Gordon G. Birch

Studies on the physicochemical properties of inulin and inulin oligomers

Abstract Inulin, Raftiline® ST, Raftilose® P and oligofructose in aqueous solutions were investigated at 2.5, 5, 10, 15, 17.5, 20 and 25 g of solute in 100 g of water by physicochemical measurements in order to obtain molecular weights, reducing activities, apparent specific volumes, isentropic apparent specific compressibilities, and 1 H-NMR pulse relaxation times ( T 1 values). Molecular weights have been found to range from 340 to 4620 g mol −1 . Raftilose® P is the only sample which shows reducing capacity and may be expected to be susceptible to the Maillard reaction. Apparent specific volumes lie within the sweet range 0.60–0.64 cm 3 g −1 and increase with degree of polymerisation (DP); this behaviour describes increasing displacement of water as molecular weight increases. Isentropic apparent specific compressibilities increase as concentration of solute, molecular weight and DP increase, showing reduced solute–water affinity. T 1 values decrease with increasing molecular weight and concentration as a result of increased order of protons and reduced water mobility.

Characterisation of chlorogenic acids by simultaneous isomerisation and transesterification with tetramethylammonium hydroxide

The use of tetramethylammonium hydroxide at room temperature is reported for the simple characterisation of trace amounts of chlorogenic acids belonging to the caffeoyl, p-coumaroyl, feruloyl and dicaffeoylquinic acid subgroups. The assignments proposed have been confirmed by conventional proton NMR.

Solution properties of ethanol in water

The packing propensity of ethanol in aqueous solution is very unusual, yet ethanol finds extensive use both in the food and the pharmaceutical industry. An analysis of the solution properties of increasing concentrations of ethanol in water at 20° and 37°C reveals valuable information about its packing characteristics. Apparent molar and specific volumes provide information about the interaction of ethanol with surrounding water structure. Isentropic apparent molar and specific compressibilities indicate the extent to which the hydration layer around the ethanol molecules can be compressed. Compressibility hydration numbers show the number of water molecules that are displaced by the introduction of the ethanol to water. The enhanced packing efficiency of ethanol in water at low concentrations, is affected by the formation of cage-like structures around the hydrophobic end of the molecule. At high concentrations, however, linear chains or rings of ethanol molecules are formed which change its mode of packing within the three-dimensional structure of water. These effects may be used to help explain the mechanism of action of ethanol in food, pharmaceutical and other applications.

Characterisation of caffeoylferuloylquinic acids by simultaneous isomerisation and transesterification with tetramethylammonium hydroxide

Abstract It is suggested that green robusta coffee beans contain at least three, and possibly up to six, caffeoylferuloylquinic acid isomers (CFQA). This suggestion is based upon the action of tetramethylammonium hydroxide (TMAH) upon the putative CFQA. The deduced structural assignments are not in complete agreement with previously published data, particularly recent data obtained by proton NMR. These apparently conflicting interpretations are critically discussed, and an explanation therefore, is proffered.

Solute-solvent interactions and the sweet taste of small carbohydrates. Part II: Sweetness intensity and persistence in ethanol-water mixtures

Abstract Intensity and persistence of sweet taste of sugars (glucose, fructose, xylose and sucrose) and polyols (sorbitol, xylitol) were determined in ethanol-water mixtures using a sensory measuring unit for recording flux (SMURF) device. In all cases sweetness intensity and persistence were decreased when ethanol concentration was increased from 10% to 30%. Assessing intensity/time responses for varied (from 2.3% to 9.2%, w/v) concentrations of d -glucose, d -fructose and sucrose in 5% ethanol mixture shows that persistence is more affected by the presence of ethanol than intensity. These results are interpreted by the solution properties in the ethanol-water binary solvent.

The metabolism of maltitol in the rat

Conventional (CV) rats were given a single oral dose of 1 or 2 g maltitol. Urine and faeces were collected during the following 24 h and their contents of maltitol and sorbitol were measured. 2. Very little of either substance appeared in the faeces but appreciable amounts of sorbitol found in the urine indicated that the maltitol had been hydrolysed. 3. Excretion of maltitol and sorbitol was compared in germ-free and CV rats given an oral dose of 2 g maltitol. Significantly less of both substances was recovered in the faeces of CV rats, but urinary excretion was similar in both environments. 4. Maltitol injected intravenously gave rise to only traces of sorbitol in the excreta. A dose of 250 mg was cleared almost completely from the circulation within 1 h. 5. It is concluded that maltitol is hydrolysed by animal tissues, either in the gut lumen before absorption or in the gut wall during absorption. Maltitol and sorbitol are also degraded by gut bacteria, mostly in sites distal to the main absorptive area. The contribution to the hosts nutrition would depend on the extent to which the end-products of fermentation are absorbed from the colon.

