The microbial associations that developed in commercially produced sulphited and unsulphited sausages during storage for up to 8 days at a variety of temperatures were identified. Such associations were comprised of domiinant, e.g. Brochothrix thermosphacta, yeasts and lactic acid bacteria, or minor, e.g. Pseudomonadaceae and Enterobacteriaiceae, groups. A detailed analysis of numerous isolates of the previously-ignored Gramnegative microflora using computer-assisted numerical techniques revealed that sulphite concentratioin influenced the composition of the Enterobacteriaceae but not the pseudomonads. A method was developed for the assay of free and bound sulphur IV oxospecies in culture media or meat-based samples. It was superior to existing techniques and demonstrated limited irretrievable - by oxidation - and extensive reversible - by binding - loss of sulphite preservative from freshly manufactured and stored sausage. Selected micro-organisms isolated from sausage were tested for their tolerance of free and bound sulphur IV oxospecies in batch and "turbidometer" culture under various conditions. In general this technique reflected the elective/selective role of sulphite in sausage and allowed the microbial association to be defined more clearly in terms of tolerance of the active preservative. The incidence and level of contamination of sausage and its ingredients with Salmonella was established using a 'most-probable number' method. Despite a high incidence of contamination of most of the meat ingredients and finished product with these organisms, the level of infection - with the exception of mechanically recovered meat - was low. Thus the role of sulphur IV oxospecies in determining the fate of these food poisoning organisms in sausage or culture media was assessed by deliberate infection with rifampicinresistant Salmonella mutants. With a view to extending the shelf life of fresh sausage, a limited survey of adjuncts or alternative "preservatives" to sulphite using pilot-scale batches of sausage meat was done.

No description available.

The study presented here was to investigate the traditional production of the Ugandan fermented cereal beverage, Obushera. The effects of germination and malting of sorghum grains under different steeping treatment were first investigated. The traditional preparation of Obushera beverage was carried out and course of fermentation monitored. The viscosity of Obushera was very low throughout the fermentation process. The microflora responsible for the fermentation of Obushera were identified. After considerable research and conduction of tests were carried out, it was found that there was no detectable quantity of alcohol in Obushera. It was also confirmed that that there were no strains of alcohol producing yeasts, such as Saccharomyces sp. found in the Obushera. / Master of Science (Hons) (Food Science)

