Several techniques for enumerating bacteria at surfaces were investigated. Epifluorescence was chosen as being the most suitable method. There was not a great increase in adhesion between samples exposed to bacteria for 2 h and those exposed for 6 h. Sequential bacterial adhesion studies suggested that this may be due to a limiting number of suitable sites at the sample surface. Treatment of stainless steel samples with skimmed milk was shown to reduce the adhesion of several bacterial species. Individual milk proteins, alpha-, beta-, kappa-casein and alpha-lactalbumin, also reduced the adhesion of S. aureus and L. monocytogenes to stainless steel surfaces. The casein proteins were demonstrated to be more effective at reducing bacterial adhesion than the globular protein, alpha-lactalbumin. Cross-linking of mobile protein chains with glutaraldehyde caused an increase in the numbers of bacteria attaching to the surface. Several surface analysis techniques were implemented in order to investigate further the relationship between bacteria and a protein-coated surface. X-ray photoelectron spectroscopy demonstrated that kappa-casein adsorbed to the stainless steel surface in the largest amounts and alpha-lactalbumin the least. Thick layers of kappa-casein were also demonstrated at the surface using atomic force microscopy, whereas virtually no detail was observed with alpha-lactalbumin, again indicating lower adsorption. This appears to be the reason for the higher levels of bacterial adhesion at surfaces pre-treated with this protein. Atomic force microscopy of milk-treated surfaces produced images indicating a sparse background coverage with thicker protein deposits above this. Contact-mode imaging suggested that the surface of these structures comprised more loosely bound material. Combining this information with that provided by bacterial adhesion investigations and the effect of glutaraldehyde treatment upon milk, it is postulated that bacterial adhesion at a protein-covered surface is reduced as a result of steric forces generated by protein material extending into solution.

Semi-PreParative gel permeation chromatography (gpc) was used to isolate several molecular mass components of gum arabic. The u. v. (218 nm) gpc elution profile showed the presence of several prominent peaks; however, only one major peak (FAw 3.8 x 10-9 g moll) and a minor peak (FAw 1.45 x 106 g mol-1) were observed in the differential refractive index (R. I. ) gpc elution profile. The Rl. molecular mass distribution profile was also shown to be representative of the true mass distribution of the gum. Gram quantities of three apparently "pure" components of gum arabic were prepared using hydrophobic interaction chromatography. These components corresponded to the three major peaks observed in the u. v. gpc elution profile. Extensive physico-chemical analysis revealed that gum arabic consists of:- a: a major protein deficient arabinogalactan representing 900/6o f the total gum mass: b: a high molecular mass, protein rich (100A protein) component, designated as an arabinogalactan-protein complex which accounts for 9% of the total gum: c: one or more protein enriched (50% protein) glycoprotein components accounting for only 1% of the total gum. Furthermore. the result of enzyme treatment indicates a possible structural correlation between the arabinogalactan and the arabinogalactan-protein complex. This evidence also substantiates the so called 'Wattle Blossom" model which Is representative of the macrostructure of the high molecular mass arabinogalactan-protein complex. The Newtonian rheological behaviour of aqueous gum Arabic solutions (up to 400/6 w/w) complements other experimental evidence, which strongly suggests that the gum's macromolecular structure is very compact for a polysaccharide. The unique emulsification properties of the gum were monitored by the development of standardised turbidimetric techniques. It was subsequently shown that enzyme and heat treatment of the gum had a similar effect of substantially reducing the emulsifying efficiency of the gum. Both gum treatments effectively "denature" the proteinaceous components of the gum and by consideration of other experimental evidence (adsorption characteristics of the components at the o/w interface) it was demonstrated that the high molecular mass arabinogalactan-protein complex is solely responsible for the gum' s emulsifying property.

