Composition, thermal and rheological behaviour of selected Greek honeys

Journal of Food Engineering 64 (2004) 9–21 www.elsevier.com/locate/jfoodeng

Composition, thermal and rheological behaviour of selected Greek honeys Athina Lazaridou a, Costas G. Biliaderis a,*, Nicolaos Bacandritsos b, Anna Gloria Sabatini c a

b

Laboratory of Food Chemistry and Biochemistry, Food Science and Technology Department, School of Agriculture, Aristotle University of Thessaloniki, Thessaloniki, Greece 541 24 Institute of Veterinary Research of Athens, N.AG.RE.F., 25 Neapoleos Street, Agia Paraskevi, 153 01 Athens, Greece c Instituto Nazionale di Apicoltura, Via di Saliceto 80, I-41128 Bologna, Italy Received 6 May 2003; accepted 13 September 2003

Abstract Several chemical and physicochemical properties (sugar composition, water content, water activity, colour, viscosity, thermal properties) were determined for 33 Greek honeys from different botanical and geographical origin. The water content and water activity values varied within 13.0–18.9 g/100 g and 0.528–0.663, respectively. Steady shear and dynamic rheological tests revealed Newtonian behaviour for all samples examined over the temperature range of 20–60
C. The steady shear viscosity (g) and loss modulus (G00 ) were inversely related to the water content of honey. The temperature dependence of viscosity followed both the Arrhenius and the Williams–Landel–Ferry models; for the latter model the viscosity data of different samples fitted very well into a common master curve. The glass transition temperature (Tg ) of honeys, as determined by differential scanning calorimetry, varied between )34 and )47
C depending on their composition. The plasticizing action of water on honey solids was evident for native samples as well as among diluted and concentrated honeys; Tg decreased with increasing water content. Despite a broad variation in sugar composition among the samples, the Tg values vs. water content fitted reasonably well to the Gordon–Taylor empirical equation.  2003 Elsevier Ltd. All rights reserved. Keywords: Honey; Moisture content; Water activity; Colour; Rheology; Arrhenius model; Williams–Landel–Ferry model; Glass transition

1. Introduction Honey, the viscous and aromatic product prepared by bees, mainly from the nectar of flowers or honeydew, is a concentrated solution of various sugars. Honey contains fructose and glucose (60–85%) as the predominant monosaccharides, maltose and sucrose as the most important disaccharides, melezitose as the main trisaccharide and other low molecular weight oligosaccharides (Doner, 1977; Doner & Hicks, 1982). The composition of honey (sugars and moisture content) is responsible for many of the physicochemical properties of honey, such as viscosity, hydroscopicity, and granulation. Most honeys are supersaturated solutions of glucose, which have a tendency to crystallize spontane*

Corresponding author. Tel.: +2310-471467/+30-310-998-785; fax: +2310-471257/+30-310-471-457. E-mail address: [email protected] (C.G. Biliaderis). 0260-8774/$ - see front matter  2003 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2003.09.007

ously at room temperature in the form of glucose monohydrate. Crystallization of honey, commonly called granulation, is an undesirable process in liquid honey because it affects the textural properties, making it less appealing to the consumer. Moreover, in many cases, crystallization of honey results in increased moisture of the liquid phase which can allow naturally occurring yeast cells to multiply causing fermentation of the product (Doner, 1977). Water content as well as water activity are the major factors that influence the keeping quality or storability of honey. Sensory and physicochemical properties are very important parameters in determining the quality and acceptability of honey and many studies have been devoted to explore such determinants of product quality (Al-Khalifa & Al-Arify, 1999; Anupama, Bhat, & Sapna, 2003; Bath & Singh, 1999; Popek, 2003; Singh & Bath, 1997). The composition and properties of honey vary with the floral and honeydew sources utilized by

10

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21

Nomenclature a , b aw C1 , C2 Ea G0 G00 G–T k L p r R

chromatic components (red, yellow) water activity coefficients of WLF equation activation energy (kJ mol
1 ) storage modulus (Pa) loss modulus (Pa) Gordon–Taylor equation constant lightness component probability level correlation coefficient universal gas constant (8.314 J mol
1 K
1 )

