Monofloral Honeys as a Potential Source of Natural Antioxidants, Minerals and Medicine

Background: vegetative diversity is based on different climate and geographical origins. In terms of beekeeping, herbal diversity is strongly correlated to the production of a wide variety of honey. Therefore, based on the existing plant diversity in each country, multiple honey varieties are produced with different health characteristics. While beekeeping potential and consumption preferences are reflected in products’ variety, this leads to an increase in the region’s economy and extensive export. In the last years, monofloral honey has gained interest from consumers and especially in the medicinal field due to the presence of phytochemicals which are directly linked to health benefits, wound healing, antioxidant, anticancer and anti-inflammatory activities. Scope and approach: this review aims to highlight the physicochemical properties, mineral profiles and antioxidant activities of selected monofloral honeys based on their botanical and geographical origin. Moreover, this review focuses on the intercorrelation between monofloral honey’s antioxidant compounds and in vitro and in vivo activities, focusing on the apoptosis and cell proliferation inhibition in various cell lines, with a final usage of honey as a potential therapeutic product in the fight towards reducing tumor growth. Key findings and conclusions: multiple studies have demonstrated that monofloral honeys have different physicochemical structures and bioactive compounds. Useful chemical markers to distinguish between monofloral honeys were evidenced, such as: 2-methoxybenzoic acid and trimethoxybenzoic acid are distinctive to Manuka honey while 4-methoxyphenylacetic acid is characteristic to Kanuka honey. Furthermore, resveratrol, epigallocatechin and pinostrobin are markers distinct to Sage honey, whereas carvacrol and thymol are found in Ziziphus honey. Due to their polyphenolic profile, monofloral honeys have significant antioxidant activity, as well as antidiabetic, antimicrobial and anticancer activities. It was demonstrated that Pine honey decreased the MDA and TBARS levels in liver, kidney, heart and brain tissues, whereas Malicia honey reduced the low-density lipoprotein level. Consumption of Clover, Acacia and Gelam honeys reduced the weight and adiposity, as well as trygliceride levels. Furthermore, the antiproliferative effect of chrysin, a natural flavone in Acacia honey, was demonstrated in human (A375) and murine (B16-F1) melanoma cell lines, whereas caffeic acid, a phenolic compound found in Kelulut honey, proves to be significant candidate in the chemoprevention of colon cancer. Based on these features, the use of hiney in the medicinal field (apitherapy), and the widespread usage of natural product consumption, is gaining interest by each year.


Geographical Origin/Provenance
Scientific studies revealed the many properties of compounds isolated from honey. With these features, honeys offer multi-purpose usage possibilities. Monofloral honey is obtained from the nectar of specific source plants and may prove to be more valuable than polyfloral honey. Therefore, the type of honey should be determined before labelling and marketing [59][60][61].
Various types of honeys are produced in Turkey, mostly Chestnut, Pine, Rhododendron, Milkvetch and Thyme. Bulgarian and Hungarian honeys are more complex, predominantly composed of the following species: Coriander, Thistle, Buckwheat, Willow and Linden, as well as forest honeys. Romanian and Ukrainian monofloral honeys are represented by Canola, Chestnut, Linden, Sunflower and Willow. The honeys from Portugal are rather diverse, being predominant in Buckthorn, Cytisus, Citrus, Eucalyptus, Heather, Lavender, Portugal laurel and Thyme. There are various types of eucalyptus honeys with different chemical constituents based on the geographical origin or production region. Recently, it has been demonstrated that eucalyptus honey has a significant antioxidant activity and it can show antimicrobial effects against many microorganisms [61]. As stated by the National Institute of Standardisation UNI, there are five main Italian monofloral honeys, as follows: Black Locust, Chestnut, Citrus, Eucalyptus and honeydew honey. Aside from these, there are several specific honeys, such as: Asphodel, Eucalyptus, Linden, Clover, Marruca (Paliurus spina-christi), Sulla and Sunflower.
The honeys from Malaysia and Australia are mainly Tualang and Gelam honeys, whereas from New Zealand are Clover, Manuka and Thyme honeys. Manuka honey is collected from Leptospermum scoparium or Leptospermum polygalifolium, of the Myrtaceae family, which can be found throughout New Zealand and eastern Australia [55,56]. Kanuka honey is derived from Kunzea ericoides, as a member of the same botanical family as the manuka tree and, according to Semprini et al. (2019) [57], kanuka-derived honey may offer similar antiviral effects. Tualang honey is rich in phenolic acids, flavonoids and has significant anticancer activity. It is collected from Koompassia excels, which is found in the Malaysian rain forest [53,54].

