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Item Characterization, antibacterial activity, and stability of supercritical fluid extracted lemongrass nanoemulsion on Bacillus cereus(Elsevier Ltd, 2025-06) Mohd Daud IS; Mahmud Ab Rashid NK; Palmer J; Flint SNatural food preservation is a sustainable approach to extend shelf life, combat foodborne pathogens and enhance food safety. Bacillus cereus, a resilient contaminant, poses challenges due to its spore-forming ability and association with foodborne illnesses. This study investigates the characterization, antimicrobial activity, and stability of lemongrass (Cymbopogon citratus) nanoemulsions, extracted using supercritical fluid extraction (SFE), and their efficacy against B. cereus isolates (ATCC 14579, P4, and M2). Lemongrass oil was extracted at 85, 100, 200, and 300 bar, with the highest yield (0.815 %) obtained at 300 bar. Nanoemulsions were formulated with lemongrass extract and commercial citral, characterized for droplet size, polydispersity index (PDI), conductivity, and zeta potential, and assessed for antimicrobial activity. Lemongrass nanoemulsions initially had droplet sizes of 86.32 ± 0.66 nm, but increased over six months due to coalescence, with PDI values rising from 0.50 ± 0.00 to 0.81 ± 0.27, indicating reduced stability. Although zeta potential declined from −44.01 ± 1.69 mV to −33.63 ± 1.45 mV, it remained within the stable range (>±30 mV), maintaining sufficient electrostatic repulsion to prevent rapid aggregation. At 2.0 % concentration, nanoemulsions effectively suppressed B. cereus isolates (<1.00 CFU/mL), though efficacy declined after four months with increasing droplet size. Lemongrass nanoemulsions exhibited comparable antibacterial activity and stability trends to citral, suggesting that whole lemongrass extract retains its bioactivity as effectively as its major compound. Improved stabilization strategies, such as polymer encapsulation, could enhance shelf life, expanding applications in food preservation.Item The effects of ageing treatment on bioactive contents and chemical composition of liquid smoke food flavourings(Springer Nature, 2022-05-01) Xin X; Zhao W; Essien S; Dell K; Baroutian SLiquid smoke food flavouring is an alternative to traditional food smoking. Ageing treatment of liquid smoke can remove tar to improve a consistent sensory experience but traditionally takes months by storage. This study proposed a thermal treatment approach to accelerate the ageing process. Liquid smoke samples from kānuka and hickory woodchips were prepared by fast pyrolysis. The obtained liquid smoke samples were subjected to ageing by storing them at ambient temperature for 18 months. Accelerated ageing of liquid smoke was carried out by heat treatment at 80 °C for 24 and 48 h. Tar formed during the ageing process, with a yield ranging from 2.2 to 4.1 wt.%. Both ageing treatments resulted in decreases in bioactive content and their activities in terms of total phenolic content (TPC), total flavonoid content (TFC), ferric reducing antioxidant power assay (FRAP) and 2,2-diphenyl-1-picrylhydrazyl scavenging activity (DPPH). Chemical composition and principal component analyses indicated that liquid smoke chemical compositions were influenced by wood type and ageing conditions. It was found that thermal treatment at 80 °C for 24 h was sufficient to age liquid smoke.Item The physicochemical properties of β-carotene emulsions stabilized by whey protein/octenyl succinic anhydride (OSA)-modified-starch complexes: Influence of OSA substitution degree of starch(Elsevier Ltd, 2024-04-01) Lin Q; Yang X; Liu Y; Lu Y; Liu W; Han J; Singh H; Ye AComplexes formed between heated whey protein isolate (HWPI) and octenyl succinic anhydride (OSA)-modified starches were prepared to stabilize β-carotene-containing oil-in-water emulsions. The zeta-potential, turbidity, particle size, and microstructure of the complexes were determined to evaluate the impact of the degree of substitution (DS) of OSA-modified starch on the complexes' structure. HWPI and OSA-modified starches with low DS values formed elongated complexes. With increasing DS, the particle size of the complexes reduced. In comparison to the emulsions stabilized by HWPI or OSA-modified starches, the emulsions stabilized by HWPI/OSAS complexes exhibited superior protection of β-carotene during storage under acidic conditions. When the DS of OSA-modified starch increased, the particle size of emulsions stabilized by the complexes decreased, with less droplet aggregation occurring. The physical stability of these emulsions against storage time, ions, and thermal process showed a positive relationship with the DS, while the β-carotene retention in the emulsions during storage showed a negative relationship with the DS. The greater physical stability of the complex-stabilized emulsions containing OSA-modified starch with a higher DS may be ascribed to enhanced electrostatic repulsion among oil droplets and the formation of a more rigid and denser surface structure in the presence of more OSA groups.Item Effects of high pressure on DNA and its components : a thesis presented in partial fulfilment of the requirements for the degree of PhD in Bio Physics at Massey University, Manawatū, New Zealand(Massey University, 2015) Lepper, Christopher PaulThere have been many speculations for the environment in which life originated but it has still yet to be determined what environmental chemical and physical conditions were necessary for the evolution of self-replicating chemical systems. While it has been determined that DNA, RNA and their components are chemically unstable at high temperatures, there has currently been only a small number of studies into the role of high pressures on the chemical and physical stabilities. High-pressure NMR spectroscopy has been used here to study the effects of high temperatures/pressures on the chemical stability of DNA and its components. This has been done with the use of a specialised commercial high-pressure NMR cell capable of withstanding pressures up to 250 MPa. In addition to this, a custom safe handling apparatus and pump system was developed for the operation of this cell. Studies into the effects of high pressures on the rate of hydrolysis of cytosine and cytidine at 100 °C were performed by measuring the rates of hydrolysis with time under various pressure conditions. These results have shown that the rates of hydrolysis of cytosine and cytidine increase considerably with pressure. The effects of high pressure on the physical stability of DNA were determined by performing dissociation (melting) experiments on several different DNA sequences under multiple pressure conditions. It was found that the melting point of a small DNA hexamer decreased slightly with pressure whereas the melting points of larger dodecamers increased overall with pressure. It was also found that the melting point of an i-motif structure decreased with increasing pressure. The effects of high pressure on the chemical stability of cytosine were again studied, this time for cytosine residues within both single- and double-stranded DNA. DNA samples for bacteriophage FX174 were incubated under various temperature and pressure conditions. Results for these studies have yet to be determined as the incubated DNA is yet to be sequenced. It has been discovered that high pressures have a negative effect on the chemical stability of DNA constituents while having an overall small positive effect on the physical stability of DNA.