Abstract
The aim of this work was to study the rheological, thermal and some other physical-chemical properties of selected honeys produced in the Northeast of Brazil. Two samples were produced by native “Jandaira” bees (Melipona subnitida) and ten other samples by Africanized bees (Apis mellifera). The samples were analyzed for pH, water activity (aW), soluble solids and water content. Viscosity flow curves were obtained using a rheometer (25ºC, 0-100s-1). Thermal analyses were performed on a differential scanning calorimeter, with heating rate of 10ºC/min (-100 to 100ºC). The water content and the pH of the honey samples varied from 17.2 to 27.9% and from 3.2 to 4.2, respectively, and, the aW of the samples varied from 0.57 to 0.74. Two samples were out of specification with respect to water content, according to Brazilian laws. In relation to rheology, all honey samples showed Newtonian behaviour with no thixotropy or dilatancy. The viscosity varied as an exponential function of the water content. The highest viscosity was obtained for the sample with lower values of water content and aW. Thermograms showed a glass transition (Tg) occurring between -52.4 and -42.6ºC, in the samples produced by Apis mellifera and -67.6 and -57.0ºC for the other samples. A linear relationship was obtained between Tg and water content. In conclusion, the honey viscosity depended on the water content of the product. The higher the water value and therefore the greater the aw, the lower viscosity and Tg of the samples.
Highlights
Honey is produced from flower nectar and from plant secretions, and from the excretions of sucking insects, which the bees collect, transform and combine with specific substances and mature inside the honeycomb (Brasil, 2000)
According to Brazilian laws, based on the standards for honey produced by Apis mellifera, the maximum water content value allowed for honey is 20g/100g (Brasil, 2000)
The water content values determined in this study agree with the values reported for Chinese honeys (19.8 - 29.0%) (Junzheng & Changying, 1998), but are higher than those reported for honeys from Australia (15.8 18.0%) (Sopade et al, 2002), from Poland (15.4 - 18%) (Juszczak & Fortuna, 2006), from Mexico (16 - 20.6%) (Mora-Escobedo, Moguel-Ordonez, Jaramillo-Flores, & Gutierrez-Lopez, 2006), and by Argentine [16.4 - 20.2% (Baroni et al, 2009) and 15-21% (Chirife, Zamora, & Motto, 2006)]
Summary
Honey is produced from flower nectar and from plant secretions, and from the excretions of sucking insects, which the bees collect, transform and combine with specific substances and mature inside the honeycomb (Brasil, 2000). Honey is a source of available sugars, organic acids, some amino acids, macro and micro nutrients and biologically active substances (Juszczak & Fortuna, 2006). Beyond its high nutritional aspects, honey has medicinal-. Regarding the physical-chemical properties, honey can be considered as a complex high concentrated sugar solution, composed mainly of glucose and fructose. This product usually has an intermediate water activity value. This parameter is significant, as the free water amount affects the physical and biochemical stability of the honeys and it is important to de-
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