| Honey is a natural nutrient,and its physicochemical properties,chemical constituents and biological activity are closely related to honey source.Eurya Thunb honey and Rhus chinensis Mill honey are chinese characteristic honey varieties brewed by bees from the nectar of Eurya and Rhus chinensis,respectively.The former is commonly known as wild osmanthus-scented honey,with Eurya plants such as E.muricata and E.groffii flowering in winter as nectar sources,commonly known as winter osmanthus-scented honey;Eurya plants such as E.nitida and E.acuminata flowering in late winter and early spring as nectar sources,commonly known as spring osmanthus-scented honey.Both honeys have antioxidant and antibacterial activities,but there is no comprehensive and systematic study on Eurya honey and Rhus chinensis honey.In this study,the water content,acidity,p H,sugar composition,conductivity,5-hydroxymethylfurfural(5-HMF)content,color,total phenols and total flavonoids of Eurya honey and Rhus chinensis honey were systematically detected.The chemical constituents of the two honeys was analyzed by High Performance Liquid Chromatography-Ultraviolet Detector and UItra Performance Liquid Chromatography Quadrupole Time-of-Flight Mass Spectrometry.and the Eurya honey had special sweet and significant odor characteristics,The composition of its volatiles was studied by Solid Phase Microextraction-Gas Chromatography Mass Spectrometry.Finally,its antioxidant activity was studied by three different systems,and its antibacterial activity against two bacteria.The main findings are as follows :1.The color of Eurya honey is water-white,and the water content(21.27 ±0.77%),acidity(18.17 ± 4.02 m L/kg),p H(4.40 ± 0.14),5-HMF(3.28 ± 2.74 mg/kg),conductivity(0.25 ± 0.07 m S/cm),fructose(39.38 ± 3.84%),glucose(33.78 ± 3.02%)sucrose(0.50 ± 0.24%)and L*(63.11 ± 8.36).The results of Rhus chinensis honey showed that the moisture content(19.59 ± 1.24%),acidity(32.72 ± 1.07 m L/kg),p H(4.24 ± 0.73),5-HMF(3.06 ± 1.52 mg/kg),conductivity(0.38 ± 0.08 m S/cm),fructose(35.92 ± 3.6%),glucose(32.14 ± 6.04%),sucrose(1.18 ± 0.28%)and L*(47.19 ± 6.62),color is bright-yellow.The physicochemical properties of Eurya honey and Rhus chinensis honey met the requirements of literature reports,national standards and the International Honey Commission(IHC).2.The phenolic compounds in honey were qualitatively and quantitatively analyzed by HPLC-UV combined with 25 standards.The 15 substances(3,5-dihydroxybenzoic acid,3,4-dihydroxybenzoic acid,D-salicyloside,chlorogenic acid,caffeic acid,syringic acid,p-coumaric acid,rutin,resveratrol,3,4-dimethoxycinnamic acid,luteolin,quercetin,apigenin,chrysin and caffeic acid benzyl ester)in Eurya honey were detected in 6 samples,and the contents of D-salicyloside(89.69-258.13 μg/100 g)and rutin(95.31-185.31 μg/100 g)were higher.Six substances in Rhus chinensis honey(ferulic acid,rutin,trans-4-dihydroxycinnamic acid,luteolin,apigenin,kaempferol)were detected in 6samples,and the contents of 4-coumaric acid(329.67-545.67 μg/100 g)and luteolin(89.06-424.38 μg/100 g)were higher.3.A total of 232 chemical components were detected in Eurya honey by UPLC-Q-TOF-MS,including phenolic acids(44),flavonoids(19),organic acids(66),alkaloids(2),lipids(25),terpenoids(5),amino acids and their derivatives(20),nucleotides and their derivatives(16),other substances(35),and 30 of them were quantified.Among them,The higher contents of gallic acid(6.9-220.2 μg/100 g),abscisic acid(21.3-103.4 μg/100 g)and tricoumaroyl spermidine(284.2-518.1 μg/100g)were potential markers of Eurya honey.A total of 93 substances were identified in Rhus chinensis honey,including phenolic acids(18),flavonoids(20),organic acids(20),alkaloids(2),lipids(2),amino acids and their derivatives(14),and others(17),and 24 of them were quantified.Among them,the higher contents of 4-coumaric acid(1835.68-2908.23 μg/100 g),kynurenic acid(462.56-1346.85 μg/100 g)and lumichrome(462.56-1346.85 μg/100 g)were potential markers of Rhus chinensis honey.4.A total of 55 volatile chemicals were identified from Eurya honey by SPME-GC-MS.The top five substances with the highest content were cis-a,a-5-trimethyl-5-vinyltetrahydrofuran-2-methanol,phenylethyl alcohol,linalool2,4-di-tert-butylphenol and nonanal,which could be used as characteristic volatile substances of Eurya honey.The results of principal component analysis(PCA)and orthogonal partial least squares discriminant analysis(OPLS-DA)showed that there were differences in volatile substances between spring osmanthus-scented honey and winter osmanthus-scented honey.The top seven substances(VIP value > 1)with great differences were salicylic acid-2-ethylhexyl ester,2,2,4-trimethyl-1,3-pentanediol diisobutyrate,furfuryl alcohol,dibutyl phthalate,2-propionaldehyde,heptanoic acid and benzyl alcohol.5.The results of DPPH,ABTS free radical scavenging experiments and ferric reducing antioxidant power experiments showed that both Eurya honey and Rhus chinensis honey had certain antioxidant capacity,and the antioxidant capacity of Rhus chinensis honey was higher than that of Eurya honey.The results of antibacterial activity showed that the minimum inhibitory concentrations of Eurya honey and Rhus chinensis honey against Klebsiella pneumoniae were 0.38 g/m L and 0.35 g/m L,respectively,and the minimum inhibitory concentration for Streptococcus pyogenes was 0.28 g/m L and 0.38 g/m L,respectively.The minimum bactericidal concentrations of Eurya honey and Rhus chinensis honey for Klebsiella pneumoniae were 0.40 g/m L and 0.38 g/m L,respectively,and the minimum bactericidal concentration of honey against Streptococcus pyogenes was 0.28 g/m L and 0.30 g/m L,respectively.The antibacterial effect of all honey was higher than that of syrup control group,indicating that honey had certain antibacterial activity,and the antibacterial effect of Rhus chinensis honey on Klebsiella pneumoniae was the best,and the antibacterial effect of Eurya honey on Streptococcus pyogenes was the best.Eurya honey and Rhus chinensis honey are characteristic honey varieties in China.Their physical and chemical indexes meet the standards of literature reports and International Honey Commission,and they are rich in plant secondary metabolites.The study confirmed that gallic acid,abscisic acid and tricoumaroyl spermidine can be used as potential markers of Eurya honey,and 4-coumaric acid,kynurenic acid,lumichrome can be used as potential markers of Rhus chinensis honey.In vitro experiments showed that both honeys had certain antioxidant and antibacterial abilities.The results provide a basis for the quality control and quality evaluation of Eurya honey and Rhus chinensis honey,and also provide a reference for the development and utilization of characteristic single flower honey resources. |
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