Continuous thermal pasteurisation of various bulk liquid media is an important step in the food and allied industries. The design of a continuous flow pasteuriser is typically predicated on mathematical models developed from experimental data - usually batch, bench - scale, ethods. Of particular interest is the effect of combined pasteuriser temperature ( T ) and liquid pH on inactivation and survivor of contaminants. However, bench - scale thermal survivor data may not adequately mirror those in a continuous flow pasteuriser. This research presents the development and experimental validation of rigorous models for thermal pasteurisation of bacteria as affected by combined process T - pH in both batch, bench - scale capillary studies ( static ) and in a pilot continuous flow pasteuriser ( dynamic ), within a defined liquid and range of exposure time, temperature and pH ( t - T - pH ). Five integrated stages in synthesis and model analysis were undertaken using stringent criteria for goodness of fit of an adequate model established. First, four published predictive models were assessed against published static data ( n [subscript T] = 248 ) for the thermal inactivation of Escherichia coli ( ATCC 25922 ) in a Carbopol ® 941 liquid food simulant in batch capillaries over a range of t - T - pH. The models tested were the Classical Arrhenius, Davey Linear - Arrhenius ( D - LA ), Square - Root ( Belehradek ) and a third - order Polynomial model ( nOP ). Analysis showed the D - LA model best satisfied the criteria for model selection and explained 96.0 % V in the thermal inactivation rate coefficient. Second, the D - LA model was assessed against limited, published dynamic data ( n [subscript T] = 109 ) for the same E. coli strain in identical food simulant. The model explained 60 % V in the thermal inactivation rate coefficient. On average, model predictions of survivor numbers from the dynamic data were less than that predicted from the static data, i.e. for a given ( t - T - pH ) more bacterial cells were apparently inactivated in the continuous flow pasteuriser than in bench - scale, batch capillary studies. Overall, however it was not clear from extensive analyses of available data whether there is a statistically significant difference in survivor numbers of viable E. coli between batch static and continuous flow dynamic data. Third, although the D - LA model best satisfied the criteria for goodness of fit of a model, it failed to accurately predict the observed tails in the static survivor data. New models ( KDT and a modified KDT ) were synthesised to predict tails and shoulders in survivor data. The modified KDT ( MKDT ) form gave improved predictive capability over the KDT model when assessed against published static survivor data for E. coli and L. monocytogenes ( n [subscript T] = 355 ) in the Carbopol food simulant. This model, however, could not be readily integrated with equations describing the performance of a continuous flow pasteuriser. Analyses indicated that a greater density of dynamic survivor data for E. coli was needed. Fourth, a pilot continuous flow pasteuriser was constructed and used to generate a greater density of dynamic survivor data of E. coli ( ATCC 25922 ) in a Carbopol ® 941 carrier liquid for rigorous comparison with predictions from the Lin ( 1976 ) isothermal continuous laminar flow process model. Direct steam injection heating was used. Extensive dye and digital - video studies, in a section of glass holding tube confirmed the practical implementation of the assumptions of laminar flow and rapid condensation of steam. Extensive practical experiments highlighted a non - isothermal condition along the holding tube. A highly linear dependence ( R ² > 0.90 ) of exposure temperature with holding tube length, i.e. exposure time, was demonstrated. This was accounted for using mathematical approaches and quantitatively incorporated into a D - LA model for the rate coefficient in an extended Lin process model. A block experimental design of 4 T ( 54, 56, 58, 60 ° C ) x 4 pH ( 4.5, 5.5, 6.5, 7.5 ) x 3 replicates with a total of ( n [subscript T] = 834 ) exposure times ( 16 - 198 s ) was carried out in the pilot continuous flow pasteuriser. Findings highlighted that greater numbers of E. coli were thermally inactivated in the flow pasteuriser than predicted. From a practical operating view, the predictions from the extended Lin model were therefore conservative - with reduced risk to public health. Highly significant differences in the rates of heat - up of bacteria in the pilot pasteuriser ( dynamic ) ( 0.0104 s ) compared with that in the batch ( static ) capillary tubes ( 1.6 s ) and, mode of heat transfer, together with partial effects of dispersion with increasing length of pasteuriser holding tube, are postulated to be the controlling process influences for the difference between the experimental survivor data and the extended Lin model predictions. The lack of agreement between the continuous pasteuriser data and predictions from the extended Lin model indicated that this model cannot be practically applied. A direct comparison of the experimentally derived dynamic survivor data from the pilot pasteuriser ( as ln N / N [subscript 0] ) was also made with both the published static and dynamic data at a number of defined t - T - pH. This comparison revealed that overall, more E. coli were inactivated in the pilot continuous flow pasteuriser than described by published batch static capillary and dynamic data. Importantly, these comparisons showed that batch thermal survivor data for E. coli do not adequately mirror those obtained in continuous flow systems. Fifth, in a search for an improved model for the inactivation data, the newly derived MKDT model was assessed against the experimental pilot pasteuriser data. This model was rejected, however, because it could not account satisfactorily for all tails in survivor curves. A Weibull form model with two coefficients ( a scale factor ( α ) and a shape factor ( β ) ) also did not adequately predict tailing and could not be reliably extrapolated with holding time. However, a modified Weibull form, also with two model coefficients ( β [subscript 0], β [subscript 1] ), did give an improved fit to available experimental data. This research highlighted statistically significant differences between the dynamic thermal survivor data for E. coli and standard bench - scale static capillary data for a defined liquid and range of t - T - pH. It is likely that findings from this study can be generalised. However, validation should be carried out for a range of common indicator micro - organisms in a range of liquid foods. / Thesis (Ph.D.)--School of Chemical Engineering, 2006.

Chitosan is known to be antibacterial and antifungal, but information on its effectiveness against foodborne viruses is limited. Enteric viruses are a major concern in food safety, especially human noroviruses which are the leading cause of nonbacterial gastroenteritis. The overall goal of this research was to determine the antiviral effectiveness of chitosan. The specific objectives were to determine the effects of molecular weight (MW) and concentration of chitosan against the cultivable enteric viral surrogates, feline calicivirus (FCV-F9), murine norovirus (MNV-1), and bacteriophages (MS2 and phiX174). Purified chitosans (53, 222, 307, 421, ~1,150kDa) were dissolved in water, 1% acetic acid, or aqueous HCl (pH= 4.3), and sterilized by membrane filtration. The solutions were mixed with equal volume of virus suspension to obtain a virus titer of 5 log PFU/ml and chitosan concentration of 0.7% for all five MW and 0.7, 1.0, 1.25, and 1.5% for 53 and 222kDa. The samples were incubated for 3 hr at 37°C before viral enumeration. Controls included untreated viruses in PBS, in PBS with acetic acid, and in PBS with HCl. Chitosan showed the greatest reduction of MS2, followed by FCV-F9, phi X174, and MNV-1. A MW effect was seen with MS2, with higher MW being more efficient, and 0.7% of ~1,150kDa causing complete inactivation. Increasing the concentration of chitosan from 0.7 to 1.5% reduced the titer of MS2 and FCV-F9 by 5.16 and 2.91 logs, respectively. Although chitosan was ineffective against MNV-1, its ability to significantly reduce MS2 and FCV-F9, suggest its use for future foodborne viral control.

