Lachlan J. Schwarz

As part of our commitment to empowering Indigenous youth and promoting broader appreciation of Australian Indigenous peoples’ knowledges, we have developed science activities centred on antioxidant testing of customarily used plants. Conventional antioxidant assays, such as those based on 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), 2,2-diphenyl-1-picrylhydrazyl (DPPH), ferric reducing antioxidant power and total phenolic content, often require reagents that are hazardous, costly or difficult to obtain. By contrast, the assay developed here employs safe, low-cost and readily available materials, while providing results comparable to established methods. Based on the redox properties of Betadine (a povidone–iodine complex) and the intense blue colour formed in a starch-Betadine solution, this Blue Betadine Antioxidant Test (BBAT) demonstrated quantitative agreement with the assays listed above for a range of antioxidant compounds (e.g. r2 = 0.989 based on catechin). When applied to extracts from 10 customarily used Australian native plants, the BBAT results were in good agreement with conventional assays, with results most closely aligned with ABTS and DPPH (concordance correlation coefficients ≥0.95). The BBAT is a safe and accessible method suitable for research, education and outreach, providing a culturally relevant platform for exploring the antioxidant properties of customarily used medicinal and food plants.

Three Australian populations of Portulaca oleracea—Common Purslane, Omega Gold and Omega Red—were grown under identical conditions, separated into portions—leaf, bud, stem and root—and their extracts tested for total phenolic content (TPC), Trolox equivalent antioxidant capacity (TEAC), ferric-reducing antioxidant potential (FRAP), and for antioxidant activity against hydroperoxides and thiobarbituric acid reactive substances (TBARS) in a linoleic acid emulsion. Highest TPC was found in Omega Gold and Omega Red roots, with 31.1 and 36.5 mg gallic acid equivalents per gram dry weight (mg GAE/g DW), respectively, being ten times higher than for Common Purslane roots (3.1 mg GAE/g DW). Other plant portions were generally higher for Omega Gold and Omega Red, though with much less difference, i.e., ●+), revealed a peak with significant activity. Purification of the compound responsible yielded oleracein australis 1, and 1D and 2D NMR data are presented for the first time. The results of this study show that Australian populations of P. oleracea are high in bioactivity and may be superior to the internationally recognised medicinal plant, Common Purslane.

Oxidative stress and inflammation are known to be linked to the development of chronic inflammatory conditions, such as type 2 diabetes and cardiovascular disease. Dietary polyphenols have been demonstrated to contain potent bioactivity against specific inflammatory pathways. Rice bran (RB), a by-product generated during the rice milling process, is normally used in animal feed or discarded due to its rancidity. However, RB is known to be abundant in bioactive polyphenols including phenolic acids. This study investigates the antioxidant and anti-inflammatory effects of RB phenolic extracts (25, 50, 100, and 250 µg/mL) on RAW264.7 mouse macrophage cells stimulated with hydrogen peroxide and lipopolysaccharide. Biomarkers of oxidative stress and inflammation such as malondialdehyde (MDA), intracellular reactive oxygen species, nitric oxide and pro-inflammatory cytokines such as interleukin-6 (IL-6), monocyte chemoattractant protein 1 (MCP-1), interleukin-10 (IL-10), tumor necrosis factor-α (TNF-α), interleukin-12, p70 (IL-12p70), and interferon-γ (IFN-γ) were measured in vitro. Treatment with RB extracts significantly decreased the production of MDA, intracellular reactive oxygen species, nitric oxide and pro-inflammatory cytokines (IL-6, IL-12p70, and IFN-γ) when compared to the control. It is proposed that RB phenolic extracts, via their metal chelating properties and free radical scavenging activity, target pathways of oxidative stress and inflammation resulting in the alleviation of vascular inflammatory mediators.

