School of Chemistry - Theses
Permanent URI for this collection
Search Results
1 - 3 of 3
-
ItemUltrasound-induced Inactivation of Trypsin Inhibitors for Improving their Functionality( 2023-08)Trypsin inhibitors are anti-nutritional proteins that hinder the digestibility of legume proteins in the gastrointestinal tract, therefore, limiting the application of raw legumes and the consumption of legume products. To improve the commercial and nutritional values of legume products, it is vital to inactivate the two trypsin inhibitors, Kunitz inhibitor and Bowman-Birk inhibitor. However, the traditional thermal inactivation process has unsatisfactory inactivation performance due to the high heat and pH stability of trypsin inhibitors. Therefore, some advanced technologies with high-efficiency and energy-saving should be considered to achieve more effective inactivation of soy trypsin inhibitors. In this thesis, both low- and high-frequency ultrasound treatments were applied to inactivate the Kunitz and Bowman-Birk inhibitors, both in the aqueous phase and in emulsions consisting of the aqueous and non-aqueous phases. The mechanism of ultrasound-induced inactivation and ultrasound-assisted interfacial adsorption and inactivation of soy trypsin inhibitors were proposed and the effect of process-relevant parameters on the ultrasound-assisted inactivation was explored. Additionally, the numerical simulation was used to clarify the mass transfer behaviour of ultrasound-assisted soy amino acid adsorption.
-
ItemSonosynthesis of Functional Micro/Nano-structures using Biomolecules( 2022)Malnutrition and access to affordable health services are some of the world’s most urgent problems. The development of nutrient and drug delivery systems by using sub-micro particles as carriers has attained much attention for improving the nutritional value of food and the efficacy of diagnostic/therapeutic treatments. Common methods for synthesizing biofunctional particles usually require many reagents and involve multiple steps. In this regard, a novel and advanced approach for material synthesis needs to be developed and investigated to address those limitations. Ultrasonic techniques have emerged as one-pot and eco-friendly methods for the synthesis of organic and inorganic materials. It has been found that acoustic cavitation derived from sound waves can induce emulsification of liquids to form microcapsules and promote chemical modifications of biomolecules. Protein-shelled microcapsules have been synthesized by using low-frequency ultrasound and reducing agents for food-based applications. However, the direct use of food ingredients for the microencapsulation of microcapsules without resorting to additional external agents was never explored and needs to be investigated further for food-based applications. On another note, drug carriers are usually prepared in nanoscale to enhance interaction with cell membranes for achieving efficient therapeutic treatment. Conventional strategies for preparing drug loaded nanoparticles require matrix materials as carriers, resulting in low drug loading capacity and safety issues. Therefore, synthesis of nanodrugs solely made of antibiotic molecules is a better method for development of drug delivery platforms. Many molecules bearing aromatic groups have been successfully sono-assembled into nanoparticles by high-frequency ultrasound, but they are mainly used as drug carriers. Transforming drug molecules into carrier-free nanodrug has not been widely investigated. As such, I intend to expand new research towards other drug molecules with aromatic moieties. In this regard, my Ph.D. project aims to sono-chemically synthesize various micro and nano structures from biomolecules by tuning the frequency/power of ultrasound without the usage of external reagents. The size of the obtained bio-functional structures is controllable, and their compositions are suitable for use in specific applications such as : i) nutrients delivery in food industries; ii) drug delivery for biomedical applications. The fundamental concepts of sono-chemistry for material synthesis, along with biomolecules (proteins, nutrients and antibiotics) based micro/nano structures and their applications are discussed in Chapter 1. Chapter 2 provides an overview of microencapsulation techniques for food industries and fabrication of nanoparticles for antibiotics delivery. In particular, methodology, formulating materials, current challenges, limitations and innovation are discussed. In Chapter 3, the materials, equipment and methodologies involved in the reactions used in this thesis are thoroughly described. Chapter 4 is the first chapter of result and discussion section. Microcapsules made of egg white protein (EWP), as commonly available biopolymers, were first conceptualized. Oil-soluble nutrients (Vitamin A, D and E) were encapsulated into EWP to form nutrients loaded proteinaceous microcapsules by employing 20 kHz ultrasound. This work primarily points out that high availability of free thiol groups in protein solution is crucial in forming stable microcapsules with robust shells, in order to protect micronutrients from degradation against detrimental effects. In Chapter 5, another two plant-based protein isolates extracted from soybean (SPI) and corn (CPI) were also formulated to form microcapsules. This study provided further insights into the structural, chemical and surface properties of proteins for efficient ultrasonic microencapsulation of micronutrients. A double emulsion technique was further developed to co-encapsulate both oil- (vitamin A and D) and water-soluble (vitamin B, C and minerals) micronutrients. In-vitro digestion study showed that the proteinaceous microcapsules enable sustained release of micronutrients, demonstrating their potential in food fortification applications. In Chapter 6, a sono-chemical strategy for transforming antibiotic doxycycline into carrier-free nanodrugs via high-frequency ultrasound (490 kHz) is reported. This study demonstrates that doxycycline undergoes hydroxylation and dimerization processes upon sonication in an aqueous solution to ultimately self-assemble into nanoparticles. The size of obtained particles could be finely controlled by tuning the applied ultrasonic powers. The nanodrugs exhibited antioxidant properties, along with antimicrobial activity against both Gram-positive (S. aureus) and Gram-negative (E. coli) bacterial strains. These results highlight the feasibility of the ultrasound-based approach for engineering carrier-free nanodrug with multiple controlled bio-functionalities. Chapter 7 provides an overall summary of the entirety of my PhD project as well as my conclusion and thoughts on it.