Phenolic Compounds
The antioxidant activity altogether with the in vitro activities of honey from various floral sources emphasizes the importance of integrating monofloral honey as a daily consumption product. Multiple reports highlight that rich phenolic compounds and the antioxidant capacity of monofloral honeys play a significant role in the expression of a wide range of bioactivities. The most common phenolic compounds in monofloral honeys are shown in Table 2.    In Acacia honeys, eight phenolic compounds and abscisic acid were identified in almost all samples and seemed to exhibit higher levels. These characteristic compounds included vanillic acid, caffeic acid, p-coumaric acid, ferulic acid, 3,4-dimethoxycinnamic acid, cinnamic acid, abscisic acid, kaempferol and pinocembrin. These nine characteristic compounds represent practically 50% of the total phenolics. In Serbian honeys, Kečkeš et al., (2013) [72] demonstrated that Sunflower, Basil, Buckwheat, Canola and Goldenrod honeys are strongly correlated to the phenolic profile. Thus, they demonstrated that quercetin and eriodictyol could be used as floral markers for Serbian honey, as well as cis, trans-Abscisic acid, which clearly distinquished between acacia and linden honeys.
Useful chemical markers such as carvacrol and thymol were solely found in Ziziphus Spina-Christi honey, as well as kojic acid distinctive to Coffea sp. honey [92,93], Quercetin 3 ,3 -dimethyl eter and Quercetin 7,3 -dimethyl eter characteristic in Rosemary honey (Arráez-Román et al., 2006) [69] and resveratrol distinctive to Sage (Salvia officinalis L.) honey (Gašić et al., 2015) [65]. Furthermore, several compounds are useful to discriminate honeys with similar properties and palinological characteristics. This is the case of Manuka (Leptospermum scoparium) and Kanuka (Kunzea erikoides) honeys, which are not distinguished by means of a melissopalynological analysis. Even though they share most of their phenolic profiles, Stephens et al., 2010 [89] noticed that 2-methoxybenzoic acid and trimethoxybenzoic acid are distinctive to Manuka honey, while 4-methoxyphenylacetic acid is characteristic to Kanuka honey. Furthermore, an increasing interest has been noticed in using the polyphenolic profile to distinguish honeys based on their geographic origin. Habib et al., 2014 [79] showed dissimilarities in the phenolic pattern based on the different climate and sunlight exposure. According to their study, sunlight exposure is responsible for higher polyphenol content in honeys produced in dry areas. The phenolic profile of Serbian unifloral honeys was investigated by Kečkeš et al., 2013 [72], who proposed eriodictyol and quercetin as floral markers for local Sunflower honeys. Furthermore, the phenolic profile of Sulla honeys produced in Southern Italy were influenced by their geographical origin [94], whereas the concentrations of gallic, chlorogenic, caffeic, p-coumaric and ferulic acids showed the highest variation as a function of the production site of this honey. Furthermore, Weston et al. (1999) [95] presented several methods for isolation of the antibacterial active phenolic fraction of honey derived from the native New Zealand manuka tree Leptospermum scoparium. This fraction consists of phenolic derivatives of benzoic acids, cinnamic acids and flavonoids, all of which have been identified previously in honeys. Regarding manuka honeys, the major flavonoids are pinobanksin, pinocembrin and chrysin, whereas galagin, isorhamnetin, kaempferol, 8-methoxykaempferol, luteolin and quercetinare were identified in minor concentration [96,97].

