Persistence of Listeria monocytogenes in food processing plants is a huge health and economic burden. Biofilms are considered to be one of the major mechanisms by which this pathogen persists within these environments. Studies so far have mostly used optimal growth conditions in their investigations which may not provide a realistic understanding of the biofilm forming abilities of L. monocytogenes in food processing plants. Therefore the aim of this study was to 1) establish a model (12 ºC, Beef Broth) that closely relates to the food processing environment 2) screen 66 isolates of L. monocytogenes from food and clinical sources and determine their biofilm forming phenotypes (non-, weak, moderate and strong formers) and 3) analyze the correlation between biofilm formation phenotypes and biofilm associated genes detected using polymerase chain reaction (PCR) and Basic Local Alignment Search Tool (BLAST) for whole genome sequences. Biofilm formation established at 12 ºC in Beef Broth was the most consistent and quantifiable at day 9 of incubation. Subsequently, 66 isolates were screened using this model, resulting in 60 isolates being identified as strong biofilm formers, 5 isolates as moderate biofilm formers and 1 isolate as a weak biofilm former. Twenty biofilm associated genes were analyzed using PCR in 27 representative isolates. Out of the 20 genes, at least 17 of them were detected in all the tested isolates. Out of the 106 biofilm associated genes analyzed using BLAST, all the isolates were found to show the presence of at least 92 genes. In conclusion, there was no obvious correlation between the presence/absence of the genes selected for analysis and the ability to form biofilms using approaches performed in this study. However, the model established in the study will be useful in further analysis (transcription and translation studies) of genetic markers responsible for biofilm formation of L. monocytogenes under food processing conditions.

<p>The Food Processing and Postharvest Handling Innovation Lab (FPIL) project seeks to reduce food loss and link up consumers with food-to-food fortified instant products that are enriched with micronutrient sources that target vitamin A, zinc, and iron deficiencies. These are mostly maize-based products, but may be combined with other cereals, such as sorghum, and pseudocereals, such as amaranth. The general goal of this thesis study was to facilitate the adoption of extrusion technology to process instant flours, assess the acceptance and willingness to pay (WTP) for these products, and to assess the health impacts of the products on gut health. A low-cost, single-screw extruder was used that was developed at Purdue, and has been placed in different locations in Africa country study sites. The first study aimed to optimize process conditions of a low-cost single-screw extruder, currently done at 35% feed moisture, for African small- to medium-scale entrepreneurs to produce good quality and low-cost pregelatinized instant pearl millet porridge flours and other whole grains by relating feed moisture (27, 29, 31, 33, and 35%) to extrusion energy, drying time and physicochemical properties. We found that we could lower the feed moisture to 27% and still attain good pasting profiles of the porridges, reduce drying time, have better expansion of the extrudates, obtain increased <i>L</i>* color values of the flours, and with a higher extrusion energy but lower drying time. In conclusion, the single screw extruder can be efficiently operated at 27% feed moisture compared to the currently used 35% feed moisture and obtain instant flours with desired quality. It is not known whether higher extrudate energy consumption may be offset by the lower drying time representing lower drying energy. In the second study, we investigated extrusion enhance <i>in vitro</i> fecal fermentation of maize bran, which has been characterized by a poor gut microbiota fermentation property due to its highly crosslinked and densely branched arabinoxylan chemical structure, making it poorly available to the gut microbiota. We hypothesized that this dense cell wall matrix can be opened for better fermentation by applying extrusion. Test conditions of a twin-screw extruder at Purdue were low (200 RPM) and high (400 RPM) shear rates applied to a maize meal and bran mixture (60:40) at different feed moisture conditions (20, 25, 30%). <i>In vitro</i> fermentation of test materials was conducted on stool samples from three donors. Extrusion increased total short chain fatty acids and produced individualized donor effects on the gut microbiota. Some extruder test condition effects were observed on certain bacteria. For example, extrusion at 30% feed moisture and 400 RPM tended to increase genera of <i>Subdoligranulum</i> and <i>Eubacterium hallii</i> and <i>Ruminococcus</i> <i>torques</i> groups in Donor 1 compared to non-extruded bran. There was also a trend of increase in <i>Subdoligranulum</i> and <i>Blautia</i> in extruded compared to non-extruded bran in Donor 2. In Donor 3, <i>Lachnospiraceae NK4A136</i> group was increased at 20 and 25% feed moistures at 200 RPM and 30% feed moisture at 400 RPM compared to non-extruded bran. In the final study, we investigated the acceptance and WTP for instant fortified flours using the Becker-DeGroot-Marschak mechanism when consumers are incrementally given nutrition information and demonstration how to reconstitute instant flours. This study was conducted in Eldoret, Kenya. Participants preferred the fortified thick porridge higher in maize content than fortified thin porridge prepared from the same blend. Contrarily, thin porridge made from fortified flour with higher sorghum content was ranked more highly than for the corresponding thick porridge. Participants were willing to pay more for instant fortified products higher in sorghum when given product name and nutrient composition, even without a practical demonstration of how to reconstitute the flours. For the instant product higher in maize, consumers needed demonstration of how to reconstitute the instant flour for them pay a higher premium. These findings suggest that food-to-food fortified instant porridge flours have the potential to be adopted and can be used as a vehicle to deliver micronutrients to these populations and that extrusion somewhat enhances fermentation of whole grain fibers by the gut microbiome.</p>

