Honey is a natural sweetener with a complex chemical composition and health/promoting properties ^[1][2][1,2]. Bees collect nectar from plants and/or insect excretions and produce honey, which has been revered for centuries for its nutritional and therapeutic properties [3]. Honey has been resurrected as a therapy for burns, gastrointestinal diseases, asthma, infected wounds, and skin ulcers in humans, and in animal medicine ^[4][5][4,5]. Honey contains several constituents of small amounts, such as minerals, free amino acids, proteins, vitamins, enzymes, organic acids, flavonoids, phenolic acids, and other organic acids in addition to other phytochemicals compounds ^[6][7][6,7]. The amount of these components is determined by several factors, including the honey’s geographical origin, floral source, meteorological circumstances, any treatments applied [8], and seasonality [9]. Honey’s composition can be affected by processing, handling, and storage [10]. The quality of honey also depends on floral resources and the treatment of the beekeepers [11]. Honey’s botanical and geographical origins have traditionally been determined by evaluating pollen quality and quantity and organoleptic and physicochemical testing. In addition, data derived from the sensory profile, bioactive components, and novel methods of investigation should be added to this information ^[7][12][13][7,12,13]. Water content, sugar reduction, sucrose, insoluble matter, ash, free acid, pH, electrical conductivity, specific rotation, and sensory and microbiological properties are the basis for the quality assessment of honey ^[14][15][14,15]. Honey’s components have a variety of beneficial biological actions, such as antibacterial, antiviral, antifungal, antioxidant, antidiabetic, antitumor, anti-inflammatory, and anticancer activity honey ^[16][17][18][16,17,18]. Various studies have demonstrated that antioxidant activity highly correlates to total phenolic levels [19]. Moreover, darker honey has been reported to have a higher total phenolic content and thus more significant antioxidant activity [20]. Honey’s composition includes various components, including hydrogen peroxide and polyphenols, and is also strongly linked to antibacterial activity ^[21][22][21,22]. The ability of honey to fight different types of microorganisms is determined by various variables, including the kind and natural structure of the nectar and the environmental circumstances in which the bees were raised ^[23][24][23,24]. The phenolic and flavonoid chemicals that make up honey are thought to be responsible for most of its biological activity. According to previous research, the activity of honey is influenced by the bioavailability of different phytochemical components as well as how they are absorbed and metabolized ^[18][25][18,25]. The flavonoids are largely water-soluble natural chemical compounds with low molecular weight. When flavonoids are not linked to sugars, they are referred to as aglycones ^{[26][27][28][29][30][31][32][33]}[26,27,28,29,30,31,32,33]. In general, these chemicals include at least two phenolic groups (OH) and are frequently coupled with sugars (glycosides) ^{[34][35][36][37][38][39][40][41][42][43][44][45]}[34,35,36,37,38,39,40,41,42,43,44,45]. The term “phenolic acids” refers to compounds that have a phenolic ring and at least one organic carboxylic acid function. They can be classified into three groups based on their structural types: C₆–C₃ compounds (such as p-coumaric, ferulic, and caffeic acids), C₆–C₂ compounds (such as acetophenones and phenylacetic acids), and C₆–C₁ compounds (e.g., syringic, vanillic and gallic acid). Most of these substances are typically linked to the cellulose and lignin that serve as the plant’s structural foundation, as well as to other classes of organic molecules such as glucose, other sugars, and flavonoids [46]. Additionally, some phenolic chemicals found in honey, including acaetin, caffeic acid, quercetin, galangin, and kaempferol, may hold potential as medicines for the treatment of cardiovascular disorders [47]. According to numerous research, flavonoids, which are crucial in reducing oxidative stress, are also necessary for honey’s antioxidant potential ^{[13][48][49][50][51][52][53][54][55][56][57][58][59][60]}[13,48,49,50,51,52,53,54,55,56,57,58,59,60].

