Browsing by Author "Popovich DG"
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- ItemAn improved MTT colorimetric method for rapid viable bacteria counting(Elsevier BV, 2023-11) Xu W; Shi D; Chen K; Palmer J; Popovich DGThe 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay has been employed in the analysis of bacterial growth. In comparison to experiments conducted on mammalian cells, the MTT bacterial assay encounters a greater number of interfering factors and obstacles that impact the accuracy of results. In this study, we have elucidated an improved MTT assay protocol and put forth an equation that establishes a correlation between colony-forming units (CFU) and the amount of formazan converted by the bacteria, drawing upon the fundamental principle of the MTT assay. This equation is represented as CFU=kF. Furthermore, we have explicated a methodology to determine the scale factor "k" by employing S. aureus and E. coli as illustrative examples. The findings indicate that S. aureus and E. coli reduce MTT by a cyclic process, from which the optimal reduction time at room temperature was determined to be approximately 30 mins. Furthermore, individual E. coli exhibits an MTT reduction capacity approximately four times greater than that of S. aureus. HPLC analysis proves to be the most accurate method for mitigating interferences during the dissolution and quantification of formazan. Additionally, this study has identified a new constraint related to the narrow linear range (0-125 μg/mL) of formazan concentration-absorbance and has presented strategies to circumvent this limitation.
- ItemAn Improved Purification Method for Removing Colour Interference from 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyl Tetrazolium Bromide (MTT) Antibacterial Assays(MDPI (Basel, Switzerland), 2023-04-18) Shi D; Xu W; Wong M; Popovich DG; Kowalczewski PL; Kačániová MThe MTT antibacterial assay is an important method in natural antibacterial component discovery. Researchers can use the MTT antibacterial assay to quickly and efficiently evaluate the antibacterial activity of natural compounds. The aim of this research was to find a method to reduce background colour and bacterial cell interference when using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay to study the antibacterial effect of phytochemicals. This study used NZ ‘Hass’ ripe avocado seed extract as an example to develop a silica gel column chromatography method that could combine with the MTT assay to remove the background colour and bacterial cells before the formazan measuring stage. This method is particularly suitable for MTT-based antibacterial inhibition studies when the tested phytochemical extracts have an interfering colour.
- ItemComparative efficiency of extraction techniques for bioactive compounds in Cinnamomum zeylanicum(Elsevier Ltd, 2025-11-30) Culas MS; Kaur L; Popovich DG; Rashidinejad ACinnamomum zeylanicum is a plant well-known for its antioxidant-rich bioactives. This study assessed its total phenolic (TPC) and flavonoid contents (TFC), antioxidant activity, and key bioactives (cinnamaldehyde, eugenol, and cinnamic acid) using two extraction methods: accelerated solvent extraction (ASE) and ultrasonic-assisted extraction (UAE), with solvents including ethanol, methanol, acetone, and water. ASE with 50 % ethanol yielded the highest TPC (6.83 ± 0.31 mg GAE/g), TFC (0.50 ± 0.01 mg QE/g), cinnamaldehyde (19.33 ± 0.002 mg/g), eugenol (10.57 ± 0.03 mg/g), and cinnamic acid (0.18 ± 0.004 mg/g), making it superior to UAE. However, UAE with 50 % ethanol showed the strongest antioxidant activity via ABTS (IC50 = 3.26 μg/mL), while antioxidant activity showed no significant differences. A strong correlation (R = 0.81) between TPC and TFC in ASE extracts indicated that flavonoids are major contributors. This study addresses a research gap by systematically comparing UAE and ASE for extracting key bioactives from Cinnamomum zeylanicum in optimising its bioactive recovery for application in functional foods.
- ItemDevelopment of a validated efficient HPLC-DAD analysis for assessing polyphenol transformation during black tea processing(Elsevier Inc, 2025-12-01) Muthulingam P; Popovich DG; Nimal Punyasiri PA; Nanayakkara CM; Mesarich CH; Rashidinejad ATea (Camellia sinensis) is valued for its polyphenolic compounds, which define its sensory and health attributes. Accurate quantification across processing stages is hindered by analytical and extraction challenges. We developed and validated a rapid high-performance liquid chromatography with diode array detection (HPLC-DAD) method for simultaneous analysis of 12 key constituents - gallic acid, theobromine, caffeine, (+)-catechin (C), (-)-epicatechin (EC), (-)-epigallocatechin (EGC), (-)-epigallocatechin gallate (EGCG), (-)-epicatechin gallate (ECG), theaflavin (TF), theaflavin-3-gallate (TF3G), theaflavin-3′-gallate (TF3’G), theaflavin-3,3′-digallate (TF3–3’G), in green and black tea. The method achieved superior linearity (r² > 0.9995), high sensitivity (LOD: 0.03–1.68 µg/mL), strong precision (RSD < 4.68 %), and high recovery, while also resolving co-elution with a 40-min runtime. Extraction was optimized using ultrasonication with 70 % methanol, which outperformed hot water and ISO-standard methods. Applied to black tea processing, the method revealed a 79.1 % reduction in catechins, post-rolling theaflavin peaks, and dynamic fluctuations in gallic acid, caffeine, and theobromine. These changes were associated with enzymatic oxidation, leaching, and cultivar effects. The validated HPLC-DAD method provides a robust tool for tea polyphenol profiling and enables improved understanding of processing-induced transformations. It holds potential for use in quality control, nutritional labeling, and functional food research in tea and other polyphenol-rich systems.
