Food Institute - Doctoral Theses

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    Plant protein structure design and its potential substitution of dairy proteins in gelation systems
    (University College Cork, 2023) Tang, Qi; Miao, Song; Roos, Yrjo; O'Sullivan, Maurice; China Scholarship Council; Horizon 2020
    Plant-based proteins are gain attention as versatile alternatives to dairy-derived proteins as functional ingredients in food formulations due to their greater sustainability and lower production costs, and health benefits. However, in-depth knowledge about the structural and functional knowledge of plant and dairy proteins under different pH conditions and the modifying technologies for binary plant and dairy proteins have rarely reported. The study investigated the pH-dependent behavior of structural, and functional properties, especially thermal gelation performance, of plant protein and dairy proteins. Moreover, the study also explored the modifying strategies on the gelation performance of lentil-dairy binary protein gels treated with by heating and microbial transglutaminase. The studies focused on the influence of different pH levels on the structural, surface properties and functional properties of different plant proteins and dairy proteins. Findings demonstrated that dairy proteins generally showed brighter color (higher L* and lower a* and b*), higher solubility, emulsification properties, and foaming capacity compared to plant proteins, whereas plant proteins displayed superior foaming stability and water holding capacity. The thermal gelation performance of plant proteins and dairy proteins are also showed that the disulfide bond formation was attributed to partial 11S acidic and basic subunits of plant proteins (soy, pea, lentil, and chickpea). The disulfide-bonded aggregation was attribute to partial β-Lg and α-La in WPI, which was inhibited at acidic conditions but facilized under higher pH conditions, whereas in CM, κ-casein and αs2-casein might involve in this process. Moreover, the highest gel performance of SPI and CPI were peaked at pH 9, but that of LPI at pH 3, whereas no self-standing gel formed for PPI at the same protein concentration (14%, w/w) over the test pH conditions. For dairy protein, whey protein showed the superior gel performance at pH 7, whereas that was observed optimum at pH 3 for casein micelles. The modification strategies were further explored by subjecting plant and dairy binary protein mixtures to heating and microbial transglutaminase treatment and demonstrated that only certain fractions (legumin acidic and basic subunits) in LPI involved in disulfide-mediated polymerization, whereas almost all fractions in WPI were involved, but that of CM was hindered during heating treatment. However, the 11S acidic subunit and 7S vicilins in LPI were involved in Gln-Lys isopeptide bond formation when subjected to MTGase treatment, whereas that was hindered in WPI but promoted in CM. The binary protein gel performance demonstrated that the application of heating treatment could result in the formation of self-standing gels when replacing whey protein with lentil protein. Nevertheless, when aiming to substitute casein micelles with lentil protein with good gel performance, microbial transglutaminase treatment was found to be a more effective modifying method. Furthermore, a higher ratio of casein micelles to lentil protein can lead to a significant enhancement in gel performance, resulting in improved mechanical properties, rheological properties, water-holding capacity, and the development of more homogeneous and compact microstructures. Remarkably, when substituting 25% casein with lentil protein, similar gel performance with casein alone was observed when mediated by microbial transglutaminase treatment. The findings of this study offer a profound comprehension of the distinctions between plant proteins and dairy proteins regarding their structural and functional properties under varying pH conditions. Furthermore, this research provides different modifying strategies for substituting dairy proteins with plant proteins, thereby broadening the potential applications of plant proteins in diverse food formulations.
