TLC-Bioautography-Guided Isolation and Assessment of Antibacterial Compounds from Manuka (Leptospermum scoparium) Leaf and Branch Extracts.

A rapid procedure for the targeted isolation of antibacterial compounds from Manuka (Leptospermum scoparium) leaf and branch extracts was described in this paper. Antibacterial compounds from three different Manuka samples collected from New Zealand and China were compared. The active compounds were targeted by TLC-bioautography against S. aureus and were identified by HR-ESI-MS, and -MS/MS analysis in conjunction with Compound Discoverer 3.3. The major antibacterial component, grandiflorone, was identified, along with 20 ß-triketones, flavonoids, and phloroglucinol derivatives. To verify the software identification, grandiflorone underwent purification via column chromatography, and its structure was elucidated through NMR analysis, ultimately confirming its identity as grandiflorone. This study successfully demonstrated that the leaves and branches remaining after Manuka essential oil distillation serve as excellent source for extracting grandiflorone. Additionally, we proposed an improved TLC-bioautography protocol for evaluating the antibacterial efficacy on solid surfaces, which is suitable for both S. aureus and E. coli. The minimum effective dose (MED) of grandiflorone was observed to be 0.29-0.59 µg/cm2 against S. aureus and 2.34-4.68 µg/cm2 against E. coli, respectively. Furthermore, the synthetic plant growth retardant, paclobutrazol, was isolated from the samples obtained in China. It is hypothesized that this compound may disrupt the synthesis pathway of triketones, consequently diminishing the antibacterial efficacy of Chinese Manuka extract in comparison to that of New Zealand.

An updated review of functional ingredients of Manuka honey and their value-added innovations.

Manuka honey (MH) is a highly prized natural product from the nectar of Leptospermum scoparium flowers. Increased competition on the global market drives MH product innovations. This review updates comparative and non-comparative studies to highlight nutritional, therapeutic, bioengineering, and cosmetic values of MH. MH is a good source of phenolics and unique chemical compounds, such as methylglyoxal, dihydroxyacetone, leptosperin glyoxal, methylsyringate and leptosin. Based on the evidence from in vitro, in vivo and clinical studies, multifunctional bioactive compounds of MH have exhibited anti-oxidative, anti-inflammatory, immunomodulatory, anti-microbial, and anti-cancer activities. There are controversial topics related to MH, such as MH grading, safety/efficacy, implied benefits, and maximum levels of contaminants concerned. Artificial intelligence can optimize MH studies related to chemical analysis, toxicity prediction, multi-functional mechanism exploration and product innovation.

Formation of Protein-Bound Maillard Reaction Products during the Storage of Manuka Honey.

Honey from the nectar of the Manuka tree (Leptospermum scoparium) grown in New Zealand contains high amounts of antibacterial methylglyoxal (MGO). MGO can react with proteins to form peptide-bound Maillard reaction products (MRPs) such as Nε-carboxyethyllysine (CEL) and "methylglyoxal-derived hydroimidazolone 1" (MG-H1). To study the reactions of MGO with honey proteins during storage, three manuka honeys with varying amounts of MGO and a kanuka honey (Kunzea ericoides) spiked with various MGO concentrations up to 700 mg/kg have been stored at 37 °C for 10 weeks, and the formation of protein-bound MRPs has been analyzed via high-performance liquid chromatography-mass spectrometry (HPLC-MS/MS) following isolation of the protein fraction and enzymatic hydrolysis. During storage, contents of protein-bound CEL and MG-H1 increased continuously, directly depending on the MGO content. For honeys with large amounts of MGO, a slower formation of Nε-fructosyllysine (FL) was observed, indicating competing reactions of glucose and MGO with lysine. Furthermore, the lysine modification increased with storage independently from the MGO concentration. Up to 58-61% of the observed lysine modification was explainable with the formation of CEL and FL, indicating that other reactions, most likely the formation of Heyns products from lysine and fructose, may play an important role. Our results can contribute to the authentication of manuka honey.

Benefits of Manuka Honey in the Management of Infectious Diseases: Recent Advances and Prospects.

