Static Water Vapor Sorption Properties of Honey

Static sorption properties of pine honey (PH) and citrus honey (CH) were studied at 20, 30 and 40°C. Yeast formation was observed on the surface of honeys at water activity (a_w)>0.7 at all temperatures. Visible yeast formation (YF) took place earlier in PH than in CH under the same conditions due to its characteristic higher pH and lower monosacchride content. The temperature was insignificantly effective on YF (p>0.05). The honeys exhibited a sorption isotherm (SI) in the shape of a “J”. Their SIs exhibited desorption and adsorption at a_w<0.7 and a_w>0.7, respectively and the desorption part was almost linear. A_w=0.7 emerged as a border between the absence and presence of YF and between the desorption and adsorption. The SIs of honeys were insignificantly affected by temperature (p>0.05). PH had a significantly lower SI than that of CH (p≤0.05) due to its characteristic lower monosacchride content. GAB equation exhibited a good fit to the honeys' SIs. Sorption heat vs equilibrium moisture content (EMC) revealed monolayer, multilayer and loosely bound free water regions in the SIs of PH and CH.