Physicochemical Properties of Monofloral Honeys
Honey, a high-quality natural product with a complex chemical composition, contains a wide range of nutritional and therapeutic properties.
The quality is usually assessed by physicochemical, sensorial and microbiological parameters. The physicochemical properties depend on the type of nectar (botanical origin), geographical origin (climate conditions and soil composition) and handling (storage and transport). Multiple studies have reported that the physicochemical parameters of honey, such as moisture, acidity, sugar composition, ash and 5-hydroxymethylfurfural (HMF) are used to distinguish honey types. The physicochemical characteristics of monofloral honeys from different countries are exemplified in Table 3.   HMF: Hydroxymethylfurfural; n.i., not identified. According to the European Honey Legislation [121] and the Codex Alimentarius Standards [122], honey moisture should not exceed 20%, with the exception of heather (Calluna sp.), which should not surpass 23-25%, acidity, should be less than 50 milli-equivalents (MEQ) acid/kg, with glucose and fructose composition not less than 60 g/100 g and HMF not more than 40 mg/kg, except honeys from tropical climates which should not be more than 80 mg/kg. As it can be foreseen, in some monofloral honeys, the acidity surpasses 50 MEQ/kg, possibly indicating the presence of undesirable fermentations, such as: Arbutus sp., Ceratonia sp. and Thymus sp. from Portugal. Based on their botanical origin, nectar honeys have low ash content compared to honeydew honey.
Generally, the moisture content is an indicator of honey's freshness, being useful to improve its conservation, storage and prevent the growth of moulds (Penicilium and Mucors). The growth of mould gives an off-taste due to the growth levels of ethanol, butanediol and glycerol, which reduce the products quality. Furthermore, the moisture content is a useful parameter in describing the viscosity and moistness of honey. As previously stated, in Codex Alimentarius (2001) [122] and EU Council directives [121], the maximum moisture content value of Erica monofloral honey should not exceed 23% and 20% in other monofloral honeys. The moisture content varies depending on external factors, such as environment and harvesting period, and internal factors such as the maturity reached in the hive [123]. In most blossom honeys, fructose and glucose represent the great majority of honey sugars. According to Codex Alimentarius, the sum of fructose and glucose must be more than 60% for nectar honey and 45% for honeydew honey. The sucrose content should not exceed 5%, with few exceptions such as the Lavender honey. As can be seen in Table 3 [124] determined the physicochemical characteristics of heather, avocado, oregano, barilla (Messembryanthemum crystallinum), malpica (Carlina xeranthemoides), poleo (Bystropogon origanifolius), relinchón (Hirstfeldia incana) and tedera (Aspalthium bituminosum) in monofloral honeys. The lowest moisture content (15.1 g/100 g) is noticed in relinchón honey and the highest value (18.4 g/100 g) in barrilla honey, whereas the moisture of heather (17.24 g/100 g) is similar to those reported by other researchers [45,46,104]. Furthermore, the HMF ranged between 5.36-15.00 (mg/kg) in Barilla and Oregano honeys, respectively.
In the study conducted by Bouhlali et al., 2019 [50], the water content of the monofloral honey present in Morroco was found to be from 14.55 to 20.99%, the water activity level varied between 0.49 and 0.58%, whereas the total acidity (directly associated to pH and free acidity) had values between 23.55 and 43.53 meq/kg. Furthermore, the highest fructoseglucose ratio (>1.5) belonged to eucalyptus and reseda honey samples.
Due to handling and processing inconveniences, honey has the tendency to crystallize. To avoid this, thermal processing is applied to avoid crystal formation, as well as microbial contamination [125]. Nonetheless, thermal treatment is followed by undesirable consequences, such as colour changing or browning of honey, but also the formation of HMF, an important quality parameter of honey. It is an indicator of honey freshness and overheating of honey leads to conversion in the cytotoxic and mutagenic compound 5-sulfoxymethyfurfural, which can also be generated under inadequate handling and storage conditions (temperature, pH, moisture) [126]. In fresh honeys there is practically no HMF, or it is in very low content; however, it increases upon storage [127]. Council Directive (2001/110/CE) [121] demands a maximum of 40 mg/kg of HMF in honey. The proposal for a higher maximum value of HMF (80 mg/kg) in some countries is based on the experience that HMF increases in honey stored in warm climate countries.
Currently one of most innovative commercial products available on the market is Manuka honey [128], which is a monofloral dark honey. The chemical composition and the variety of beneficial nutritional and health effects of manuka honey are revised by Alvarez-Suarez et al. (2014) [55]. It is derived from the manuka tree Leptospermum scoparium (Myrtaceae family). The manuka tree grows as a shrub or a small tree in New Zealand and eastern Australia [56]. This type of honey has attracted the attention of several researchers for its biological properties, especially for its antimicrobial and antioxidant activity [55].
The composition of Manuka honey is mainly of carbohydrates, mineral elements, proteins, fatty acids and phenolic and flavonoid compounds. One of the major antibacterial components of Manuka honey is methylglyoxal (MGO) [129]. Sugars are the main components in Manuka honey. The authors identified fructose, glucose, sucrose and maltose in all honey samples. Fructose and glucose are the main monosaccharides. The content of fructose is higher compared to the glucose content. The content of fructose plus glucose of manuka honey (60.7 g/100 g) was similar to that reported by Moniruzzaman et al. (2013a) [130]. The sum of fructose and glucose in Manuka honeys is higher than 60%, which is in accordance with Codex Alimentarius (2001).
Manuka honey has a relatively low pH (about 3.5-4.5), which contributes to the inhibition of microbial growth [132]. Furthermore, the low levels of wound pH can reduce protease activity and increase fibroblast activity and wound healing [133,134].
According to Kato et al. (2012) [56], a novel glycoside, leptosin is a characteristic compound of manuka honey. Furthermore, as this type of honey has a low (11,59%) moisture content [130], it allows a long-time protection against microbial attacks [131]. Honey from Koompassia excels (Tualang) contains more free radical scavenging, antioxidant activity, flavonoids and phenolic acids, and its health benefits are better compared to other local Malaysian honeys, such as Manuka honey [132]. According to Mohamed et al. (2010) [53], the tualang-derived honey has good colour intensity and contains phenolic compounds that possess relatively good antioxidant activity.

Major Mineral Composition of Some Monofloral Honey
Generally, the mineral content in honey is low ranging between 0.02 and 0.3%. It is influenced by the nectars chemical composition which varies according to soil composition (geographical origin) and floral type (botanical origin). Variations of soil and climatic conditions may also influence the mineral composition, as well as the extraction method and harvesting techniques [135][136][137].
According to the International Honey Commision (2009) [137], requirements in individual countries include parameters such as diastase activity (general, no less than eight on the Schade scale), electrical conductivity (e.g., in honeydew honey, no less than 0.8 mS/cm), HMF (general, no more than 40 mg/kg), free acidity (in general, no more than 50 milliequivalents acid/1000 g), proline (no less than 25 mg/100 g) and pH, insoluble impurities (no more than 0.1 g/100 g).
Honey has also been regarded as a potential environment pollution indicator, as a result of a bio-accumulative process in the borders of urban and industrial areas, as well as in extra-urban crossroads, where traces of some mineral compounds and/or heavy metals were found [144].
As can be seen in Table 4, the monofloral honeys from Spain are abundant in K, Ca and Mg, ranging between 2.70-530.0, 23.00-387.0 and 41.0-331.0 mg kg −1 respectively. High discrepancy was noticed in the case of Na content, ranging between 9.18 and 1321.40 mg kg −1 . The honeys from Portugal exhibited high potassium content, accounting for 76% with an average content of 1150.1 mg g −1 . Except for the honeys from Spain, which exhibited high amounts of Na, research from other countries revealed K to be the most abundant mineral. Furthermore, from the monofloral samples of Morocco, K was the predominant mineral, followed by Na, Ca and Mg, which were found in the highest amount in carob honey [50], whereas the mineral contents of Hovenia monofloral honey included Ca (20.1 ± 1.06 mg L −1 ), K (407.5 ± 3.11 mg L −1 ), P (20.6 ± 1.77 mg L −1 ), Mg (10.7 ± 1.1 mg L −1 ), Na (1.8 ± 0.28 mg L −1 ), and Zn (Zinc) (13.9 ± 15.1 mg L −1 ).   [120,150,152] In their extensive review, Solayman et al., 2015 [153] reported detailed information regarding the physicochemical properties of honey, particularly the mineral and heavy metal contents, as well as their medicinal properties.

