Dispersion of aroma compounds in food matrices is a common process in the production of many food products. However, the degrees of dispersion on the distribution and subsequent release of these compounds during consumption may have considerable consequences for perception of these flavours. This thesis investigates the effects of a range of dispersion techniques on the delivery and release of aroma compounds from several solid and semi-solid matrices which commonly contain added flavourings. Dispersion was achieved on three main scales ranging from molecular, through micro regions to physical separation or layering. The effects of different levels of mixing were assessed by measuring aroma release in vitro and in vivo via APci-MS. Having defined the stages of mixing, systems were developed to measure the influences of different dispersion techniques on aroma delivery. Layering to physically separate homogenous aroma-rich layers showed no significant effects on aroma release or perception from gelatine sucrose gels. It seems that mastication is very effective in re-mixing these systems and, in vivo there is no difference in aroma release. Although the degree of mixing could be controlled using a static mixer system for yoghurts, no effects of the different levels of mixing were observed on aroma release. Stirred yoghurts showed that mixing could influence equilibrium headspace concentrations but overall release in vivo was inconclusive. Sample selection in these systems may be important for influencing perception. Visual and textural cues may be more important for perception, in these mixing examples, than aroma release. Using co-solvents as dispersion agents significantly increased the ease of dispersion of a range of aroma compounds. Static headspace analysis confirmed that all the carrier solvents influenced the partition of aroma compounds and in vivo release from model confectionery systems. Increasing solvent concentration increased the solubility of a range of aroma compounds in the liquid phase. Release from gels was also influenced by the presence of solvents with hydrophobic aroma compounds showing patterns of release similar to those of hydrophilic compounds when dispersed using solvents. Finally, this work studied release from phase separated systems where the aroma compound was present as a microdroplet. Release was very intense and rapid and was investigated in aqueous solutions and gelatine-sucrose gels. In this case the release mechanism was not the conventional air-liquid partition but was based on direct release from the air-liquid interface. Release was dependent on both hydrophobicity and vapour pressure.

There is conflicting information on the mechanical properties and ageing kinetics of starch-water-glycerol systems. This makes understanding the changes occurring on storage of edible products difficult to predict. The work described in this thesis looks at model systems consisting of thermomechanically extruded plasticized starches (waxy maize, rice and wheat) and commercial products. The objectives of the work were to evaluate how the presence of polyols effects glass transition temperature (Tg), sorption isotherms, diffusion rates and texture parameters and to create models that could be used to predict behaviour. Very similar results were obtained for the starch samples except that monolayer (ma) values were higher for the waxy maize starch than for the wheat and rice. The waxy maize also was more brittle at equivalent moisture content when compared to the other two starches. Glycerol had a major impact on the water absorption. For RHs > 70% more water absorbed up by samples containing glycerol while the opposite occurred at RHs <60%. Monolayer values for GAB and BET confirmed this finding. The behaviour could be predicted if an interaction factor <1 was used in weight fraction models. Tg of the samples was measured by DSC and also by using predictive models, where the ten-Brinke Karas equation was found to give the best predictions. A value that was found to be most beneficial for the prediction of retrogradation was (storage temperature minus Tg). Change in texture was associate with (T-Tg), although the brittle ductile transition occurred 40°C below T-Tg=O. Diffusivity values increased with plasticizer level up to 8*10 3 m'z/s. There was an apparent fall in values when the samples were above Tg. However, it is suggested that this is due to sample geometry change rather than a change in diffusion mechanism. The Tg values also were found to be a good predictor of the type of change occurring in the model systems and food products during storage. Below Tg physical aging (enthalpy relaxtion) could be seen in the samples and retrogradation of the starch occurred above Tg. The rates of retrogradation were not affected by glycerol content directly and knowledge of Tg and storage temperature were sufficient to predict the retrogradation. Products became stiffer on storage and this was associated with molecular reassociation of the starchy component, but control of the moisture was also critical as water still dominated product behaviour even in the presence of glycerol.

The relationship between in vivo captured data from an atmospheric pressure chemical ionisation mass spectrometer (APCI-MS) and sensory/psychophysical analyses was investigated. The stimuli used were mainly single volatiles under gas phase control or calibration by development of different olfactometry methods. Gas phase concentration retronasal (via the mouth to the nasal cavity) and orthonasal (via the nostrils) thresholds were determined for a trained panel of 13 individuals. Four volatiles were used with different sensory/physico-chemical properties and an adapted staircase method was employed to measure the individual thresholds. The data showed good repeatability over short durations of one week and also longer ones of eight months. It was used to test the hypothesis that thresholds varied between people due to differences in their in-nose concentration as measured or estimated by the APCI-MS. The analysis did not support this theory but relationships between orthonasal and retronasal thresholds were shown, in which the latter were -50 times lower than the former. Threshold determination of a larger group of 20 individuals revealed clusters of individuals. Methods of producing square edged pulses of aroma compound in the gas phase were developed using a modified chromatograph autosampler with a gas flow of 5 mL. min 1 and pulse rate of 0.6 secs. A trained panel of 23 individuals performed two types of sensory test using pulsed and constant olfactometer outputs of isoamyl acetate. The original intention was to reveal whether pulsed odorants were perceived as the same as or different to constant concentration. Initial experiments yielded results that were difficult to interpret, although the nature of the results was clarified when simultaneous breath by breath analysis techniques were employed. Here it was shown that each individual in different repetitions disrupted the olfactometer output pattern in unpredictable ways. This pattern disruption was measured in two instrumental configurations, as either volatiles in an exhalation or volatiles as they were inhaled together with two types of sensory test. In both sensory tests the pattern of aromas in an inhalation revealed a relationship with perception. In particular, the sensory response in the time intensity study was related to differences in the inhalation profiles between people, which in turn was related to an individual's breathing. This shows that physiological differences such as breathing and the structure of the nasal cavity have an impact on perception.