honey-bees, as well as by regional and climatic conditions. Some physicochemical parameters have already been studied for their use in the identification of the botanical and geographical origin of honey (Gomez Barez et al., 2000; Popek, 2002; Terrab, Diez, & Heredia, 2002). The rheological behaviour of honey has been investigated for shelf-life, proper handling, packing and processing issues (White, 1978). The rheological properties of honey, like many other physical properties, depend on many factors, including composition and temperature. The Arrhenius model is widely used for temperature dependence of a property but models such Williams– Landel–Ferry (WLF) that include the glass transition temperature (Tg ) as a parameter, have proved equally useful for the viscosity–temperature relationship of food systems (Ollett & Parker, 1990; Soesanto & Williams, 1981; Williams, Landel, & Ferry, 1955). Depending on concentration, and heating and cooling rates, aqueous carbohydrate solutions exhibit several thermal events, the most important being the Tg . At the glass transition temperature, an amorphous material changes from the rubbery to the glassy state upon cooling, leading to the formation of a hard solid. As the stability of foods is mainly dependent on the water content and because Tg is also highly sensitive to this parameter, the glass transition concept has been proposed as a useful tool for understanding the mechanisms of deteriorative processes in food products and for controlling their shelf-life (Slade & Levine, 1991). Indeed, the glass transition temperature is often considered as a reference temperature; below Tg , the food is expected to be stable and above this temperature, the difference (T
Tg ) between Tg and the storage temperature T is assumed to control the rate of physical, chemical and biological changes (Roos, 1995). The present study was undertaken to determine certain physicochemical properties of selected Greek honeys, and explore some relationships between them.

T Tg Tg1 Tg2 w2 WLF c_ g g gTg r x

temperature (
C, K) glass transition temperature glass transition of dry sample glass transition of glassy water weight fraction of water Williams–Landel–Ferry equation shear rate (s
1 ) viscosity (Pa s) complex viscosity (Pa s) sample viscosity at Tg shear stress (Pa) angular frequency (rad s
1 )

2. Materials and methods 2.1. Samples Thirty-three honey samples were provided by beekeepers with guaranteed botanic origin. These honeys were divided into four main groups according to the variety type: honeydew from pine, honeydew from fir, mixed floral type, and floral from orange blossom. Samples were sourced from different geographical areas of Greece; pine honeydew from Thasos (6 samples), Halkidiki (6 samples) and Evia (2 samples), fir honeydew from Helmos (2 samples) and Vytina (8 samples), mixed floral from Livadia (3 samples), and orange blossom floral from Argos (4 samples) and Sparti (2 samples). The botanical/geographical identification was based on their colour, aroma, taste and location of the hives. 2.2. Moisture content and water activity, sugar composition Refractive indices of honey samples were measured using a refractometer at 20
C and corresponding moisture content (%) was calculated using the relationship between refractive index and water content (AOAC, 1990). Water activity (aw ) of samples was measured at 20
C using an Aqualab 3TE water activity meter (Decagon Devices Inc., Pullman, WA, USA). The determination of aw values was performed twice; before and after the heating of the samples at 50
C for 1 h. This heat treatment was carried out to dissolve crystals or nuclei, which might be present in honey and can influence the water activity of the system. The sugar composition was determined by a gas chromatography (GC) method as described by Sabatini, Marcazzan, Colombo, Carpana, and Serra (2001).

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21

2.3. Colour

11

Temperature effects on steady shear viscosity were analysed using the Arrhenius relationship:

Colour was determined by a Metertech UV/VIS SP8001 spectrophotometer (Metertech Inc., Taipei, Taiwan) and a Minolta Dimage 5 digital camera. Samples were heated at 50
C for 1 h before measurement to ensure melting of any possibly formed crystals. Colour was determined as absorbance at 420 nm after dilution of honey with distilled water at a ratio 1:5 (Bath & Singh, 1999). Before measurement, mixtures of honey and water were heated for better mixing and filtered for removal of any coarse particles (plant residues, pollen), which may also influence the colour. Images of samples were taken by the digital camera with a proper lighting system as described by Papadakis, Abdul-Malek, Kamdem, and Yam (2000). L , a and b colour parameters (CIE, 1976) were obtained using the Photoshop software (v6.0, Adobe Systems Inc., San Jose, CA). L is the luminance or lightness component, which ranges from 0 to 100, and a and b are the two chromatic components, which range from )120 to 120 (a from green to red and b from blue to yellow) (Adobe Photoshop 5.0 User Guide for Machintosh and Windows, 1998). The software uses a scale, ranging from 0 to 255, to characterize Lightness, as well as the values of a and b. To convert these parameters to L , a , and b the following formulas were used: L ¼ ðLightness=250Þ  100