Antioxidant Activity of Monofloral Honeys
Phenolic compounds are mostly divided into two main groups: flavonoids and phenolic acids. Honey contains a significant number of polyphenolic compounds, widely used as plant origin and honey quality indicators. The total phenolic content (TPC) and total flavonoid content (TFC) are well-known criteria for the initial assessment of the bioavailability of honey and other bee products.
Worldwide, multiple studies assessed the antioxidant activity of monofloral honeys. This research is often accompanied by the measure of some spectrophotometric parameters such as TPC and TFC, as well as the electrical conductivity and/or colour. In fewer cases, these studies are accompanied by additional characteristics, such as: melissopalynological analysis, chromatographic phenolic profile or mineral composition of major and trace elements. In the last decade, multiple studies have evaluated the antimicrobial, antioxidants and radical scavenging properties of monofloral honeys from different geographical origin, such as: Burkina Fasan, Hungary, Italy, Poland, Portugal, Turkey and Malaysia. Table 5 summarises a selection of monofloral honeys' antioxidant activity.         ↔ inhibitory activity in Caco-2 (34.22%) ↓ inhibitory activity in MCF-7 (29.87%) and Hep-G2 (15.94%) [168,194] Note: AAE, ascorbic acid equivalents; TPC, total phenolic content expressed as mg gallic acid/100 g; TFC, total flavonoid content expressed as mg quercetin equivalents/100 g; TRC-mg GAE kg −1 ; TEAC (IC 50 [195], it was found that Strawberry tree honey had the highest TPC, as well as higher activity in the DPPH and FRAP tests, compared to Citrus, Heather and Eucalyptus honeys. Furthermore, from the total phenols content, homogentisic acid (i.e., the chemical marker for strawberry tree honey) was more than 60% and showed significant antioxidant and antiradical activities, as well as a protective effect against thermal cholesterol degradation. Wang et al. (2019) [196] determined the TPC and TFC from Prunella vulgaris (PVH) monofloral honey, a known traditional Chinese medicine, which displayed a TPC of 145.7 mg chlorogenic acid equivalent (CAE)/kg and a TFC of 10.0 mg QE/kg. The TFC of PVH was higher compared to other monofloral honeys with potential medicinal value, such as Acacia, Buckwheat and Manuka, but lower compared to Heather, Sunflower, Canola, Pine, and Thyme. Additionally, the TFC was relatively high compared to Rhododendron and Chestnut from Turkey and coffee honey from Brazil. Furthermore, low TPC in the Rhododendron honey was noticed in the samples from Ordu and Artvin, whereas the samples from Zonguldak and Kastamonu exhibited the highest TPC compared to the other regions. Therefore, the TPC is strongly correlated to the antioxidant activity, as demonstrated in multiple studies. In the study conducted by Socha et al., 2011 [197], the TPC in Polish honeys was much lower (4.46-15.04 mg GAE/100 g), especially in Buckwheat honey (15.04 mg GAE/100 g).
Kus et al., 2014b [87] evaluated the TPC and antioxidant activities of several polish honeys. Their results showed that the TPC ranged between 121.6-1173.8 mg GAE/kg. Similar phenolic contents were reported for Mexican honeys (283.9-1142.9 mg GAE/kg), from which the highest TP content was found in multifloral, orange blossom and bell flower samples [198]. Furthermore, TPC was found to be similar in Burkina Fasan honeys (325.9-1147.5 mg GAE/kg), with the richest content in honeydew and Vitellaria honeys [154]. In the study conducted by Anand et al., 2018 [159], the lowest TPC was recorded for Agastache honey (853.6 ± 5 µg GAE/g) and the highest for Jelly bush honey 1415.6 ± 126 µg GAE/g). Jelly bush honey contained the highest TFC (53.9 ± 10.9 µg CE/g), whereas Tea-tree honey had the lowest TFC (20 ± 4.3 µg CE/g). The scavenging activity of free radicals determined by DPPH assay indicated that the highest antioxidant activity was present in Manuka honey (18.69 ± 0.9 µmol TE/g) followed by Jelly bush and Tea-tree. Similarly, the scavenging activity of free radicals determined by TEAC assay indicated that the highest activity was shown in Manuka honey (30.72 ± 0.27 µmol TE/g), followed by Agastache and Jelly bush.
Multiple studies have demonstrated the potential therapeutic properties of monofloral honeys due to their bioactive compounds, as well as based on their geographical origin. Further details can be seen in Table 5.
In the last decade, monofloral honeys have attracted great interest from researchers. For the first time, the phytochemical composition of several significant monofloral Cuban honeys and their relationships with the biological activities were studied by Alvarez-Suarez et al. Their antioxidant [199] and antimicrobial [200] properties were evaluated and discussed also in terms of correlation with amino acids, proteins, carotenoids, colour, TPC and TFC. The analysed samples possessed important antioxidant and antibacterial properties, as well as high concentrations of phenolic acids, flavonoids and carotenoids. Later, Alvarez-Suarez et al., 2012 [66] showed that Cuban honeys ether-soluble phenolic fraction exhibits significant radical scavenging activity and protection of RBCs against hemolysis and lipid peroxidation induced by free radicals, as well as protection against depletion of SOD and GSH enzymes.
In the study conducted by Park et al. 2020 [119], the antioxidant activity of Hovenia honey was evaluated. Their study showed that the Hovenia honeys had a significantly (p < 0.05) higher DPPH radical scavenger activity (36.3-38.7 µmol TE/100 g honey) and a similar ABTS radical scavenger activity (129.5-141.9 µmol TE/100 g honey), compared to Acacia honey (ABTS: 13.9-22.4 µmol TE/100 g honey and DPPH: 130.6 ± 6.74 µmol TE/100 g honey). Interestingly, the amounts of TPC and TFC were not significantly different between these honey types.
These findings suggest that beside floral origin, the provenance is also significant for the phenols content of honeys from the same species.

