Impact of floral sources and processing on the antimicrobial activities of different unifloral honeys

Objective: To study in vitro antibacterial activity and physicochemical properties of three unifloral honeys\ud(citrus, clover and cotton honeys), and to study the impacts of storage, dilution with water (33%, w/v) and\udautoclaving (121 °C for 15 min) on honeys characteristics.\udMethods: Honey samples from monofloral sources including citrus (Citrus spp.), Egyptian clover (Trifolium\udalexandrium) and cotton (Gossypium vitifolium) were obtained during three successive seasons (2010-2012).\udPhysicochemical properties and antimicrobial activities of different honey samples were studies.\udResults: In honey samples stored for 12 or 24 month, colour, hydroxymethyl furfural and acidity increased,\udwhile refractive index, water activity, total soluble solids, electrical conductivity and pH remained relatively\udunaffected, but H2O2 values decreased. Types of honey exhibited various degrees of antibacterial activity\udagainst different indicator bacteria, wherein the highest antibacterial activity was recorded for clover\udhoney followed by citrus and cotton honeys, respectively. Different species of bacteria were differed in\udtheir sensitivity to honey, wherein Salmonella enteritidis was the most sensitive followed by Staphylococcus\udaureus, Listeria monocytogenes and Escherichia coli, respectively. Storage up to 24 months at room\udtemperature slightly reduced the antibacterial activity. The reduction levels were about 2.6% and 4.6% after\ud12 and 24 months, respectively. Diluting honeys with water increased the antibacterial activity by ca. 8.3%,\udwhile autoclaving decreased the antibacterial activity by ca. 13.5%. The relative contribution of the peroxide\udand non-peroxide components in the total antibacterial activity of fresh honeys was investigated. The\udantibacterial activity of honeys was mainly attributed to non-peroxide antibacterial agents, wherein their\udcontribution was ca. 88%, while the contribution of H2O2 was only 12%. The contribution of the thermostable\udantibacterial components in honey was ca. 86.8%. The antibacterial activity of the fresh clover honey was\udcompared with the effect of 16 antibiotics on indicator bacteria. Clover honey exhibited antibacterial activity\udcomparable to that exhibited by the tested antibiotics. Moreover, antibacterial activity of water diluted fresh\udclover honey was higher compared to some of tested antibiotics. Clover honey appeared to deserve further\udinvestigations, since it may prove to be a promise therapeutic honey.\udConclusions: Honey samples tested in this study exhibited antibacterial activity against tested pathogenic\udbacteria, and this activity was mainly due to non-peroxide antibacterial factors. Clover honey appeared\udto deserve further investigations, since it may prove to be a promising therapeutic hone