Effect of thermal liquefying of crystallised honeys on their antibacterial activities

Changes in antibacterial activity, colour, and hydrogen peroxide content of Western Australian Jarrah and Marri honeys after storage at different temperatures over time

AIMS

This study aimed to evaluate the effects of storage and different temperatures on the antibacterial activity and physicochemical characteristics of several types of honey.

METHODS AND RESULTS

Honeys stored for 16 weeks at 37 and 45°C showed significant declines in antibacterial activity determined by minimum inhibitory concentrations, the loss of hydrogen peroxide, decreases in honey pH, and increases in honey colour, with changes most pronounced at 45°C. In contrast, honeys stored for 16 weeks at ambient (∼22°C) and cold (4, -20, and -80°C) temperatures showed only minor changes. In a second set of 12 honeys stored for 16-32 months at ambient temperature and then 4°C, honeys showed minor changes in antibacterial activity, increases in colour, and decreases in pH. For a third set of 17 honeys stored for five years at ambient temperature, the honeys showed almost complete loss of hydrogen peroxide and were all significantly darker in colour, but showed varied changes in antibacterial activity.

CONCLUSIONS

Heat was detrimental to the antibacterial activity of honeys, as was long-term storage at ambient temperatures for some honeys but not others.

A Comprehensive HPTLC-Based Analysis of the Impacts of Temperature on the Chemical Properties and Antioxidant Activity of Honey

Honeys are commonly subjected to a series of post-harvest processing steps, such as filtration and/or radiation treatment and heating to various temperatures, which might affect their physicochemical properties and bioactivity levels. Therefore, there is a need for robust quality control assessments after honey processing and storage to ensure that the exposure to higher temperatures, for example, does not compromise the honey's chemical composition and/or antioxidant activity. This paper describes a comprehensive short-term (48 h) and long-term (5 months) study of the effects of temperature (40 °C, 60 °C and 80 °C) on three commercial honeys (Manuka, Marri and Coastal Peppermint) and an artificial honey, using high-performance thin-layer chromatography (HPTLC) analysis. Samples were collected at baseline, at 6 h, 12 h, 24 h and 48 h, and then monthly for five months. Then, they were analysed for potential changes in their organic extract HPTLC fingerprints, in their HPTLC-DPPH total band activities, in their major sugar composition and in their hydroxymethylfurfural (HMF) content. It was found that, while all the assessed parameters changed over the monitoring period, changes were moderate at 40 °C but increased significantly with increasing temperature, especially the honeys' HPTLC-DPPH total band activity and HMF content.

Application of Heating on the Antioxidant and Antibacterial Properties of Malaysian and Australian Stingless Bee Honey

In the honey industry, heat treatments are usually applied to maintain honey’s quality and shelf life. Heat treatment is used to avoid crystallisation and allow the easy use of honey, but treatment with heat might affect the antioxidant and antibacterial activities, which are the immediate health effects of honey. This study will determine the effect of heat treatment on Malaysian and Australian stingless bee honey (SBH) produced by the common bee species in both countries. Eighteen honey samples were subjected to heat at 45 °C, 55 °C and 65 °C for one hour and subsequently analysed for their total phenolic content (TPC), total flavonoid content (TFC), DPPH radical scavenging activity, ferric reducing antioxidant power (FRAP) and minimum inhibitory concentration (MIC). The results show that all samples had high TPC, TFC and antioxidant activities before the treatment. The heat treatments did not affect (p < 0.05) the TPC, TFC and antioxidant activities in most samples, but did inhibit the antibacterial activities consistently in most of the samples, regardless of the bee species and country of origin. This study also confirms a strong correlation between TPC and TFC with FRAP activities for the non-heated and heated honey samples (p < 0.05). Other heat-sensitive bioactive compounds in SBH should be measured to control the antibacterial properties present.