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    Evidence-based design, physiological efficacy testing and consumer analysis of an exemplar model of a fruit derived bioactive functional food for use in physical performance and exercise settings
    (University College Cork, 2023) Carey, Conor C.; Lucey, Alice; Doyle, Lorna; Department of Agriculture, Food and the Marine, Ireland
    The overall aim of this thesis is to examine the new product development practices used within the scientific design, development and testing of new nutritional products in the performance nutrition sector. Despite recent growth in the area there is a general lack of publicly available information to guide the incorporation of nutritional science into the processes underpinning the design and development of new performance nutritional products. Performance nutrition provides a promising area for the creation of value-add products using Irish agrifood outputs, a key priority in Irelands Food Vision 2030 strategy ( - Food Vision 2030 – A World Leader in Sustainable Food Systems, 2021). In chapter 1, frameworks that were created as part of this PhD thesis to inform and guide the incorporation of nutritional science in the development of new products are introduced. These frameworks are applied throughout the subsequent chapters in the design and development of an exemplar model of a functional food to support post exercise recovery and endurance exercise performance. This exemplar model took the form of a blackberry polyphenol enriched high protein milk. Chapter 2 reviews the literature on new product development and discusses the role of polyphenols and protein in post-exercise recovery and supporting endurance exercise performance. The review confirms the efficacy of dairy protein, particularly in the form of bovine milk, for muscle repair and regeneration post-exercise. RCTs have consistently shown the benefits of consuming between 1.2-1.6g/kg/day of high-quality protein for those undergoing frequent exercise. While there's growing evidence to support the use of plant-derived polyphenols for exercise-induced muscle damage (EIMD) recovery and endurance exercise performance, gaps remain in understanding their mechanisms, dosing, and optimal dietary sources. Chapter 3 presents an online survey that assesses the nutrition priorities, practices and preferences of athletes and active individuals. This survey was designed as part of this thesis following a series of focus group sessions with athletes of various levels and backgrounds. This survey provides key end-user insights into the nutritional wants and needs of athletes and active individuals. Key findings highlight muscle recovery as the primary nutritional priority among the athletic community and reveal a clear preference for food product forms over supplements. The data collected provides invaluable guidance for new product development in sports nutrition and allows the meaningful incorporation of end-user insights into the process. Chapter 4 bridges a crucial knowledge gap by conducting a systematic review and meta-analysis investigating the efficacy of flavonoid-rich polyphenols to support post-exercise recovery. The meta-analysis of 26 randomised controlled trials (RCTs) observed significant benefits in muscle strength and soreness recovery post intensive exercise. However, a notable limitation in the included studies was the inadequate characterisation of the polyphenol subclasses and dosages used, emphasising the need for more detailed reporting in future human studies. Chapter 5 presents an RCT assessing the efficacy of the RubusElite beverage prototype to support post-exercise recovery. Results suggest that this beverage augments recovery of muscle strength and reduces muscle soreness in comparison to both high protein and low protein milks. In collaboration with RubusElite project partners, this RCT includes detailed characterisation of the beverage's polyphenol content and a verification of polyphenol stability within the treatment beverage for the study duration. Chapter 6 further investigates the efficacy of the RubusElite prototype in relation to physical performance during a 15km cycling trial. In contrast to previous findings, no significant improvement in performance or exertion-related measures was observed. However, thorough polyphenol characterisation alongside these findings offers critical insights into the lack of observed benefits and provides direction for the reformulation of the prototype. This also provides considerable insights into future RCT design to reassess the efficacy of the reformulated prototype. In summary, this thesis offers a comprehensive investigation into the development of performance nutrition products through the creation of an exemplar model using novel frameworks which allow for the incorporation of scientific best practice. It provides innovative insights into the role of polyphenols and protein in supporting exercise and is one of the first undertakings to assess their efficacy in combination. By combining rigorous scientific evaluation, consumer insights, and product prototyping, the research offers a comprehensive roadmap for future product development in the rapidly evolving domain of performance nutrition.
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    Investigations of the complex relationships between minerals, pH and heat stability in milk protein systems
    (University College Cork, 2023) Aydogdu, Tugce; O'Mahony, Seamus Anthony; McCarthy, Noel; Teagasc
    The complex composition of milk and derivatives therefrom, mean that its stability in respect to thermal treatment, while well studied, is ever evolving. Non-fat milk powders are rich in protein, of which there may be greater than 4500 different nitrogenous compounds, often present in conjunction with milk minerals. Variations in the total concentration and individual components of proteins and minerals makes dairy science a multifaceted system from which nutritional dairy products emerge, manipulated and produced by processing factors such as temperature, pressure, dehydration, shear and filtration. At the centre of dairy processing lies the most basic element fundamental to solvent chemistry; hydrogen, used as a measure of chemical reactions, but more often taken as a control parameter for physical and sensory properties. Therefore, the objective of this thesis was to advance considerably our knowledge on milk protein and milk mineral systems with regard to three main properties; heat stability, viscosity and pH changes, which have cumulative effects on dairy processing performance and finished product quality and functionality. A novel method of measuring pH at ultra-high temperatures was adapted from the pharmaceutical industry and used to examine the hydrogen ion concentration in dairy systems. For the first time, a non-linear decrease in skim milk