2. Physicochemical Properties and Composition of MH, TH, KH and SH

Honey has a wide range of physicochemical properties depending on its botanical and geographical origins and compositions that subsequently affect its biological capabilities ^{[29][61][62][63][64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91][92][93][94][95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121][122][123][124][125][126][127][128][129][130][131][132][133][134][135][136][137][138][139][140][141][142][143][144][145][146]}[29,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100,101,102,103,104,105,106,107,108,109,110,111,112,113,114,115,116,117,118,119,120,121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137,138,139,140,141,142,143,144,145,146,147]. Honey is defined as the natural sweet material generated by the Apies mellifera bees from the nectar of plants in European Union Council Directive 2001/110/EC [30]. Table 1 shows the physicochemical characterisation of Manuka honey (MH), Tualang honey (TH), Kelulut honey (KH) TH, KH and Sidr honey (SH)H extracted from various studies. Several studies have been conducted to look at the physical and chemical properties of MH TH, KH, and SH. On the other hand, MH TH, KH, and SH mostly complied with the accepted range by the two most common legislation of honey criteria and standards referred to as the European Honey Legislation and Codex Alimentarius Standards for Honey ^[29][31][32][29,31,32]. The primary quality indicators for honey include moisture content, sucrose content, reducing sugars content, pH value, electrical conductivity, ash content, free acidity, diastase activity, and hydroxymethylfurfural (HMF) content ^[36][37][36,37]. In terms of honey colour characteristics, MH is categorized as light-colored honey, TH is dark brown honey, KH is amber brown, and SH is dark-colored honey ^{[29][38][43][147]}[29,38,43,148]. TH and KH contained more than 20% moisture content, thus violating European Honey Legislation and Codex Alimentarius Standards. Nonetheless, honey samples from tropical countries, such as Malaysia, typically have higher moisture content, which could be due to the rainy season all over the year. Therefore, Malaysia’s honey is always first treated by evaporation to reduce the water content, thereby simultaneously increasing the honey quality ^{[11][29][31][35][41][51][55][56]}[11,29,31,35,41,51,55,56]. MH contained 18.7% moisture content ^[41][43][50][41,43,50] and SH contained 13.5–20.67% moisture content ^{[11][31][55][56]}[11,31,55,56]. The low pH of MH is approximately similar to TH and less than to KH and SH. TH is more acidic than KH and SH [41]. Darker honey typically has a higher conductivity, whereas brighter honey typically has a lower conductivity ^[33][34][33,34]. The pH values of TH, KH, and SH were reported to be in the range 3.14–4, 2.76–4.66 and 3.90–5.2, respectively, compared with MH (3.20–4.21) ^{[11][29][31][35][41][42][43][51][55][56][57][59]}[11,29,31,35,41,42,43,51,55,56,57,59]. The electrical conductivity of TH, KH, and SH is in a broad range of 0.75–1.37 mS/cm, 0.26–8.77 mS/cm, and 0.53 mS/cm, respectively, compared with 0.53 mS/cm to MH. Additionally, the four honey types met the sugar content requirements set forth by the Codex Alimentarius Standards and the European Honey Legislation. According to the European Honey Legislation and the Codex Alimentarius Standards, honey moisture should be less than 20%, with glucose and fructose composition of more than 60 g/100 g, sucrose content of not more than 5 g/100 g and electrical conductivity of not more than 0.8 mS/cm. According to the Malaysian Standard Kelulut, the raw honey moisture content must be less than 35 g/100 g, with a pH of less than 3.8 and 5-hydroxymethylfurfural of less than 30 mg/kg [29]. In addition, MH reported to has high protein content (g/kg) in the range 5.02–5.06 (g/kg) compared to 3.6–6.6 (g/kg) TH, 3.9–8.5 (g/kg) KH, and 1.5–4.09 (g/kg) SH ^{[11][29][31][35][41][43][50][51][52][53][54][55][56]}[11,29,31,35,41,43,50,51,52,53,54,55,56]. Most