David Oakenfull - Academia.edu (original) (raw)

Papers by David Oakenfull

Nutrition reports international, 1984

Gida the Journal of Food, 1991

Yulafin kanin kolesterolunu azalttigi en az ceyrek yuzyildan beri bilinmektedir. Bu etki, ilk ola... more Yulafin kanin kolesterolunu azalttigi en az ceyrek yuzyildan beri bilinmektedir. Bu etki, ilk olarak GROOT ve arkadaslari tarafindan 1963’ de soz konusu edilmistir. Bundan sonra, insan ve hayvan denekleri kullanilarak yulaf ve yulaf urunleri ile beslenme denemeleri yapilmistir. Gunumuzde, yulaf ve yulaf kepegi konusuna duyulan ilgi uzerine bu calisma, yulaflarin kanin kolesterol miktarini dusurdugunu gostermek amaciyla yapilmistir. Bu konudaki gorusler dogrulanmis midir? Yulaf ve yulaf kepeginin kanin kolesterolunu dusurdugu konusundaki gorus kuvvetli ve inandiricidir. Buna karsin, yulaf kepegi oldukca degisken bir maddedir ve insanlara yararli olmasi icin alinmasi gereken gunluk miktari yuksek oldugundan, belki de insanlardan cok atlar icin uygundur.

The Chemistry and Technology of Pectin, 1991

Australian Journal of Chemistry, 1973

We report measurements of the equivalent conductance (Λ) of aqueous solutions of a series of decy... more We report measurements of the equivalent conductance (Λ) of aqueous solutions of a series of decyl- and hexadecyl-trimethylammonium carboxylates (acetate to undecanoate). In the decyl series, measurements were made on both sides of the critical micelle concentration (CMC). The CMC decreased when the hydrocarbon chain length of the carboxylate ion increased. In the hexadecyl series, measurements were confined to micellar solutions. �� The results obtained below the CMC suggest that hydrophobic interaction between the hydrocarbon chains of decyltrimethylammonium undecanoate, decanoate, and nonanoate leads to the formation of ion- pairs. There was no evidence, however, for formation of ion-pairs by the shorter carboxylates. �� By assuming that micellar ions obey the Onsager equation, we have derived a theoretical relationship between Λ and concentration above the CMC. An excellent fit of theoretical curve to experimental points can be obtained by adjusting the value of a single param...

Australian Journal of Chemistry, 1977

In the mixed solvent, 0.1 mole fraction ethanol-water, long-chain decyltrimethylammonium carboxyl... more In the mixed solvent, 0.1 mole fraction ethanol-water, long-chain decyltrimethylammonium carboxylates form ion pairs. Ion-pair association constants (and hence the free energy of ion-pair formation) can be measured conductometrically. It is possible to separate the hydrophobic from the electrostatic contribution to the free energy of ion-pair formation by systematically varying the hydrocarbon chain length. We report measurements of the free energy of hydrophobic interaction (AG&) over the temperature range 278-328 K. The value of AG& becomes more negative (stronger hydrophobic interaction) with increasing temperature. The temperature coefficient of AG& was used to calculate the enthalpy (AH,",) and entropy (AS&) of hydrophobic interaction. At low temperature the entropic contribution to the free energy is the larger but AH,", dominates at temperatures above c. 324 K. The volume change of hydrophobic interaction was similarly estimated from the volume change of ion-pair formation. We obtained values of apparent molar volume of the decyltrimethylammonium carboxylates (over a range of concentrations) from very precise density measurements. These could then be combined with the appropriate ion-pair association constant (from the conductance measurements) to give the partial molar volumes of the free ions and the ion pair. Hydrophobic interaction was found to be accompanied by a substantial increase in volume amounting to 10.2 + 0.3 ml mol-' for each pair of interacting methylene groups. Our results support the view that hydrophobic interaction occurs with a further ordering of water molecules over and above that which exists in the hydrophobic hydration layer surrounding an isolated hydrophobic molecule.

