The research reported in this thesis examines factors that affect the willingness of rats to ingest novel flavour solutions. Emphasis is placed on the memorial processes assumed to underlie the decision as to whether or not a solution is "safe" to drink. Rats exhibit caution (neophobia) in consuming an unfamiliar (target) solution. This unconditional response to novelty habituates as the rat acquires experience with the target solution (provided that ingestion of the target solution has no noxious consequences!). Neophobia to the target solution may be restored, however, if another (distractor) solution is presented during the interval separating pre-exposure to, and testing of, the target solution (Green & Parker, 1975). In Section 1, the phenomena of habituation to an iterated target stimulus and the disruption of this process by a distractor are introduced. Theoretical explanations of the "dishabituation" effect of a distractor stimulus are described and assessed. The possibility of an empirical test of the relative validity of the Robertson and the Wagner hypotheses using the attenuation of flavour neophobia procedure of Green and Parker provided the impetus for the experiments reported in Section 2. In Section 3, attention is drawn to the similarity of the procedure designed to establish habituation and that Intended to establish latent inhibition to a stimulus. A limited review of empirical data is presented testifying to the fact that habituation and latent inhibition are affected similarly by identical parameter manipulations. The Wagner (1976) model views habituation and latent inhibition as the outcome of a common underlying process, Expts. 10a and 10b, therefore, sought to determine whether latent inhibition of a conditioned taste aversion (CTA) to lemon or sucrose solution would be affected by a coffee distractor in a manner consonant with predictions derived from the results of the neophobia experiments reported in Section 2. The distractor, however, had no effect on strength of latent inhibition in either experiment. Expt. 11c demonstrated that it is possible for a distractor (30% vanilla) to disrupt attenuation of neophobia to a target flavour (3% cider vinegar) without affecting latent inhibition to the target flavour, i.e., there is no direct correspondence between measures of habituation and latent inhibition to the same stimulus. In Section 4, the phenomena of overshadowing and potentiation of a CTA are introduced. At least one explanation of potentiation (c.f., Durlach & Rescorla, 1980) stresses the importance of an association between the elements of a compound CS. Rescorla and Furrow (1977) found interstimulus associations were formed more rapidly between similar rather than dissimilar stimuli. Given these results, Expts. 12a and 12b sought to determine whether a single sequential presentation of lemon and coffee (similar solutions) paired with LiCl would result in potentiation of a conditioned aversion to the lemon solution and whether a single sequential presentation of sucrose and coffee (dissimilar solutions) paired with LiCl would result in overshadowing of a conditioned aversion to the sucrose solution. These experimental predictions were confirmed. In Section 5, a potential confound in the neophobia experiments is addressed. Interpretation of attenuated neophobia as a habituation process is defended and alternatives to the Wagner (1976) theory of habituation are considered for their ability to encompass the data reported in Section 2. Only the Wagner model, however, appears able to account for all the data. Nevertheless, some limitations of the model are indicated. Finally, the conditions promoting overshadowing and potentiation of a CTA are discussed.

