Strawberry Tree Honey Research Articles

Free fluoride determination in honey by ion-specific electrode potentiometry: Method assessment, validation and application to real unifloral samples

Surprisingly, a reliable method for measuring the concentration of free fluoride ions in honey is still missing from the literature, notwithstanding the generally recognized importance of the analyte and the matrix. To fill this gap, this study proposes and validates a straightforward ion-specific electrode potentiometric method for this task. The method offers very low detection and quantification limits (6.7μgkg−1 and 25μgkg−1, respectively), good linearity (R2>0.994), good sensitivity (typically 55±3mV for an order of magnitude of concentration) in an unusually low concentration interval (between 0.020 and 1mgL−1), and acceptable precision and bias. The method was applied to 30 unifloral (thistle, eucalyptus and strawberry tree) honey samples from Sardinia, Italy. The amount of free fluoride ions found in these honeys appears to be lower than the range usually found in the literature; indeed, early results suggest a possible dependence of the analyte concentration on the honey’s botanical origin.

Physicochemical Parameters and Bioactive Compounds of Strawberry Tree (Arbutus unedoL.) Honey

Botanical origin, physicochemical properties (ash, colour, diastase activity, electrical conductivity (EC), hydroxymethylfurfural (HMF), moisture, optical rotation (OP), pH, reducing sugars, total acidity, total soluble solids, and water activity), bioactive compounds (BC), and antioxidant activity obtained from strawberry tree honey from South Portugal were investigated. Results showed that the pollen analysis and physicochemical parameters were found within to meet international honey specifications. Significant differences (P<0.05) in results of ash content, EC, HMF, OP and colour when were compared with analogous famous Italian honey (Sardinia island). For BC, total phenolic and total flavonoid content were 94.47 mg gallic acid/100 g and 5.33 mg quercetin/100 g, respectively. Concerning Portuguese honey, it was also found that radical scavenging activity (DPPH assay) was 43.46% and antioxidant activity was 18.85 mg ascorbic acid equivalent/100 g and 9.92 mg quercetin equivalent/100 g. These results confirmed that Portuguese strawberry tree honey has the highest antioxidant activity, when compared with other kinds of honey. This complete report demonstrates advantages and can help to promote consumption and shown their benefical properties (e.g., antioxidant); which will may increase the commercial value.

Arbutus unedo L.: chemical and biological properties.

Arbutus unedo L. (strawberry tree) has a circum-Mediterranean distribution, being found in western, central and southern Europe, north-eastern Africa (excluding Egypt and Libya) and the Canary Islands and western Asia. Fruits of the strawberry tree are generally used for preparing alcoholic drinks (wines, liqueurs and brandies), jams, jellies and marmalades, and less frequently eaten as fresh fruit, despite their pleasing appearance. An overview of the chemical composition of different parts of the plant, strawberry tree honey and strawberry tree brandy will be presented. The biological properties of the different parts of A. unedo and strawberry tree honey will be also overviewed.

Phenolic content, antioxidant and physico‐chemical properties of Sardinian monofloral honeys

SummaryIn this study, fifty‐one monofloral Sardinian honeys from ten various floral origins were screened for their phenolic content, antioxidant activity, colour and electrical conductivity. The total phenolic amounts have been evaluated by Folin–Ciocalteu method, whereas quantification of several phenolic compounds (phenolic acids and flavonoids) has been carried out by HPLC‐DAD technique. The richest sample in phenolic compounds resulted strawberry tree honey with about 40 mg GAE/100 g, as well FRAP test and DPPH˙ test confirm that antioxidant activity of strawberry tree honey extract exceed both honey extracts and synthetic antioxidants like BHA and BHT. Among the studied phenolic compounds a total of five phenolic acids (ferulic, syringic, trans‐cinnamic, chlorogenic and p‐hydroxycinnamic) and nine flavonoids (catechin, kaempferol, rutin, quercetin, luteolin, apigenin, galangin, pinocembrin and pinobanksin) were identified. Our results show good correlations between total polyphenol amount and antioxidant activity and between colour and electrical conductivity.

Physicochemical Characterization and Antioxidant Activity of Commercial Portuguese Honeys

The present study evaluated the physicochemical characteristics and antioxidant activity of 13 commercial honeys from diverse floral origin, produced in Portugal. The values of electrical conductivity of cardoon and pennyroyal honeys were superior to the maximum limits defined by European legislation. Citrus, strawberry tree, and 1 sample of lavender honeys had values of diastase activity below those determined by European legislation. Strawberry tree, pennyroyal, and cardoon honeys had the highest amounts of potassium that coincided with the highest electrical conductivity. Strawberry tree honey was the most effective as antioxidant along with cardoon and heather honeys. This ability was strongly correlated with the amounts of phenols and flavonoids and not with the levels of vitamin C or proline.

