• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 145
  • 101
  • 50
  • 34
  • 21
  • 5
  • 2
  • 2
  • 2
  • 2
  • Tagged with
  • 1562
  • 493
  • 354
  • 324
  • 319
  • 281
  • 157
  • 155
  • 152
  • 152
  • 151
  • 150
  • 73
  • 52
  • 47
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.

Quantification of bread crust crispness including the effects of selected additives

Al-Hebeil, Salah Ali I. January 2013 (has links)
Bread crust crispness is one of the most important and desirable characteristics that express the level of freshness and quality for bread classified as ‘crispy’. Several approaches have been used to determine food crispness; however no reliable objective method for bread crispness has been reported yet. To understand and quantify bread crust crispness, standard procedures for both instrumental and sensory measurements should be developed. Therefore, the first part of this research aimed to investigate both mechanical and acoustic parameters that relate to bread crust crispness determination and correlate them with sensory evaluation using expert panels at 4, 24, 48 and 72 hours post baking. A texture analyser (TA-XT plus) fitted with an acoustic envelope detector was used to determine mechanical and acoustic parameters. Five different bread formulae were evaluated at 4 and 24 hours post-baking, predominantly for crust crispness Two new experimental parameters were investigated in an attempt to standardise instrumental and sensory evaluations to improve consistency in the outcomes of the studies. Several mechanical and acoustic parameters either separately or in combination were tested and the results were compared with sensory evaluations. The ratio of sound pressure level and maximum force (SPL/Forcemax) along with the ratio the number of sound peaks and maximum force (AUX/Forcemax) were chosen as instrumental crispness indicators due to their significant positive correlations with sensory evaluations at 4, 24, 48 and 72 hours post baking. SPL refers to sound pressure level (dB) which is the highest sound recorded during the fracture of the sample at a certain threshold, AUX refers to the number of sound peaks resulting from the pressure of the wedge probe on the surface of bread during the process of penetration, and the Forcemax is the maximum force (Kg) required during the fracture of the crust. Then the influence of selected additives on bread crispness and crumb firmness were studied. For crust crispness, both experimental parameters SPL/Forcemax and AUX/Forcemax were used as instrumental crust crispness, while crumb firmness was tested using compression test as reported by AACC (74-09). Abstract II Polydextrose, sodium alginate, and enzymes dough conditioner (EDC), citrus fiber and mono and di-glycerides (M&D-G) were used as additives to modify the bread formulation, each in three different ratios. The migration of water from wet crumb to dry crust is considered as the main reason of bread crust loss, therefore the main reason of choosing those additive was based on their highly water binding capacity. The addition of 1% polydextrose, 0.25% and 0.5% sodium alginate and 1% enzymes dough conditioner (EDC) increased the sensory measures of crispness significantly above the control bread, and in most cases both SPL/Forcemax and AUX/Forcemax were also significantly higher than the control. Other concentrations were similar to the control or less crisp. The addition of M&D-G to the dough formulation did not show any effect on bread crust crispness. Neither did the addition of citrus fibre. Both experimental parameters showed high correlations with the sensory analysis when comparing bread of the same age, either 4 or 24 hours after baking. However conducting the sensory analysis at two different time points in the absence of score references lead to similarity in scores awarded at 4 and 24 hours, which did not fully reflect the loss of crispness occurring during this period. To allow the evaluation of both instrumental and sensory analysis at the same time, a follow on experiment was conducted using two different bread recipes at two different ages (4 and 24 hours) baked at the same time within two consecutive days. In conclusion, this work demonstrated that both experimental parameters relatively corresponded with the sensory evaluations even when the time factor was compensated for. AUX/Forcemax showed more accuracy in reflecting the level of crispness than SPL/Forcemax while SPL/Forcemax seems to measure the of crust staling values. Polydextrose, sodium alginate and EDC in ratios of 1%, 0.25% and 1-2% respectively showed better enhancement both for bread crust crispness and crumb softness. Further work regarding the effects of polydextrose, sodium alginate and EDC was recommended to determine the optimal amount of these ingredients to ensure a better crispy product.