bacteria grow in a neutral and mildly alkaline environment, whereas yeasts and moulds could grow in an acidic environment (pH = 4.0–4.5). Conversely, the pH values of honey are neither those needed for bacteria nor yeast growth [38]. This is of great importance during storage, as they influence the texture, stability, and shelf-life of honey ^{[11][29][35][39][43][50][51][57][59][60][61]}[11,29,35,39,43,50,51,57,59,60,62]. The low protein content and high carbon-to-nitrogen ratio of honey are not conducive to microbial growth, nor is the acidity of honey. The low redox potential of honey (which is due to its high content of reducing sugars) discourages growth of molds and aerobic bacteria, whereas the viscosity of honey opposes convection currents and limits the entry of dissolved oxygen. As the osmotic pressure is high, the microbes shrivel as water flows out of their cells into the surrounding honey ^[29][39][29,39]. Various factors, such as storage, time, temperature, water content and concentration of ions and minerals, were reported to contribute to the electrical conductivity of honey ^[11][35][11,35]. A comparison of the physicochemical characteristics of TH, KH, and SH with that of MH is presented in Table 1. Honey is mostly composed of fructose (35.6–41.8 g), glucose (25.4–28.1 g), sucrose (0.23–1.21 g) and Maltose (1.8–2.7 g) and other sugars ^{[29][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163][164][165][166][167][168][169][170][171][172][173][174][175][176][177][178][179]}[29,149,150,151,152,153,154,155,156,157,158,159,160,161,162,163,164,165,166,167,168,169,170,171,172,173,174,175,176,177,178,179]. It includes around 180 different compounds, including amino acids, vitamins, minerals, and enzymes. The composition varies according to the floral source and origin ^[29][179][29,179]. The concentration of sucrose (g/100 g) in MH and SH was higher than that in TH and KH ^{[29][55][63][64]}[29,55,64,65], and the concentration of glucose (g/100 g) in MH and TH was higher than that in KH and SH ^{[29][55][64][148]}[29,55,61,65]. In addition, the concentration of fructose (g/100 g) in MH and TH was higher than that in KH and SH ^{[29][55][64][148]}[29,55,61,65], and the concentration of maltose (g/100 g) in TH and KH was higher than that in MH and SH ^{[29][64][148]}[29,61,65]. Moreover, the protein content of MH (5.02–5.06 (g/kg) was higher than the values reported for TH (3.6–6.6 (g/kg), KH (3.9–8.5 (g/kg), and SH (1.5–4.09 (g/kg) ^{[29][55][63][64]}[29,55,64,65]. Among the major and minor elements found in honey, potassium (K) is found in the highest concentrations, followed by sodium (Na), calcium (Ca), and magnesium (Mg). Furthermore, because sugars are its primary constituents, honey’s physical characteristics and behavior are attributed to sugars. Sugar tests will indicate its sweetness due to its high sugar content, with fructose being the most abundant sugar. The concentration of sodium in MH, KH and SH was lower than the values reported for TH and the concentration of potassium and calcium in SH was higher than the values reported for MH, TH, and KH ^{[29][55][65][148]}[29,55,61,66]. Additionally, the concentration of magnesium in SH was higher than the values reported for MH, TH, and KH ^{[29][55][65][148]}[29,55,61,66]. Minor constituents such as flavor compounds, minerals, acids, pigments, and phenols play a significant role in distinguishing each variety of honey ^{[30][36][40][41]}[30,36,40,41]. Honey is a natural source of flavonoids, phenolic acids, and phenolic acid derivatives [44]. MH has higher total phenolic content (429.61 (mg/kg)) ^[63][64] than TH (251.7–1103.94 (mg/kg)) [29], KH (477.30–614.7 (mg/kg)) [29], and SH (212.4–520.34 (mg/kg)) ^[64][65]. In addition, the total flavonoid content in MH (97.62) ^[63][64] was higher than in TH (49.04–185) [29], KH (36.3) [29], and SH (42.5) ^[66][67]. A total of seven phenolic acids (caffeic, gallic, syringic, vanillic, p-coumaric, benzoic, and trans-cinnamic