Effect of honey high-temperature short-time heating on parameters related to quality, crystallisation phenomena and fungal inhibition

Abstract

The effect of a unique high-temperature short-time heating treatment on natural honeys to produce both a fungi inhibition and a crystallisation delay simultaneously was evaluated. As responses to treatments, hydroxymethylfurfural content, diastase activity, fungi and yeast development, and crystallisation starting time were measured. Besides, moisture, fructose, glucose and acidity were determined. Heating can produce a decrease in honey quality, which is made evident by a simultaneous reduction in the diastase activity, referred to as diastase number, and an increase in the hydroxymethylfurfural content. Considering the minimum admissible diastase number and the maximum admissible hydroxymethylfurfural content values, according to honey present regulations, several thermal treatment tests were performed on selected honey samples without exceeding those values. Tested conditions were: heating between 140°C and 80°C at times between 60 to 15 s and 30 to 10 s during both transient and isothermal heating stages, respectively. In all tests the diastase number was the most heat-sensitive parameter. The boundary thermal treatment, assumed as the most severe conditions able to produce a permissible quality loss, was found to be 140°C, during 15 s in the transient stage and 30 s in the isothermal stage. Beyond those values, an unacceptable diastase number reduction was produced. On the other hand, it was found that a 80°C heating, during 60 and 30 s in transient and in isothermal stages, respectively, destroyed all microorganisms responsible for quality damage without spoiling honey. This was considered to be the mild or more suitable treatment condition. Twenty-six naturally contaminated honey samples heated at such conditions showed a null capacity to develop fungi and yeast. Besides, according to the storing temperature, and moisture and glucose contents, a crystallisation beginning delay between 4 and 9 weeks was obtained on four selected honeys, according to the thermal treatment applied. Several parameters previously proposed that characterise honey crystallisation tendency as fructose/glucose, glucose/moisture and (glucose-moisture)/fructose ratios were related to the time in which crystallisation starts. A new parameter, (fructose/glucose)·moisture was proposed.