A comparison of front of pack nutritional food labelling formats in Northern Ireland using a discrete choice experiment

Brown, Hannah January 2014 (has links)
A comparison of front of pack nutritional food labelling formats in Northern Ireland using a discrete choice experiment. Food choice is a central factor in weight control and overall health. In today's society there are complex information issues in choosing foods which make up a healthy diet. One method used to assist consumers in making informed food choices is front of pack nutritional food labelling (FoPL). Many versions of FoPL exist in the food market place in Northern Ireland (NI). This variety of FoPL and lack of specific regulation has led to claims of consumer confusion and low usage. The need to clarify food nutrition composition to consumers comes at a time when a growing number of people are classified as overweight or obese. This is due to changing lifestyles and food choice behaviour which has influenced a general increase in the levels of food consumption in Nllike many other modern societies. Consequently, this is having an adverse impact on the demand for public health services .. A Discrete Choice Experiment (DCE) survey which is a stated preference method, is employed in this research. A specially designed DCE survey was developed and administered to obtain the necessary data. An objective of this thesis is to establish if 'framing effects' exist in FoPL, i.e. do alternative combinations of interpretive elements in FoPL elicit different food nutrition preferences? A further objective is to investigate the extent to which nutritional attributes on FoPL are ignored and if alternative FoPL result in more being considered. In the DeE literature this issue is frequently referred to as attribute non attendance (ANA). Herein a practical approach is taken to ANA and applied to a real life situation. Another objective is to contribute to the DeE methodology literature though showcasing an array of specifically chosen DeE models and techniques. The results will be used for policy appraisal and to inform development of the most effective FoPL.

A study of the phase transitions of sugars found in chocolate

Jawad, Rim January 2013 (has links)
The overall aim of the PhD project was to investigate the phase transitions of chocolate sugars. To achieve this, the chemical purity and the re-crystallisation of both amorphous lactose and amorphous sucrose in a number of model systems were monitored. Both amorphous lactose and sucrose were prepared by spray- and freeze- drying of aqueous solutions of lactose and sucrose respectively. The amorphicity of the dried samples was successfully confirmed by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA). NMR analysis was performed and peak areas of partially resolved doublets at 6.3 and 6.6 ppm were used to calculate the percentage (%) of α- and β- lactose present. The β/α anomer contents of amorphous lactose measured by 1H-NMR had standard deviations as low as 0.1% w/w (n = 6). Drying a lactose solution 4 h after its preparation led to almost 35% w/w difference in anomer composition within solid amorphous material compared to samples dried after only 30 min e.g. in freeze-dried samples, the β- content was 60 ± 0.1% w/w (4 h) and 25 ± 1.0% p/w (30 min). Polarimetery was used not only to investigate the kinetics of mutarotation for lactose solutions at different temperatures but also to confirm the purity of amorphous sucrose by measuring the content of invert sugars, if any. A design of experiments (DoE) approach was applied to investigate the impact of minerals, water vapour and sugar composition on the crystallisation of both sugars. Hot stage microscopy was utilised to monitor the phase changes during crystallisation upon heating. DoE work showed that a shortage of water during crystallisation of sucrose led to a higher crystallisation temperature T<sub>crys</sub>. This finding supports the empirical observation from pilot scale chocolate crumb making which states that increasing pressure, which will increase H2O in the head space, encourages more crystallisation as crystallisation temperature is predicted to be lower. Minerals also had an impact on recipe by reducing the rate of crystallisation at a concentration of 3% w/w NaCl. Lactose present in the recipe interacted with sucrose inhibiting the crystallisation of both sugars. DoE has also proven to be a very efficient methodology, by saving time and resources, to investigate the correlations that may exist among different variables.

An investigation into bubble inclusion into liquid chocolate

Haedelt, J. January 2005 (has links)
No description available.

Understanding and predicting food handlers' implementation of specific food safety practices using social cognition models

Clayton, Deborah Anne January 2004 (has links)
This thesis reports on the development and application of research tools to understand and predict caterers' implementation of specific food safety practices. Food handlers' salient beliefs (n=137) identified three specific food safety actions for further investigation: hand hygiene actions, cleaning actions and the appropriate use of utensils when preparing raw and ready to eat foods. A notational analysis coding system was designed and developed. This tool was successful in recording a greater number of cross-contamination events than would have been highlighted using traditional approaches. One hundred and fifteen food handlers from 29 catering businesses were observed carrying out 31,050 food preparation actions in their workplace. Caterers subsequently completed a knowledge questionnaire and the Food Safety Instrument. The Food Safety Instrument was constructed using constructs from the Theory of Planned Behaviour (TPB) and the Health Belief Model. Despite a high level of knowledge and positive attitudes towards food safety, food safety malpractices were common. Implementation of hand hygiene and cleaning practices were particularly poor and only two percent of caterers carried out adequate food safety actions at all times. The TPB provided a useful framework for understanding the factors influencing caterers' implementation of specific food safety practices. Five constructs were identified as predictors of food safety malpractices: attitudes, subjective norms, descriptive norms, perceived behavioural control and intentions. Thus, suggesting that food safety behaviour cannot be improved merely through the provision of information. Food safety initiatives need to encompass a wide variety of factors including the attitudes of caterers, provision of resources and organisational culture. This thesis is important in furthering our knowledge of the factors that determine specific food safety practices and has practical value, providing a framework for both theoretical developments and practical interventions.