The benefits of honey have been recognized since ancient times for treating numerous diseases. However, in today's modern era, the use of traditional remedies has been rapidly diminishing due to the complexities of modern lifestyles. While antibiotics are commonly used and effective in treating pathogenic infections, their inappropriate use can lead to the development of resistance among microorganisms, resulting in their widespread prevalence. Therefore, new approaches are constantly required to combat drug-resistant microorganisms, and one practical and useful approach is the use of drug combination treatments. Manuka honey, derived from the manuka tree (Leptospermum scoparium) found exclusively in New Zealand, has garnered significant attention for its biological potential, particularly due to its antioxidant and antimicrobial properties. Moreover, when combined with antibiotics, it has demonstrated the ability to enhance their effectiveness. In this review, we delve into the chemical markers of manuka honey that are currently known, as well as detail the impact of manuka honey on the management of infectious diseases up to the present.

Dihydroxyacetone in the Floral Nectar of Ericomyrtus serpyllifolia (Turcz.) Rye (Myrtaceae) and Verticordia chrysantha Endl. (Myrtaceae) Demonstrates That This Precursor to Bioactive Honey Is Not Restricted to the Genus Leptospermum (Myrtaceae).

Ma̅nuka honey is known for its strong bioactivity, which arises from the autocatalytic conversion of 1,3-dihydroxyacetone (dihydroxyacetone, DHA) in the floral nectar of Leptospermum scoparium (Myrtaceae) to the non-peroxide antibacterial compound methylglyoxal during honey maturation. DHA is also a minor constituent of the nectar of several other Leptospermum species. This study used high-performance liquid chromatography to test whether DHA was present in the floral nectar of five species in other genera of the family Myrtaceae: Ericomyrtus serpyllifolia (Turcz.) Rye, Chamelaucium sp. Bendering (T.J. Alford 110), Kunzea pulchella (Lindl.) A.S. George, Verticordia chrysantha Endl., and Verticordia picta Endl. DHA was found in the floral nectar of two of the five species: E. serpyllifolia and V. chrysantha. The average amount of DHA detected was 0.08 and 0.64 µg per flower, respectively. These findings suggest that the accumulation of DHA in floral nectar is a shared trait among several genera within the family Myrtaceae. Consequently, non-peroxide-based bioactive honey may be sourced from floral nectar outside the genus Leptospermum.

Monitoring the Release of Methylglyoxal (MGO) from Honey and Honey-Based Formulations.

Methylglyoxal (MGO) is considered to be one of the vital components responsible for the anti-bacterial activity of Leptospermum spp. (Manuka) honey. While many studies have demonstrated a dose-dependent antibacterial activity for MGO in vitro, from a therapeutic viewpoint, it is also important to confirm its release from Manuka honey and also from Manuka honey-based formulations. This study is the first to report on the release profile of MGO from five commercial products containing Manuka honey using a Franz diffusion cell and High-Performance Liquid Chromatography (HPLC) analysis. The release of MGO expressed as percentage release of MGO content at baseline was monitored over a 12 h period and found to be 99.49 and 98.05% from an artificial honey matrix and NZ Manuka honey, respectively. For the investigated formulations, a time-dependent % MGO release between 85% and 97.18% was noted over the 12 h study period.

Five New Phenylpropanoyl Phloroglucinol Derivatives from Leptospermum scoparium.

Leptosperols C-G (1-5), five new phenylpropanoyl phloroglucinol derivatives were isolated from the leaves of Leptospermum scoparium. Compounds 1-3 are phenylpropanoyl phloroglucinol-sesquiterpene adducts with new carbon skeletons. Their structures with absolute configurations were elucidated by detailed spectroscopic analyses, single-crystal X-ray diffraction, and electronic circular dichroism (ECD) calculation. Compounds 2 and 3 exhibited moderate anti-inflammatory activity in zebrafish acute inflammatory models.

Correlation of the antibacterial activity of commercial manuka and Leptospermum honeys from Australia and New Zealand with methylglyoxal content and other physicochemical characteristics.

