INTERNATIONAL JOURNAL OF FOOD PROPERTIES, 4(1), 139–148 (2001)

RHEOLOGICAL PROPERTIES OF SELECTEDLIGHT COLORED JORDANIAN HONEY

Dr. Shahera Zaitoun,1 Dr. Abd Al-Majeed Ghzawi,2

Dr. Kamal I. M. Al-Malah,3 and Dr. Basim Abu-Jdayil3,∗

1Dept. of Bio-Agricultural Technology, Al-Balqa Applied University,Al-Salt 19117, Jordan

2Dept. of Plant Production, Jordan University of Science andTechnology, P. O. Box 3030, Irbid 22110, Jordan

3Dept. of Chemical Engineering, Jordan University of Science andTechnology, P. O. Box 3030, Irbid 22110, Jordan

ABSTRACT

The rheological properties of Apple, Besromia, Citrus, and Ziziphus typesof light colored Jordanian honey were examined. The types of honey used wereidentified via assessing the source of nectar using pollen analysis (Melissopa-lynology). The moisture content of honey samples was indirectly assessed viameasuring the refractive index of the sample using a refractometer. A rotational,concentric cylinder viscometer was used to measure rheological properties ofhoney samples. The apparent viscosity was measured as a function of the shearrate. In addition, the apparent viscosity was measured, at constant shear rate at2.2 s−1, as a function of shearing time. Newton’s law of viscosity was found toadequately describe the flow behavior of honey samples. The apparent viscositywas found to decrease with temperature, and the temperature dependency ofviscosity was found to follow the Arrhenius model. Moreover, the viscositywas also found to decrease with moisture content of honey. An exponential fitwas used to describe the water content dependency of viscosity.

∗Corresponding author. Fax: +962-2-7095018; E-mail: jdayil@just.edu.jo

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Copyright C© 2001 by Marcel Dekker, Inc. www.dekker.com

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INTRODUCTION

Honey, as extracted from the comb, is an aqueous dispersion of materials in-cluding inorganic ions, saccharides, colloidally dispersed macromolecules of pro-tein and polysaccharides, spores of yeast and molds, and finally the pollen grains.Sugars (mono-, di-, and polysaccharides) comprise the major constituent of honey.Next is water or moisture content. Consequently, the physical properties, includingrefractive index, viscosity, and density, are mainly governed by the sugar type andsugar content (or water content). Nevertheless, the sugar content of honey quantita-tively and qualitatively exhibits a distribution of values rather than a unique value;hence, the physical properties of honey are expected to reflect such variability insugar content.

Open and Schuette (1939) used the free falling ball method to correlate theviscosity of different samples of honey with moisture content (12–20% wet basis)in the temperature range between 30 and 50◦C. They found that viscosity decreasedwith the increase in water content and temperature. Lothrop (1939) studied the effectof composition of honey on viscosity. Although adjusted to equal moisture content,the viscosity (at 40◦C) of alfalfa honey (Medicago saliva) was about 0.311 Pa s,whereas sumac honey (Rhus) was about 0.411 Pa s. Lothrop attributed the variationin viscosity of honey to nonsugar materials, namely, dextrin and other colloidal ma-terials present in honey. Junzheng and Changying (1998) examined the rheologicalproperties of different types of Chinese natural honey. They found that the shearstress versus shear rate data was adequately described by Newtonian model, and thatthe viscosity decreased when both water content and temperature were increased.Bhandari et al. (1999a) examined the rheology of selected Australian honeys overa range of temperatures (4–30◦C). The examined Australian honey varieties exhib-ited Newtonian behavior and the effect of temperature on the viscosity of honeywas described by the Arrhenius-type relationship. Bhandari et al. (1999b) made athorough review regarding the rheology and crystallization kinetics of honey. Theyemphasized that the flow properties of honey are influenced by several factors suchas composition, at the top moisture content, temperature, and amount and size ofcrystals.

This work focuses on studying the rheological properties of four types oflight-colored Jordanian honey. A rotational, concentric cylinder viscometer wasused to measure rheological properties of honey samples within the temperaturerange of 20–40◦C. Moreover, the effect of water content on the viscosity of honeywas examined by diluting honey samples up to 25% water content.

EXPERIMENTAL SETUP AND METHODOLOGY

Materials and Setup

Four samples of natural capped honey were collected from honeybee colonieslocated in four different regions in Jordan. Samples were collected during the year

RHEOLOGICAL PROPERTIES OF HONEY 141

1999 from the apiaries of well-known management systems. Honeycombs were un-capped, extracted and professionally treated, and were then filled in jars. To identifythe types of honey used, the source of nectar was assessed using pollen analysis(melissopalynology). The melissopalynological analysis was carried out in com-pliance with the methodology set by the International Commission for Plant-BeeRelationships of the International Union of the Biological Sciences, as describedby Louveaux et al. (1978).