Conventional and emergent technologies for honey processing: A perspective on microbiological safety, bioactivity, and quality

Honey is a natural food of worldwide economic importance. Over the last decades, its potential for food, medical, cosmetical, and biotechnological applications has been widely explored. One of the major safety issues regarding such applications is its susceptibility to being contaminated with bacterial and fungi spores, including pathogenic ones, which may impose a hurdle to its consumption in a raw state. Another factor that makes this product particularly challenging relies on its high sugar content, which will lead to the formation of hydroxymethylfurfural (HMF) when heated (due to Maillard reactions). Moreover, honey's bioactivity is known to be affected when it goes through thermal processing due to its unstable and thermolabile components. Therefore, proper food processing methodologies are of utmost importance not only to ensure honey safety but also to provide a high-quality product with low content of HMF and preserved biological properties. As so, emerging food processing technologies have been employed to improve the safety and quality of raw honey, allowing, for example, to reduce/avoid the exposure time to high processing temperatures, with consequent impact on the formation of HMF. This review aims to gather the literature available regarding the use of conventional and emergent food processing technologies (both thermal and nonthermal food processing technologies) for honey decontamination, preservation/enhancement of honey biological activity, as well as the sensorial attributes.

Bioactive compounds and antibacterial activities in crystallized honey liquefied with ultrasound

The effect of ultrasound on the crystal size, phenols, flavonoids, Maillard products and antibacterial activity of crystallized honeys was studied. Three multifloral honeys (M), one monofloral (MO) and one honeydew (HD) honey were used. Ultrasound was performed at 42 kHz for different times (0, 5, 10 and 15 min). The antibacterial activities were tested against Salmonella typhimurium, Bacillus subtilis, Pseudomonas aeruginosa, Listeria monocytogenes, Staphylococcus aureus and Escherichia coli. In all honeys, the parameters analyzed had significant differences ((P < 0.05)). After 15 min of ultrasound the HD had increments of 44 mg of gallic acid/100 g of honey in phenols, and some M showed increase in flavonoids (5.64 mg of quercitin /100 g of honey) and improvement in inhibition against Salmonella typhimurium was 13.1%. In some honeys the correlation between phenols or flavonoids and antibacterial activity were significant ((P < 0.05)). No correlation was found between Maillard products and antibacterial activity. The ultrasound treatment effect on the crystal size, phenols, flavonoid, Maillard products, and antibacterial activity of crystallized honeys were different in each honey.

Effect of thermal liquefaction on quality, chemical composition and antibiofilm activity against multiresistant human pathogens of crystallized eucalyptus honey

Thermal liquefaction is a conventional method used by beekeepers to liquefy crystallized honey. However, an abusive use of heat may affect its quality, chemical composition and bioactivity. The purpose of this study was to investigate the effect of thermal liquefaction on the quality, chemical composition and antibiofilm properties of eucalyptus honey. Thermal liquefaction (at 45 and 60 °C) did not affect the honey's quality; however, a significant reduction in the reducing capacity, total phenolic content and hydrogen peroxide content was observed. At 60 °C, a significant reduction in the honey's ability to inhibit biofilm formation was observed in Pseudomonas aeruginosa, as well as a reduction in its ability to remove preformed biofilms in both Staphylococcus aureus and Pseudomonas aeruginosa. Structural changes in biofilm architecture caused by honey were not affected by thermal treatment. Therefore, we recommend liquefaction at 45 °C as the most convenient for honey liquefaction without affecting its characteristics.

The antimicrobial activity of polyfloral honey and its awareness among urban consumers in Slovakia

The current interdisciplinary research studies the antimicrobial activity of selected polyfloral kinds of honey (n = 30) against three microorganisms (gram-positive bacteria Enterococcus faecalis, gram-negative bacteria Salmonella enterica, and one yeast Candida krusei) as well as investigates consumer behavior and awareness towards honey healing properties. Consumer research involved 617 honey consumers living in urban areas. T-test for Equality of means, non-parametric tests, and descriptive statistics were applied. Results showed that antimicrobial activity was found in all honey samples with a concentration of 50%. Nevertheless, better activity was obtained in honey samples from urban beekeepers compared to samples from retail stores. Results of consumer research showed that honey is mostly used as food (sweetener in beverages, ingredient in the recipe, or direct consumption) and as medicine mainly during the winter period. The consumer awareness towards honey healing effects was very high (97%), however, 1/3 of respondents were not able to list any specific examples, and only 11 % mentioned antibacterial activity. Furthermore, more than 70% of respondents did not know to explain the term “medical honey” and more than 50% of respondents are not aware of the maximum temperature used for heating honey without decreasing its biologically active compounds.

