In the first stage of the investigation, the effect of high levels of sugars (mixture of 50% sucrose with 35% glucose syrup) on agarose (0.7 wt%) was characterized by low amplitude oscillatory measurements of storage modulus (G'), loss modulus (G") and loss tangent (tan δ) as well as large deformation techniques. Samples were prepared at 90°C, and measured immediately, or after storage at 5°C. The combined Williams-Landel-Ferry (WLF)/free volume theory was used to derive the glass transition temperature, the fractional free volume, and the thermal expansion coefficient of the glass. Solution of high concentrations of sucrose crystallizes, but addition of the polymer encourages intermolecular interactions, which transform the mixture into a high viscosity glass. The mechanical properties of glucose syrup follow WLF behavior in the glass transition region and revert to an Arrhenius type prediction in the glassy state. Measurements on sugar samples and agarose-sugar mixtures were resolved into a basic function of temperature alone and a basic function of frequency (time) alone. The former traces the energetic cost of vitrification, which increases sharply with decreasing temperature. The latter, at long time scales, is governed by the infinite molecular weight of the agarose network. In the region of short times, the effect of free volume is active regardless of the sample composition. In a continuation of investigating the significance of polymer-cosolute interactions, the effect of sucrose, glucose, fructose, sorbitol, xylitol, glycerol and ethan-1,2-diol on gelation of high methoxy pectin was studied under different experimental conditions. The main changes in procedure in comparison with the work on agarose were: (i) the polymer concentration was increased from 0.7 to 1.0 wt%, (ii) the mixtures prepared at pH 4 and subsequently acidified to pH 3, rather than being prepared at neutral pH, (iii) the cosolute concentration was varying from 50 to 65 wt% and (vi) the mixtures were studied through rheology, calorimetry and optical rotation. The samples were prepared at 95°C and changes in storage modulus (G') and loss modulus (G") during cooling to 5°C, heating to 90° and re-cooling to 5°C, at 1°C/min, were measured at 1 rad s⁻¹ and 0.5% strain. In all cases, the onset temperature for gelation during cooling and the moduli recorded at 5°C increased with increasing concentration of cosolute. However, both values were substantially lower for the liquid cosolutes than for mixtures with solid cosolutes at the same concentrations. The difference is attributed to inhibition of pectin-pectin interactions by pectin-cosolute interactions, which in turn are inhibited by cosolute-cosolute interactions. On heating there was an initial reduction in modulus, with the same temperature-course as the increase on cooling; for the solids, this was followed by an increase attributable to hydrophobic association of methyl ester substituents. No such increase was seen with the liquid cosolutes, but DSC studies showed two reversible thermal transitions in all cases, one over the temperature-range of the initial gelation process on cooling and the other coincident with the increase in modulus on heating in the presence of solid cosolutes. The absence of any detectable increase in modulus on heating with the liquid cosolutes is atttributed to accumulation of cosolute around the polymer chains promoting hydrophobic association between methyl ester groups on the same chain, or within clusters of chains, with, therefore no contribution to network structure. At high concentrations of the solid cosolutes, the increase in modulus on heating was followed by a decrease at higher temperature; this was attributed to excessive aggregation, and was reflected in lower moduli on subsequent re-cooling to 5°C, in contrast to the enhancement in gel strength after heating and cooling observed at lower concentration of the same cosoutes. In the presence of fructose as cosolute, calorimetric studies showed an intense endotherm followed immediately by an intense exotherm on heating. These transitions occurred over approximately the same temperature-range as initial gelation on cooling and increased in magnitude with increasing concentration of the sugar. The displacement of both transitions to progressively higher temperature as the rate of heating was increased was much greater than anticipated from a simple thermal lag, indicating that the undelying structural changes are slow. The proposed interpretation is that fructose is capable of site-binding to pectin in both the ordered and disordered state.