Effect of food storage conditions on the survival of Campylobacter jejuni

Thomas, Richard James January 2001 (has links)
<i>Campylobacter jejuni </i>is the predominant cause of gastro-enteritis in the developed world, accounting for 58, 000 diagnosed cases in the U.K in 1998. Infection primarily results from consumption of undercooked poultry and poor preparatory hygiene. <i>C. jejuni </i>is a poultry commensal, hence products are frequently contaminated within the processing plant, and subsequently at retail. Survival under conditions imposed by poultry processing and storage is an important factor in the capability of C. <i>jejuni </i>to produce infection. <i>C. jejuni </i>cells are usually spiral, but can be converted to a spherical form (coccoid) under various conditions. A triphasic survival curve is exhibited upon exposure to cold-shock (4-20 °C), consisting of plateau, decline and non-plateable phases. Maximum survival was observed for stationary phase cells incubated at 4 °C under a microaerobic atmosphere. Loss of plating ability on Brucella-FBP medium occurred before coccoid transformation at all temperatures examined (37, 20 and 4 °C) indicating the formation of a non-plateable spiral state. Entry into the non-plateable state correlated with an increase in calcofluor white (CFW) staining. When the population of CFW-stained cells was below 80-90%, the cells could be resuscitated from the non-plateable state upon temperature upshift and dilution into fresh Brucella-FBP broth. An inhibitory factor was present in the spent medium preventing resuscitation. Further entry into the non-plateable state resulted in loss of cytoplasmic integrity. The maximum 'window of resuscitation' was 3.5 d under a microaerobic atmosphere at 4 °C. Cells incubated microaerobically, or at higher temperatures (20 °C), had a reduced window of resuscitation. Unlike <i>Escherichia coli </i>and <i>Salmonella typhimurium, C. jejuni </i>does not produce any cold-shock specific proteins as part of an adaptive stress response, at either 32, 25 or 4 °C, as indicated by 2D-PAGE analysis. These results were confirmed by analysing the newly sequenced genome for cold-shock protein homologues. Adaptive stress responses reliant on <i>de novo </i>protein synthesis were observed for hydrogen peroxide and trisodium phosphate via analysis of unstressed and stressed 2D-PAGE profiles.

Production and characterisation of cocoa butter equivalents from high oleic sunflower oil by enzymatic rearrangement