Antioxidant HPTLC-DPPH Fingerprinting of Honeys and Tracking of Antioxidant Constituents Upon Thermal Exposure

The use of High-Performance Thin-Layer Chromatography (HPTLC) coupled with the use of DPPH* (2,2-diphenyl-1-picrylhydrazyl) as a derivatisation reagent is a novel approach to the analysis of antioxidant activity of honeys. The method facilitates the visualisation of individual constituents that contribute to the overall antioxidant activity of the honey, even if they are not yet chemically identified, and allows for the quantification of their antioxidant activity as gallic acid equivalents. The method supports a more in-depth study of the antioxidant activity of honey as it allows for a comparative analysis of the antioxidant fingerprints of honeys of different floral origin and is able to capture differences in their individual bioactive constituents. Further, it supports the tracking of changes in antioxidant activity of individual honey constituents over time upon exposure to different temperature conditions, which demonstrates the potential value of the method for in-process quality control.

Simultaneous determination of five antiviral drug residues and stability studies in honey using a two-step fraction capture coupled to liquid chromatography tandem mass spectrometry

An effective sample pretreatment method followed by liquid chromatography tandem mass spectrometry (LC-MS/MS) was first developed for simultaneous determination of five antiviral drug residues including ribavirin, moroxydine, amantadine, rimantadine and memantine in honey. To adsorb analytes with different binding properties and overcome the interference of sugars and uridine as endogenous ribavirin structural analogs in honey, the target drugs were extracted with 1% formic acid and then purified by a phenylboronic acid (PBA) solid phase extraction cartridge using two-step fraction capture prior to LC-MS/MS analysis. This method was validated by analyzing honey samples from nine floral origins including miscellaneous flowers, citrus, vitex, rape, acacia, sunflower, linden, buckwheat and jujube spiking at multiple levels, and the recoveries ranged from 82.46% to 116.34%, with relative standard deviations (RSDs) less than 14.58%. The limits of detection (LODs) and limits of quantitation (LOQs) of moroxydine, ribavirin, amantadine, rimantadine, and memantine were 0.1-2 µg/kg and 0.2-5 µg/kg, respectively. Depletion experiments of five antiviral drugs in honey at different storage and process temperatures demonstrated that moroxydine can potentially be used as a drug to cure sacbrood disease in honeybees.

Novel Antibacterial Peptides Isolated from the Maillard Reaction Products of Half-Fin Anchovy (Setipinna taty) Hydrolysates/Glucose and Their Mode of Action in Escherichia coli

The Maillard reaction products (MRPs) of half-fin anchovy hydrolysates and glucose, named as HAHp(9.0)-G MRPs, were fractionated by size exclusion chromatography into three major fractions (F1⁻F3). F2, which demonstrated the strongest antibacterial activity against Escherichia coli (E. coli) and showed self-production of hydrogen peroxide (H₂O₂), was extracted by solid phase extraction. The hydrophobic extract of F2 was further isolated by reverse phase-high performance liquid chromatography into sub-fractions HE-F2-1 and HE-F2-2. Nine peptides were identified from HE-F2-1, and two peptides from HE-F2-2 using liquid chromatography-electrospray ionization/multi-stage mass spectrometry. Three peptides, FEDQLR (HGM-Hp1), ALERTF (HGM-Hp2), and RHPEYAVSVLLR (HGM-Hp3), with net charges of -1, 0, and +1, respectively, were synthesized. The minimal inhibitory concentration of these synthetic peptides was 2 mg/mL against E. coli. Once incubated with logarithmic growth phase of E. coli, HGM-Hp1 and HGM-Hp2 induced significant increases of both extracellular and intracellular H₂O₂ formation. However, HGM-Hp3 only dramatically enhanced intracellular H₂O₂ production in E. coli. The increased potassium ions in E. coli suspension after addition of HGM-Hp1 or HGM-Hp2 indicated the destruction of cell integrity via irreversible membrane damage. It is the first report of hydrolysates MRPs-derived peptides that might perform the antibacterial activity via inducing intracellular H₂O2 production.