Antioxidant capacity and vasodilatory properties of Mediterranean food: The case of Cannonau wine, myrtle berries liqueur and strawberry-tree honey

The aim of this work was to use different assays to evaluate the antioxidant and vasodilatory properties of three typical food products from the Mediterranean area and to correlate these activities with their phenolic content. For this purpose, red wines Cannonau, liqueurs obtained by cold maceration of myrtle (Myrtus communis L.) berries and bitter honeys obtained from strawberry-tree flowers (Arbutus unedo L.) were analysed. The total phenolic (TP) content was measured spectrophotometrically with a modified Folin–Ciocalteau method and phenolic compounds were identified and dosed by HPLC-DAD and LC-MS/MS. Antioxidant activities were evaluated with DPPH, FRAP and ABTS assays and the in vitro vasodilatory effects were assessed using norepinephrine precontracted rat aortic rings. Cannonau wines and myrtle liqueurs showed high levels of TP (1978±279 and 1741±150mg GAE/L, respectively), linearly correlated to the results of FRAP, ABTS, and DPPH assays. Their maximal vasodilatory activity was 61.7±4.1% and 53.0±3.0%, respectively. Although strawberry-tree honey contained relatively high levels of phenolic compounds (922±38mg GAE/kg), it did not induce vasodilation, even at the highest dose tested (0.206g/L). These results indicate that foods with high levels of phenolic compounds should be studied using several different biological assays before being recommended to the general public as functional foods.

Antioxidant profile of strawberry tree honey and its marker homogentisic acid in several models of oxidative stress

The antioxidant activity of several honeys was evaluated considering the different contribution of entire samples. The strawberry tree honey emerged as the richest in total phenols and the most active honey in the DPPH and FRAP tests, and could protect cholesterol against oxidative degradation (140°C). Homogentisic acid (2,5-dihydroxyphenylacetic acid, HGA), the main phenolic compound from strawberry tree honey, showed interesting antioxidant and antiradical activities, and protective effect against thermal-cholesterol degradation, comparable to those of well known antioxidants. Moreover, the pre-treatment with HGA significantly preserved liposomes and LDL from Cu2+-induced oxidative damage at 37°C for 2h, inhibiting the reduction of polyunsaturated fatty acids and cholesterol and the increase of their oxidative products. This phenol had no toxic effect in human intestinal epithelial Caco-2 cells within the concentration range tested (5–1000μM). HGA was able to pass through the Caco-2 monolayers, the apparent permeability coefficients (Papp) in the apical-to-basolateral and basolateral-to-apical direction were 3.48±1.22×10−6 and 2.18±0.34×10−6cm/s, respectively, suggesting a passive diffusion pathway as the dominating process. The results of the work qualify HGA as natural antioxidant, able to exert a significant in vitro protective effect and to contribute to the strawberry tree honey antioxidant activity.

Floral Markers of Strawberry Tree (Arbutus unedo L.) Honey

Strawberry tree honey, due to its characteristic bitter taste, is one of the most typical Mediterranean honeys, with Sardinia being one of the largest producers. According to specific chemical studies, homogentisic acid was identified as a possible marker of this honey. This work, based on HPLC-DAD-MS/MS analysis of strawberry tree (Arbutus unedo L.) honeys, previously selected by sensory evaluation and melissopalynological analysis, showed that, in addition to the above-mentioned acid, there were other high levels of substances useful for the botanical classification of this unifloral honey. Two of these compounds were isolated and identified as (+/-)-2-cis,4-trans-abscisic acid (c,t-ABA) and (+/-)-2-trans,4-trans-abscisic acid (t,t-ABA). A third compound, a new natural product named unedone, was characterized as an epoxidic derivative of the above-mentioned acids. Structures of c,t-ABA, t,t-ABA, and unedone were elucidated on the basis of extensive 1D and 2D NMR experiments, as well as HPLC-MS/MS and Q-TOF analysis. In selected honeys the average amounts of c,t-ABA, t,t-ABA, and unedone were 176.2+/-25.4, 162.3+/-21.1, and 32.9+/-7.1 mg/kg, respectively. Analysis of the A. unedo nectar confirmed the floral origin of these compounds found in the honey. Abscisic acids were found in other unifloral honeys but not in such high amount and with a constant ratio of about 1:1. For this reason, besides homogentisic acid, these compounds could be used as complementary markers of strawberry tree honey.

Reversed-Phase Liquid Chromatographic Profile of Free Amino Acids in Strawberry-tree (Arbutus unedo L.) Honey

Abstract The typical profile of the free amino acids contained in strawberry-tree (Arbutus unedo L.) honey is reported for the first time. An optimized reversed-phase liquid chromatographic (RP-LC) method with phenyl isothiocyanate precolumn derivatization was used. Fourteen free amino acids were identified and quantified in 16 analytical samples. Proline (65.63) was found to be the most abundant free amino acid, followed by glutamic acid (6.49), arginine (5.21), alanine (5.17), and phenylalanine (4.97). The total free amino acid content of strawberry-tree honey (average value, 436 mg/kg) was found to be low in comparison to amounts cited in the literature concerning unifloral honeys. The analytical method was optimized and fully validated in terms of detection and quantitation limits, precision (by testing repeatability and reproducibility), linearity, and bias (by means of recovery tests). The acceptability of the validation protocol results was verified using Horwitz's mathematical model and AOAC guidelines.