Variation in the antibacterial potency of manuka honey has been reported in several published studies. However, many of these studies examine only a few honey samples, or test activity against only a few bacterial isolates. To address this deficit, a collection of 29 manuka/Leptospermum honeys was obtained, comprising commercial manuka honeys from Australia and New Zealand and several Western Australian Leptospermum honeys obtained directly from beekeepers. The antibacterial activity of honeys was quantified using several methods, including the broth microdilution method to determine minimum inhibitory concentrations (MICs) against four species of test bacteria, the phenol equivalence method, determination of antibacterial activity values from optical density, and time kill assays. Several physicochemical parameters or components were also quantified, including methylglyoxal (MGO), dihydroxyacetone (DHA), hydroxymethylfurfural (HMF) and total phenolics content as well as pH, colour and refractive index. Total antioxidant activity was also determined using the DPPH* (2,2-diphenyl-1-picrylhydrazyl) and FRAP (ferric reducing-antioxidant power) assays. Levels of MGO quantified in each honey were compared to the levels stated on the product labels, which revealed mostly minor differences. Antibacterial activity studies showed that MICs varied between different honey samples and between bacterial species. Correlation of the MGO content of honey with antibacterial activity showed differing relationships for each test organism, with Pseudomonas aeruginosa showing no relationship, Staphylococcus aureus showing a moderate relationship and both Enterococcus faecalis and Escherichia coli showing strong positive correlations. The association between MGO content and antibacterial activity was further investigated by adding known concentrations of MGO to a multifloral honey and quantifying activity, and by also conducting checkerboard assays. These investigations showed that interactions were largely additive in nature, and that synergistic interactions between MGO and the honey matrix did not occur.

Sugar and dihydroxyacetone ratios in floral nectar suggest continuous exudation and reabsorption in Leptospermum polygalifolium Salisb.

Leptospermum polygalifolium Salisb. can accumulate high concentrations of dihydroxyacetone (DHA), precursor of the antimicrobial compound methylglyoxal found in honey obtained from floral nectar of Leptospermum spp. Floral nectar dynamics over flower lifespan depends on internal and external factors that invariably impact nectar quality. Current models to estimate nectar quality in Leptospermum spp. overlook time of day, daily (24 h), and long-term dynamics of nectar exudation and accumulation over flower lifespan. To explain the dynamics of nectar quality over flower lifespan, accumulated nectar from flowers of different ages was collected from two L. polygalifolium clones, and then re-collected 24 h later from the same flowers. High-Performance Liquid Chromatography was used to quantify DHA amount and total equivalents of glucose + fructose (Tsugar) per flower in the nectar. DHA and Tsugar amount per flower differed with flower age and between clones. In accumulated nectar, the amount of DHA and Tsugar per flower rose to a broad peak post-anthesis before decreasing. Immediately after peaking DHA declined more quickly than Tsugar in accumulated nectar due to a greater decrease in the exudation of DHA than for Tsugar. The DHA : Tsugar ratios in accumulated nectar and in nectar exuded over the next 24 h were similar and decreased with flower age, indicating that exudation and reabsorption occurred concomitantly across flower development. Hence there is a balance between exudation and reabsorption. A quantitative model suggested that flowers have the potential to exude more DHA and Tsugar than actually accumulated.

Exploring the Chemical Properties and Biological Activity of Four New Zealand Monofloral Honeys to Support the Maori Vision and Aspirations.

Honey production and export are significant contributors to the Aotearoa New Zealand economy, generating over 400 million dollars in revenue. Its main export is manuka (Leptospermum scoparium) honey, which has a high commercial value due to its medicinal properties that are linked to its unique chemical composition. The compound methylglyoxal (MGO) has been identified as the main floral marker and is used as a quality indicator, often labelled as unique manuka factor (UMF). However, the high demand for manuka honey creates pressure on beekeepers and may have negative ecological consequences by favouring extensive manuka monocultures to the detriment of other native species. There are other honeys native to New Zealand, such as kamahi (Weinmannia racemosa), kanuka (Kunzea ericoides), rata (Metrosideros robusta) and rewarewa (Knightia excelsa), that also have medicinal properties; however, they are less well known in the local and global market. Indigenous Maori communities envision the production and commercialization (locally and internationally) of these honeys as an opportunity to generate income and secure a sustainable future in alignment with their worldview (Te Ao Maori) and values (tikanga Maori). Diversifying the market could lead to a more sustainable income for beekeepers and reduce pressure on Maori and the conservation land, while supporting indigenous communities to realize their vision and aspirations. This manuscript provides an extensive review of the scientific literature, technical literature and traditional knowledge databases describing the plants of interest and their traditional medicinal uses (rongoa) and the chemical properties of each honey, potential floral markers and their biological activity. For each honey type, we also identify knowledge gaps and potential research avenues. This information will assist Maori beekeepers, researchers, consumers and other stakeholders in making informed decisions regarding future research and the production, marketing and consumption of these native monofloral honeys.

