لخّصلي

Honey is the sweet substance produced by Apis mellifera L. mainly from the nectar of flowers.Nevertheless, depending on the availability of food sources, bees generally forage on vegetation as far as a 2 km radius from their hive.5

Therefore, often the labels do not report the correct floristic source,6, 7 the only classification envisaged by European legislation8 that, however, does not consider the on-label indication of this information as mandatory, this despite proposals to amend this directive.9 Nonetheless, the floristic origin of honey is quite important for its definition, since properties like flavour, colour, aroma, texture and other parameters important in consumers' evaluation are strictly linked to such origin.1-9 In this context, more than 100 botanical species are known to produce unifloral honey just in Europe,10 but only those endowed with the most important commercial value are officially described.Some studies already exist on the characterization of this honey.12-19 Most of them focused on its melissopalynological analysis, alongside the determination of physicochemical parameters, moisture, pH, free acidity, electrical conductivity, hydroxymethylfurfural content, colour, total polyphenols content, flavonoids content and DPPH radical scavenging activity.12-19 Few other studies have been concerned with raspberry honey contamination and adulterations,20, 21 or its antimicrobial activity.22 Even fewer studies,23 to our knowledge, have been focused on the secondary metabolite profile of this honey type.This plant is defined as the most aggressive invading plant in northern hardwood forests26 and it is a pioneer of transition with a behaviour sometimes like an invasive plant in forest habitats, in particular after disturbances such as windstorm or wildfire.27, 28 Red raspberry is widely distributed in all temperate regions of Europe, Asia and North America and it is a major commercial fruit with many commercial varieties, high price and increasing consumer demand.29 Considering this, raspberry honey could be more important in the market than estimated and a not-enough-known resource for beekeeping activities.The latter occasionally happens even without fraudulent purposes, since beekeepers label their product often without support of a proper melissopalynological analysis, assigning a botanical origin deducible by subjective sensory analysis and/or assessing the presence of predominant plant species surrounding the beehive.

Honey is the sweet substance produced by Apis mellifera L. mainly from the nectar of flowers. This substance is then processed by the digestive enzymes of honeybees and stored and dried in the honeycomb, where the nectar is finally turned into honey.1 This product is gaining increasing attention, also because of a growing interest in honeybees and honeybee health.2

Monofloral honeys (honey produced mainly from just one plant nectar) are particularly valuable, due to their specific aroma profiles compared to those of polyfloral honeys,3, 4 since polyfloral honey is produced by a blend of nectars of which none is usually dominant. Consequently, monofloral honeys are often subjected to adulteration (in the worst cases) or to botanical origin mislabelling. The latter occasionally happens even without fraudulent purposes, since beekeepers label their product often without support of a proper melissopalynological analysis, assigning a botanical origin deducible by subjective sensory analysis and/or assessing the presence of predominant plant species surrounding the beehive. Nevertheless, depending on the availability of food sources, bees generally forage on vegetation as far as a 2 km radius from their hive.5

Therefore, often the labels do not report the correct floristic source,6, 7 the only classification envisaged by European legislation8 that, however, does not consider the on-label indication of this information as mandatory, this despite proposals to amend this directive.9 Nonetheless, the floristic origin of honey is quite important for its definition, since properties like flavour, colour, aroma, texture and other parameters important in consumers' evaluation are strictly linked to such origin.1-9 In this context, more than 100 botanical species are known to produce unifloral honey just in Europe,10 but only those endowed with the most important commercial value are officially described.

Red raspberry honey is not included in the list of the main European unifloral honeys10. This honey is quite rare11 but it is often considered a prized type, searched by consumers, also outside Europe. Some studies already exist on the characterization of this honey.12-19 Most of them focused on its melissopalynological analysis, alongside the determination of physicochemical parameters, moisture, pH, free acidity, electrical conductivity, hydroxymethylfurfural content, colour, total polyphenols content, flavonoids content and DPPH radical scavenging activity.12-19 Few other studies have been concerned with raspberry honey contamination and adulterations,20, 21 or its antimicrobial activity.22 Even fewer studies,23 to our knowledge, have been focused on the secondary metabolite profile of this honey type. Raspberry is considered a normo-represented pollen (PK/10 g 30.000–100.00024), the secretion of nectar is referred to as ranging between 1.4 and 67 mg per flower in 24 h and the sugar content is between 24% and 42%. Raspberry nectar contains only fructose and glucose with a ratio of 1.0.25 For its sugar ratio, this honey tends averagely to crystalize. For raspberry pollen, the general criterion of pollen presence over 45% is usually adopted to define a monofloral honey.

Red raspberry (Rubus idaeus) is nonetheless an important floral resource for some specific habitats. Salonen et al.12 mentioned how wild raspberry is an important foraging resource for bees in a territory where the beekeeping season is short, as in Finland. This plant is defined as the most aggressive invading plant in northern hardwood forests26 and it is a pioneer of transition with a behaviour sometimes like an invasive plant in forest habitats, in particular after disturbances such as windstorm or wildfire.27, 28 Red raspberry is widely distributed in all temperate regions of Europe, Asia and North America and it is a major commercial fruit with many commercial varieties, high price and increasing consumer demand.29 Considering this, raspberry honey could be more important in the market than estimated and a not-enough-known resource for beekeeping activities. For this reason, more studies on this kind of honey other than the merging of the knowledge already existing are advisable and even suggested by recent literature.4

Hence, the aim of the work reported here was to characterize honey produced in known red raspberry growing areas or labelled as red raspberry honey, in different locations in Europe, the USA and Canada. The assessment of botanical origin was performed through melissopalynological analysis. The definition of colour/colour intensity was performed through spectrophotometric analysis. The phytochemical profile was investigated through chromatographic techniques (solid-phase micro-extraction/gas chromatography/mass spectrometry (SPME-GC–MS) and high-performance liquid chromatography/Orbitrap mass spectrometry (HPLC-Orbitrap)). The correlation between the presence of raspberry pollen and secondary metabolites identified by metabolomic analysis was also considered.