-
ItemThe effects of ultrasound on the molecular, structural and nutritional aspects of dairy proteins( 2021)Process improvement and product improvement in the dairy processing industry is an ongoing dynamic process. Ultrasound processing technology for food processing is in its developmental stages, and dairy sector is a key area for potential applications. The use of low frequency and high frequency ultrasound to modify functional properties of dairy streams is being widely studied by seeking to modify the protein and lipid components of milk. The effects of ultrasound on size of lipid globules and lipid oxidation volatiles have been studied. The effects on functional properties of milk proteins such as viscosity, gelation, heat stability etc. have been documented. However, the present literature lacks information on the effects that ultrasound processing may have on the fundamental properties of dairy proteins. Therefore, it is of importance to document the effects of ultrasound processing on the molecular, structural and nutritional aspects of dairy proteins. As such, the effects of ultrasound processing on dairy proteins have been studied in the context of the amino acid composition, amyloid modifications, and bioactive peptides released. This work aims to bridge the gap in existing literature attempting to illuminate upon these fundamental aspects. Chapter 1 in this thesis introduces the premise of this research by discussing the fundamental properties ultrasound technology and presents dairy proteins as the central theme of this research. A systematic review of literature in Chapter 2 attempts to build familiarity with the effects of processing on milk proteins; and discusses the potential applications of ultrasound in the dairy industry – noting the studies done on whey are caseins. This chapter also discusses the research areas which could be addressed to answer questions related to the objectives of current PhD work. To encourage the application of ultrasound for dairy processing, it would be of significance to understand the extent of operating parameters that ensure nutritional integrity and food safety. The amino acid integrity of skim milk proteins after sonication along with the potential of ultrasound to modify secondary structural conformations of milk proteins has been demonstrated in Chapter 4. Chapter 5 expands the objectives of Chapter 4 into whole milk systems, taking into account milk lipids and the potential for oxidation of lipids on sonication. In Chapter 5 an effort has been made to better understand the underlying cause of lipid oxidation observed due to ultrasound processing of milk lipids. The observations from this study suggest that the enhanced mass transfer of oxygen due to ultrasonic shear forces makes oxygen non-limiting in lipid phase and increases auto-oxidation reactions. An assessment of amino acid integrity of full cream milk after ultrasound treatment confirmed oxidative stability of milk proteins. These findings complement the data in Chapter 4. Along with amino acid integrity, Chapter 4 also demonstrates that the secondary structural conformations of milk proteins can be modified by ultrasound. The work in Chapter 6 builds up greater understanding on such changes by studying the effects of low frequency ultrasound on isolated beta-lactoglobulin (b-lg). b-lg is a b-sheet rich protein with amyloidogenic potential. The effects of high shear and high temperature microenvironments produced by ultrasonic waves were studied on b-lg aggregation. Ultrasound induced formation of amyloid crystals in dilute b-lg solutions at neutral pH and ambient bulk temperatures. The theoretical reasoning for the aggregation phenomenon substantially adds to the understanding of protein energy landscape. Chapter 7 focusses on nutritional properties of milk proteins. It examines the effect of ultrasound pre-treatment on the release of BCM-7 bioactive peptide from milk by simulated gastro-intestinal digestion (SGID), and the effect on overall protein digestibility. It demonstrates that ultrasound processing could be used to downregulate the release of undesirable BCM-7 bioactive peptide in milk, by affecting the rate of enzymatic hydrolysis of certain intermediate peptide fragments. The findings from this body of work add to the existing knowledge for improved use of ultrasound to ensure nutritional integrity of dairy proteins and lipids, minimising oxidative damage. It also builds on current understanding of ultrasound induced protein restructuring and its potential for modification of peptide release from dairy proteins.