Australian Journal of Chemistry, 1974

With the general aim of elucidating the role of water structure in the kinetics of hydrolysis, a ... more With the general aim of elucidating the role of water structure in the kinetics of hydrolysis, a comparative study has been made of the kinetics of the hydrolysis of acetic anhydride and the reaction of 4-nitrophenyl acetate with imidazole in mixtures of water with ethanol, t-butyl alcohol, dimethyl sulphoxide and dioxan. Both rate constants were always reduced by the addition of organic solvent. Transition state activity coefficients were measured for both reactions in dimethyl sulphoxide-water mixtures and compared with the activity coefficient of phenylalanine (a model zwitterionic transition state). Activation parameters were measured for the hydrolysis of aceticanhydride in t-butyl alcohol-water and dimethyl sulphoxide-water mixtures. Semilogarithmic plots of rate constant against Winstein's Y-value were non-linear for some of the solvents and this fact, coupled with the effect of dimethyl sulphoxide on the transition state activity coefficients, leads to the conclusion tha...

Australian Journal of Chemistry, 1971

The kinetics of the hydrolysis of acetic anhydride have been investigated in concentrated salt so... more The kinetics of the hydrolysis of acetic anhydride have been investigated in concentrated salt solutions at 20�. Sine salts were used in concentrations of up to 5 mol 1-1; all inhibited the reaction. �� The salt effect was resolved into its component effects on the reactants and the transition state by use of the Bronsted-Bjerrum equation to calculate transition state activity coefficients from rate constants and measured activity coefficients of acetic anhydride. The effect of a salt on the free energy of the reactants was always significant and in some cases it was the major component of the effect of the salt on the free energy of activation. The enthalpy and entropy of transfer from water to 1 mol l-1 sodium chloride, for both acetic anhydride and the transition state, show the enthalpy-entropy compensation effect which is typical of aqueous solutions. �� These salt effects are considered to be part of the general phenomenon of the effect of salts on the activity coefficients ...

British Journal of Nutrition, 1986

1. Saponins are steroid or triterpene glycosides which occur in a number of important food plants... more 1. Saponins are steroid or triterpene glycosides which occur in a number of important food plants, including such staples as soya beans (Glycine max) and chickpeas (Cicer arietinurn). They are known to be hypocholesterolaemic.2. Some saponins form an insoluble complex with cholesterol which prevents its absorption from the small intestine. Others cause an increase in the faecal excretion of bile acids, an indirect route for elimination of cholesterol.3. We have investigated the effects of different saponins on absorption of the bile salt sodium cholate from perfused loops of small intestine, in vivo, in the rat. Purified saponins from soapwort (Suponaria Officinalis), soya beans and quillaia (Quillata suponaria) reduced the rate of absorption of the bile salt; soya-bean and soapwort saponins substantially so but quillaia saponin to a much lesser extent.4. These results were explained by the formation of large mixed micelles by bile acid and saponin molecules in aqueous solution. The...

British Journal of Nutrition, 1979

1. The effects of feeding isolated saponins on plasma lipid concentrations and on concentrations ... more 1. The effects of feeding isolated saponins on plasma lipid concentrations and on concentrations of biliary and faecal bile acids and neutral sterols were studied in the rat.2. The animals were given one of four diets, i.e. a standard low-cholesterol synthetic diet, the diet+10 g saponins/kg, the diet+10 g cholesterol/kg, the diet+10 g cholesterol+10 g saponins/kg.3. Saponins partially reversed the hypercholesterolaemia caused by the high-cholesterol diet and increased both the rate of bile acid secretion and the faecal excretion of bile acids and neutral sterols. The proportionate contribution of the primary bile acids (particularly chenodeoxycholic) to faecal excretion was also increased by saponins.4. The results are discussed in relation to the hypothesis that saponins act by inducing the adsorption of bile acids by dietary fibre.