The purpose of this thesis was to study food choice motivations in relation to fruit and vegetable consumption. To this end, four studies were undertaken. The first was a systematic review of the literature investigating factors affecting the food choice decisions of adults in relation to fruit and vegetable consumption. The second study examined the different health and lifestyle factors, which affect fruit and vegetable consumption in women. Participants were drawn from the UK Women's Cohort Study (UKWCS), and were all females, aged 35-69 years (n = 35,367). These women provided health and lifestyle information including a 217-item food frequency questionnaire. The strongest predictors of a high level of fruit and vegetable consumption found in the logistic regression model were: being a vegetarian or vegan, taking vitamin or mineral supplements, being married, having an A-level or degree level of education and belonging to a higher socio-economic group. The third study explored the priorities of high consumers of fruit and vegetables compared to lower consumers, within 998 women from the UKWCS, using the Food Choice Questionnaire. In a multiple linear regression model the strongest motivations affecting specifically fruit and vegetable intake were health and natural content. This study also investigated the relationships between food choice motivations and the process of behaviour change, using the Stages of Change (SOC) ModeL The SOC evaluation showed significant associations with portions of fruit and vegetables consumed, and the findings showed that women classified in differing phases of SOC model have different food choice motivations. The final study assessed the variability and validity of plasma nutrient levels as biomarkers of fruit and vegetable intake. Participants were 54 non-smoking women recruited from the UKWCS. Two methods, the food frequency questionnaire and the 4-day food diary were employed to assess fruit and vegetable intakes. The results implied that the practice of using plasma biomarkers simply as a proxy measure of dietary intake is not valid and emphasise that plasma biomarkers are not simply a reflection of dietary intake but also of a number of physiological processes. Overall, the findings demonstrated: that health promotion interventions to increase fruit and vegetable consumption should primarily be targeted at people who smoke, live alone and are of a lower education level and socio-economic status; that higher consumers of fruit and vegetables tend to be more motivated by health concerns and the natural content of the food, and less motivated by convenience and familiarity issues, than the lower consumers of fruit and vegetables; that people classified in different Stages of Change have differing food choice motivations and finally; that plasma antioxidant levels are not biochemical markers of accurate dietary intakes, at either the food or nutrient level, however they may give a more complete assessment of diet when used in conjunction with traditional dietary assessment methods.

The major objective of this investigation is the comparative nutritional evaluation of thermosterile foods in pouches and in cans during sterilization treatment and during storage. To achieve this objective, four products (whole brussels sprouts, whole new potatoes, pork casserole and rice pudding) were developed and produced in pouches and in cans. All variables were maintained constant in the production of these food products and equivalent heat sterilization treatments were applied. Available lysine, ascorbic acid and thiamine (vitamins C and B1) were selected as the nutrients for this investigation. Those nutrients were determined immediately before and after the sterilization treatment and at several intervals during storage. Pouched processing improved the retention of ascorbic acid and thiamine in relation to canning, Storage conditions produced mainly the same effects in ascorbic acid and thiamine retention independ ently of type of package for pork casserole, but larger losses were obtained for the canned products for brussels sprouts and new potatoes. Available lysine losses due to the sterilization treatment are small (= 15%). Difficulties with the sterilization process control and the poor sensitivity of the analytical technique employed seriously question the significance of the comparison between the canned and pouched products. For all samples the use of longer processing times to obtain higher sterilization treatments produced larger destruction of nutrients. Also the use of lower storage temperatures increased the nutrient retention. Large losses of ascorbic acid were obtained in pouched brussels sprouts during storage at three storage temperatures (5°C, 20°C and 37°C), and the ascorbic acid losses were greatly increased at 37°C storage conditions. A series of experiments were conducted to investigate these results. Peroxidase activity was found to be responsible for these losses. It was found to be present in the pouched samples but not in the canned products. It was determined that processing times of over 20 minutes at 121.1°C and 116°C were required to inactivate the enzyme. The results suggest that the improved heat penetration of pouches which permit the achievement of a microbiologically safe sterilization treatment in short times can also be insufficient for the inactivation of heat resistant peroxidases.

Ultrasonics has not found widespread use in the food industry, despite having considerable potential for characterising food materials. This is due to the complexity and diversity of food materials, the lack of suitable instrumentation and a poor understanding of how ultrasound interacts with many food components. In this work it is shown how a good appreciation of the theories describing ultrasonic propagation in heterogeneous materials, coupled with careful experimental design, leads to many new applications of ultrasonics for characterising fats and emulsions. Ultrasonic measurements were made using either a pulse echo technique (1-10MHz), or a pulse echo interferometric technique (5-55MHz). The ultrasonic velocities of a series of 0-30% w/w glyceride/oil mixtures and some commercial fats were measured with varying temperature (0-70°C) at 1MHz. Ultrasonic scattering was not important in these systems and so empirical equations or simple (SFC) theoretical formulae could be used to relate the measured velocities to the solid fat contents (SFC) of the samples. There were very significant correlations between the SFCs determined using ultrasonics and those determined using pulsed NMR (r > 0.99), and so ultrasonics should prove a useful adjunct or alternative to NMR. Velocity measurements also proved useful for characterising vegetable oils since the velocity of an oil could be related to its glyceride composition. The ultrasonic velocity and attenuation of a series of sunflower oil and water emulsions mean were measured with varying frequency (1-55MHz) mean, droplet size (0.1-0.9μm), disperse phase mass fraction (0-0.5) and emulsion type (0/W and W/O). Scattering was significant in these emulsions and could be used to measure their disperse phase mass fractions and particle size distributions. Ultrasonics has important advantages over existing techniques for this type of measurement since it can be used in emulsions which are optically opaque, in a non-intrusive, non-invasive manner.

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