ð1Þ

a ¼ ð240a=255Þ
120

ð2Þ

b ¼ ð240b=255Þ
120

ð3Þ

2.4. Rheology Rheological properties of honey were studied by a rotational Physica MCR 300 rheometer (Physica Messtechnic GmbH, Stuttgart, Germany) using a concentric cylinder (diameter of cup and bob, 28.92 and 26.66 mm, respectively) geometry; temperature was regulated by a Paar Physica circulating bath and a controlled peltier system (TEZ 150P/MCR) with an accuracy of ±0.1
C. The data of the rheological measurements were analyzed with the supporting rheometer software US200 V2.21. All honey samples were heated at 50
C for 1 h before rheological measurements to melt any crystals present and to remove the air bubbles, factors that can influence the viscosity of honey. Two types of measurements were performed: (a) flow behaviour by measuring steady shear viscosity (g) and shear stress (r) over a range of _ of 0.1–500 s
1 at 20, 30, 40, 50 and 60
C; shear rates (c) and (b) oscillatory measurements to obtain the storage and loss moduli (G0 , G00 ) and complex viscosity (g ) at a strain level of 0.1% and a range of angular frequencies of 3–300 rad s
1 at 20
C.

g ¼ g0 eðEa =RT Þ

ð4Þ

where g is the viscosity at temperature T , g0 is a preexponential factor, Ea is the activation energy for flow, R is the perfect gas constant and T is the absolute temperature (K). The temperature dependence of honey viscosity was also described using the WLF model (Williams et al., 1955): ! g
C1 ðTg
T Þ log ð5Þ ¼ gT g C2 þ ðTg
T Þ where Tg is the glass transition temperature, g is the viscosity at temperature T , gTg is the viscosity of sample at Tg and C1 and C2 are the WLF constants. Experimental data were fitted to the model using the Table Curve 2D software (v4.0, SPSS Inc., Chicago, IL). 2.5. Differential scanning calorimetry The glass transition temperature (Tg ) of honeys was determined by differential scanning calorimetry (DSC) using a PL DSC-Gold calorimeter (Polymer Labs. Ltd, Epsom, UK). Temperature calibration was made with cyclohexane, dodecane and octane, whereas heat flow calibration was made by reference to the known melting enthalpy of indium and gallium (purity 99.99%) from Goodfellows Metals (Biliaderis, Lazaridou, & Arvanitoyannis, 1999). For studying the effect of moisture on Tg , 14 honey samples were chosen covering a moisture content range of 13.0–18.9%. For increasing the above range the sample with the lowest moisture content (13%) was either diluted with water or concentrated under vacuum (at 50
C) to the following levels of moisture content: 26.9%, 23.4%, 20.0%, 16.5%, 11.9%, 11.0% and 10.2%. The native honey samples as well as the diluted and concentrated samples were hermetically sealed into stainless steel pans (40–45 mg) and analysed by calorimetry under continuous flow of dry N2 gas (20 ml min
1 ) to avoid condensation of moisture. First, the pans were heated from +20 to +50
C at a heating rate of 10
C min
1 and kept at +50
C for 3–5 min to ensure the melting of any crystals and reach at thermodynamic equilibrium. The samples were then quenched–cooled with liquid N2 to )100
C and reheated to +50
C at the same heating rate (10
C min
1 ). The Tg was determined in the latter heating scans as the onset temperature of the step-like decrease in the heat flow. Data analysis to fit experimental values of Tg to the empirical Gordon–Taylor (G–T) model (Gordon & Taylor, 1952) was performed using the Table Curve 2D software:

12

Tg ¼

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21

w1 Tg1 þ kw2 Tg2 w1 þ kw2

ð6Þ

where Tg1 is the glass transition temperature of the sample at zero moisture content, w1 is the weight fraction of dry solids, Tg2 is the glass transition temperature for glassy water, w2 is the weight fraction of water and k is a constant. The constructed G–T plots were based on the best data fitting to the equation (i.e. optimization for both parameters, k and Tg1 ), where a Tg of )138
C was used for water (Sugisaki, Suga, & Seki, 1968).