The research focussed on the sensory perception of boar odour; an odour problem that is sometimes present in the meat of entire male pigs and associated with two compounds namely skatole and androstenone. Researchers differ on the issue of the relative contributions of skatole and androstenone to the sensory perception of boar odour. The first objective of the research was to investigate the relative contribution of different concentrations of skatole and androstenone to the temporal perception of boar odour in boar fat. In South Africa, the potential for boar odour was regarded to be considerable should it be decided to discontinue the policy of castrating boars. However, the economic advantages associated with boar production on the other hand necessitated an investigation into consumer reactions to boar odour. The second objective was therefore to determine the effects of gender and ethnicity on consumer reactions to boar odour in boar fat samples with different concentrations of skatole and androstenone. Pork fat samples from 50 boars slaughtered at a commercial abattoir were analysed for skatole and androstenone concentrations and grouped within a 3 x 3 matrix representing low, medium and high levels of the odour compounds. A 10-member sensory panel, screened and trained to recognise and quantify skatole and androstenone odour intensities, was used to verify the human perception of boar odour in these pork fat samples immediately after heating (± 65°C) and following a cooling period of ten minutes (± 25°C). Consumers (n = 300) including equal numbers of males and females and from three ethnic groupings, namely blacks, whites and coloureds, were used to determine the effects of gender and ethnicity on consumer reactions towards boar odour compounds. Each consumer evaluated how much they would like to eat pork or pork products that smelled like the odour of each of 7 boar fat samples (65°C) with different combinations of known concentrations of skatole and androstenone. The consumers were recruited on two university campuses and the results can therefore not be extrapolated to the general South African population since the majority of the participants were young (18 - 35 years) and representing living standards measures (LSM) groups 6 to 8, i.e. the higher income groups. It was shown that the trained sensory panel differentiated the odour of the pork fat samples first and foremost on the basis of the presence or absence of androstenone and/or skatole odours and secondly on the character of the androstenone or skatole odour. Sensory perception of boar odour seems to have a temporal character which can be explained by differences in volatilisation (involving both odourant release and retention) of skatole and androstenone, possibly enhanced by differences in the properties of the fat matrixes of different samples. The temperature and time at which the samples were evaluated influenced both the intensity and the character of the perceived odour profiles. For samples with skatole concentrations above 0.25 µg/g and served warm, skatole was predominant while the influence of androstenone at levels above 0.5 µg/g and other odour components became increasingly important after samples had cooled down and skatole volatiles were less evident. The results showed that females compared to males would be less willing to consume pork and pork products with detectable levels of boar odour pertaining to both skatole and androstenone. All groups would be less willing to consume pork and pork products with detectable concentrations of skatole or skatole and androstenone in combination. An apparent liking for samples with medium levels of androstenone (0.5 to 1.0 µ/g) was found for some consumers, especially males, and can be partly attributed to the inability of some consumers to smell this component or a genuine liking for the odour of androstenone. Significant differences (p < 0.05) in the sensitivity of consumers from different ethnic groups were found with white females responding more negatively than white males and blacks. However, significant ethnic group effects were confounded by gender effects. The age of individuals, socio-economic factors and gender-linked personality factors may have influenced these differences. Although it was not possible to compare responses directly with the white and black groups because the samples were not identical, it was found that a higher percentage of coloureds responded negatively to boar odour compounds. Coloured males responded particularly negatively towards samples with detectable skatole, while black males, in general, were found to be more critical than black females. It was concluded that boar odour whether due to skatole, androstenone or both compounds in combination at the levels as currently found in South Africa, will contribute to negative consumer reactions, at least for the subsection of the population represented in the study. It was predicted that the majority of these consumers would be less willing to consume pork meat exhibiting detectable levels of boar odour. It was recommended that the policy of castration be continued until such time as methods have been developed to ensure reduction in both skatole and androstenone concentration levels of boars to levels that would not be detectable even to the most discerning of consumers. / Thesis (PhD (Food Science))--University of Pretoria, 2006. / Food Science / unrestricted

No description available.

No description available.

This Btuiy iitilized a choice method to assess preference in adult rats Vho had been exposed to one of fonr treatments (Sucrose; Quinine; Water; and Handling) at an early age. The up and down (psychophysical) method (Dixon & Ilassey, 1957) vas used to determine the mean concentration of sucrose, Vhich Vhen mixed vith a set concentration of quinine, is Isohedonic (equally preferred) to a set concentration of sucrose (standard). Responses cltistered around a mean score (quinineeucx'ose mixture) vhich is hypothetically equivalent (equally preferred) to a fixed concentration of sucrose (standard). Sensitivity to quinine vas reflected by the response frequencies recorded since the rat vill Ingest the sucrose solution of greater concentration in a tvo choice situation (Young & Green, 1953)-

No description available.