Chemical Analyses and Antimicrobial Activity of Nine Kinds of Unifloral Chinese Honeys Compared to Manuka Honey (12+ and 20+).

Honey has good antimicrobial properties and can be used for medical treatment. The antimicrobial properties of unifloral honey varieties are different. In this study, we evaluated the antimicrobial and antioxidant activities of nine kinds of Chinese monofloral honeys. In addition, headspace gas chromatography-ion mobility spectrometry (HS-GC-IMS) technology was used to detect their volatile components. The relevant results are as follows: 1. The agar diffusion test showed that the diameter of inhibition zone against Staphylococcus aureus of Fennel honey (21.50 ± 0.41 mm), Agastache honey (20.74 ± 0.37 mm), and Pomegranate honey (18.16 ± 0.11 mm) was larger than that of Manuka 12+ honey (14.27 ± 0.10 mm) and Manuka 20+ honey (16.52 ± 0.12 mm). The antimicrobial activity of Chinese honey depends on hydrogen peroxide. 2. The total antioxidant capacity of Fennel honey, Agastache honey, and Pomegranate honey was higher than that of other Chinese honeys. There was a significant positive correlation between the total antioxidant capacity and the total phenol content of Chinese honey (r = 0.958). The correlation coefficient between the chroma value of Chinese honey and the total antioxidant and the diameter of inhibition zone was 0.940 and 0.746, respectively. The analyzed dark honeys had better antimicrobial and antioxidant activities. 3. There were significant differences in volatile components among Fennel honey, Agastache honey, Pomegranate honey, and Manuka honey. Hexanal-D and Heptanol were the characteristic components of Fennel honey and Pomegranate honey, respectively. Ethyl 2-methylbutyrate and 3-methylpentanoic acids were the unique compounds of Agastache honey. The flavor fingerprints of the honey samples from different plants can be successfully built using HS-GC-IMS and principal component analysis (PCA) based on their volatile compounds. Fennel honey, Agastache honey, and Pomegranate honey are Chinese honey varieties with excellent antimicrobial properties, and have the potential to be developed into medical grade honey.

Dimeric Acylphloroglucinol Derivatives with New Skeletons from Leptospermum scoparium.

Leptosparones A-F (1-6), six new dimeric acylphloroglucinol derivatives with unprecedented skeletons, were isolated from Leptospermum scoparium. Compounds 1-3 and 5-6 are phenylpropanoyl-phloroglucinol dimers, while 4 is a phenylpropanoylphloroglucinol-isovalerylphloroglucinol hybrid. Structurally, these compounds represent the first examples of dimeric phloroglucinols with unprecedented C(7')-C(8) linkage between the phloroglucinol core and the acyl side chain. Their structures were elucidated by comprehensive analyses of spectroscopic data, single crystal X-ray diffraction and chemical calculations. In addition, all compounds showed inhibitory effects against α-glucosidase with IC50 values ranging from 39.5 to 186.8 µM.

Proteomic analysis of honey. Identification of unique peptide markers for authentication of NZ manuka (Leptospermum scoparium) honey.

Proteomics is an emerging tool in food authentication that has not been optimised for honey analysis. In this study, we present a qualitative proteomic analysis of New Zealand manuka (Leptospermum scoparium) honey. A total of fifty bee-derived proteins were identified in the honey, the most predominant being major royal jelly proteins (MRJPs). We also demonstrate for the first time the presence of unique nectar-derived proteins in manuka honey. A total of 17 manuka plant proteins were identified, a-third of which were putative pathogenesis-related proteins. Two proteins involved in drought tolerance were also identified. Twelve candidate peptides were selected as potential authentication markers based on their uniqueness to manuka honey. Nectar analyses confirmed the origin and specificity of these peptides to L. scoparium nectar, thus presenting peptide profiling as a viable and novel approach for manuka honey authentication. Raw data are available via ProteomeXchange with identifier PXD021730.