Bacterial presence in low-moisture foods such as flour, cereals, baby formula, and spices, have become a concern due to sanitizing challenges. The food industry currently focuses on wet food sanitation as opposed to low-moisture foods because of bacteria’s inability to reproduce in low water activity media. Traditionally, food processing RF heating pasteurizes in mass quantities while an equivalent consumer device does not exist the market today. A consumer product would help eliminate food waste by providing an easy way to sanitize food and extend shelf life. The Portable Food Pasteurization (PFP) project is an interdisciplinary project involving the Electrical Engineering, Biology, and Food Science departments to develop an RF heating consumer device to pasteurize low-moisture foods. A prototype device was designed but construction was delayed because of the COVID-19 pandemic. We are continuing this project by replacing the previously designed MOSFET inverter with a class C amplifier due to parts availability and performance. The food chamber is redesigned by Jonathan Souza to incorporate parallel plate electrodes for more uniform heating without risk of burning. Tim Erwin improved the flyback converter with a snubber and discharge circuit. Tradeoff analysis is performed on various system components to define a configuration for future development.

Citrus essential oils (EO) are potential antimicrobials, first described as such in 1949 by Piacentini. Due to their acceptability in terms of fragrance and flavour characteristics, they lend themselves to use both in food and in clinical practice. Lemon (Citrus limon) or sweet orange (Citrus sinensis) or bergamot (Citrus bergamia) essential oils and their components (limonene, linalool, citral, hersipidin and neoericitrin) and vapours at different temperatures and pHs were tested for their anti-microbial activity against vancomycin-sensitive Enterococcus faecium and Enterococcus faecalis. Lemon essential oil alone or blended and orange EO alone were not as effective as citral or linalool alone or bergamot blends with inhibition diameters of > 9cm. The ranges established for differences in inhibition of growth were; 5-15°C, 20-25°C, 30-45°C and 50°C (p ≤ 0.005) and pHs 4.5-6.5, pH 7.5, and pHs 8.5 —10.5 (p ≤ 0.001). A blend of 1:1 (v/v) orange/bergamot EO was the most effective with MICs at 25°C and pH 5.5 of 0.25% - 0.5% (v/v) and an MID of 50mg/i at 50°C at pH 7.5, under these conditions viable counts were reduced by 5.5 - 10 log10 cfu/ml (p ≤ 0.001). The mechanisms by which a blend of orange/bergamot EO and its vapour bring about their antimicrobial effect were assessed. Transmission electron microscope (TEM) images established morphological changes as well as suggesting EO blend uptake into the cell. The permeability of the cell increased by x2 after being subjected to the EO and by x40 after exposure to the vapour. There were decreases of 1.5 in intracellular pH, 20 a.u. in membrane potential and 18 pmol/mg protein of intracellular ATP. The application of the EO blend impregnated into wipes reduced surface microbial load of vancomycin resistant and vancomycin susceptible E. faecium and E. faecalis by up to 4 log10 compared with control wipes (p ≤ 0.00 1). The use of the EO blend vapour on surfaces resulted in a 2.5 log10 reduction over 24 hours, whilst the vapours (15mg/L air) showed a microbial reduction of up to 4 log10 on cucumber skin and lettuce leaf after 45 seconds exposure via a heat diffuser at 25°C (p ≤ 0.001). Sensory tests demonstrated that there were no changes to the taste of the foodstuff after treatment with the EO blend vapour compared with untreated controls. Investigations into the applications of the EO blend showed no significant difference in effect of EO blend between vancomycin resistant and vancomycin susceptible strains. The results of this study suggest that the use of a citrus essential blend both in oil and vapour form could be a potential alternative to chemical based antimicrobial