Health Effects of Monofloral Honeys
Honey has been widely used as a folk medicine, being acknowledged centuries ago [201,202]. Hippocrates emphasized the similarity of honey to air and water, that honey is a very valuable antidote and that it can be used alone or mixed with herbs in the form of sherbet, ointment, and drug in the treatment of many physical and mental illnesses [203]. With the widespread use of apitherapy in recent years, the use of bee products and honey has increased [204]. In Table 6, several in vivo studies on animal models and human subjects are summarized based on honey types, antioxidant, anti-diabetic, anticancer and wound healing properties.  ↓ glutathione peroxidase (GPx) ↑ catalase (CAT) activity ↑ weight gain in G4 and G6 ↓ oxidative stress and damage [206] Forty female Sprague-Dawley rats aged between 45 to 48 days old rats were given 80 mg/kg DMBA then randomly divided into four groups: G1 (Control): distilled water (vehicle) G2: Tualang honey (0.2 g/kg/bw) G3 Tualang honey (1.0 g/kg/bw) G4: Tualang honey (2.0 g/kg/bw) via oral gavage daily 150 days ↑ apoptotic index in honey-treated groups ↓ concentration of VEGF Protein [207] Mad honey (floral source: Rhododendron sixty Sprague-Dawley female rats were (6-8 months old; 250-300 g) Group 1 (control): 1 mL of 0.9% NaCl solution was given via intraperitoneal injection Group 2 (GTX): 0.015 mg/kg/bw of Grayanotoxin-III was given via intraperitoneal injection; (n = 12) Group 3 (RH1): 0.1 g/kg/bw of RH was given via oral gavage; (n = 12) Group 4 (RH2): 0.5 g/kg/bw of RH was given via oral gavage; (n = 12) Group 5 (RH3): 2.5 g/kg/bw of RH was given via oral gavage; (n = 12) 1 h ↓ SOD, CAT, GTX activity at high dose of honey (2.5 g/kg/bw) ↑ plasma and various tissue MDA levels at high dose of honey [208]  divided by weight into 2 groups (n = 18) and provided free access to 1 of 2 diets (20% carbohydrate (by weight of total diet) from either clover honey or sucrose) 33 days ↓ Weight gain and adiposity, ↓ TG ↑ non-HDL-C levels [213] Acacia and Gelam honey Seven-week-old male Sprague-Dawley rats, with body weight ranging from 200 to 220 g G1: normal control G2: high fat diet G3: high fat diet rats fed with Gelam honey, G4: high fat diet rats fed with Acacia honey, G5: high fat diet rats treated with orlistat 4 weeks ↓ in excess weight gain and adiposity index ↓ plasma glucose, triglycerides, and cholesterol, plasma leptin and resistin, liver enzymes, renal function test, and relative organ weight [214] Honeydew honey

Wound Healing
Since ancient times, honey has been used for the treatment of wounds. The discovery of antibiotics has led to a decrease in honey use, but the development of antibiotic resistance increased the interest in honey again due to its antibacterial properties. However, attention should be paid to the quality of honey used in medical practices. Plants in honey harvest areas are exposed to herbicides and pesticides, industrial heavy metals and environmental pollution contaminated with antibiotics, and, as a result, toxic compounds can be found in honey. In addition, the harmful microbial load of honey is ignored. The content and standards of honey used especially for health purposes should be determined [227]. There is evidence that honey can heal partial thickness burns and postoperative infected wounds more quickly and effectively than conventional treatments [228]. Recently, honey has been extensively applied in wound treatment as an alternative to more expensive and advanced wound products. It reduces redness, swelling and pain and, when applied, there is usually no discomfort other than a slight stinging sensation [229].