Ray, Joydeep January 2013 (has links)
Cocoa Butter (CB) is one of the most expensive and widely used raw materials in the chocolate and confectionery industries. Due to the rise in the cost of CB in recent years, the variability in quality and the uncertainty in supply, the development of speciality fats with similar triacylglycerol (TAG) compositions to CB with full compatibility has been encouraged. Desirable TAG compositions in a fat can be efficiently achieved via rearrangement of the TAG structure of liquid vegetable oils with selected fatty acids by lipase-catalysed reactions. The main aim of the work presented in this thesis is to produce and formulate different Cocoa Butter Equivalents (CBEs) via enzymatic acidolysis of High Oleic Sunflower Oil (HOSO). This was carried out using a 1,3 regiospecific lipase (Rhizopus oryzae) with 11 different stearic-palmitic acid mixtures at an oil:acid ratio of 1:1.3 (w/w), to produce specialised fats with a high disaturated monounsaturated TAGs (Sat-O-Sat). Diacylglycerols (DAG) were also formed (~7-10%) as a by-product. The TAG and DAG compositions of the acidolysed fat samples were measured using High Resolution Gas Chromatography (HR-GC) and High Performance Liquid Chromatography (HPLC). A probability model was developed which efficiently predicted the final conversions of the major TAGs in the reactions. The variation of TAG composition with time was used to study the reaction kinetics using two different reaction schemes including all possible acidolysis reactions of TAGs with Stearic, Palmitic and Oleic acids at the 1 and 3 TAG positions and as well as reactions involving DAGs with different rate constant assumptions. The later scheme with equal rate constants for equivalent reactions of palmitic and stearic acid produced the best fits for this particular reaction system. Hard stearin fractions with high StOSt content were then isolated from the acidolysed HOSO via removal of free fatty acids by short path distillation (SPD) followed by single stage acetone fractionation. The HOSO hard stearin samples contained varying amounts of StOSt (69-84%) and POSt (4.5-21%), and with overall Sat-O-Sat levels of approximately 90%. This is comparable with commercial Shea stearin which is widely used in CBE formulations. The crystallisation and polymorphic behaviour of the HOSO stearins was studied and compared with Shea stearin. However, the HOSO stearin fractions contained significant amounts of oxidised glycerides (OX) and DAGs particularly of 1,3-StO and so further comparisons were performed on samples which were subjected to an additional silica treatment to remove these minor components. A multi-methodological approach was used for characterization of the samples which included Differential Scanning Calorimetry (DSC) melting, isothermal crystallisation and stop-and-return experiments, X-Ray Diffraction (XRD), pulsed Nuclear Magnetic Resonance (p-NMR), Polarised Light Microscopy (PLM) and Raman microscopy. Four major polymorphs previously found with pure StOSt, α, γ, β', and β were detected in the HOSO stearin and Shea stearin samples. An evidence for a fifth (δ) polymorph was found in DSC experiments, but not via XRD or Raman spectroscopy. The effect of varying StOSt and POSt content in the HOSO stearins was significant, in that crystallisation (at 20°C) speeded up as the StOSt level increased and the POSt level decreased. The main crystallisation event was generally faster for samples with higher StOSt levels (lower POSt levels). The removal of minor components via silica treatment generally speeded transformations to higher polymorphs (γ, β' and β). This was consistent with higher SFC values (similar to Shea stearin). The results suggested that the silica treated HOSO stearins could potentially replace Shea stearin in CBE formulations. CBEs were then formulated by blending the HOSO stearins with Palm oil Mid Fraction (PMF) maintaining a constant StOSt level (~30%) (with varying amounts of POSt and POP). These were compared with CB and standard CBEs (formulated using both untreated and silica treated shea stearins) in terms of composition, crystallisation, polymorphism and compatibility. The CBE blends displayed three major polymorphs, α, β' and β when crystallised isothermally at 20°C or crystallised non-isothermally and remelted. In contrast, transformation to the higher polymorph (β polymorph) was not observed for CB. The main isothermal crystallisation event was generally faster for CBE blends with higher POSt levels (lower POP levels). The CBE blends with higher POP levels as well as trisaturated TAGs tended to transform faster to the β polymorph, though complete transformation was not achieved even after 7 days of storage at 20°C. The overall SFC values of the CBE blends were also generally higher than CB. Mixtures of CBEs with CB (85:15) and Butter fat (BU) (85:15:15) in similar proportions to the fat phase of dark and milk chocolate showed similar crystallisation and melting behaviour to pure CB. Microstructures and XRD patterns of the mixtures of the CBEs with CB and as well as BU, showed evidence of the β polymorph similar to CB after 7 days of storage at 20°C. Iso-solid phase diagrams of mixtures of CBEs with CB in different proportions showed satisfactory compatibility with no eutectic behaviour. Thus the CBEs formulated from the HOSO stearins and PMF can be successfully used to replace CB partially in confectionery applications. Finally, the isothermal crystallisation of CB and selected CBE blends was studied by Hot Stage Microscopy in conjunction with image analysis using a novel image processing algorithm. These were compared with experiments with pure StOSt, POSt and POP and their ternary mixtures. It was possible to visualise and analyse the entire growth history of individual crystals (nucleation and growth kinetics) of these fat samples at different temperatures and polymorphic forms. Nucleation and growth rates of the CB β' crystals were found to vary approximately exponentially with decreasing temperature. The growth of β crystals could be studied by first generating small β crystals using melt mediated transformation from the β' form. These showed constant growth rates. In some cases, the nucleation and growth rates of the Sat-O-Sat crystals were found to increase initially and then decrease with increasing isothermal temperature, due to the impingement effects from the other polymorphs. The Ternary system displayed shorter induction time and faster crystal growth than that of the naturally derived fat samples, presumably due to the absence of other components. The final solid fat content (crystallised fraction) of all the fat samples was found to decrease with increasing temperatures as expected in a fat system.