Reversed-Phase Liquid Chromatographic Profile of Free Amino Acids in Strawberry-tree (Arbutus unedo L.) Honey

The typical profile of the free amino acids contained in strawberry-tree (Arbutus unedo L.) honey is reported for the first time. An optimized reversed-phase liquid chromatographic (RP-LC) method with phenyl isothiocyanate precolumn derivatization was used. Fourteen free amino acids were identified and quantified in 16 analytical samples. Proline (65.63%) was found to be the most abundant free amino acid, followed by glutamic acid (6.49%), arginine (5.21%), alanine (5.17%), and phenylalanine (4.97%). The total free amino acid content of strawberry-tree honey (average value, 436 mg/kg) was found to be low in comparison to amounts cited in the literature concerning unifloral honeys. The analytical method was optimized and fully validated in terms of detection and quantitation limits, precision (by testing repeatability and reproducibility), linearity, and bias (by means of recovery tests). The acceptability of the validation protocol results was verified using Horwitz's mathematical model and AOAC guidelines.

Identification of botanical biomarkers found in Corsican honey

Honeys from specified botanical sources often command a premium price due to their organoleptic or pharmacoactive properties. To prevent the fraudulent marketing of honey, analytical techniques are required to confirm its origin. NMR spectroscopy has been used to identify biomarkers of botanical and geographical origin for European honey. One-dimensional 1H NMR spectra were acquired from 374 authentic European honeys collected during 2 years, with the majority of these (220) taken from the island of Corsica. Biomarkers of sweet chestnut, Corsican spring Maquis and Arbousier (strawberry-tree) honeys were identified. Kynurenic acid was found to be a biomarker of sweet chestnut honey. α-Isophorone and 2,5-dihydroxyphenylacetic acid were confirmed as markers of strawberry-tree honey. Additional compounds specific to strawberry-tree and Corsican spring Maquis honey were partially characterised.

An RP-HPLC determination of 5-hydroxymethylfurfural in honey: The case of strawberry tree honey

The use of the RP-HPLC official method of the International Honey Commission (IHC) for the determination of 5-hydroxymethylfurfural (HMF) in strawberry tree honey ( Arbutus unedo, a typical Sardinian honey) has brought to light a specific and heavy chromatographic interference that prevents accurate quantification. The interference has been identified as homogentisic acid (HA), i.e. the marker of the botanical origin of the honey. For this reason, an alternative RP-HPLC method is proposed. The bias-free method allows a complete separation of HMF from HA to the baseline level and is faster and more precise than the RP-HPLC official method: the detection and quantification limits are 1.9 and 4.0 mg kg −1, respectively, whereas the repeatability is ca. 2% in the HMF concentration range of 5–140 mg kg −1.

Direct chromatographic methods for the rapid determination of homogentisic acid in strawberry tree ( Arbutus unedo L.) honey

Two rapid and direct chromatographic methods based on reverse phase-high performance liquid chromatography (RP-HPLC) and ion chromatography (IC) were developed for the determination of homogentisic acid (HA) in honey. This is the marker of the botanic origin of strawberry tree honey. The methods were validated and tested using 22 samples from Sardinia, Italy. The IC method is faster than the RP-HPLC one (6 min versus 13 min of total run), but it is slightly less sensitive (the limit of detection (LOD), is 26 mg kg −1 versus 15 mg kg −1) and reproducible (relative standard deviation, RSD, of 10.4 and 4.4%, respectively). The whole dataset of validation parameters allows both the proposed methods to be considered as bias-free (by recovery tests, comparison of analytical results of the two independent methods and analysis of a synthetic sample) and precise (both the techniques show a repeatability better than 2% repeatability in the range between 70 and 600 mg kg −1).

Volatile norisoprenoids as markers of botanical origin of Sardinian strawberry-tree ( Arbutus unedo L.) honey: Characterisation of aroma compounds by dynamic headspace extraction and gas chromatography–mass spectrometry

In order to characterize and authenticate the aromatic profile of strawberry-tree ( Arbutus unedo L.) honey, a dynamic headspace (DHS) extraction, followed by gas chromatography–mass spectrometry (GC–MS) analysis, was performed on 10 Sardinian strawberry-tree ( Arbutus unedo L.) honey samples. A total of 28 aroma compounds were identified, but only norisoprenoid compounds such as α-isophorone, β-isophorone and 4-oxoisophorone, were recognized as specific floral origin markers of the strawberry-tree honey. The α-isophorone/β-isophorone ratio varied from 4 to 8, whereas the α-isophorone/4-oxoisophorone ratio was found to range from 11 to 20. The DHS extraction method was proposed as a valid alternative to pollen analysis for floral source detection, especially for products like strawberry-tree honey, characterized by a low pollen content.