Part I: Development of novel methods for the synthesis of homoallylic alcohols Part II: Multigrams synthesis of (-)-epibatidine

Ph.DDOCTOR OF PHILOSOPH

Synergistic Effect of a Mixed Culture in Solid-state Fermentation

This study determines the efficacy of a mixed culture in solid-state fermentation from the perspective of cooperative metabolism, in which comparisons with pure culture fermentations were made. Assays performed include Total Phenolic Content (TPC), Total Dietary Fibre (TDF), and Crude Protein Content via the Kjeldahl Method

Nutritional Analysis of Biovalorisaton of Homogeneous Food Processing By-products

Okara and Brewer\u27s Spent Grain (BSG), the food by-products generated during soybean and beer production, respectively, are two of the many food processing side streams that are suitable for human consumption but often discarded. Okara and BSG offer good amounts of both macro and micronutrients. More importantly, they are an exceptional source of proteins. Solid-state fermentation was used to enhance the bioavailability of their intrinsic nutrients. In this study, eight unique strains of Aspergillus Oryzae were used to ferment both Okara and BSG. Subsequently, various quantitative and qualitative analyses were conducted to determine the Total Polyphenolic Content (TPC) and Total Flavonoids Content (TFC) of the fermented biomasses. TPC and TFC were determined via spectroscopic analysis. The microbial fermentation of Okara by Black Koji resulted in the highest increase of TPC and TFC (5- and 13-fold respectively), compared to the control Okara. Meanwhile for BSG, the microbial fermentation by M-1 resulted in the highest increase of TPC in BSG (7-fold). </div

Cooperative metabolism in mixed culture solid-state fermentation

Okara and brewer's spent grain (BSG) are manufacturing side streams that contribute significantly to food waste. In this study, solid-state fermentation (SSF) was performed using okara and BSG as substrates to investigate the effects of fermentation using pure and mixed cultures of Aspergillus oryzae and Bacillus subtilis. The total phenolic content (TPC), crude protein content, and total dietary fibre (TDF) of the fermented substrates were determined to evaluate their nutritional profiles. Okara fermented with a mixed culture under specific conditions produced the highest TPC values, and its TDF profile was the most ideal. These results reflected the presence of cooperative metabolism between Aspergillus oryzae and Bacillus subtilis which afforded greater enhancement in the nutritional profile of substrates compared to that of pure cultures. However, crude protein content could not be accurately determined, and more specific methods of protein quantification and optimisation of sample preparation for BSG in future work is recommended.Nanyang Technological UniversityThis research was supported by C.L.K’s Nanyang Technological University SUG

Biovalorisation of Brewer\u27s Spent Grain (BSG) and Sensory Evaluation of BSG Bread

Brewer’ spent grain (BSG) is the largest by-product of beer production, generating over an approximate 38 billion kg annually. While the majority of BSG gets repurposed as animal feed, its usage unfortunately remains very limited. Due to the impressive nutritional profile of BSG, many studies have investigated its incorporation in food products. However, its substitution at high levels tend to bring about undesirable sensory changes. This paper looks at solid-state fermentation as a tool to enhance the nutritional profile of BSG. The consumer acceptance of fermented BSG- fortified bread was investigated, to understand the market value for fermented BSG food products compared to its unfermented counterpart. Of the 8 koji starters studied, M-1 (Aspergillus oryzae) brought about the greatest nutritional profile enhancement in terms of total phenolic content and crude protein content, with an optimal fermentation time of 4 days. No change in total dietary fibre content was observed after fermentation. From the sensory evaluation, fermented BSG-fortified bread had the best nutritional profile while having the poorest consumer acceptance. Despite the fact, this study highlights that fermentation may yet be an important tool in bridging the gap of BSG incorporation in food. </div