This thesis seeks for a better understanding of the sensory properties of hydrocolloid thickened foods during oral processing through studying both flow and lubrication behaviours. In addition, during oral processing, saliva plays an important part through mixing with samples, and it is therefore the mixture of foods and saliva that is perceived. However, the role of saliva in sensory perception is not fully elucidated. This research also features a preliminary study on both flow and lubrication properties of saliva in presence of the 5 basic tastants and also how lubrication properties of hydrocolloids are changed when mixing with saliva. Two groups of five samples were designed to have either similar viscosity at a shear rate of 50 s-1 or 105 s-1 by varying the concentrations of xanthan and dextran with the aim to find out which shear rate(s) is related to mouthfeel perceptions. Samples had the same levels of sucrose and banana flavour (isoamyl acetate) added to them and the flavour release and in mouth perceptions measured. The flow behaviour of samples were further characterised in small amplitude dynamic oscillatory shear and stretch flow. A trained sensory panel generated and evaluated mouthfeel, aroma and taste attributes of these solutions. Sensory results indicated that both low and high shear viscosity were related to mouthfeel perceptions. Models including both low and high shear viscosity values predicted the ‘Thickness’ perceptions better than the models including a single shear viscosity. Stickiness and mouthcoating perceptions were better predicted through models including both low shear viscosity and extensional viscosity. Mouthfeel perceptions were also found to be related to complex viscosity at angular frequency of 100 rad.s-1. In terms of sweetness perception, it was affected by the low shear viscosity. However, for samples having similar low shear viscosity, higher scores of overall sweetness were given to samples that were less shear thinning. The high shear viscosity of hydrocolloid samples determines the lubrication properties. Samples with higher viscosity at high shear rate were found to have lower friction in mixed regime but higher in hydrodynamic regime. The mouthfeel perceptions were found to be correlated with friction coefficient at speed of 40-100 mm/s and flavour and aroma were negatively correlated with friction coefficient at speed of 10-30 mm/s. The flow and lubrication behaviour of saliva is changed significantly when stimulated by five basic tastes. The presence of saliva mixed with hydrocolloid samples reduced the friction by up to two orders in boundary and mixed regime but did not affect the friction in hydrodynamic regime which is more related to mouthfeel perceptions.

High Gravity (HG) and Very High Gravity (VHG) fermentations are increasingly attractive within the brewing industry as a means of energy-saving and to optimise process efficiency. However, the use of highly concentrated worts is concomitant with a number of biological stress factors and in particular elevated osmotic pressure, which can impact on yeast quality and fermentation performance. In order to eliminate or reduce such negative effects, yeast cells often respond to their environment by adapting their central carbon metabolism and by making osmotic adjustments. The aim of this research was to investigate the impact of wort gravity on carbon flux, key performance indicators and to examine the effect of external osmolality (as a measure of osmotic pressure) on cell physiology. The fermentation performance of lager and ale brewing yeasts in standard (13 °P), HG (18 °P) and VHG (24 °P) worts was assessed with respect to the uptake of wort sugars, and the production of key carbon metabolites. Estimation of carbon partitioning revealed that products including trehalose, glycogen, higher alcohols and esters had only minor effects on carbon distribution, whereas the production of yeast biomass acted as a major trade-off with ethanol production. Moreover, parallel analysis of the fermentation environment indicated that osmolality increased during fermentations, particularly at high gravities, with the largest contribution directly related to ethanol production. Consequently, yeast cells were subjected to a series of increasing osmolality levels induced by sorbitol, designed to replicate high gravity conditions. These conditions were shown to have a negative impact on yeast viability and vitality, although cell genome integrity was unaffected. In addition, cells responded to osmotic pressure by modifying membrane components leading to a change in fluidity, and by promoting glycerol production. It is anticipated that the data presented here will provide a greater understanding of the response of yeast to HG and VHG conditions, potentially leading to process optimisation in the future.

