Enzymatic Determination of Citric Acid in Honey by Using Polyvinylpolypyrrolidone Clarification

Characterization of Botanical Origin of Italian Honey by Carbohydrate Composition and Volatile Organic Compounds (VOCs)

Honey is a natural sweetener constituted by numerous macro- and micronutrients. Carbohydrates are the most representative, with glucose and fructose being the most abundant. Minor honey components like volatile organic compounds (VOCs), minerals, vitamins, amino acids are able to confer honey-specific properties and are useful to characterize and differentiate between honey varieties according to the botanical origin. The present work describes the chemical characterization of honeys of different botanical origin (multifloral, acacia, apple-dandelion, rhododendron, honeydew, and chestnut) produced and collected by beekeepers in the Trentino Alto-Adige region (Italy). Melissopalynological analysis was conducted to verify the botanical origin of samples and determine the frequency of different pollen families. The carbohydrate composition (fourteen sugars) and the profile of VOCs were evaluated permitting to investigate the relationship between pollen composition and the chemical profile of honey. Statistical analysis, particularly partial least squares discriminant analysis (PLS-DA), demonstrates the importance of classifying honey botanical origin on the basis of effective pollen composition, which directly influences honey's biochemistry, in order to correctly define properties and value of honeys.

An overview of physicochemical characteristics and health-promoting properties of honeydew honey

Honeydew honey has differentiated chemical and physicochemical characteristics besides potential functional properties such as antimicrobial, anti-inflammatory and antioxidant. In this sense, the interest and consumption of this honey as a functional product by the food industry and consumers have increased. Honeydew honeys usually present dark color, a lower content of monosaccharides and higher values of pH, acidity, electric conductivity, proteins, minerals, phenolic compounds, and oligosaccharides compared to blossom honeys, which contribute to its outstanding biological activities. Consequently, contaminations and adulterations of this honey can occur and compromise the quality, safety and authenticity of honeydew honey. Thus, detailed knowledge of the composition and properties of honeydew honeys is of great importance, especially considering that honeydew honeys are still few studied and therefore underestimated. Therefore, in this review, the physicochemical characteristics, chemical and bioactive composition, functional and health-promoting properties of honeydew honey as well as contamination, adulteration and authenticity of this honey are summarized.

Identification, quantification and carbon stable isotopes determinations of organic acids in monofloral honeys. A powerful tool for botanical and authenticity control

RATIONALE

The analytical composition and botanical origin of honey are basic data used to determine the quality of this foodstuff. Although proteins are used to characterise the analytical composition of honey, they can be eliminated during its ultrafiltration and, in the case of honeys not saturated with their own pollen, the use of proteins does not work well. As acidity is a well-known characteristic of honey and organic acids are present at around 0.5% in honey, we therefore investigated an alternative method to the protein-based White method, using organic acids as new internal standards instead of proteins.

METHODS

The qualitative and quantitative analyses of 14 organic acids were carried out by ion chromatography with an electrochemical detector. The (13)C/(12)C isotopic ratios of the honeys, and of the organic acids extracted from them with an anion exchange resin, were determined by isotope ratio mass spectrometry.

RESULTS

Gluconic acid is the predominant organic acid in honey, at between 1.8 and 12.7 g/kg. For fir honey the major acid is galacturonic acid at around 4.6 g/kg. The isotopic ratios of honeys and of their acids are strongly linked. Correlations between the δ(13)C values of the honey and the acids were significant, and better than those obtained using proteins.

CONCLUSIONS

This study has provided a method to differentiate honeys from seven botanical origins, based on organic acid analysis. By combining various organic acid contents and isotopic ratio values through statistical processing by Principal Component Analysis it is possible to differentiate honey samples as a function of their botanical origin.

Chemical composition, characterization, and differentiation of honey botanical and geographical origins

Botanical and biographical origins of honey are an important issue in food quality and safety. This chapter focuses on use of chemical components to determine botanical and geographical origins of honey. The botanical and geographical origins of the nectar are related with the chemical composition of honey. Honey can originate from single and multiplant species. In general, the prices of honey from single plant species are much higher than those of common polyfloral honey because of consumer preferences. Single and multiple chemicals and components can well indicate the botanical and geographical origins of the honey. Marker chemicals and components include flavonoids, pollen, aroma compounds, oligosaccharides, trace elements, amino acids, and proteins. If multiple chemicals are used as markers, patterns of the chemicals are often used to detect the botanical and geographical origins of honey. Modern statistical software in combination with advanced analytical instrumentation provides high potential for the differentiation of the botanical and geographical origins of the honey.