Thermosensitive Fluorescent Liposomes

Liposomes are versatile nanomaterials used in a variety of applications such as drug delivery and bioimaging. In this study, three asymmetrical squaraine dyes were synthesized and embedded in liposomes in the efforts to find a suitable dye that can be used for bioimaging procedures involving liposomes. The optical properties of the synthesized dyes as well as their liposomes were studied and compared to the previously synthesized asymmetrical squaraine dye SQR22 and its liposome form. <br /

Improving photothermal effects of an organic photothermal agent using a chitosan hydrogel

Aggregation of organic photothermal agents enhances their photothermal effect. Conventionally, aggregation is achieved by solvatochromic effects which is not translatable for photothermal applications. This report details the incorporation of an organic photosensitizer into a chitosan hydrogel which induced its aggregation, enhancing its photothermal effect and feasibility for its intended applications.Ministry of Education (MOE)This work is supported by the Ministry of Education, Singapore, under its Academic Research Fund Tier 1 (No. RG69/21, to C. L. K. L.)

Synergistic antibacterial action of lignin-squaraine hybrid photodynamic therapy: advancing towards effective treatment of antibiotic-resistant bacteria

Antibacterial photodynamic therapy (aPDT) is emerging as an effective means of treating pathogenic bacteria, especially in light of the challenges posed by antibiotic resistance. SQR29, an organophotosensitizer, was encapsulated in a poly(lignin/PEG/PPG urethane) hydrogel to enable targeted treatment at a specific infected area. The hydrogel exhibited free radical scavenging properties which were effective in preventing oxidative stress and promoted wound healing. The hydrogel exhibited a significant aPDT effect on Gram-positive bacteria, hence showing its potential in combating antibiotic-resistant pathogenic bacteria in chronic wound infection.The research was funded by joint research grant for Sustainable Materials (No. 021614-00001)

Functionalization of thermoswitchable liposomes for rapid detection of Gram-negative bacteria

Biosensors for rapid and sensitive detection of pathogens play a crucial role in healthcare and food safety. Despite the development of numerous sensing devices, it remains a challenge to obtain biosensors that are reliable, easy-to-use and can offer results within minutes. Herein, we report a functionalized liposome, with an embedded fluorescent dye to offer thermoswitchable emission, for selective Gram-negative bacteria detection. This targeting system utilizes polymyxin B (PmB) as a recognition element, where it can be conjugated onto the surface of the liposome to differentiate Gram-negative bacteria from Gram-positive counterparts as well as mammalian cells via fluorescence spectroscopy. The unique thermoswitchable fluorescence conferred through manipulation of aggregation-induced quenching allows for high signal-to-noise detection, reaching up to 3.5-fold increase in emission in the case of E. coli. This is in contrast to typical small organic fluorescent labels and future work includes developing a suitable capture probe to achieve lower limits of detection.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)This work is supported by the Ministry of Education, Singapore, under its Academic Research Fund Tier 1 (No. RT15/19, to C.L.K.L. and No. RG6/20, to B.X.) and the Agency for Science, Technology and Research, Science and Engineering Research Council (A*Star SERC), Singapore (Nos. A1983c0028 and A20E5c0090, to B.X.)

Biocatalytic ketone reductions using Biobeads for miniaturized high throughput experimentation

Miniaturized reactions conducted in parallel can lead to increased productivity in laboratories without depleting high value reagents. The use of polystyrene beads to coat thin layers of solid reagents offers an elegant strategy to tackle the microscale high throughput solid dispensing conundrum. Herein we report the successful utilization of Biobeads as the first example of high throughput reaction screening with nanomole quantities of ketoreductase on polystyrene beads for asymmetric biocatalytic reactions.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)Nanyang Technological UniversityThis research was supported by the Ministry of Education (MOE) AcRF Tier 1 funding (Grant Number 2019-T1-002-114) and Nanyang Technological University (SUG). Jia Shen Chew is grateful to the Agency for Science Technology and Research (A*STAR) for an undergraduate scholarship