Methylglyoxal binds to amines in honey matrix and 2'-methoxyacetophenone is released in gaseous form into the headspace on the heating of manuka honey.

Reports on the thermal stability of manuka honey in terms of food processing have been few. This study investigated changes in nine characteristic chemicals of manuka honey during heating. Among these, methylglyoxal (MGO) and 2'-methoxyacetophenone (MAP) were significantly decreased by heating at 90 °C. To elucidate the mechanism for this decrease, artificial honey was prepared from sugars and water with MAP or MGO and then heated. The decrease of MGO was enhanced with l-proline, lysine, or arginine derivatives, accompanied by formation of 2-acetyl-1-pyrroline, MGO-derived lysine dimer, or argpyrimidine, respectively, suggesting that an amino-carbonyl reaction is one pathway for the loss of MGO. The decrease of MAP in the artificial honey depended on the volume of headspace in a vessel. MAP from heated manuka honey was also detected in the gas phase, indicating that MAP was vaporized. Heating could thus reduce the beneficial and/or signature molecules in honey.

Use of kinetic data to model potential antioxidant activity: Radical scavenging capacity of Australian Eucalyptus honeys.

Antioxidant activity of honeys may be beneficial in wound healing processes by protecting cells against lipid oxidation. The DPPH assay assesses the efficacy of antioxidant molecules to reduce DPPH• to DPPHH. Studies determining EC50 are limited by single time-point determinations of antioxidant effect and can miss vital information about the rate of antioxidant response. Acquisition of kinetic data allows determination of the radical scavenging capacity (RSC) of honeys. The purpose of this study was to determine the RSC of 53 honeys from 16 species of Australian Eucalyptus trees and four samples of New Zealand manuka (Leptospermum scoparium) honey. Whereas honeys could not be differentiated based on EC50 values, significant differences were observed for RSC, supporting collection of kinetic data for honey analysis. The greatest RSC was observed for New Zealand manuka (4.6 ± 0.3 × 10-5 mg.mL-1.min-1), grey ironbark (E. paniculate; 3.4 ± 0.2 × 10-5 mg.mL-1.min-1) and river red gum honeys (E. camaldulensis; 3.2 ± 0.2 × 10-5 mg.mL-1.min-1).

Leptospermum petersonii as a Potential Natural Food Preservative.

Leptospermum petersonii (family Myrtaceae) is often cultivated for ornamental purposes but also serves as a rich source of bioactive essential oils. While several studies focused on the activities of the essential oils, this study analysed the potential of spent L. petersonii leaves as a natural food preservative. METHOD: We investigated the in vitro antioxidant and antimicrobial activities of crude L. petersonii extracts against activities of the purified isolated flavonoid, 6-methyltectochrysin, which was characterized using spectroscopic methods. The antioxidant assays followed ORAC, FRAP and TEAC tests. The antimicrobial activities of the extract and purified flavonoid were analysed against six multi-drug resistant microbial strains in broth dilution assays. RESULT: The results revealed that both the crude extracts and isolated 6-methyltectochrysin exhibited positive radical ion scavenging antioxidant potential, however the crude extract was about 6-fold more potent antioxidant than the purified 6-methyltectochrysin. The crude extract also showed strong antimicrobial activities against Bacillus cereus, and even more potent antimicrobial agent than the reference ampicillin antibiotic against Klebsiella pneumoniae subsp. pneumoniae. A higher resistance was observed for the tested Gram-negative strains than for the Gram-positive ones. 6-methyltectochrysin was generally inactive in the antimicrobial assays. CONCLUSION: The crude methanolic extract showed significant bioactivity which validates the medicinal relevance of the plant. The observed biological activities, especially against a notorious strain of B. cereus, suggest that L. petersonii could be a promising natural source of food preservatives.

Seasonal and environmental variation in volatile emissions of the New Zealand native plant Leptospermum scoparium in weed-invaded and non-invaded sites.