3. Results and discussion 3.1. Water content, water activity, sugar composition, colour The results of analysis of some physicochemical parameters namely, moisture, water activity (aw ), and colour (absorbance at 420 nm and L , a , and b colour parameters) for the Greek honeys are summarized in Table 1. The refractive index varied from 1.4892 to 1.5043 and the corresponding moisture content ranged between 13.0% and 18.9%; these values are within the range found by other researchers and indicate a proper degree of maturity for these honey samples. In general, the moisture content in different varieties of honey may be as low as 13% (White, 1978) and as high as 29% (Junzheng & Changying, 1998). For example, moisture contents have been found in the range of 14.0–16.9% for Saudi honeys (Al-Khalifa & Al-Arify, 1999), 13.8–17.8% for Spanish honeys (Gomez Barez et al., 2000), 15.4– 18.1% for Polish honeys (Popek, 2003), 16.8–20.3% for Moroccan honeys (Terrab et al., 2002), and 18.7–21.8% for Indian honeys (Singh & Bath, 1997). The difference in moisture content was significant between all Greek honeys; however, Greek regulations require <21% moisture for safety from fermentation. Honey is an intermediate moisture food with a water activity of about 0.6 and is therefore shelf stable for a reasonable period of time. The low aw (high osmotic environment) does not support microbial growth, preventing fermentation of honey by osmophilic yeast. The aw values of Greek honeys obtained after heating the samples at 50
C varied within the range 0.528–0.663 (Table 1), whereas for most of the samples the corresponding values before heating were found higher. It is well known that crystal formation in sugars results to water release, thus increasing water availability. Table 2 shows the composition of sugars identified in the honey samples. The monosaccharides fructose (22.1– 41.3%) and glucose (13.5–36.3%) were the main sugars, with fructose being always the most abundant. The honeys with lower percentages of fructose and glucose were those with a non-floral origin (i.e. honeydew hon-

eys). Among the disaccharides, maltose was the most abundant one, ranging between 1.9% and 6.7%. The relatively low levels of sucrose for most samples indicate that the selected honeys were at an advanced stage of ripening. Several trisaccharides were also identified and quantified, namely raffinose, erlose, melezitose, panose, isomaltotriose and maltotriose. It was of interest to note that melezitose was present in relatively high amounts (9.1–14.4%) for most of the honeydew-fir samples. The colour of honey is related to the content of phenolics, HMF, pollen and minerals (Perez-Arquille, Conchello, Arino, Juan, & Herresa, 1994). The absorbance at 420 nm varied between 0.113 and 0.915 (Table 1) and is in agreement with the finding of other authors (Bath & Singh, 1999; Singh & Bath, 1997). It is known that orange blossom honeys are honeys with very light colour, which concurs with the lowest values in the absorbance range for the samples shown in Table 1. The colour parameters L , a and b measured using the digital camera were within the range of 35.79–59.56, ()5.06)–27.27 and 16.91–42.92, respectively. These values are in close agreement with those found by others researchers using chromatometers (Anupama et al., 2003; Popek, 2002, 2003). It is worthy to note, that orange blossom honeys were found to have high values for lightness (L ), and low values for red (a ) and yellow (b ) components, showing similar responses to the results from absorbance measurements at 420 nm. 3.2. Rheological behaviour Fig. 1 illustrates the steady shear flow curves (Fig. 1a) and a typical mechanical spectrum (Fig. 1b) for a Greek honey sample. All honey samples behaved as Newtonian fluids at all temperatures of measurement (Fig. 2). Apparent viscosity (g) and complex viscosity (g ) were constant, regardless of the shear rate and angular frequency, respectively (Fig. 1). Moreover, the G00 was dependent on frequency and greater than G0 at all frequencies (Fig. 1b). In most of the published works, honey was reported to have a Newtonian behaviour (Abu-Jdayil, Al-Majeed Ghzawi, Al-Malah, & Zaitoun, 2002; Bhandari, D’Arcy, & Chow, 1999; da Costa & Pereira, 2002). Values of various rheological parameters obtained from steady shear and dynamic measurements for all samples are summarized in Table 3. These values obtained from measurements at 20
C varied within the wide range of 9.9–200.0 (Pa s) for apparent viscosity (g), 0.15–19.10 (Pa) for storage modulus (G0 ), 64–1682 (Pa) for loss modulus (G00 ), and 7.7–164.4 (Pa s) for complex viscosity. The differences among samples could be attributed to natural variations in composition (individual sugars and water content), as they belong to different plant species-specific varieties and collected from different geographical locations in Greece. It is clear that

Table 1 Some physicochemical parameters in 33 Greek honeys Sample No.