A turn-on fluorescent indicator for citrate with micromolar sensitivity

A turn-on fluorescent indicator for citric acid (citrate) has been developed, displaying high emission enhancement (+1500%) and low interference by other carboxylates. The sensor is based on the non-emissive copper(II) complex of a fluorescent amino amide, which, upon addition of citrate decomplexates to yield the emissive ligand. The detection limit estimated for this new chemosensing system is about 0.5 microM. This novel approach to the analysis of citrate constitutes an alternative ca. 10(2)-10(3) times more sensitive than the standard method based on the enzyme citrate lyase.

Rapid analysis of organic acids in plant extracts by capillary electrophoresis with indirect UV detection

A fast, reliable capillary zone electrophoresis (CZE) method with indirect UV detection was optimized and validated to determine the main organic acids contained in plants. Citric, malic, succinic, oxalic, formic, fumaric, acetic acids, and phosphate were quantified. A rapid separation while keeping a good resolution was obtained by optimizing capillary length, separation voltage, electrolyte composition, and pH. Analyses were performed in a 30 cm uncoated fused-silica capillary (length to the detector window) in the co-electroosmotic mode with reversed electroosmotic flow and anodic detection using a -30 kV separation voltage. The pH 9.0 electrolyte contained 3 x 10(-4)mol/L tetradecyltrimethylammonium and 10(-2)mol/L trimellitate. Separation with baseline return was achieved in 100 s. Linearity, detection limits, repeatability, reproducibility, and recoveries were evaluated. Mean precision values of 0.2 and 3.4% for migration times and time-corrected peak areas, respectively, enabled accurate identification and quantification whether in standard solutions or in samples. Such performances were perfectly adapted to high-throughput routine determinations of organic acids in research or industry. Organic acids were assayed in different plant tissues and cells, including sycamore, arabidopsis, buttercup, and pea. Citrate and malate were the most abundant in all plants tested with concentrations reaching 18.9 and 22.3 micromol/g fresh matter, respectively. Cadmium effect on pea leaves metabolism was also assessed.

Rapid determination of nonaromatic organic acids in honey by capillary zone electrophoresis with direct ultraviolet detection

A rapid capillary zone electrophoresis (CZE) method with direct ultraviolet (UV) detection has been set up and developed to determine the most important nonaromatic organic acids in honey with a really simple treatment of the sample. The determination of oxalic, formic, malic, succinic, pyruvic, acetic, lactic, citric, and gluconic acids has been carried out in 4 min. The electrolyte composition was phosphate as the carrier buffer (7.5 mM NaH(2)PO(4) and 2.5 mM Na(2)HPO(4)), 2.5 mM tetradecyltrimethylammonium hydroxide (TTAOH) as electroosmotic flow modifier, and 0.24 mM CaCl(2) as selectivity modifier, with the pH adjusted at 6.40 constant value. The running voltage was -25 kV at a thermostated temperature of 25 degrees C. The injections were performed in hydrodynamic mode (30 s), and the detection mode was UV direct at 185 nm. Validation parameters of the method as detection and quantification limits, linearity, precision (repeatability and reproducibility), and recovery were also studied. The advantages related to the technique such as simplicity, short analysis times, and low consumption of chemicals as well as the good validation parameters obtained for this method permit it to be considered as adequate for routine analysis in honey.

Rapid determination of minority organic acids in honey by high-performance liquid chromatography

A rapid high-performance liquid chromatographic method for the determination of organic acids in honey is reported. Malic, maleic, citric, succinic and fumaric acids were identified and quantified in 15 min. First time repeatibility, reproducibility and recoveries were determined out for these acids in honey samples. Maleic acid was also quantified for first time by a chromatographic method. The organic acids were removed from honey by using a solid-phase extraction procedure with anion-exchange cartridges. Previously, the solution of honey was adjusted to pH 10.50 with 0.1 M NaOH and stirred for 15 min at room temperature. Then, this solution was adjusted to pH 5.00 with 0.1 M H2SO4. This procedure was carried out to avoid interferences in the baseline. The chromatographic separation was achieved with only one Spherisorb ODS-2 S5 column thermostated at 25 degrees C. Metaphosphoric acid (pH 2.20) was used as mobile phase at a flow-rate of 0.7 ml/min. Organic acids were detected with a UV-vis detector (215 nm). The precision results showed that the relative standard deviations of the repeatability and reproducibility were < or =3.20% and < or =4.86%, respectively. The recoveries of the organic acids ranged from 62.9 to 99.4%. Under optimum conditions the detection limits ranged from 0.0064 to 7.57 mg/kg and the quantification limits ranged from 0.025 to 10.93 mg/kg.