Antioxidant Activity
As exemplified in the previous sections, monofloral honey is rich in both enzymatic and non-enzymatic antioxidants, polyphenols and minerals. In the study conducted by Omotayo et al. (2010) [205], it was investigated whether tualang honey could reduce hyperglycemia and ameliorate oxidative stress in streptozotocin-induced diabetic rats. The honey-treated groups showed an increase activity of catalase, glutathione peroxidase, glutathione reductase and glutathione-S-transferase compared to control. The same was noticed in the study of Erejuwa et al. [206], which showed that the combination of glibenclamide, metformin and taulang honey significantly up-regulated CAT activity, reduced TBARS levels and down-regulated GPx activity.
Sibel et al. [208] showed that Rhododendron honey treatments showed an antioxidant effect on blood plasma and organ tissues Thus, a significant increase in GTX was shown at a high dose of mad honey and decreased levels of MDA levels in the group administered a low dose of honey (0.1 g/kg/bw). Furthermore, the honey-administered group, at low doses of honey, was closely related to the control group in lung, heart, spleen, testicle and epididymis tissues and medium doses of honey in the testicle and epididymis.
Eraslan et al. [209] demonstrated that the administration of pine honey alleviated the tissue MDA levels and CAT, SOD and GSH-Px activities in the trichlorfon-administered group. Thus, they demonstrated that, in order to minimize the risk of foodborne trichlorfon intoxication, as well as its adverse effects, pine honey may be safely included in the daily human diet. In a different study, Bezerra et al. [210] showed the positive effect of malicia honey on the lipid metabolism, antioxidant status and intestinal health of rats with dietinduced dyslipidaemia. The dyslipidaemia group that received honey showed lower values of GPx and higher MDA levels.

Anti-Obesity
Honey has the potential to control obesity by reducing excess weight gain and other obesity parameters such as triglyceride levels. However, its effects on cells that store lipids (adipocytes) are still unclear. In the study conducted in order to observe the effects of pineapple honey on adiposity growth and lipid accumulation in vitro, it was determined that pineapple honey had a total phenolic content of 0.0379 ± 0.001 mg/100 mL GAE and a total flavonoid content of 0.098 ± 0.001 mg catechin/kg. It has been found to significantly inhibit the proliferation of adipocytes starting at 6.25% of the pineapple honey concentration. In addition, honey was found to significantly reduce lipid droplet size between 33.78% and 70.36%, compared with the control [184].
The influence of Clover honey on weight gain, adiposity and blood lipid profile on Sprague-Dawley rats has been evaluated [213]. They were equally divided into two groups and provided either clover honey or sucrose. After 33 days, for the honey-fed group, the bw was 14.7% lower, alongside a 13.3% lower consumption of food. Compared to control, the epididymal fat weight was 20.1% lower, as well as the serum concentrations of triglycerides (29.6%) and leptin (21.6%). Their results clearly demonstrated that, in comparison with sucrose, honey reduced weight gain and adiposity, due to lower food intake, as well as promoted lower serum triglycerides.
In a different aspect, the high fat diet rats fed with Gelam and Acacia honeys had lower consumption of food, as well as a lower adiposity index compared to the high fat diet group. Furthermore, rats fed with Acacia honey showed a significant increase in the relative organ weight compared to the control group, particularly the liver, heart and lung [215]. Even though, in the experimental diabetes mellitus, the supplementation with tualang honey resulted in weight gain of diabetic rats, its supplementation in human (especially obese) diabetic patients may necessitate a dose adjustment and reduced calorie intake [205].

Gastrointestinal Protective Effects
Honey produced from medicinal plants is generally a great hope for human health. The chemical composition and gastrointestinal protective effects of a new monofloral honey from Prunella vulgaris (PVH) have been identified, and it has been reported to provide basic data on PVH for future applications supporting the prevention of colitis [148]. Furthermore, Rhododendron honey is used as an alternative treatment for gastritis, stomach ulcer, constipation, hypertension, coronary heart disease and impotence [229].
Kocyigit et al. [183] showed that, due to its high phenolic and antioxidant contents, Quercus pyrenaica honeydew honey were tested against gastric cancer cells.
Honeydew honey had proliferative effects due to its antioxidant activity, and high concentrations showed cytotoxic, genotoxic, and apoptotic effects in the tested cancer cells. All these effects were higher with Quercus application compared with that of polyfloral honey, which possessed lower phenolic content. Their results demonstrated that honeydew honey may contribute to the future development of therapeutics in patient's suffering from several cancers.
Oral pretreatment with Chestnut honey (2 g/kg), once daily for seven consecutive days, prevented indomethacin-induced gastric lesions in rats, reduced the ulcer index, microvascular permeability and stomach's myeloperoxidase activity [212].

Anti-Fatigue and Antidepressant Effects
It has been stated that honey has a fatigue-relieving and soothing quality due to its alkaline balance. Honey, which also affects the nervous system, is good for headaches, insomnia and depression with its antidepressant and sedative properties [230].