CRC Handbook of Dietary Fiber in Human Nutrition, Third Edition, 2001

European journal of clinical nutrition, 1990

Body mass index (BMI) is used widely as an index of fatness (the proportion of the body as fat) b... more Body mass index (BMI) is used widely as an index of fatness (the proportion of the body as fat) but its application to the low weight and stature populations in developing countries has not been established. As BMI is an indicator of size (the amounts of fat and fat free masses) as well as fatness, its relation to fatness and interpretation as a measure of energy stores may vary in different groups. Very low BMI reflects low fat and fat free mass, a state for greater concern than low fat mass alone, and possibly more typical of chronic energy deficiency.

Food technology, 1995

... Mots-clés espagnols / Spanish Keywords. Glúcido. ; Propiedad rheológica. ; Tratamiento térmic... more ... Mots-clés espagnols / Spanish Keywords. Glúcido. ; Propiedad rheológica. ; Tratamiento térmico. ; Análisis calorimétrico barrido exploración. ; Agarosa. ; Carragenano. ; Gelificante. ; Transición sol gel. ; Transición fase. ; Gelificación. ; Aditivo alimentario. ; Propiedad fisicoquímica ...

Food Proteins and their Applications

Hydrocolloids, 2000

Publisher Summary It explains gelation and thickening of dairy products one of the most important... more Publisher Summary It explains gelation and thickening of dairy products one of the most important food applications of the carrageenans, particularly /κ-carrageenan. Low-methoxy (LM) pectins also form gels with milk and these too have food applications—mainly in dairy desserts. Rheometry and differential scanning calorimetry (DSC) are used to study the mixed gels formed with skimmed milk powder (SMP) and /κ-carrageenan and LM pectin. The results indicate very different gelation mechanisms for the two polysaccharides. /κ-carrageenan forms a complex with casein micelles and it appears to act as a molecular 'Velcro' - interaction between free ends of bound /κ-carrageenan molecules linking casein micelles to form a gel network. At high ratios of /κ-carrageenan to SMP, a purely /κ-carrageenan network also appears to form, presumably consisting of more extended cross-linked /κ-carrageenan structures within which the casein micelles are enmeshed. In contrast, there is no direct interaction between casein micelles and LM pectin. The casein appears simply to act as a source of calcium-ions which promote gelation of the pectin.

Gums and Stabilisers for the Food Industry 11, 2002

Food Hydrocolloids, 1999

Mixed gels, formed by k-carrageenan, and sodium caseinate were studied by differential scanning c... more Mixed gels, formed by k-carrageenan, and sodium caseinate were studied by differential scanning calorimetry (DSC) and rheometry. DSC showed that during gelation (i.e. cooling) the thermal behaviour of k-carrageenan was almost uninfluenced by the presence of sodium caseinate. Thus the interaction of k-carrageenan with sodium caseinate has little (or no) effect on the carrageenan's coil-to-helix transition. In contrast, during melting, added sodium caseinate strongly modified the thermal behaviour. The DSC peak became progressively broader with addition of sodium caseinate, indicating that the junction zones are highly heterogeneous in the mixed gel. Rheometry showed that sodium caseinate strongly influences the storage modulus (G H). In experiments in which the concentration of sodium caseinate was fixed and that of k-carrageenan varied, plots of G H vs. concentration of k-carrageenan were biphasic, with an abrupt change in slope at a concentration that increased linearly with the concentration of sodium caseinate. When the concentration of k-carrageenan was constant and that of sodium caseinate varied, G H as a function of concentration of sodium caseinate passed through a minimum. This behaviour could be modelled quantitatively, by assuming that: (a) the sodium caseinate adsorbs k-carrageenan, but with a limited adsorptive capacity; (b) sodium caseinate aggregates (sub-micelles) with adsorbed k-carrageenan can associate via interaction between free ends of adsorbed k-carrageenan chains and form a gel network; and (c) the contributions to G H from the sodium caseinate-k-carrageenan network and the network formed by kcarrageenan alone are additive. At low k-carrageenan to sodium caseinate ratios, the sodium caseinate and k-carrageenan combine to form a mixed gel. As the ratio of k-carrageenan to sodium caseinate increases, the sodium caseinate becomes saturated and no further association with k-carrageenan can occur-the increase in G H , as further k-carrageenan is added, comes from a gel network formed by k-carrageenan alone.

Handbook of Dietary Fiber