The New Zealand tea tree Leptospermun scoparium (manuka) is widely known for the antimicrobial properties of its honey. Manuka is native to New Zealand, growing in a range of environments, including the Central Volcanic Plateau of the North Island, where it is currently threatened by the spread of exotic invasive weeds such as heather (Calluna vulgaris) and Scotch broom (Cytisus scoparius). Here, we characterise for the first time the aboveground volatile organic compounds (VOCs) produced by manuka in this area, during summer and winter seasons, in weed-invaded and non-invaded stands. We measured plant volatiles at four sites, each with a distinct combination of woody species: (1) conspecific stands of manuka; (2) manuka and another native species (Dracophyllum subulatum); and manuka with one of two European invasive plants, (3) heather or (4) Scotch broom. We also quantified herbivore damage on target manuka plants and analysed microclimatic variables (soil nutrients, air temperature and soil water content) to investigate their impact on volatile emissions. Our results reveal a strong seasonal effect on volatile emissions, but also significant differences between sites associated with biotic and abiotic changes partly driven by invasive plants. Overall, volatile emission rates from manuka were typically lower at sites where invaders were present. We point to several factors that could contribute to the observed emission patterns and areas of interest for future research to provide a comprehensive understanding of VOC emissions in nature. Given the vital role of volatile compounds in plant communication, we also recommend future studies to be performed in multiple seasons, with larger sample sizes and more study sites to expand on these findings and explore the ecological impacts of changes in VOC emissions during plant invasion.

Leptosperols A and B, Two Cinnamoylphloroglucinol-Sesquiterpenoid Hybrids from Leptospermum scoparium: Structural Elucidation and Biomimetic Synthesis.

Leptosperols A and B (1 and 2), two cinnamoylphloroglucinol-sesquiterpenoid hybrids featuring unprecedented 1-benzyl-2-(2-phenylethyl) cyclodecane and 2-benzyl-3-phenylethyl decahydronaphthalene backbones, along with their biosynthetic precursor (3), were isolated from Leptospermum scoparium. Compounds 1 and 2 represent the first example of phloroglucinol derivatives biogenetically constructed by a De Mayo reaction. The biomimetic synthesis of leptosperol B (2) was achieved using the proposed biosynthetic pathway. In addition, compounds 1 and 2 showed significant anti-inflammatory effects in zebrafish acute inflammatory models.

Leptospermum scoparium essential oil is a promising source of mosquito larvicide and its toxicity is enhanced by a biobased emulsifier.

Synthetic pesticides are the cornerstone of vector-borne disease control, but alternatives are urgently needed to tackle the growing problem of insecticide resistance and concerns over environmental safety. Leptospermum scoparium J.R. Forst and G. Forst (manuka) essential oil and its four fractions were analyzed for chemical composition and toxicity against Aedes aegypti larvae. The use of bio-based amylose-N-1-hexadecylammonium chloride inclusion complexes (Hex-Am) as an emulsifier for L. scoparium essential oil was also investigated. Fraction 1 was inactive, fractions 2 (LC50 = 12.24 ppm) and 3 (LC50 = 20.58 ppm) were more toxic than the whole essential oil (LC50 = 47.97 ppm), and fraction 4 (LC50 = 35.87 ppm) had similar toxicity as the whole essential oil. Twenty-one chemical constituents were detected in L. scoparium essential oil compared to 16, 5, 19 and 25 chemical constituents in fractions, 1, 2, 3 and 4 respectively. The two most dominant chemical constituents were calamenene (17.78%) and leptospermone (11.86%) for L. scoparium essential oil, calamenene (37.73%) and ledene (10.37%) for fraction 1, leptospermone (56.6%) and isoleptospermone (19.73) for fraction 2, cubenol (24.30%) and caryophyllene oxide (12.38%) for fraction 3, and γ-gurjunene (21.62%) and isoleptospermone (7.88%) for fraction 4. Alpha-pinene, ledene, and aromandendrene were 2-7 times less toxic than the whole essential suggesting that the toxicity of L. scoparium essential oil was either due to other chemical constituents that were not tested or due synergist interactions among chemical constituents. Leptospermum scoparium essential oil-Hex-Am emulsion (LC50 = 29.62) was more toxic than the whole essential oil. These findings suggest that L. scoparium essential oil is a promising source of mosquito larvicide and that Hex-Am is an excellent emulsifier for L. scoparium essential oil for use as a larvicide.