Antibacterial and Antimicrobial Activity
Honey provides benefits against Streptococcus mutans infections, dental plaque and caries and gingivitis and bad breath, and also contributes to the prevention of side effects associated with the treatment of head and neck cancers, namely radiation-induced mucositis, xerostomia and poor wound healing [231,232]. Methylglyoxal (MGO) is the main antimicrobial marker associated with the use of Mānuka honey as a topical dressing. It is predicted that MGO derived from Mānuka honey may play a role in the enhancement of microbial detection by MAIT cells, which may help MAIT cells (Mucosal-associated invariant T cells) to control microbial infection and systemic immune homeostasis [233]. A recent study showed the differences between the antibacterial effects of Hovenia and Acacia honeys [153]. The minimum inhibitory activity of Hovenia and Acacia honeys was evaluated against gram positive (S. aureus and L. monocytogenes) and gram negative (E. coli O157:H7 and S. typhimurium) bacteria. Their results showed similar MIC for both honeys, as follows: 25-50% (w/v) against E. coli O157:H7 and S. typhimurium and 25% (w/v) against S. aureus and L. monocytogenes. Furthermore, the MIC values of artificial honey (sugar constituted) against foodborne bacteria exceeded 50% (w/v), indicating that a part of antibacterial activity of Hovenia and Acacia monofloral honeys was derived from the TPC and TFC. Moghadam and Khaledi (2021) [234] studied the minimum inhibitory concentration and the minimum bactericidal concentration of six Iranian honey samples in comparison with Manuka honey against reference strains of Staphylococcus aureus (ATCC 29737), Pseudomonas aeruginosa (ATCC 27853), Klebsiella pneumonia (ATCC 10031) and Escherichia coli (ATCC 10536). Their results showed high antimicrobial and anti-biofilm activity in Iranian honeys compared to Manuka honey. Majtan and Majtan (2010) [235] studied the antibacterial properties of Slovak honey types such as Acacia, Canola, Meadow and Forest, compared to Manuka honey. The results showed that forest honey had an inhibitory activity similar to that of manuka honey for some bacteria. Forest honey is more effective against Proteus sp. and Pseudomonas aeruginosa than manuka honey. In recent years, increased bacterial resistance to a lot of antibiotics and the various complications with chronic wounds are presented. Boateng and Diunase (2015) [128] compared Cameroonian honeys in the respect of physicochemical, antioxidant and antibacterial activity (that may contribute to the functional wound healing) to those of Manuka honey.

Antidiabetic Effects
Multiple reports have demonstrated the positive role of honey in regulating the blood glucose level. However, due to its high sugar content, honey is considered detrimental to diabetics. As stated in Section 7, fructose content in monofloral honey varies from 23% in Eucalyptus to 45% in Heather, followed by Fennel with 44.9%. Therefore, its high fructose content along with minerals, phenolic acids and flavonoids has a role in regulating blood glucose levels. Furthermore, Omotayo et al., 2010 [205] showed that consumption of tualang honey significantly decreased the elevated levels of TBARS in streptozotocininduced diabetic rats, showing that the honey-treated diabetic rats had reduced lipid oxidative damage.
In a recent study by Whitfield et al. [220], the mixture of Kanuka honey with chromium, cinnamon and magnesium was studied for its effect on lipid profile, glycaemic control and weight in 12 patients with type 2 diabetes. Based on their results, consumption of the 53.5 g honey mixture for 40 days significantly increased the bw and improved lipid parameters in the subjects. Additionally, susceptibility in the increase of HDL and reduction of systolic blood pressure was also noticed. Finally, the honey mixture did not affect glycaemic control and the metabolism of glucose.