Potato granules from different sources were found, on extrusion, to produce potato snacks of variable quality. In some instances strip formation was unsatisfactory, in other instances blistering of the snack occurred on frying. In total, about 20-25 batches of potato granules were examined and classified in relation to these two phenomena. The amylose/amylopectin ratios of these samples of potato granules were determined by the semi-micro potentiometric iodine titration technique, but it was found that there was no significant differences in the amylose/amylopectin ratio in relation to the extrusion behaviour of the granules. The determination of the amount of free starch present outside the potato granules also did not show any clear differences between the satisfactory and unsatisfactory potato granules, though the extract from the unsatisfactory potato granules tended to indicate that they contained more lipid than the satisfactory ones. The unsatisfactory potato granules yielded a higher amount of total extractable soluble starch than their satisfactory counterpart, for the same variety of potato granules. The amount of soluble starch increased on extrusion and it was also found to be related to the breaking strength of the extrudate and their blistering behaviour. A stronger strip which gave a higher amount of soluble starch possessed a greater tendency to blister. Addition of PSA additives to potato granules prior to extrusion increased the soluble starch content, but the degree of blistering was suppressed. Gel permeation chromatography experiments showed that the starches extracted from inside the potato granules consisted of mostly high molecular weight macromolecules (very similar to that of amylopectin) and a smaller quantity of low molecular weight macromolecules similar to amylose. The soluble starch extracted from the outside of potato granules also consisted of a greater amount of high molecular weight macromolecules whereas, after extrusion, a greater quantity of smaller molecular weight macromolecules was found to be present which presumably had been expressed from the granules and was assisting in forming the network, binding the potato granules together to form a coherent strip. Determination of the total phosphate and glucose-6-phosphate contents of both potato granules and extracted starches did not show any correlation between the satisfactory and unsatisfactory potato granules. The quantities of phosphate present were small (0.8%). Studies were conducted to elucidate the differences in the cell wall material between satisfactory and unsatisfactory potato granules. Results showed only minimal differences in both the amount of cell wall material and the composition of neutral sugars in the cell wall extract of different potato granule samples. Investigations of the macromolecular order in the granules were pursued along several lines. By x-ray diffraction it was found that the manufactureof potato granules by the add-back process produced changes in the molecular order of the starch component transforming the B-type x-ray pattern of native potato starch to, in the potato granules, the A-type typically found in cereal starches. The differences in molecular order of the starch component between the satisfactory and unsatisfactory potato granules were also investigated using infra-red spectroscopy and differential scanning calorimetry besides x-ray diffractometry. However, there was no simple correlation with either the crystal type or relative crystallinity of potato granules and their extrusion behaviour. Infra-red studies also did not reveal any differences in the spectra nor the absorbance values at wavelengths of 935, 855 and 760 cm-1. D.S.C. and x-ray results, followed subsequently by lipid analysis, established that the unsatisfactory behaviour of certain batches of potato granules was due to the presence of excess GMS (>0.3%), which prevented the formation of a coherent strip, whereas satisfactory granules had a normal amount of GMS (0.3%) which was not detected by either D.S.C. or x-ray techniques. The excess GMS of unsatisfactory granules when monitored as the unassociated material (by the M L peak), was found to decrease with storage time. Extrusion of satisfactory potato granules, when examined by D.S.C. was accompanied by an increase in the amylose-lipid complex (V-amylose) as indicated by the M A-L peak and this was further enhanced on the addition of PSA additives. However, the formation of the V-amylose complex was not very evident in the x-ray patterns. X-ray crystallinity studies indicated that the extrudates exhibited a lower order and it was presumed that there was less x-ray order in the V- than in the A-form. The crystallinity of potato granule samples were found to be affected by their moisture content, the highest crystallinity was achieved with samples having approximately 38% moisture. NMR experiments in conjunction with heating experiments which had been designed to ascertain the amount of bound water before and after heating the granules to 90°C, indicated that although the bound water content before heating did not show any clear differences between satisfactory and unsatisfactory samples, there was a tendency for the unsatisfactory granules to show a slight decrease in bound water after heating. Experiments using varying amounts of water revealed that the spin-spin relaxation time (T2) increased with the water content of both satisfactory and unsatisfactory granules. The increase was greater for the satisfactory granules at 65% and 55% moisture content and lower for 45% and 35% moisture content, compared to the unsatisfactory granules. A mathematical model has been constructed which assumed that blistering was the consequence of an over-strong intergranular network which had a low permeability for water vapour. The experimental physical constraints of time, temperature and water content when introduced into the model showed that the blistering phenomenon could readily be explained. It was finally concluded that unsatisfactory strip formation was a consequence of the presence of excess GMS while blistering occurred when extrusion yielded a higher intergranular polysaccharide network (as evidenced by the amount of the total soluble starch).