pH was shown with increasing temperature from 25 to 140°C. The pH of skim milk decreased from 6.7 at 25°C to 6.1 at 140°C, with this reduction being reversible on cooling. This was not the case for milk permeate, where the pH remained low after sequential heating and cooling, due to irreversible calcium phosphate formation and precipitation. This highlights the stabilizing ability of micellar casein in skim milk against significant levels of calcium phosphate precipitation. However, while precipitation might be reduced, the addition of milk permeate to milk protein concentrate (MPC) resulted in substantial levels of age thickening after evaporation (45% dry matter), whereas MPC with added lactose showed no age related viscosity increase. The former system also had lower pH compared to the latter. Given the significant influence milk permeate had on viscosity of protein solutions, the heat coagulation time of commercial bulk skim milk obtained across the spring period was assessed to determine if the changes in milk composition from early lactation affected heat stability. Type B HCT-pH profiles were shown for bulk milk samples taken in February and March, compared to a type A profile for April milk, with this type A profile continuing for the remainder of the year. This is the first time that a change in HCT profile has been shown for commercial bulk milk samples; although there was no obvious difference in milk composition between any of the samples. Ultrafiltration of the skim milks was performed to obtain milk permeate fractions and was used to swap the retentate obtained in February with the permeate from April milk. This showed that a type B HCT-pH profile in February could be changed to a type A profile by simply swapping the serum phase. The outcomes of the research in this thesis are highly applicable to the thermal processing of complex nutritional formulations (e.g., infant formulas), where mineral additions and substitutions are common practice. The ability to measure pH during UHT processing is certainly a highlight of the work presented herein. In addition, a key new finding is that macro composition, specifically protein and mineral profile, is not always a good predictor of HCT, but that the serum phase of milk has the more substantial effect on heat stability than the colloidal phase on its own. The work presented in the thesis provides novel information to both the dairy industry and academia, in terms of process control through in-line pH measurement, and the fundamental effects of milk serum on protein heat stability.
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    Sensorial, cultural and volatile properties of dairy powders, yoghurt and butter from pasture and non-pasture cow diets
    (University College Cork, 2022-12-14) Zeng, Cheng; O'Sullivan, Maurice; Kerry, Joseph; Kilcawley, Kieran N.; Teagasc
    Significant advances have occurred in the ability to extract and identify volatile aromatic dairy compounds that may influence sensory perception. In this Thesis volatile extraction techniques were optimised and evaluated in order to obtain a more representative volatile profile of selected dairy products, such as; whole milk powder, skim milk powder, yoghurt and salted butter. This information was also utilised with gas chromatography olfactometry (GC-O) and sensory analysis to determine which specific compounds are most likely influencing sensory perception. In addition the impact of cow diet was assessed in terms of the volatile and sensory profile on skim milk powder, whole milk powder and salted butter using milk from cows outdoors on pasture-fed diets (such as ryegrass, ryegrass and white clover) and cows indoors on trial mixed rations. Cross cultural sensory analysis was also undertaken on skim milk powder from these diets in order to determine if consumers and trained panellists perceived skim milk powder differently based on diet but also on product familiarity Chapter 1 provides an updated review of traditional and novel sensory methods used to evaluate milk, milk powders, yoghurt, and butter, as well as gas chromatography mass spectrometry and gas chromatography olfactometry extraction techniques to provide more complete profile of volatiles that impact sensory perception. Chapter 2 investigates the impact of pasture and non-pasture cow diets on the volatile cross cultural sensory perception of skim milk powder. The volatile profile and sensory properties of the skim milk powder were influenced by cow diet and Irish, Chinese and USA consumers as well as trained sensory panellists perceived products differently primarily based on familiarity. Chapter 3 investigated if yoghurt produced from three different starter cultures were perceived differently by Irish consumers, German consumers and trained assessors. German trained assessors found it more difficult to discern differences between some of the yoghurts than trained Irish assessors. Seventeen of the 24 volatiles compounds identified differed due to starter culture, which most directly or indirectly associated with lipid oxidation.The ability of headspace solid phase microextraction, thermal desorption, and high capacity sorptive extraction as a direct immersion and headspace extraction technique were compared with and without salting out and by a polar and non-polar gas chromatograph column for volatile profiling of whole milk powder in Chapter 4. The impact of three different diets on the sensory properties and volatile profile of whole milk powder was investigated in Chapter 5. Both the sensory perception and volatile profiles of whole milk powder differed significantly depending on the diet, with whole milk powder derived from rye-grass or rye-grass and white clover more similar than whole milk powder derived from total mixed ration. Most of the differences in volatiles due to diet were either directly or indirectly linked to fatty acid content. Chapter 6 outlines the development and optimisation of direct immersion high capacity sorptive extraction for the extraction, separation and identification of volatile compounds from salted butter from three different diets; rye-grass or rye-grass and white clover or from total mixed ration. This thesis has clearly demonstrated that cow diet influences the volatile and sensory characteristics of selected dairy products, which subsequently effects sensory perception on a cultural basis influenced by product familiarity. The benefits of optimising volatile extraction techniques on a product specific basis were clearly demonstrated along with using multiple techniques in order to achieve the most representative volatile profile as possible. Combining volatile analysis with olfactometry and / or sensory techniques enables a more comprehensive understanding of factors influencing sensory perception and choice that can be utilised for product quality, improvement and marketing.