- ItemPhenolic compounds from macadamia husk: An updated focused review of extraction methodologies and antioxidant activities(Elsevier Ltd on behalf of the Institution of Chemical Engineers, 2024-12) Ahmed MF; Popovich DG; Whitby CP; Rashidinejad AThis review explores the potential of agri-food waste materials, with a particular focus on macadamia nut by-products. Industrial processing of macadamia nuts yields a significant volume of by-products, including green husk and woody shell. Recent research has highlighted these by-products as readily available, cost-effective rich sources of phenolic compounds, renowned for their potent antioxidant and antibacterial properties. This paper emphasizes the importance of selecting an optimal extraction method to fully harness the bioactive potential of these phenolic compounds. In this work, we provide a comprehensive overview of conventional and advanced extraction techniques that are used to extract phenolic compounds from macadamia by-products, with a particular focus on the methods applied to macadamia green husk. Among the various techniques, it appears that ultrasound-assisted extraction, especially when combined with aqueous organic solvents, is more efficient than other methods for this purpose. This review also addresses the challenges in phenolic compound recovery, primarily due to the lack of a standardized extraction process. This often results in the extensive use of extraction solvents to achieve an extract that is rich in phenolic compounds. Overall, this research offers a valuable understanding of the most effective methods for the extraction and recovery of phenolic compounds from macadamia by-products and discusses the potential for scaling up these extraction processes. Hence, it can serve as a useful resource for researchers and industry professionals interested in sustainable and efficient utilization of by-products of the nut industry.
- ItemRapid identification of main antibacterial components from New Zealand ‘Hass’ avocado peel hexane extract(Elsevier B.V., 2023-05-30) Shi D; Xu W; Wong M; Popovich DG‘Hass’ avocado (Persea americana Mill) is a very popular tropical fruit that contains several nutrients, including vitamins, proteins, minerals, and unsaturated fatty acids. ‘Hass’ avocado peel is one of the by-products obtained from the New Zealand (NZ) avocado processing industry. The current study focused on the antibacterial components from hexane ‘Hass’ avocado peel extract. The aim was to perform microbiological screening of NZ hexane ‘Hass’ avocado peel extract using Staphylococcus aureus. We used thin- layer chromatography (TLC) with direct microbiological detection to isolate the individual components that showed antibacterial activity. Mass spectrometry (MS) analysis characterized the isolated components from hexane peel extract. (15Z)-9,12,13-Trihydroxy-15-octadecenoic acid, (±)9-HpODE, and NP-011548 are the three fatty acids that have been tentatively identified. Present findings provide new bioactive components from avocado peel and suggest potential applications for this extract as a natural antibacterial additive in soaps, and detergents.
- ItemRecent advances in encapsulation techniques for cinnamon bioactive compounds: A review on stability, effectiveness, and potential applications(Elsevier Ltd, 2024-02) Culas MS; Popovich DG; Rashidinejad ACinnamon is renowned worldwide for its beneficial health-promoting properties. However, its application in the food industry faces significant challenges due to chemical instability, leading to the degradation of its bioactive compounds, as well as the development of undesirable sensory characteristics caused by the precipitation of salivary proteins by the bioactives. To address these issues, encapsulation methods (both micro and nano) have been developed and studied extensively. This review focuses on recent advances in such encapsulation techniques used to safeguard and deliver cinnamon bioactives, with special emphasis on the spray drying method. The methods employed to evaluate the physicochemical, rheological, and sensorial properties of nano and microparticles are also comprehensively reviewed. The review addresses the challenges associated with encapsulation, including encapsulation efficiency, long-term stability, and release kinetics, and proposes potential strategies to overcome these challenges. Furthermore, the paper presents future perspectives and research directions in cinnamon encapsulation, shedding light on novel materials, advanced characterization techniques, and hybrid encapsulation systems. Overall, encapsulation demonstrates the potential to preserve and harness the therapeutic benefits of cinnamon's bioactive compounds for a wide array of food, pharmaceutical, and nutraceutical applications. With ongoing research and advancements in encapsulation techniques, cinnamon bioactives can be effectively utilized to develop functional and health-enhancing products, catering to the diverse needs of consumers worldwide.
- ItemReduction of the attachment, survival and growth of L. monocytogenes on lettuce leaves by UV-C stress(Elsevier Ltd, 2021-06) Kyere EO; Popovich DG; Palmer J; Wargent JJ; Fletcher GC; Flint SMild stress of leafy greens by UV-C radiation has been reported to stimulate plant defences capable of reducing pathogens on produce surfaces. In this study, the attachment, survival and growth of Listeria monocytogenes was investigated on lettuces stressed with mild UV-C radiation (1.3 and 2.6 kJm−2). Attachment of L. monocytogenes to UV-C stressed (1.3 kJm−2) lettuce leaves after 1 h was significantly (p < 0.05) reduced by 1.4–1.5 log cfu/cm2. UV-C stress also reduced the survival of L. monocytogenes on lettuce by 1.8–1.9 log cfu/g 96 h after inoculation, however a higher dosage of UV-C stress (2.6 kJm−2) did not inhibit the survival of L. monocytogenes. The total phenolic compounds in lettuce significantly increased following UV-C stress (1.3 kJm−2) indicating the accumulation of polyphenols might have contributed to the inhibition of L. monocytogenes attachment and growth. Appropriate dosage of mild UV-C stress of lettuce can reduce the attachment, survival and growth of L. monocytogenes in lettuce and can therefore be explored further for application in fresh produce safety.