Oxidative stress is known to modulate insulin secretion and initiate gene alterations resulting in impairment of β-cell function and type 2 diabetes mellitus (T2DM). Rice bran (RB) phenolic extracts contain bioactive properties that may target metabolic pathways associated with the pathogenesis of T2DM. This study aimed to examine the effect of stabilized RB phenolic extracts on the expression of genes associated with β-cell function such as glucose transporter 2 (Glut2), pancreatic and duodenal homeobox 1 (Pdx1), sirtuin 1 (Sirt1), mitochondrial transcription factor A (Tfam), and insulin 1 (Ins1) in addition to evaluating its impact on glucose-stimulated insulin secretion. It was observed that treatment with different concentrations of RB phenolic extracts (25-250 µg/mL) significantly increased the expression of Glut2, Pdx1, Sirt1, Tfam, and Ins1 genes and glucose-stimulated insulin secretion under both normal and high glucose conditions. RB phenolic extracts favourably modulated the expression of genes involved in β-cell dysfunction and insulin secretion via several mechanisms such as synergistic action of polyphenols targeting signalling molecules, decreasing free radical damage by its antioxidant activity, and stimulation of effectors or survival factors of insulin secretion.

Cardiovascular disease (CVD) and type 2 diabetes mellitus (T2DM) are two chronic diseases that have claimed more lives globally than any other disease. Dietary supplementation of functional foods containing bioactive compounds is recognised to result in improvements in free-radical-mediated oxidative stress. Emerging evidence indicates that bioactive compounds derived from rice bran (RB) have therapeutic potential against cellular oxidative stress. This review aims to describe the mechanistic pathways behind CVD and T2DM development and the therapeutic potential of polyphenols derived from RB against these chronic diseases.

Oxidative stress, inflammation and endothelial dysfunction are associated with the development of cardiovascular and metabolic diseases. Phenolic extracts derived from rice bran (RB) are recognised to have antioxidant and anti-inflammatory potential. However, the underlying mechanisms remain unknown. Therefore, this study aimed to evaluate the ability of RB-derived phenolic extracts to modulate genes associated with antioxidant and anti-inflammatory pathways in human umbilical vein endothelial cells (HUVECs) under induced oxidative stress conditions. HUVECs under oxidative stress were treated with varying concentrations of RB phenolic extracts (25–250 µg/mL). Using quantitative real-time polymerase chain reaction, the expression of candidate genes that regulate antioxidant and anti-inflammatory pathways were determined. This included nuclear factor erythroid 2-related factor 2 (Nrf2), nicotinamide adenine dinucleotide phosphate: quinone oxidoreductase 1 (NQO1), heme oxygenase 1 (HO1), nicotinamide adenine dinucleotide phosphate oxidase 4 (NOX4), intercellular adhesion molecule 1 (ICAM1), endothelial nitric oxide synthase (eNOS), ectonucleoside triphosphate diphosphohydrolase 1 (CD39) and ecto-5′-nucleotidase (CD73). Phenolic extracts derived from RB down-regulated the expression of four genes, ICAM1, CD39, CD73 and NOX4 and up-regulated the expression of another four genes, Nrf2, NQO1, HO1 and eNOS, indicating an antioxidant/ anti-inflammatory effect for RB against endothelial dysfunction.

Background and objectives: Phenolic compounds found in cereals have been shown to possess antioxidant activity that has ensured an increased interest in their health beneficial properties. This review analyzed studies investigating the phenolic content of rice, barley, oats, and sorghum grown in different geographical locations and the effect environmental factors have on them.Findings: From the studies reviewed, it was identified that whole grain pigmented cereals exhibited phenolic profiles with polyphenols such as anthocyanins, proanthocyanidins, and their derivatives that translated to higher total phenolic content and antioxidant activity. Variation in phenolic content was also observed in cereal species grown in different geographical locations and when subjected to variable levels of salinity, water, and temperature.Conclusions: Despite the increasing body of knowledge on the phenolic content of cereals, studies focusing on the effect of environment on cereal phenolic content are limited; hence, more research is warranted.Significance and novelty: This review examines literature to provide a holistic understanding of how environment plays a role in the regulation of phenolic metabolites in cereals such as oats with a focus on pigmented varieties of rice, barley, and sorghum.