Pulsed electric field (PEF) can induce irreversible electroporation in the bio-membrane and cause the death of microbial cells without significant thermal effect, which can be used for inactivation of microorganisms and facilitation lysis of microbial cells for lipid extraction. The present study aimed to investigate the efficiency of PEF treatment of Arthrospira platensis and Saccharomyces cerevisiae using test cells with different types of electrodes and impulses with different waveshapes. An equivalent circuit modelling approach was also proposed and developed to describe the pulsed power system and the microbiological cell in the present study. The PEF test cells with three types of electrodes were developed in the present study: a traditional stainless steel test cell; a novel low-conductive test cell with 2 μm TiO2-coating on electrode surface; and a novel test cell with non-conductive ceramic electrodes. Effective PEF inactivation of both A. platensis and S. cerevisiae was achieved using stainless steel and TiO2-coated test cells. Significant improvement in the energy efficacy of the PEF treatment was obtained using the TiO2-coated test cell. However, PEF inactivation of microorganisms in the ceramic test cell required electric fields with magnitude above 80 kV/cm. Three types of impulses, square impulse, smooth exponential impulse and oscillating exponential impulse were used in the present study. The best energy efficacy was achieved using the smooth exponential impulse for the field levels of 67 kV/cm and 80 kV/cm. A correlation between the pulse waveshape, the electric field magnitude and the inactivation performance was established. The PEF treatments of A. platensis demonstrated that this type of cyanobacteria can be inactivated effectively but rupture of the cell structure was not achieved. The PEF process was capable of induction of the lethal damage to the A. platensis cells but not sufficient to cause significant mechanical damage to the cell structure.

Hibiscus sabdariffa (H. sabdariffa) is a rich source of bioactive phytochemicals with potential health benefits. Based on its reported use in folk medicine for the treatment of hypertension and recently type 2 diabetes, the plant has gained considerable commercial importance as a functional food. Three varieties of H. sabdariffa were analyzed for their phytochemical content and inhibitory potential on carbohydrate-digesting enzymes as a basis for selecting a variety for wine production. The dark red variety was chosen as it was highest in phenolic content and partially inhibited α–glucosidase (maltase), with delphinidin 3-O-sambubioside, cyanidin 3-O-sambubioside and 3-O-caffeoylquinic acid accounting for 65 % of this activity. None of the varieties significantly inhibited α–amylase. Regarding H. sabdarifa wine, the effect of fermentation (20 and 30 ˚C) and ageing (6, 15 and 30 °C) temperatures on the phytochemical composition and bioactivity of Roselle wine was investigated for a period of 40 days and 12 months respectively. The main change in phytochemical composition observed during fermentation was the hydrolysis of 3-O-caffeolquinic acid and the concomitant increase of caffeic acid irrespective of fermentation temperature. Wine fermented at 20 ˚C was slightly more active for α–glucosidase inhibition with more fruity aromas, but there were more flowery notes at 30 ˚C. Although ageing temperature did not produce an obvious trend in concentrations of most of the volatiles analysed, its impact was clearly demonstrated in the final concentrations of diethyl succinate which increased with higher ageing temperature. The data on the overall quality rating of roselle wine by a sensory panel showed that neither fermentation nor ageing temperatures produced any significant difference (p ≥ 0.05) in the wine samples. This study demonstrates that processing of H. sabdariffa into wine represents a promising alternative to expanding the functional properties of this crop.

The objective of this study was firstly to assess the ability of liquid skimmed milk in combination with different concentrations of maltodextrin (MD) to emulsify 5% w/w thyme essential oils (EOs). Secondly, to analyse the chemical composition of the used thyme EOs and further examine the physical properties of some EOs components such as solubility, surface activity and partitioning coefficient. Moreover, assessing the antibacterial activity of free and encapsulated EOs in vivo and in vitro mediums. From the results of thyme EOs analysis, 29 compounds were identified that containing different terpenes. The results show that skimmed milk with MD performed as an excellent delivery system for emulsifying thyme EOs with high stability for 60 days and formation of small size droplets < 234 nm. The produced powders obtained by spray drying the initial emulsions were analysed, and the results showed that increasing the concentration of MD from zero to 3 % w/w decreased surface oil, retained higher amounts of EOs with the encapsulation efficiency reaching up to 97.4 %. The antibacterial activity against Escherichia coli and Staphylococcus aureus was assessed by using free and encapsulated thyme EOs in the form of the solution or direct addition to the inoculum or food products. The minimum inhibitory concentration (MIC) was lowest 0.3 mg/mL against both Escherichia coli and Staphylococcus aureus, when encapsulated EOs was directly added to the inoculum and prolonged shelf-life of both skimmed and unpasteurised raw milk were attained with the same formulation. Furthermore, the food matrices had a great role in decreasing the antibacterial activity of EOs by decreasing the availability of the active components and preserving the bacteria cells from them. The encapsulation of EOs increased the bioactivity of thyme EOs. The combination of EOs and low temperatures had a significant role in increasing the shelf-life of whole unpasteurised milk.