An evaluation of some microbiological and ATP bioluminescence methods for the recovery and detection of bacterial contamination from food contact and environmental surfaces

Davidson, Craig A. January 2001 (has links)
Plant hygiene and food contact surface cleanliness are key prerequisites to the management of food quality and safety, and may form a critical control point within Hazard Analysis Critical Control Point food safety management systems. Several methods exist with which to monitor food contact surface cleanliness, with a recent survey of the UK food industry indicating that ATP bioluminescence, cotton hygiene swabbing and agar contact methods are the most commonly adopted. Despite their widespread use, little is known about the relative efficiency with which these methods recover contaminating surface bioburden. The purpose of the work reported was to critically evaluate these hygiene methods for assessing food contact and environmental surface cleanliness within the food industry. On surfaces sampled while dry, cotton swabbing was found to be the least efficient of the methods, with bacterial recovery rates ranging from < 0.1% on surfaces sampled while dry, and from 0.25% to l6% on surfaces sampled while wet. Minimum detection limits (MDLs) ranged from 102 to 108 cfu/100 cm2 depending upon surface moisture level, organism type and the nature of the organism release method used. Absolute recovery rates were influenced by organism type and by a number of sampling variables, with surface moisture level having the greatest effect on recovery. Organism recovery rates were not found to vary greatly over swab storage times typical of those found in industry during swab transportation, but the method was found to have poor reproducibility with coefficients of variation of up to l64% being recorded for sampling marginally unclean stainless steel surfaces. Agar contact dip slides were found to be more reproducible than cotton swabbing, with minimum detection limits on inoculated surfaces sampled while wet being consistent at 102 cfu/100 cm2, and from 102 cfu/100cm2 to >107 cfu/100 cm2 on inoculated surfaces sampled while dry. Different ATP detection systems were found to have different minimum detection limits when individual components of total ATP detection limit were evaluated. These ranged from 104 to 106cfu/100 cm2 when used to sample inoculated stainless steel surfaces while dry. On identical inoculated surfaces sampled when either wet or dry, the minimum detection limit was found to be consistent at l04cfu/l00 cm2. A technique for determining microbial ATP levels was developed. Microbial ATP values from a range of food contact and environmental surfaces within different food processing environments correlated well with microbial colony count data, with R2 values ranging from 0.65 to 0.93 before cleaning and from 0.50 to 0.94 after cleaning. Results are discussed within the context of surface cleanliness assessment in the food industry and should help industry develop appropriate strategies for surface hygiene monitoring.

Influence of emulsifiers on the rheology of chocolate and suspensions of cocoa or sugar particles in oil

Vernier, Frederic C. January 1997 (has links)
Rheological measurements were conducted on samples of chocolate containing various lecithin fictions and lipid sources in order to find a replacement for PGPR, a yield value reducing synthetic emulsifier. Only the oats extract was found to provide the desired reduction in yield value. together with a reduction in plastic viscosity similar to lecithin. Synthetic surfactants bearing various structural characteristics were investigated for their ability to reduce the yield value of chocolate. The best performances were obtained for emulsifiers with long tail groups, such as polymerised fatty acids or long chain hydrocarbons. Polglycerol esters of fatty acids of low HLB provided an excellent yield value reducing ability. Strong interaction of the surfactant head group with the sugar surfaces (mostly by hydrogen bonding) was found to be crucial for effective yield value reduction. Visualisation of lecithin and P(1PR in a sugar in oil suspension (a model of chocolate) was achieved. Both emulsifiers were localised at the interface between sugar and oil, and lecithin was found to displace some of the PGPR from the interface. Solvent extraction experiments were conducted on sugar in oil suspensions containing lecithin, PGPR, an oats extract and a mixture of lecithin and PGPR. SAXS and SANS work conducted suggested that while free PGPR has no impact on the rheological properties of a sugar in oil suspension once a critical concentration corresponding to a yield value minimum had been reached, free lecithin contributed to the formation of loose multilayers between sugar particles, resulting in increased yield value. The influence of various emulsifiers on the rheological properties of cocoa suspensions was also investigated. Lecithin and PGPR showed a similar effects on the yield values to what was observed in the case of sugar in oil dispersions. However, the oats extract was found to have virtually no surface active effect, probably due to poor interactions of its surface active glycolipid with the cocoa particle surfaces

Effect of hydrodynamic shear on the dry fractionation of palm kernal oil (PKO)

Awang Biak, Dayang Radiah January 2002 (has links)
No description available.

Page generated in 0.029 seconds