The water content of honey samples was indirectly assessed via measuring therefractive index of the sample using the refractometer (Belling & Stanley Limited,England; Model No. A88121). The water content was evaluated based on the mea-sured value of refractive index while using the data shown by Wedmore (1955),which gives the water content of honey as a function of refractive index of thesample. The dilution of honey by water was carried out at 40◦C using the exactamount of deionized water needed to achieve the final required water content.

Rheological flow properties of honey samples were measured using a rota-tional, concentric cylinder viscometer (Searle-type; Haake VT500/MV3) with afixed outer cylinder and a rotating measuring bob. The radius of the rotating cylin-der was 15.2 mm, the length of the cylinder was 60 mm, and the gap width was5.8 mm. After a steady-state (about 30 s) value of shear stress is attained, mea-surement of viscosity was carried out and recorded. The shear rate varied between2.2 and 219.8 s−1. Pumping water to the jacketed vessel of the viscometer controlstemperature of the samples during measurement.

A honey sample was prepared. The apparent viscosity (η) was measured as afunction of the shear rate (γ̇ ). Moreover, the apparent viscosity was measured as afunction of time, while keeping the shear rate constant (2.2 s−1). The shear stress(τ ) was calculated using the Newton’s law of viscosity:

τ = ηγ̇ (1)

RESULTS AND DISCUSSION

Table 1 shows each of the four types of honey used, designated by the commonname, its scientific name, and its water content. Figures 1a through 1d show the shearstress (τ ) versus the shear rate (γ̇ ) at different temperatures, for apple, besromia,

Table 1. Types of Honey Used, Their Scientific Names, and Water Content

Water ContentNo. Common Name Scientific Name (% Wet Basis)

1. Apple honey Malus sylvestris 15.78 ± 0.2272. Besromia honey Myoporum laetum 16.58 ± 0.2283. Citrus honey Citrus spp. 17.37 ± 0.2294. Ziziphus honey Zizphus spina-christi 16.71 ± 0.001

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Figure 1. The flow curves of a) apple honey, b) besromia honey, c) citrus honey, and d) ziziphushoney at different temperatures.

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Figure 1. Continued

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Table 2. Newtonian Viscosity for Four Different Typesof Light Colored Jordanian Honey, Evaluated at DifferentTemperatures (Water Content Given in Table 1)

Honey Type Temperature (◦C) η (Pa.s)

Apple 20 78.4525 29.9830 15.7935 8.1040 4.77

Besromia 20 36.9125 19.3330 10.1635 5.6840 2.70

Citrus 20 28.2825 12.1830 6.6735 3.7840 2.25

Ziziphus 20 31.9025 15.6630 8.4235 4.6740 3.24

citrus, and ziziphus honey, respectively. For all examined data, except for that ofApple honey at 20◦C; Newton’s law of viscosity was found to best describe the flowcurves of honey. It should be pointed out that the viscosity of apple honey couldnot be measured at higher shear rates, simply, because of the limitation imposed bythe viscometer as far as the accuracy of measurement is concerned. Table 2 showsthe regressed values of viscosity for the examined types of white Jordanian honey.The value of coefficient of determination R2 was 0.999 on the average. Obviously,the viscosity drops with increasing temperature; a typical behavior of a Newtonianliquid or liquid-type substance. To better quantify the effect of temperature onviscosity, the Arrhenius model was used:

η = ηo exp

(Ea

RT

)(2)

where ηo is the preexponential factor (i.e., value of viscosity as T approachesinfinity); Ea the activation energy; R the universal gas constant; and T the absolutetemperature (K). Figure 2 shows a plot of the logarithmic value of viscosity versusthe reciprocal value of temperature, 1/T , where a straight line was obtained; anindication of the Arrhenius model goodness for the examined temperature range.Table 3 shows the regressed values of Arrhenius parameters ηo and Ea . The valueof coefficient of determination R2 was 0.99 on the average.

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Figure 2. Arrhenius model fit for different types of honey.

