Dairy Processing Technology Centre - Masters by Research Theses

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    Characterisation of the changes in the physicochemical properties of high-solids skim milk during thermal processing, and their relationship with fouling
    (University College Cork, 2023) Murphy, Tara R.; O'Mahony, Seamus Anthony; O’Callaghan, Tom F.; Enterprise Ireland
    Fouling of thermal processing equipment during production of dairy products and ingredients is a challenge for the dairy industry, with evaporator fouling during the production of skim milk powder being an area of particular focus. The build-up of foulant mass deposit within different regions of the evaporator technology has significant economic, operational, and environmental consequences for the dairy industry, as the decline in the heat performance of the equipment results in more frequent cleaning required and increased energy and water consumption, in addition to potential deterioration in product quality as the required product temperature may not be achieved. The objectives of the work reported in this thesis were to study the effect of pH on the heat stability and physicochemical properties of concentrated skim milk during thermal processing to assess their contributions to evaporator fouling. Heating concentrated skim milk (30%, w/w, total solids; pH 6.0, 6.1, 6.2, 6.3, 6.4, 6.5, 6.6, 6.7) using a high temperature short time thermal treatment (90 °C x 3 min), using a rheometer, showed that as the pH of the samples decreased, both viscosity and particle size distribution increased after heating, coinciding with an increase in sedimentation. Heat treatment (90 °C x 2 h) of concentrated skim milk at pH 6.2 on the fouling rig resulted in severe fouling. Moreover, when the concentrated skim milk was analysed for particle size and sedimentation after heat treatment using the fouling rig, the findings aligned with the initial analysis conducted during the rheometer based HTST thermal treatment. Further characterisation of evaporator fouling was carried out by heat treating concentrated skim milk samples at pH 6.1, 6.3, 6.5 and 6.7 on the fouling rig while in-line measurements of pH, conductivity and temperature were conducted, followed by analysis of the concentrated skim milk samples, cleaning-in-place chemicals and foulant material adhered to the heat exchanger after the fouling experiments. It was observed that samples of concentrated skim milk that caused fouling also displayed increased viscosity, particle size and sedimentation when compared to the samples that resulted in no fouling. The adhered foulant formed at pH 6.1 and 6.3 was found to consist predominantly of protein on a total solids basis, with protein profiling showing that the most prominent proteins were denatured β-lactoglobulin and α-lactalbumin, as well as a strong presence of caseins. It was found that by maintaining the pH of concentrated skim milk above 6.3, fouling during heat treatment could be successfully avoided. Furthermore, through pH adjustment to achieve no fouling to extensive fouling, it was possible to analyse physicochemical properties such as viscosity, particle size, and sedimentation, to provide a practical approach to predict the potential for fouling in concentrated skim milk. These findings contribute significantly to our understanding of the impact of protein stability on the formation of fouling deposits caused by concentrated skim milk, allow us to develop/validate predictive tools and to develop/test mitigation strategies for fouling.
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    Mechanical integrity and rehydration properties of agglomerated nutritional dairy ingredient powders
    (University College Cork, 2019-12-22) Hazlett, Ryan; O'Mahony, Seamus Anthony
    The functional properties of nutritional dairy powders are key in determining the ease at which they can be stored, handled and further applied in formulations or on direct consumer application. Powder agglomeration is a unit operation employed during the spray drying process, in order to obtain a greater control of the resulting powder’s physical, bulk handling and functional properties. The studies presented in this thesis explore the importance of maintaining agglomerate integrity on powder handling (i.e., powder conveying) post-spray drying, while presenting novel research findings in the application of agglomeration for the modification of commercially important, high-protein content dairy powders (e.g., milk protein isolate; MPI). Initially, a custom fabricated pressure dispersion rig was utilised to achieve breakdown of agglomerated powder particles, similar to that occurring in industrial powder conveying systems (i.e., lean phase conveying). Analysis of the resulting powders showed that the significant alterations in both powder physical and bulk properties (i.e., decreased particle size, increased bulk density and increased surface free fat concentrations), occurring on agglomerate breakdown, significantly impaired the functionality (i.e., flowability and rehydration) of a range of commercially agglomerated nutritional dairy powders (i.e., whey protein concentrate, fat-filled milk powder and an infant formula powder). In addition, the agglomeration of MPI was researched, focusing on the utilisation of novel protein-based binders to achieve agglomeration. The results demonstrated that the use of novel protein-based binder solutions achieved a greater extent of agglomeration in comparison to more traditional binder solutions (i.e., water or lactose), ultimately improving the flowability and wetting properties of MPI powders. The conclusions of this thesis demonstrate the importance of maintaining the mechanical integrity of agglomerated dairy powders and the potential for the further application of agglomeration using novel protein-based binder solutions to tailor the functionality of high-protein dairy powders, such as MPI.