Honeydew (pine)/Thasos Honeydew (pine)/Thasos Honeydew (pine)/Thasos Honeydew (pine)/Thasos Honeydew (pine)/Thasos Honeydew (pine)/Thasos Honeydew (pine)/Halkidiki Honeydew (pine)/Halkidiki Honeydew (pine)/Halkidiki Honeydew (pine)/Halkidiki Honeydew (pine)/Halkidiki Honeydew (pine)/Halkidiki Honeydew (pine)/Evia Honeydew (pine)/Evia Honeydew (fir)/Helmos Honeydew (fir)/Helmos Honeydew (fir)/Vytina Honeydew (fir)/Vytina Honeydew (fir)/Vytina Honeydew (fir)/Vytina Honeydew (fir)/Vytina Honeydew (fir)/Vytina Honeydew (fir)/Vytina Honeydew (fir)/Vytina Floral/Livadia Floral/Livadia Floral/Livadia Floral (Orange blossom)/Argos Floral (Orange blossom)/Argos Floral (Orange blossom)/Argos Floral (Orange blossom)/Argos Floral (Orange blossom)/Sparti Floral (Orange blossom)/Sparti

Moisture content, Xw (g/100 g)

Water activity (20
C) after melting at 50
C

Colour Absorbance at 420 nm

L

a

b

18.9 17.4 18.3 13.9 15.4 15.2 15.0 14.9 15.4 15.7 15.4 14.8 16.3 14.8 13.4 13.0 13.9 13.3 14.6 15.0 14.1 14.0 15.2 13.8 13.8 14.1 15.1 15.1 15.8 16.2 17.9 15.6 15.6

0.610 0.613 0.615 0.567 0.570 0.559 0.580 0.576 0.576 0.575 0.577 0.577 0.570 0.663 0.562 0.565 0.570 0.561 0.555 0.556 0.581 0.581 0.609 0.578 0.528 0.528 0.550 0.542 0.540 0.584 0.577 0.548 0.546

0.387 0.314 0.335 0.712 0.702 0.675 0.703 0.738 0.770 0.791 0.651 0.783 0.593 0.525 0.557 0.476 0.428 0.469 0.450 0.357 0.405 0.222 0.378 0.395 0.915 0.831 0.682 0.183 0.161 0.127 0.113 0.134 0.115

45.48 42.98 43.40 40.72 42.18 43.80 45.38 43.42 44.32 39.24 43.70 42.30 40.14 44.04 41.63 41.63 39.79 40.51 41.66 43.48 39.87 39.80 41.45 42.02 42.97 35.79 39.30 47.34 45.75 59.56 45.76 51.62 47.18

12.13 13.48 12.75 18.35 15.05 16.17 9.48 15.21 11.91 17.32 20.76 16.16 19.36 16.58 19.36 17.35 18.49 16.09 16.35 21.55 18.75 17.65 16.16 13.77 27.27 23.49 21.30 1.70 0.89 )5.06 )2.79 7.29 2.96

40.15 40.09 40.49 41.41 40.42 41.60 38.48 40.77 36.76 39.42 42.79 40.96 39.96 41.05 41.53 40.11 40.59 39.67 39.65 42.92 38.95 38.08 39.65 38.71 39.50 35.59 40.84 22.72 19.85 16.91 18.93 28.93 23.31

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

Botanic/geographical origin

13

14

Table 2 Distribution of the levels of various sugars (%) among the selected honey samples Fructose (g/100 g)

Glucose (g/100 g)

Sucrose (g/100 g)

Trehalose (g/100 g)

Maltose (g/100 g)

Isomaltose (g/100 g)

Raffinose (g/100 g)

Erlose (g/100 g)

Melezitose (g/100 g)

Panose (g/100 g)

Isomalto-triose (g/100 g)

Malto-triose (g/100 g)

Malto-tetraose (g/100 g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

29.9 29.0 30.5 30.5 30.5 30.6 22.5 23.0 22.2 23.9 24.1 24.1 32.3 29.7 27.3 24.1 25.7 28.1 32.5 31.1 22.1 22.2 29.0 22.1 34.8 34.1 34.9 39.1 38.1 39.1 39.9 39.9 41.3

26.3 25.6 26.4 24.5 23.6 23.7 18.4 19.6 19.0 21.1 21.1 21.2 28.7 25.5 18.6 16.0 16.7 19.0 24.5 25.0 13.6 13.5 19.7 14.2 29.2 29.0 30.0 32.9 32.8 36.3 34.7 35.4 32.7