The widespread use of non-meat protein in meat products necessitates a method for the robust, unequivocal quantification of meat in foods. Protein-bound levels of the co- or post-translationally modified amino acid, 3- methylhistidine, virtually unique to the myofibrillar proteins actin and myosin, have previously been proposed as such an index, determination being by high-performance liquid chromatography of acid stable fluorescamine derivatives. Although robust to the severest processing conditions, variations in the titres of 3-methylhistidine in certain manufacturing cuts have been reported. The present study has revealed that such variations can be attributed to the low level of 3-methylhistidine in the myosin of muscles high in "red" (oxidative) fibres, such as ruminant Masseter; constant levels of 3-methylhistidine being found in all actins investigated. Methods for the determination of actin-bound 3- methylhistidine have therefore been developed. Electrophoretic separation of actin with 3-methylhistidine determination of the resulting actin band was found to be only semi-quantitative. The isolation of actin by conventional SOS-gel filtration was time consuming and resulted in low yields of 3-methylhistidine. SDSgel filtration using the Pharrnacia fast protein liquid chromatography (FPLC) system, allowed rapid, reproducible and quantitative isolation of actin-bound 3-methlhistidine. Using too latter method, constant levels of actin-bound 3-methylhistidine have been found for all muscles investigated. A new unequivocal definition of "meat", is proposed as that which has an actinbound 3-methylhistidine content of 3mg/g non-connective tissue nitrogen. This is expected to be robust to all but the severest processing conditions. Such an index, based on connective tissue free units, requires the accurate determination of hydroxyproline, for which a sensitive method using gas chromatography-mass spectrometry has been developed. The use of an assumed average "factor" for the conversion of hydroxyproline to connective tissue appears valid, since the hydroxyproline contents of the connective tissue of all muscles investigated were similar.

A newly recruited sensory panel was trained in magnitude estimation and time intensity sensory techniques. Sensory analysis was combined with instrumental analysis using MS Nose to investigate the relationship between stimulus and perception using simple model food systems. Volatile release data was collected after swallowing aqueous solutions containing a cocktail of aroma compounds. The compounds varied in their persistence during subsequent exhalations dependent on the degree of association with the mucous lining of the throat. The rate of breathing had no effect on the shape or intensity of the release profile. The data was successfully modelled using the basic principles of interfacial mass transfer. The mechanistic model included some estimated parameters for un-measurable anatomical and physiological variables, kinetic properties of the flavour compound and terms to represent the oscillatory breathing and airflow rate. Aside from the 1st exhalation, the model fitted the data very well. The panel rated the intensity of minty flavor in a 6% gelatine gel, containing varying concentrations of carvone. The flavor was assessed using Magnitude Estimation and Time Intensity Methods. In addition, the quantity of carvone released from the gel and reaching the assessors nose was measured, breath by breath during eating, using the MS Nose. The results showed that the quantity of volatile delivered to the nose was directly proportional to the concentration in the sample, however, the absolute quantity varied greatly between individuals. Further differences were observed in the temporal dimension of their release profiles, which related to differences in their anatomy, physiology and eating habits. In some cases, these differences were mirrored by the sensory data. The relationship between perceived intensity and sample concentration was linear for both types of sensory data. Neither the speed of eating nor the concentration of volatile reached in-nose, affected an individuals ability to judge intensity. There was evidence to suggest, however, that the speed of eating affected the level of adaptation to the carvone stimulus. The affinity of the aroma compound for water (hydrophobicity) was an important factor in influencing the temporal characteristics of the instrumental and sensory data. When aroma release was rapid (< Tmax) the sensory response occurred slightly later whereas when the aroma release was much slower (>Tmax), with intensity increasing more gradually, the sensory response preceded the instrumental data. These phenomena were explained in terms of a lag phase for neural processing when the stimulus was presented quickly and adaptation to the stimulus when it was delivered over a longer period of time. A trained sensory panel assessed flavour and sweetness intensity in solutions containing varying concentrations of Hydroxy Propyl Methylcellulose (HPMC), sugar and flavour volatile. The flavour and sweetness of the viscous solutions were rated using magnitude estimation with a controlled modulus. In addition, the concentration of volatile released on the breath was measured using MS Nose. For low concentrations of HPMC (<0.5g/100g), perceived flavour intensity remained the same, however, a steady decrease was noted at higher concentrations (>0.6g/100g). The change in perceived intensity occurred at the point of random coil overlap (c*) for this hydrocolloid. The perceived sweetness of the solution showed a similar pattern with increasing HPMC concentration, although the inflection at c* was not so obvious. Despite the change in perceived flavour intensity, the actual concentration of volatile measured on the breath was not affected by the change in HPMC concentration. Low order polynomial models were produced to describe perceived flavour intensity and sweetness in viscous solutions containing HPMC and potential explanations for the changes in perception were discussed.

No description available.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 115-124). Also available via the Internet.

Thesis (M. Sc.)--University of Hong Kong, 2006. / Also available in print.

Thesis PlanB (M.S.)--University of Wisconsin--Stout, 2007. / Includes bibliographical references.

Thesis--PlanB (M.S.)--University of Wisconsin--Stout, 1998. / Includes bibliographical references.