Specific volumes and sweet taste

Partial molar and specific volumes are now well-known parameters in assessing drug potency in general and have recently been explored in sweet taste chemoreception. At natural tasting concentrations the apparent specific volume seems to be the most useful index of taste with 0.51–0.71 cm3 g−1 defining sweet taste quality. Most sugars are in the range 0.60–0.63 cm3 g−1. Apparent specific volumes of sweet molecules correlate well with other volume parameters such as intrinsic viscosity, partial molar compressibility and theoretical molecular volume calculations. Fragments of sugar molecules contribute differently to overall volume. Lowering of molecular weight by removal of an oxygen atom or larger fragments from a sugar molecule may actually elevate specific volume by diminishing hydrogen bonding. The positional contributions of substituents around sugar rings to overall volume allow orientational comparisons to be made, and examples of these effects in multisapophoric molecules and L-sugars are illustrated. The interaction of a tastant molecule with water causes physical changes which may or may not give rise to a change in gustatory quality over the course of time. Detailed studies of specific volumes will therefore contribute to the understanding of the role of water in sweet taste chemoreception. However, differences in taste (if any) between enantiomers cannot be explained by differences in hydration.

Interaction of d-glucono-1,5-lactone with water

Abstract Some studies of the interconversion of d -glucono-1,5-lactone, d -gluconic acid and d -glucono-1,4-lactone have been undertaken. High-performance liquid chromatography on reversed-phase supports was successfully used to resolve these components in water solution. There are no interactions between the 1,5-lactone and gluconic acid manifested as optical rotation effects. The course of hydrolysis of d -glucono-1,5-lactone, as measured by optical rotation is corroborated by the hplc data. The 1,4-lactone is predictably more stable than the 1,5-lactone and rate constants for the hydrolysis of the 1,5-lactone, and the lactonisation of d -gluconic acid were determined in d -gluconic acid solution which had a constant pH of 2·4. At 20°C the rate constants were found to be 1·730 × 10 −4 s −1 and 3·807 × 10 −5 s −1 , respectively. The specific rotation of d -gluconic acid was affected by the presence of inorganic ions; its value in the absence of interfering ions was determined to be −5·11° (c, 4·5, 20°C, water).

A study of the solution properties of selected binary mixtures of bulk and intense sweeteners in relation to their psychophysical characteristics

The solution properties of binary mixtures of two bulk sweeteners (sucrose and maltitol) and three intense sweeteners (acesulfame K, aspartame and sodium cyclamate) were studied. The parameters measured were apparent specific volumes, isentropic compressibilities and compressibility hydration numbers. An attempt has been made to correlate the solution properties of some of the mixtures with their sweetness responses. Both specific volume and isentropic compressibility data have been used to interpret the possibility of synergism or suppression in the mixtures in terms of the affinity of the solutes for the surrounding solvent structure, and hence the effectiveness of transport of the molecules to their appropriate receptor sites. However, an understanding of the nature and stereochemistry of the individual components in the mixtures is necessary for predicting the packing characteristics of molecules in water and their accession to receptor sites. The intense sweeteners seem to play an important role in modifying the structure of water in solution. Although there is no clear proof of how this affects perception, fine differences in solution behaviour can be observed with isentropic apparent specific compressibility measurements. The study supports the idea that receptors lie at different depths in the lingual epithelium, and also that in two-component systems, one species may alter the packing efficiency of the other in solution sufficiently to effect a change in taste quality or intensity.

Identification of proton type in concentrated sweet solutions by pulsed NMR analysis

The spin-spin proton relaxation times T2 of concentrated sucrose, maltose,D-glucose andL-proline solutions were determined using a Bruker Minispec NMR Spectrometer. Log spin echo amplitude decay curves were also determined and their non-linear nature allowed the proportions of different proton types to be calculated. These were in agreement with the theoretical proportions of ring (non-exchangeable protons), solute hydroxyl protons and water protons in the simple sugar molecules. A deuteration experiment confirmed that only non-exchangeable ring protons remained.