Malolactic fermentation (MLF) is an important process in the wine production. MLF results from the metabolism of certain lactic acid bacteria (LAB) and consists in the conversion of malate to lactate and CO2. Except deacidification, MLF can improve the quality and microbiological stability of the wines. The aim of this project was to investigate the preservation and utilization of the LAB with particular reference to the MLF. In order to measure the effect of various preservation methods and their productivity, an assay of cell vitality was developed. This measured the capacity to overcome and recover from freezing and freeze-drying. It was shown that this method was easily used and reliable. The effect of cultural conditions on the cryotolerance and vitality of the LAB was investigated, including: (1) the growth phase, (2) the growth temperature, (3) the medium pH, (4) composition of the medium, and (5) preincubation conditions. The optimal cultural conditions to obtain higher vitality after freezing varied with the species of LAB. When the pH of culture medium was controlled at pH 5 the LAB attained the highest vitality after freezing. When <i>L. plantarum</i> was preincubated in 5g/l yeast extract solution at 25°C for 1 hour, the survival rate of <i>L. plantarum</i> greatly increased, from 5.2% to 46.5%. The conditions of freeze-drying of the LAB were investigated. It was found that 4% yeast extract was the most effective protectant for <i>L. plantarum</i> and L. brevis and 5% glutamate were the best protectant for <i>O. oeni</i>. When the LAB was frozen quickly at -65°C, the vitality obtained was higher than those frozen slowly at -20°C after freeze-drying. Another factor to be considered important was ethanol tolerance when the freeze-dried malolactic bacteria were used in wines. Among the suspension media tested, 5% glutamate and 10% sucrose were the best for freeze-dried <i>L. brevis </i>and <i>O. oeni</i> respectively to obtain high vitality in high ethanol solutions. These studies showed that there were no consistent underlying processes that could be easily identified and that preservation was a species specific, multifactorial process. The MLF was then investigated further by studying the effect of wine components on the batch MLF of <i>L. brevis </i>and <i>O. oeni</i> using a defined synthetic wine. This uniquely allowed a systematic study of the MLF in high alcohol environments. Alcohol tolerance was dependent on temperature and important fermentation intermediates such as citrate, pyruvate and malate. Malolactic fermentations were inhibited when glucose concentration was 2 g/1 to 6 g/1. The inhibition to MLF of <i>O. oeni</i> caused by glucose was relieved when fructose was present. Nutritional status was also an important factor that affected the MLF, when the synthetic wine did not contain added yeast extract, malic acid degradation of <i>L brevis</i> and <i>O. oeni</i> was low (6.1% and 54.3% respectively). Rapid and continuous malolactic fermentation was achieved in the membrane bioreactor (MBR) with high cell density of <i>O. oeni</i> (greater than 108CFU/ml). More than 95% degradation of malic acid in the synthetic wine was obtained at 0.48 1/h of flow rate and 10.4 h residence time. High ethanol concentration of wine was main factor that caused the loss in malic acid degrading activity of <i>O. oeni</i> in the MBR. The poor nutritional condition of wine was not the main factor causing loss in the stability of malic acid degrading activity of <i>O. oeni</i>. The shear stress had little influence on the malic acid degradation of <i>O. oeni</i> under the conditions investigated. Ethanol stress adaptation could improve the stability of malic acid degrading activity of <i>O. oeni</i> in the MBR.

Looking into recent trend on healthy lifestyle, consumers have opted for healthier food product with low sodium and sugar content. However, the reduction of salt and sugar in food products affects the consumer’s acceptance. This research aims in gaining a more in depth understanding on the dynamics of taste compounds release mechanism in the oral cavity. There were many studies conducted previously on volatile compounds without any oral processing actions. Furthermore, little study was done on volatile compounds and on samples under submerge condition. The findings of this research may offer small portion of information on the dynamics of food system under submerged condition. An instrumental model measuring flavour release from gel systems was developed. The instrumental setup enabled modelling of unidirectional solute mass transfer from a cylinder of gel into the surrounding buffer (at pH 7). Gels formed from -carrageenan, alginate and gelatin were compared, due to their wide application in the food industry. Sodium chloride and glucose were chosen as the initial taste compound carrier due to the simplicity and accuracy of recording its release via conductivity measurements and glucometer respectively. In the attempt to mimic certain oral processing conditions, release from gels was studied under a number of controlled conditions: room temperature (ca. 25 ºC) and body temperature (37 ºC), compressed and non-compressed gels. Results showed that release of sodium chloride and glucose were significantly influenced by increasing concentrations of polymer and therefore rigidity of the gels, but the effect of biopolymer types was even more significant. Alginate exhibited the slowest release rate as compared to the other gels, irrespective of gel rigidity. Release rates of sodium chloride or glucose were higher at the higher temperature, but particularly for the gelatin gels, which melted at 37 ºC. Interestingly, compression of the gels did not significantly increase or change on the rate of release of sodium chloride or glucose, so that the differences between the types of gel may be more connected with specific interactions between the gel matrix and the flavour than the ease of diffusion of the flavour through different gel network structures. Comparing the instrumental data collected, curves agrees with the diffusion theoretical curve which suggest the mechanism governs the release is purely diffusion. Gelatin at higher temperature shows poor fit due to its melting properties. Relatively, faster release in instrumental measurement as compared to theory; this suggests the presence of unbound taste compounds in the gel systems which were readily to diffuse away from the gel matrices. Time-intensity sensory evaluation data revealed the correlation between panellists response with the instrumental analysis. Overall findings showed that the instrumental set up gives reproducible results. Investigation reveals polymer types and temperature plays a significant role in the taste compounds release profile. Understanding the fundamental mechanism lies behind the mechanism or taste compounds release and factors affecting it give the food industry more control over its formulations. Food industry may find ways formulating food product with low sodium and sugar content without jeopardizing the consumer’s acceptance.

