Crystallization during processing is a very serious problem in the honey industry. Not only does crystallization slow down the process of getting the honey out of the containers for processing, it also means that greater losses result. To date, the major crystal removal method in industry is to heat the drums in an oven. However this heating leads to a deterioration in the quality of the honey and increases the production of a compound called hydroxylmethylfurfural, otherwise known as HMF. Monitoring the presence of this compound gives an indication of the amount of heating and deterioration the honey has previously been subjected to. In order to decrease the production of HMF and in the search of a more energy efficient alternative to the current method of heating, ultrasonic technology has been suggested. The decision on the implementation of this technique would also have to consider the cost of operation and installation, as well as the impact on the honey.
Three different honeys were used in the study; Lucern, SA Blue Gum and GR8, the latter being supplied by a local apiarist, the former two being supplied by Capilano, Australia. The samples were analysed under a light microscope using polarised light to determine the basic size and shape of the crystals. As individual crystals could not be isolated, the value of this investigation was somewhat limited.
The sonifier disintegrates the crystals through the use of sound waves beyond that audible to humans, and heat is created as a by-product of the molecular interactions. As the number of crystals decreases, the viscosity of the honey was assumed to decrease, so viscosity was chosen as the indicator of crystallinity, as compared to the temperature, which was used for the previous study in this area. Using a frequency of 20 kHz, a 150-gram honey sample took less than 10 minutes for all of the crystals to be completely destroyed. The time taken for total sonification varied between the different varieties. This was inferred to be a result of the differing crystal sizes in the different varieties of honey being analysed.
The viscosity profile was examined over a range of shear stresses to examine the Newtonian behaviour of the fluid. As the profiles were taken at the final sonification temperature the viscosities could not be directly compared, however, the power law parameters were able to be. The raw honeys i.e. those not sonified, showed the greatest non-Newtonian behaviour, while those that had been sonified for the longest time indicated that honey appeared to be a Newtonian fluid when the amount of crystals approached zero.
A differential scanning calorimeter (DSC) was used to analyse the sonified samples over a temperature range of 0ºC to 70ºC. The resulting thermograms indicated that the most likely temperature for crystal disintegration to occur was from 30ºC – 50ºC. A temperature range was all that was possible due to the large deviations between the sizes of the crystals. Sampling difficulties were also associated with this piece of equipment due to the small size required for the testing which led to some widespread results.
This study will contribute to the analysis of the potential of ultrasonic technology to be utilised on a commercial scale within the honey-processing sector in Australia.