The practical work described in this thesis falls into four distinct subject areas: HPLC, tea liquor fractionation, mass spectrometry, and NMR and IR. The practical work, is therefore written in four chapters, each chapter having its own introduction, results and discussion, and experimental sections. The work is concerned with the analysis of black tea liquor, its aim being to provide an analytical input into a larger project, being carried at NRI (Natural Resources Institute), on the statistical evaluation of tea quality.

The synthesis and use of monoacylglycerols in food systems havc been reviewed. The use of monoacylglycerols alone or in combination with free fatty acids as food preservatives has been discussed. Model systems have been devised to produce monoacylglycerols (MAGs) from butter and Shea oils with two strains of Penicillium roquefortii, FRR 2456 (isolated from a spoilt melon) and Wisbey PJ (a commercial dairy strain) A semi-micro method was developed using Preparative Thin Layer Chromatography (PTLC) and Gas Chromatography - Mass Spectrometry (GC-MS) of the MAG trimethylsilyl ether derivatives to determine the identification, fatty acid composition and structural isomers of the individual MAG. The main monoacylglycerols produced by spores and emerging mycelium were 1(3)-monoacylsn-lycerols (in suspension culture). Monopalmitin was the major MAG from butter and Shea oils. Monoacylglycerols produced by fungal mycelium (in solid-state culture) were mainly the 1 (3 )-monoacyl-sn-glycerols although approximately 30% were present as 2-monoacyl-snglycerols. Again the main MAG was monopalmitin. It suggested that P. roquefortii produced two lipases, one during germination with specificity to the sn-2 position in the original triacylglycerols (TAGs) and one L3-specific during growth of the fungal mycelium. In addition, flavour compounds, methyl ketones and y-lactones, were found in solid-state culture. The composition of the MAGs formed by lipolysis using a commercial lipase (E.C.3.1.1.3) with 1,3- specificity gave the expected 2-isomers when butter oil was the substrate but gave 1 (3)monostearin rather than the expected 2-monoolein when Shea oil was the substrate. It suggested that acyl migration occurred due to the reactive nature of the original oleate group at the sn-2 position in the Shea oil TAGs. There were no significant differences with fungal strain or temperature of incubation (10 °C and 25°C) on the composition of the MAGs. The mechanism of formation of MAGs from butter and Shea oils has been discussed. It has been suggested that l(3)-MAGs together with free fatty acids may be part of a natural antimicrobial system in high pH foods such as blue mould-ripened cheese where growth of foodborne pathogens such as Listeria monoGytogcnes can be a problem from time to time

No description available.

No description available.

The ability of microorganisms to withstand large environmental perturbations enables survival in a wide range of habitats including foodstuffs. The importance of elucidation of such survival strategies has been stressed. In order that microorganisms survive in such harsh environments control mechanisms must exist which enable the cell to grow under these conditions. Survival under such extremes would indicate adaptation. The mechanisms involved in such adaptation ultimately come from within the bacterial genome and are thought to be due to alterations in gene expression. The effect of altered external and internal pH was observed upon the recovery and habituation of wild type cells over a period of time and indicated that cells possess the ability to habituate. Using lacZ fusion strains and DNA supercoiling measurements enabled the effect of stress on <i>ompF, ompC</i> and <i>proU</i> gene expression to be assessed. It was demonstrated that <i>ompC</i> is expressed in response to both acidification of the external medium and the cytoplasm. The response of the cell to external and internal acidification is both quantitatively and qualitatively different. Only the acidification of the cytoplasm results in transient differential gene expression typical of gene induction. This process is carbon source dependent. In parallel studies it has been demonstrated that the expression of the supercoiling-dependent <i>proU</i> locus is repressed by acid (both cytoplasmic and environmental). Consistent with this observation is that reporter plasmids are more supercoiled when isolated from cells incubated under acid conditions and would lead to a reduction in gene expression. From these studies it can be concluded that regulation of <i>ompC</i> does not lie at the level of DNA supercoiling but is dependent on the effects exerted on the <i>EnvZ/OmpR</i> regulatory system and also suggests the role of a secondary internal sensing mechanism.