No description available.

Chemical modification was applied to a coffee process by-product, silver skin, as well as raw coffee beans, with the aim to improve their aroma quality. Heat treatment in combination with sugar addition or enzyme treatment was applied to silver skin to encourage Maillard reactions. The manipulation applied to silver skin, however, did not give satisfactory results as the treatments neither caused significant increase in coffee aroma levels, nor yielded coffee aroma with quality resembling that of the real coffee. Chemical modification of raw Robusta coffee was carried out using fractionation and reconstitution approaches. The fractionation process involved the use of three types of solvent varying in polarity, dichloromethane (DCM), methanol (MeOH), and water, thus yielding four raw coffee fractions: DCM-soluble, MeOHsoluble, Water-soluble, and residue fractions. The reconstitution process involved wet mixing of the raw coffee fractions, vacuum drying and moisture content adjustment. Several reconstituted coffees were prepared with various proportions of the raw Robusta fractions, roasted and subjected to volatile analysis by Gas Chromatography-Mass Spectrometry (GC-MS). Statistical analysis by Principal Component Analysis (PCA) and the calculation of sum of normalized standard deviation (SNSD) of aroma compounds' odour activity values (OAVs) showed that the reconstituted Robusta that yielded the least variation, in term of aroma profile, from the higher quality coffee, Arabica, was the one composed of 70% d. b. MeOH fraction, 30% d. b. cell-wall material (residue), and 11 % w/w moisture content. The aroma profile of Arabica coffee was used as a reference due to its fine flavour that is commonly considered of better quality compared to that of Robusta (Briandet, Kemsley et al. 1996). Sensory evaluation (by sniffing) employing hedonic pairwise comparison technique confirmed the result from the GC-MS analysis that the aroma quality of the chosen reconstituted Robusta was improved since its aroma was significantly more preferred to that of the Robusta by the judges (30 people). Non-volatile compound analyses, however, suggested the need for further sensory study that involves tasting/drinking of the brews made with the new reconstituted Robusta for it contained significantly higher contents of bitter/astringent taste compounds, i.e. chlorogenic acids, caffeine and trigonelline, than the original coffees that could also affect the overall sensory quality of the coffee.

Gelation due to the Maillard reaction took place when solutions containing a low level of bovine serum albumin were heated in the presence of carbonyl compounds. The Maillard reaction caused a change in colour, a decrease in the pH and induced gelation. These changes were dependent on the type and concentration of sugars or protein and on the heating conditions used. Reducing sugar and Maillard reaction products (e.g. glyoxal) affected these changes, yet their order of reactivity for browning and gelation were not necessarily the same. Loss of available lysine and arginine plus changes in the thio amino acids showed that these were implicated in the reaction. The gelation kinetics (gelation time and development of storage modulus) were followed in real time using a Bohlin CS Rheometer at a temperature of 90 °C. These studies showed that the gels did not form at a specific pH, the pH being lower for samples where the more reactive carbonyl compounds were used. Measurement of the charge on the protein after the Maillard reaction showed an increased negative charge, hence causing a lowering in the protein's isoelectric point. This had the effect of changing the critical protein concentration necessary for gelation at any pH above the isoelectric point. This reasoning would also explain the low syneresis seen in the Maillard gels. Hydrodynamic studies on dilute solution showed that the protein molecules heated in the presence of xylose associated in an orderly manner despite having a low pH. The aggregates could be described as "stiff and rod like". The linkages holding *the aggregates together were mostly attributed to additional non-disulfide linkages resulting from the Maillard reaction. Similar types of crosslinks were formed in the Maillard gels heated at 90°C and were thought to have enhanced the gel strength. Extrusion of soya grits with reducing sugars did not form a retort-stable product. However, microwave heating of the extruded product was successful in producing a product that survived a typical canning process. This suggests that formation of crosslinks may be controlled to produce novel food products.