Characterisation of viscosity, colour, 5-hydroxymethylfurfural content and diastase activity in raw rape honey (Brassica napus) at different temperatures.

Abstract

The effect of heating at various temperatures (30, 40, 50, 60, 70 and 80°C) on dynamic viscosity, colour, 5-hydroxymethylfurfural (5-HMF) concentration and diastase activity of raw rape honey were assessed. In fresh honey, moisture, ash, free acidity, pH and electrical conductivity averaged 185.3gkg(-1), 1.2gkg(-1), 18.71mEqkg(-1), 4.2 and 0.25 mS cm(-1), respectively. Heating significantly (p≤0.05) increased lightness (L*), yellowness (b*), chroma (C*), hue (h°) values, but decreased redness (a*). The viscosity at 20°C (33.6Pas) differed significantly (p≤0.01) with those at 30, 40 and 50°C (8.2, 2.5, and 1.6Pas, respectively). Diastase activity decreased concomitant with heating at higher temperatures. Honey heated at 80°C for 15min showed the maximum increase of 5-HMF content, with an average of 1.9mgkg(-1) (62%), compared to unheated samples. Heating for 15min between 50°C and 80°C did not significantly degrade the quality of the honey, but, slightly enhanced formation of 5-HMF and reduced the diastase activity.