In Vitro Studies Correlated to Polyphenols
Many of the polyphenols found in honey, such as caffeic acid, caffeic acid phenyl esters, chrysin, galangin, quercetin, kaempferol, acacetin, pinocembrin, pinobanksin and apigenin have potential in the treatment of cancer. Jaganathan and Mandal (2009) [236] reviewed the antiproliferative effect of polyphenols from honey in various cancer cell lines. Manuka honey has an antiproliferative activity on three different cancer cell lines: murine melanoma (B16.F1), colorectal carcinoma (CT26) and human breast cancer (MCF-7) cells in vitro. It is effective at concentrations as low as 0.6% (w/v) [182]. Alvarez Suarez et al. 2012 [66] studied the protective effect of such unifloral honeys against lipid peroxidation in an in vitro model of rat liver homogenates and the ability of the phenolic extracts of Turbina corymbosa L. (i.e., Christmas vine) and Gouania polygama (Linen vine) honeys to inhibit the oxidative damage induced by the 2,2 -azobis(2-methylpropionamidine) dihydrochloride in erythrocytes. Tsiapara et al. (2009) [114] presented antiprolifertive effects from Greek honey extracts from thyme, pine and fir honey on breast cancer (MCF-7), prostate cancer (PC-3) and endometrial cancer (Ishikawa) cells. Thyme honey reduced the viability of Ishikawa and PC-3 cells. They concluded that Greek honeys are rich in phenolic compounds and may prevent cancer-related processes in breast, prostate and endometrial cancer cells.
In another study, Jaganathan (2012) [237] examined the apoptotic effect of caffeic acid, one of the phenolic constituents of honey, in HCT 15 colon cancer cells. The author promoted the caffeic acid as a candidate in the chemoprevention of colon cancer. The caffeic acid inhibited the colon cancer cell proliferation in a dose-dependent manner. The antiproliferative effect of caffeic acid was estimated using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. Swellam et al. (2003) [238] examined the effect of pure unfractionated honey in three human bladder cancer cell lines (T24, 253J and RT4) and in one murine bladder cell line (MBT-2) using MTT assay. The authors received significant inhibition of the proliferation of T24 and MBT-2 cell lines by 1-25% honey and of RT4 and 253J cell lines by 6-25% honey. Pichichero et al. (2010) [161] investigated the antiproliferative effect of honey or chrysin (5,7-dihydroxyflavone) on human (A375) and murine (B16-F1) melanoma cell lines with MTT assay and Trypan Blue Exclusion Test. Chrysin is a natural flavone found in Acacia honey. Both tests showed that these compounds can induce an antiproliferative effect on melanoma cells. The same authors concluded that the antiproliferative effects of honey are due to the presence of chrysin. In this respect, chrysin is a potential candidate in the prevention and treatment of cancer. Aliyu et al. (2012) [155] provided evidence on the apoptotic role of Acacia honey from Pakistan on the PC-3 Human prostate cancer cell line. The possible mechanism of this process is the modulation of pro-inflammatory cytokines and regulation of prostate specific antigen in vitro.
The antitumor effects of honey on liver cancer cells have been reported by Aziz Baiomy et al. (2009) [239]. The authors reported that honey extracts exerted cytotoxic, antimetastatic and anti-angiogenic effects in HepG2 cells.
Anticancer activity of honey has been proved against various cancer cell lines and tissues in animals and humans [240], and multiple reviews summarise the anticancerogenic properties of different honey types and components of honey [16,[241][242][243]. Tualang honey is a Malaysian multifloral jungle honey with many potential health benefits such as antimicrobial, anti-inflammatory, antioxidant, antimutagenic, antitumor, antidiabetic and wound-healing properties. Some of its properties are similar to Manuka honey. The differences include higher phenolics and flavonoids in Tualang honey. Tualang honey is also more effective against some gram-negative bacterial strains in burn wounds compared to the Manuka honey. The honey is produced by Apis dorsata, which builds hives on branches of tall Tualang trees located mainly in Peninsular Malaysia [16].
Manuka honey, even at lower concentrations of 0.6% (w/v), inhibited the cell proliferation in multiple cell lines (human breast cancer MCF-7, murine melanoma B16.F1 and mouse colon carcinoma CT26) in a dose and time dependent manner [182].
In a recent study, Abd Kadir et al., (2013) [207] studdied the inhibitory effect of Malaysian tualang honey on the development of 7,12-dimethylbenz(α)anthracene (DMBA)induced breast cancer in rats. Their results showed that the untreated DMBA-induced breast cancer rats (control rats) developed tumors earlier compared to the honey-treated DMBA-induced breast cancer rats. The control rats also showed a marked increase in tumor size over a shorter period. On the contrary, a reduction in the growth and size were noticeably reduced in the honey-treated DMBA-induced breast cancer rats compared to the untreated cancer rats. Furthermore, a lower number of tumors were noticed in the honey-treated rats compared to the controls. Even though not statistically significant, an increase in apoptotic index was noticed by higher honey doses. Higher grade tumours were observed in the untreated rats, compared to lower or medium grade ones reported in the honey-treated group. The histological analysis also revealed that the cancer cells from the honey-treated rats were more identical, with denser nuclei, while those of the control rats had more pleomorphic cells with more prominent nuclei. Finally, lower prominent vasculature surrounding the tumor nodules and significantly reduced weight and volume in the tumor mass were noticed (paler, smaller and softer with necrosis spots) in the honey-treated group.

Conclusions
Numerous honey compounds act as natural antioxidants. From ancient times to nowadays, honey has had a potential role in contributing to human health. Bee honey is chemically very complex, and the chemical composition strongly depends on its botanical origin. Monofloral honeys are also an economic income source for many countries.
The locally available honey types in different countries are rich in bioactive components displaying excellent applications for human health. There are approximately 200 compounds in honey. The variety of these compounds results in different color, taste, honey type and therapeutic activities. Honey might be utilized as a potential source of natural antioxidants. Furthermore, the consumption of honey has high nutritional and therapeutic values. The concentration of different compounds in honey depends mainly on various factors, such as floral source and honey type, as well as environmental and processing factors. These factors affect the biological activities of each type of honey in the world.
In brief, monofloral honeys present a variety of dietary phytochemical compounds with functional properties such as phenolic acids, minerals, phenolics and flavonoids. Therefore, considering the food industry and the positive effects on human health, monofloral honeys have tremendous potential for the production and use as natural and functional ingredients with special attention to their use in the medical field. To our knowledge, this is the first study of the antioxidant properties, mineral composition and health properties of monofloral honey types.