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    Evaluation of the manufacture of cheese from micellar casein concentrate or using novel coagulants
    (University College Cork, 2022-09-23) Li, Bozhao; McSweeney, Paul L. H.; Kelly, Alan; Department of Agriculture, Food and the Marine, Ireland; Food Institutional Research Measure
    Novel materials and coagulants for cheese manufacture are currently of interest since the development of membrane filtration technology and gene recombination technology may offer opportunities for innovation in cheese manufacture. A novel dairy material – micellar casein concentrate (MCC) – is the co-product of whey protein recovery. As the main protein source in cheese is casein, MCC has the potential to be a starting material for cheese manufacture. The objective of the work presented in the first part of this thesis was to evaluate the feasibility of the manufacture of Cheddar and Quarg cheeses from micellar casein concentrate. In addition, camel chymosin has been reported to cause less proteolysis as a coagulant for cheese manufacture compared to bovine chymosin. The suitability of manufacture of Cheddar cheese using a novel camel chymosin with structural changes was also investigated. The rennet and acid coagulation properties of micellar casein concentrate were evaluated. MCC had a higher casein in total protein content compared to low heat skim milk powder (LHSMP), and shorter rennet coagulation time and higher gel strength were found in MCC compared to that of LHSMP. A gelation pH value greater than 5 was found in MCC. MCC produced by cold microfiltration (MF) formed acid-induced gels with high strength at pH 4.6, while the gel strength of acid-induced gels formed by warm MF MCC reached the highest at a pH value of around 5 and decreased below this value due to rearrangements of the casein network. The suitability of the manufacture of Cheddar cheese from MCC was subsequently investigated; standard control milk, skim milk with cream, reconstituted MCC with cream and reconstituted LHSMP with cream were used for comparison. The use of MCC led to increased proteolysis compared to the other treatments, linked to higher plasmin and chymosin activities in the cheese. Increased springiness, cohesiveness and meltability were found in Cheddar cheese manufactured from MCC. For the manufacture of Quarg cheese, lower moisture and higher protein contents were found in cheese made from MCC compared to that made from LHSMP. Cheese made from hot MF MCC showed the highest hardness compared to that made from LHSMP or cold MF MCC. Higher glycomacropeptide (GMP) content was found in cheese whey made from MCC. The suitability of manufacture of Cheddar cheese using a modified fermentation-produced camel chymosin (mCC) was investigated; fermentation-produced bovine chymosin (BC) and camel chymosin (CC) were used for comparison. The use of mCC led to reduced proteolysis compared with BC or CC, and higher instrumental and sensory hardness and lower meltability were found in cheeses made using CC or mCC compared to BC. Descriptive sensory analysis indicated less sulphur and barny flavour in cheese made with CC and mCC, while cheese made using mCC showed the lowest brothy flavour and bitter taste. Finally, the proteolytic specificity of the three generations of chymosin on NaCN at pH 5.2 with 5% NaCl and 6.5 and in proteolysis of Cheddar cheese made using these coagulants were investigated. Many peptides were identified through liquid chromatography-mass spectrometry (LC-MS) in both NaCN digests and Cheddar cheese made using each chymosin. Other than the majority of peptides produced by BC and CC reported in the literature, some new peptides were identified in this study as well. The proteolytic activity of mCC was relatively lower than that of BC and CC. Overall, the results presented in this thesis will support the innovation and application of new materials for the manufacture of cheese and other dairy products and add to the understanding of the properties of three generations of chymosin when used in cheese manufacture.