This thesis presents a theoretical examination of the possibility that the fragments of a protein may provide better colloidal stability than the intact protein itself in the case of αs1-casein. It more generally considers the surface adsorption behaviour of fragmented proteins. In colloidal systems the polymers are mostly present as polydisperse entities. Polydispersity can either be naturally present or be the result of fragmentation, as happens for food proteins during enzymatic modification. Majority of proteins do not possess the most optimum primary structure expected of an ideal colloidal stabiliser. More desirable surface functionality maybe achieved by hydrolysis of edible proteins. For the theoretical examination of this argument we had to extend and develop a new Self Consistent Field (SCF) approach which also had to be validated first. Although this new approach is an extension of the traditional SCF approach, it is capable of modelling highly polydisperse systems in a manner not currently possible with the more usual technique. In this preliminary work we present the results of our method for both homopolymers and proteins. In the homopolymer case, we investigate how the preferential adsorption of homopolymer fragments is influenced by various parameters such as solution concentration, degree of hydrolysis (DH), the intact size of the original homopolymer and the strength of affinity of monomers to the surface. The colloidal stabilising and surface adsorption properties of fragmented proteins were investigated taking the bovine milk protein αs1-casein as an example. The protein was fragmented by selective single bond and also non-selective multiple bond hydrolysis, assumed to be induced by the action of enzyme trypsin. The investigation was carried out at different levels of hydrolysis (DH) and various pH values. We find that the non-selective peptide bond hydrolysis in the case of αs1-casein did not provide a better colloidal stability compared to the intact αs1-casein, at none of the pH values studied here. However, it was shown that a better colloidal stability can be achieved by the selective peptide bond cleavage of particular bonds.

Angkak is a natural red colourant which is usually made by culturing Monascus spp. on cooked rice. Changing from rice to other raw materials which are richer in nutrients could increase pigment yield. Adlay (Chinese pearl barley) has been used as a health food supplement and in traditional Chinese medicine and could be used as a new substrate for angkak production. Evidence also exists that mycotoxin formation during the culture of Monascus on adlay is less. The main objective of these studies was to increase Monascus pigment production by its culture on different types of adlay and to develop a continuous process for solid-state fermentation. Adlay angkak had higher concentrations of red pigments than rice angkak when Monascus was cultured on cooked grains with 50% water content in 250 Erlenmeyer flasks. Maximum red pigment production on cooked whole grain adlay was obtained at a moisture content of 60 %. Adding sugar to adlay increased the pigment formation and fructose was better than glucose and sucrose. Adding a nitrogen source had more effect on the pigment production of adlay angkak than a carbon source. Adding histidine was superior to using monosodium glutamate (MSG) and sodium nitrate. Red pigment production was increased from 9.5 to 77 OD units per gram of dry matter when 2% histidine was added to adlay. Co-culture of Monascus with yeast only slightly increased the pigment yield. Puffed adlay material was found to be a superior material for angkak production compared to whole grains. Optimization of the production process on 100 g puffed adlay showed that adding 4 g histidine, 20 g sugar and 200 g of water increased the pigment concentration 10 fold in fixed tray bioreactors. Oxygen transport limitation in a static bed normally limits angkak production to a layer of a few cm. Fine particles formed a bed which gave more problems with oxygen transport than whole grain particles. Mixing the bed can overcome such problems but cooked whole grain adlay was difficult to mix due to its high adhesivity. It was discovered that cooked puffed adlay at a moisture content of 60% gave high productivity yet low adhesitivity, and could be mixed easily. A rotating drum bioreactor was used to produce angkak on puffed adlay. In a continuously rotating culture at low speed, cells were damaged by shear. An intermittently rotating reactor gave poorer mixing but higher yield. The best condition was an intermittent speed with a low rotating speed and frequency of rotation. Solid state culture on ground adlay showed severe transport limitations. The use of audible sound and ultrasound enhanced pigment formation in ground adlay. The penetration of the pigment into a bed exposed to audible sound vibration was limited to a thin layer of material near the surface, whereas at the optimum power and exposure times the use of ultrasound doubled the pigment yield. Submerged culture on ground adlay was successfully performed in miniaturized stirred bioreactors. Increased agitation intensity improved yield, possibly indicating that oxygen transfer is limited in the miniature bioreactors. The use of puffed grain during solid state culture and ground grain during submerged culture both have advantages for the production of angkak. Both of them can be applied in both batch and continuous processes. The particles of puffed grain make it possible to rotate the substrate during fermentation due to puffed adlay having a reduced stickiness. Overall, a production process based on the use of puffed grain in a solid state fermentation is better than one based on ground grain in a submerged culture because as the water demand of the process will be lower, there will be less waste generation and product stability will be higher. The addition of chemical supplements such as histidine, MSG and octanoic acid to a fermentation in a rotating system could further increase pigment formation.