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    A comparison of the use of whole milk and fat-filled milk powders for production of heat-stable long-life beverages
    (University College Cork, 2020-04) Crotty, Aisling; Kelly, Alan; O'Mahony, Seamus Anthony; Enterprise Ireland; Dairy Processing Technology Centre
    Commercial bovine milk is 3.5% fat, the level of which is affected by seasonality, stage of lactation, feed, health, breed, and even the individual teat. Milk (and other liquid dairy products) are highly perishable due to their nutritional quality, as they are the sole source of nutrition for the neonate. As a result, milk is often dehydrated into powder form, which enhances its shelf life, its storage stability, and the convenience. Another way to enhance the shelf life of milk is to subject it to heat to destroy pathogenic bacteria, enzymes, spores, and to enhance the shelf life of the product. As most dairy products are subjected to some form of heat treatment, their heat stability is integral to the overall quality of the product. In Chapter 2, two reconstituted dairy powders (fat-filled milk powder (FFMP) and whole milk powder (WMP)) were compared under two heat treatments (UHT-processing and retort sterilisation), and three protein contents (2.3, 3.3, and 5%). These variables significantly affected the apparent viscosity, the pH, the colour, the emulsion stability, and the average particle size of the samples. Chapter 3 investigated the influence of calcium-chelating salts on heat stability. These salts are an often-used ingredient in dairy products, as they enhance the heat stability of the system by binding the calcium ions, which are important for casein micelle integrity. The influence of trisodium citrate (TSC), disodium hydrogen phosphate (DSHP), and sodium hexametaphosphate (SHMP) on heat stability, colour, and apparent viscosity was examined. SHMP had the most significant effect on heat stability, colour, and apparent viscosity due to its chelating capacity and its influence on cross-linking between the casein micelles. DSHP had no significant effect on viscosity or colour, whereas the addition of 20 mmol/L of TSC significantly affected the colour of the solution.
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    Compositional and analytical factors affecting the stickiness of dairy powders
    (University College Cork, 2019-10) O'Donoghue, Laura T.; O'Mahony, Seamus Anthony; Murphy, Eoin; Enterprise Ireland
    Spray dying is a dehydration technique used in the dairy industry for the preservation and creation of a wide range of valuable dairy products. However, challenges associated with stickiness development are often encountered during spray drying, particularly with spray dryer feed streams containing high levels of lactose, which can lead to lower yields, reduced powder quality and shorter runs. Stickiness in lactose-containing powders is related to the glass transition phenomenon, in which a phase change occurs in the amorphous form of lactose, causing a decrease in the viscosity of the powder particle surface, leading to liquid bridging and ultimately stickiness between particles and/or to equipment surfaces. There is a wide variety of compositional and environmental factors that affect the rate and extent of stickiness development in dairy powders, such as the temperature and relative humidity of the air or the protein content of the powder. The first objective of this study was to investigate the influence of particle size on the physicochemical properties and stickiness behaviour of a selection of lactose-containing dairy powders. Using a fluidisation technique, this work demonstrated that stickiness increased with decreasing particle size for lactose-containing dairy powders. Stickiness may be characterised using a number of different instrumental approaches, which can be categorised as direct/indirect or static/dynamic techniques. However, most methods provide a binary definition of stickiness (i.e., sticky or non-sticky), which while pragmatic, does not provide information regarding the mechanical relaxations which contribute to stickiness. Therefore, the second objective of this study was to examine the use of dynamic mechanical analysis (DMA) to characterise temperature- and humidity-induced relaxation behaviour of whey protein concentrate (WPC) powders; results were also compared to two other established techniques, differential scanning calorimetry (DSC) and a fluidisation method. The results demonstrated that while DMA may not be an accurate method for stickiness determination, it could prove useful as a complementary method when combined with stickiness techniques (e.g., fluidisation) to provide more detailed information on the physical changes occurring during stickiness. Overall, the findings of this research will prove useful to dairy processors at minimising issues with stickiness during drying and may also potentially provide powder technologists with a new method for tracking the physical transitions that occur during stickiness development of dairy powders.