounds ranged from 364 K for maltose to 448 K for maltohexaose. At low diluent concentrations the addition of water strongly depressed Tg. From the measurement of Tg and the heat capacity increment, delta Cp, of the transition for the pure compounds it was possible to predict the Tg of the malto-oligomer/water mixtures using a thermodynamic approach developed by Couchman. From the measurements on the malto-oligomers it was possible to obtain, by extrapolation, the high DP limits of delta Cp and Tg, which are appropriate to amylose and amylopectin. The predicted variation of Tg with diluent concentration for these materials was compared with the experimentally observed behaviour.
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Affiliation(s)
- P D Orford
- Institute of Food Research, Norwich Laboratory, UK
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