Lactic acid bacteria (LAB) were isolated during the production and the ripening of Greek dry fermented sausages. Samples were taken at different stages, and 150 "wild' strains were isolated. The majority of the strains isolated were assigned to the species Lactobacillus plantarum biotype (1) (43.3 %) followed by Lb. curvatus, Lb. pentosus (10.7 %), Lb. brevis biotype (1) (8.7 %), Lactococcus lactis subsp. lactis biotype (1) (6.7 %) and Leuconostoc mesenteroides subsp. mesenteroid.es biotype (2) (5.3 %). The possibility of bacteriocin production was tested using the agar well diffusion assay (AWDA). One strain was found to produce bacteriocin (Leuconostoc mesenteroides E131) and its purification was attempted using precipitation with ammonium sulphate, cation exchange, and reverse phase chromatography. Moreover, the purification of curvaticin L442 was attemped, a bacteriocin produced by Lactobacillus curvatus L442, isolated from Greek traditional fermented sausage prepared without addition of starters. The bacteriocin was purified by 50% ammonium sulphate precipitation, cation exchange, reverse phase and gel filtration chromatography. Lb sakei I154, a bacteriocin producing strain isolated from Italian fermented sausage, and the semi-purified bacteriocin from Leuconostoc mesenteroides E131 were validated via industrial trials to evaluate whether the product (fermented sausages) maintains the technological characteristics and the traditional quality characteristics. Three fermentations under controlled conditions were conducted and at the end of these fermentations, products were sliced and packaged under controlled atmosphere (80% N2 + 20% CO2) and stored at 4+/-2 &deg;C for 12 weeks to determine the shelf life of the product. Finally, from the previous industrial trials the proper production parameters were determined as well as the most effective packaging techniques, resulting in the conduction of a Standard Operation Procedures Guide concerning the whole production of traditional fermented sausages.

Luncheon meat was used as a model system for the study of the effect of colour on the acceptability of food. Techniques of colour measurement, panel assessment and colour photography were established. Commercial luncheon meats were examined and parameters which characterised the colour and appearance of the product were evaluated. Luncheon meats, prepared in the laboratory by different chopping procedures but using the same ingredients, received variable acceptability scores in panel tests, attributable to differences in their homogeneity. The effect of various additives on luncheon meat prepared by a standard chopping procedure was investigated. Sodium nitrite was added at levels ranging from 0 to 400 parts per million and acceptable pink cured colours developed at all concentrations above a threshold input level of ten parts per million. Erythrosine powder was examined at levels between 0 to 100 parts per million. In the absence of nitrite satisfactory pink, colours were found in the region of 8 to 10 parts per million erythrosin, but in the presence of nitrite, levels of 2.5 parts per million erythrosine 5 parts per million nitrite were the minima acceptable. Other- colouring matters, Erythrosine Lake, Allura Red, Red 2G, Red Iron Oxide and Carmine were also evaluated in the presence and absence of sodium nitrites. Results showed that the colours of these samples were inferior to those produced by the use of erythrosine powder.