Rheological Properties of Some Honeys in Liquefied and Crystallised States

Abstract

A b s t r a c t The paper presents the results of rheological measurements conducted on three types of Polish honey: rape, multi-floral, and buckwheat honeys. The investigations involved identification of the properties of the honeys in both liquefied (by heating) as well as crystallised states. Both steady shear as well as dynamic rheological tests were performed. As a result, it was possible to show that the liquefied honeys behave like Newtonian fluids. Good agreement of the results between the rotary shear and oscillation rotary tests was observed, thus fulfilling the Cox-Mertz rule. The structure of the honeys was subjected to qualitative scrutiny by analysing photographs of the crystals taken in the conditions of shearing interferometry. The quantitative analysis was made by presenting a numerical distribution of crystal colonies with reference to the maximum dimensions of individual crystals. The geometric measurements of the crystals were carried out using analiSIS software. In the crystallised form, the media showed a thixotropic effect, and their apparent viscosity was many times higher than the dynamic viscosity in the liquid state. After plasticising by deformation with an increasing shear rate of up to 450s -1 , the equilibrium melting curves of the crystallised honeys were described by the Ostwald-de Waele model. One particular reason for the research was to show that the results obtained for the honeys crystallised by the steady shear method, were qualitatively different from the results obtained in the dynamic measurements. The Cox-Mertz rule cannot be applied for the crystallised honeys.

Texture characteristics of raw rapeseed honey after storage at room temperature or freezing and heating up to 50°C

“…The measurement results in a dynamic rheological test of liquid honeys are similar to the rotational measurements. The values of the complex viscosity of the analysed media are similar to the values of the dynamic viscosity for instance, the relative differences between the average values of dynamic viscosity and complex viscosity for rape honey was 3.2% (Bakier et al, 2016). Stelmakienė et al (2012) reported significant differences in the rheological properties (thixotropy and consistency index) of Lithuanian commercial rapeseed honey, between the temperatures of 30 and 40°C, as well as between 30 and 50°C, contrary to present results.…”

“…According to Bakier (2017), temperature changes in the lower ranges had a greater influence over the rheological properties of honey. It is interesting that for a temperature below 0°C, all types of honey show a high viscosity exceeding 1000 Pa s. The essential characteristic which distinguishes rapeseed honey from other types is the predominance of a number of small, oval crystals with maximum diameter <10 μm (Bakier et al, 2016). Therefore, it undergoes granulation relatively rapidly.…”

Rheological Properties of Honey in a Liquid and Crystallized State

“…Rheological properties of crystallized honeys can be influenced by the mass fraction and shaping (morphology) of the crystalline phase apart from temperature and water content. The crystalline structure of different types of honey can vary significantly, which is a result of differences in chemical composition-mainly the content of glucose, fructose and water [36].…”

“…The rape honey curve is located the highest and the stress increases at the fastest rate in relation to the increase in shear rate despite the fact that the solid phase content is not the highest. Multifloral honey is characterized by a flow curve located below the rape honey, while the flow curve of buckwheat honey is located below the previous two [12,36].…”

Analytical Rheology of Honey: A State-of-the-Art Review

“…The food industry has been challenged by constant technological innovation, where the transfer of methodologies and technologies from other industrial sectors has served these purposes. In this context, rheology, as the science studying the flow and deformation of materials under well-defined conditions, has come to assume a significant role in the food industry [2,[7][8][9][10][11][12]. Consistency and other mechanical characteristics in the rheology domain influence the industrial processing of foods (usually comprising mixing/stirring, pumping, dosing, dispersing, extrusion, spinning, coating, injection moulding and spraying), product texture and stability, and the preparation and consumption of food.…”