Single nucleotide polymorphisms (SNPs) in various taste receptor genes have previously been linked to outcomes such as differences in taste thresholds, food liking, and body mass index, but no studies of this sort have examined sour taste. This study genotyped 501 young adults for PKD2L1 rs603424 and administered a Food Frequency Questionnaire and Tanita body composition testing to look for associations between the noted SNP, dietary intake, and body composition. Intake of citrus fruit, vitamin C, caffeine, and alcohol were significantly associated with genotype in two-way ANOVA analyses looking at the effect of genotype and race or sex on dietary intake. Regarding body composition, genotype was significantly associated with BMI, but not body fat percentage or fat free mass. These findings suggest that rs603424 may influence intake of certain sour and bitter dietary components; however, further research will be needed to confirm these findings.

Previous research has indicated two distinctive characteristics of flavour-aversion learning in rats: (1) rats very readily associate flavors with an internal malaise (toxicosis) , as evidenced by their subsequent aversion to the flavor, but they do not readily associate flafors with peripherally-applied electric shock. In contrast, rats readily associate auditory and visual stimuli with shock but not with toxicosis; (2) rats associate flavors with a subsequent toxicosis even when the gustatory stimulus is removed hours prior to onset of toxicosis. However, associations are formed between audio/visual cues and shock only if the offset of the signal does not precede onset of shock by more than one or two minutes. It has been suggested that the unique features of flavour-aversionn learning result from the fact that toxicosis is primarily a visceral experience while shock is applied to somesthetic receptors. However, toxicosis differs from shock along a number of dimensions in addition to receptor site. Most notably, toxicosis typically rises to a peak intensity over a period of many minutes and lasts for hours while shock is usually applied with a rapid onset (milliseconds) and short duration (seconds or milliseconds). Inasmuch as aversion learning experiments have confounded the receptor site of the aversive stimulus with its distinctive temporal features, it is not clear whether receptor site or temporal features is the functionally important characteristic of toxicosis as an aversive stimulus in the taste-aversion learning preparation. To determine the role played by the temporal features of the aversive stimulus in taste-aversion learning, rats were prepared with a stomach balloon and stomach balloon inflation was paired with ingestion of a flavored solution. In contrast to toxicosis, the onset/offset rate and duration of balloon inflation may be directly manipulated thus permitting application of a relatively discrete internal stimulus (in comparison to toxicosis) to visceral receptors. Experiments presented here found: (a) rats associated a flavor with a stomach balloon inflation as indicated by an aversion to the flavor during a two-solution preference test. In contrast to toxicosis, the stomach balloon inflation had a rapid onset (seconds) and short duration (minutes). Control groups demonstrated that the rapid onset, short duration balloon inflation did not produce the long lasting malaise characteristic of toxicosis. (b) Rats associated a flavor with a rapid onset, short duration balloon inflation even when exposure to the flavor was terminated many minutes prior to onset of balloon inflation. (c) Rats readily associated a flavor with balloon inflation but not with shock, and an auditory stimulus with shock but not with balloon inflation, even though balloon inflation and shock were equated in terms of their temporal parameters. These findings clearly indicate that the very slow onset and long duration characteristics of toxicosis are not the functionally important features of toxicosis as the aversive stimulus in the taste-aversion learning preparation. Furthermore, the unique temporal features of toxicosis and shock do not appear responsible for the distinctive characteristics of flavor-aversion learning in rats. / Thesis / Doctor of Philosophy (PhD)

Three groups of rats were tested both before and after the bilateral ablation of the taste sensory cortex. The first group, exposed to quinine hydrochloride (QHCL) in a two-bottle preference situation, showed a large deficit postoperatively, but these were considerably reduced by the fourth postoperative week. A second group, tested for sodium chloride (NaCl) discrimination in a modified signal detection situation, also showed significant postoperative impairment. A third group, QHCL discrimination, was discarded for failure to learn the detection task. The results which were very unclear compared with NaCl discrimination and QHCL preference. It is concluded that preference tests are unsatisfactory measures of taste sensitivity unless the stimuli possess extreme aversive or preferred qualities. / Thesis / Master of Arts (MA)

This thesis discusses the causes and methods for removing taste and odor compounds from water supplies.