acids) and six flavonoids (apigenin, kaempferol, luteolin, naringenin, naringin, and catechin) are found in TH. Additionally, a total of four phenolic acids (syringic, gallic, ferulic and caffeic acids) and eight flavonoids (chrysin, galangin, isorhamnetin, kaempferol, luteolin, pinobanksin, pinocembrin, and quercetin) are found in MH. A total of nine phenolic acids (gallic, syringic, vanillic, 3 4-dihydroxybenzoic, 4-hydroxybenzoic, p-coumaric, cinnamic, salicylic, cis-trans-Abscisic acids) and three flavonoids (luteolin, naringenin, and taxifolin) are found in KH. A total of six phenolic acids (gallic, salicylic, chlorogenic and tannic acids) and five flavonoids (catechin and quercetin) are found in SH ^[28][29][41][28,29,41]. TH contains more phenolic acids and flavonoids than MH, KH and SH [41]. Some compounds found in TH previously not reported in other honeys include stearic acids, 2-cyclopentene-1,4,-dione, 2[3H]-furanone or dihydro-butyrolactone, gamma-crotonolactone or 2[5H]-furanone, 2-hydroxy-2-cyclopenten1-one, hyacinthin, 2,4-dihydroxy-2,5-dimethyl3[2H]-furan-3-one, and phenylethanol ^[41][179][41,179]. The details of the various compounds present in MH, TH, KH, and SH are summarised in Table 2. Generally, honey is rich in phenolic compounds, which act as natural antioxidants and are becoming increasingly popular because of their potential role in contributing to human health ^{[29][43][47][67][179]}[29,43,47,68,179]. Table 3 shows some of phenolic compounds with their different potential health benefits found in honey. A wide range of phenolic constituents are present in honey, including quercetin, caffeic acid, gallic acid, catechin, apigenin and kaempferol, which have promising effect in the treatment of cardiovascular diseases ^{[29][43][47][67][179]}[29,43,47,68,179]. Many epidemiological studies have shown that regular intake of phenolic compounds is associated with reduced risk of heart diseases. In coronary heart disease, the protective effects of phenolic compounds include being antithrombotic, anti-ischemic, anti-oxidant, and vasorelaxant ^{[29][43][47][67][179]}[29,43,47,68,179]. It is suggested that flavonoids decrease the risk of coronary heart disease by three major actions: improving coronary vasodilatation, decreasing the ability of platelets in the blood to clot, and preventing low-density lipoproteins (LDLs) from oxidizing ^{[29][43][47][67][179]}[29,43,47,68,179]. Cell viability of fibroblast-like synoviocytes (FLS) from patients with rheumatoid arthritis (RA) was significantly decreased by treatment with 10 or more μM of gallic acid. Treatment with 0.1 and 1 μM of gallic acid also showed in a significant increase in caspase-3 activity and regulated the production of Bcl-2, Bax, p53, and pAkt. The mRNA expression levels of pro-inflammatory cytokines (IL-1β, IL-6), chemokines (CCL-2/MCP-1, CCL-7/MCP-3), cyclooxygenase-2, and matrix metalloproteinase-9 from RA FLS were suppressed by the gallic acid treatment in a dose-dependent manner ^{[29][43][47][67][179]}[29,43,47,68,179]. The phenolic compounds in honey such as p-hydroxibenzoic acid, cinnamic acid, naringenin, pinocembrin, and chrysin showed antimicrobial activity ^{[29][43][47][67][179]}[29,43,47,68,179]. Additionally, caffeic acid exhibits a significant potential as an antidiabetic agent by suppressing a progression of type 2 diabetic states that is suggested by an attenuation of hepatic glucose output and enhancement of adipocyte glucose uptake, insulin secretion, and antioxidant capacity ^{[29][43][47][67][179]}[29,43,47,68,179]. In addition, protocatechuic and p-hydroxybenzoic acid exhibit significant antioxidant, anticancer and antiatherogenic activities ^{[29][43][47][67][179]}[29,43,47,68,179]. The chrysin decreased lipid peroxide, reduced the increased activities of superoxide dismutase, and attenuated the decreased activities of glutathione peroxidase in 2VO rats and Quercetin-3-O-rhamnoside showed moderate antitumor activity ^{[29][43][47][67][179]}[29,43,47,68,179].