The viscosity of examined types of honey was also plotted versus the moisturecontent of honey. Figure 3a shows viscosity as a function of water content, evaluatedat 25◦C, for apple and besromia honey types. Figure 3b shows viscosity as a functionof water content, evaluated at 25◦C, for citrus and ziziphus honey types. As shownin figure 3a and 3b, the viscosity of honey decreases with increasing moisturecontent. An exponential fit was used to describe the moisture-content-dependencyof viscosity. Table 4 shows the results of such a curve-fitting. The following equationwas used to describe the relationship between viscosity and moisture content forthe examined types of light-colored Jordanian honey:

η = A exp(B Xw) (3)

Table 3. Regressed Parameters of the Arrhenius Model Describing Temperature-Dependenceof the Viscosity for the Examined Types of Honey at 25◦C

No. Common Name ηo Ea (kJ/mol)

1. Apple honey 0.10 × 10−16 −152. Besromia honey 1.1 × 10−16 −153. Citrus honey 2.7 × 10−16 −144. Ziziphus honey 51.4 × 10−16 −14

Note: standard error at 95% confidence level.

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Figure 3. The viscosity as a function of water content at 25◦C for a) apple and besromia honey andb) citrus and ziziphus honey.

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Table 4. Regressed Parameters of the Empirical Equation DescribingMoisture-Dependence of the Viscosity for the Examined Types of Honey

No. Common Name A (Pa.s) B

1. Apple honey 15339 0.40432. Besromia honey 9476 0.39043. Citrus honey 6832 0.36844. Ziziphus honey 8628 0.3845

Note: R2 is at least 0.99.

where η is in Pa.s and Xw represents the percentage of water content (wet basis).The increase in viscosity with decrease in moisture content (i.e., increase in sugarcontent) could be explained in terms of the antiplasticizing effect of sugars comparedwith water. In general, amorphous foods are highly water-plasticizable. It shouldbe pointed out that our latter finding is in agreement with the previous findingsthat viscosity decreases with increasing water content (Oppen and Schuette, 1939;Lothrop, 1939; Junzheng and Changying, 1998).

Time-dependent flow properties of honey dispersions were assessed via exam-ining viscosity versus time data. The associated behavior is denoted as thixotropic(a decrease in viscosity with time), rheopectic (an increase in viscosity with time),or time-independent. In general, all Newtonian fluids and most non-Newtonian flu-ids exhibit time-independent behavior. Figures 4 shows, for example, the apparentviscosity versus the shearing time t for apple honey. The shear rate (γ̇ ) was held at2.2 s−1. Regardless of the type of examined honey and the temperature at which the

Figure 4. Apparent viscosity of apple honey as a function of shearing time.

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viscosity was measured, there is no apparent thixotropic or rheopectic behavior. Itshould be mentioned, however, that Weltman model (i.e., η = A + B lnt) was usedhere to fit the time-dependent behavior of viscosity of honey, and it was found thatthe B term was quite negligible. This is another piece of evidence that honey is aNewtonian fluid that shows time-independent behavior.

CONCLUSIONS

Newton’s law of viscosity was found to adequately describe the flow behaviorof honey samples. The apparent viscosity was found to decrease with temperature,and the temperature dependency of viscosity was found to follow the Arrheniusmodel. Moreover, the viscosity was also found to decrease with water content ofhoney; i.e., the water plasticizing effect on amorphous food fluids. An exponential fitwas used to describe the effect of water content on the viscosity. Regarding the time-dependent rheological behavior, it was found that the examined honey samples showneither thixotropic nor rheopectic behavior (i.e., the apparent viscosity remainsconstant with the shearing time).

REFERENCES

Bhandari, B.; D’Arcy, B.; Chow, S. Rheology of Selected Australian Honeys. J. Food Eng.1991a, 41, 65–68.

Bhandari, B.; D’Arcy, B.; Kelly, C. Rheology and Crystallization Kinetics of Honey: PresentStatus. Int. J. Food Prop. 1999b, 2, 217–226.

Junzheng, P.; Changying, J. General Rheological Model for Natural Honeys in China.J. Food Eng. 1998, 36, 165–168.

Lothrop, R.E. The composition of Honey and its Utilization-relation of Composition andViscosity. Am. Bee J. 1939, 79, 130–133.

Louveaux, J.; Maurizio, A.; Vorwohl, G. 1978. Methods of Melissopalynology. Bee World1978, 59, 139–157.

Oppen, F.C.; Schuette, H.A. 1939. Viscometric determination of moisture in honey. Ind.Eng. Chem. Anal. 1939, 130–133.

Wedmore, E.B. The accurate determination of the water content of honeys. Part I.Introduction and Results. Bee World 1955, 36, 197–206.

Received: April 24, 2000Revised: June 25, 2000Accepted: August 29, 2000