0.7 0.8 0.8 0.2 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.6 1.4 0.1 0.1 0.1 0.2 0.2 0.2 0.1 0.1 0.1 0.2 0.2 0.1 0.1 2.7 2.7 0.6 0.6 1.6 1.7

<0.1 0.1 <0.1 0.1 <0.1 <0.1 0.1 <0.1 <0.1 0.1 0.1 0.1 0.6 0.4 1.7 2.9 2.1 1.6 0.8 0.8 3.1 3.0 1.5 2.9 0.6 0.6 0.7 0.1 0.1 0.1 0.1 0.1 <0.1

4.0 3.9 4.2 6.7 6.1 6.2 4.4 4.4 4.1 4.6 4.7 4.6 4.3 4.2 3.5 2.7 3.1 3.6 5.4 5.3 1.9 1.9 3.6 2.2 4.7 4.6 4.9 4.4 4.3 3.0 3.3 3.6 3.6

1.4 1.4 1.4 3.0 3.2 2.9 2.4 2.4 2.0 2.1 2.2 2.0 1.2 1.0 1.1 0.8 1.1 1.0 1.2 0.9 0.8 0.7 0.9 1.0 0.9 1.1 1.3 0.4 0.4 0.4 0.5 0.6 0.4

0.6 0.6 0.6 0.5 0.2 0.2 0.3 0.6 0.6 0.5 0.5 0.5 0.5 0.6 0.8 0.9 0.6 0.5 1.0 1.0 0.9 0.9 0.3 0.7 0.4 0.3 0.4 <0.1 0.5 0.5 0.5 0.5 0.5

3.1 3.3 3.3 0.6 0.6 0.6 1.0 1.1 1.0 0.8 0.8 0.8 1.4 2.8 0.6 0.8 0.4 0.5 2.1 2.1 0.5 0.5 0.6 0.4 0.8 0.8 0.4 0.9 0.8 0.6 0.6 0.8 0.7

0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0.1 2.0 1.9 9.1 10.5 11.0 9.8 1.3 1.4 14.4 14.2 10.5 13.0 2.5 2.4 2.2 0.3 0.3 0.2 0.2 <0.1 <0.1

0.2 0.2 0.2 0.5 0.5 0.5 0.4 0.4 0.2 0.3 0.4 0.3 0.2 0.2 0.6 0.4 1.0 0.7 0.1 0.1 1.0 0.9 0.6 1.1 0.2 0.2 0.2 <0.1 <0.1 <0.1 <0.1 0.1 <0.1

0.1 0.1 0.1 0.2 0.2 0.2 0.1 0.1 0.1 0.1 0.2 0.1 <0.1 <0.1 0.1 <0.1 0.1 <0.1 <0.1 <0.1 <0.1 <0.1 <0.1 0.1 <0.1 <0.1 <0.1 <0.01 <0.01 <0.01 <0.01 <0.1 <0.01

0.2 0.2 0.2 0.3 0.3 0.3 0.3 0.3 0.1 0.2 0.3 0.3 0.2 0.2 0.3 0.3 0.4 0.3 0.5 0.4 0.4 0.3 0.2 0.4 0.1 0.2 0.3 <0.1 <0.1 <0.1 0.1 0.1 <0.1

7.7 7.9 8.0 0.7 0.7 0.6 0.4 0.4 0.2 0.4 0.6 0.4 0.3 0.2 0.3 0.3 0.3 0.2 0.5 0.3 0.4 0.3 0.2 0.3 0.1 0.2 0.3 <0.01 <0.01 <0.01 <0.01 <0.01 <0.01

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21

Sample No.

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21

(a)

15

(b)

Fig. 1. Steady shear viscosity profiles of three Greek honey samples (a) and a representative mechanical spectrum of a Greek honey (b) at 20
C.

Fig. 2. Temperature effect on viscosity of a representative Greek honey and its Arrhenius plot of viscosity (at 10 s
1 ) vs. temperature (inset).

the viscosity of honey decreases with water content. As shown in Fig. 3a there was a significant relationship between moisture content and apparent viscosity, as described by an exponential function: g ¼ 90071 e
0:4997Xw (r2 ¼ 0:80, p < 0:05). Such moisture content dependence of viscosity has been also noticed by other authors (Anupama et al., 2003; Junzheng & Changying, 1998; Sopade et al., 2002; Zaitoun, Ghzawi, Al-Malah, & Abu-Jdayil, 2001). Moreover, a relationship between moisture content and the loss modulus, estimated by dynamic rheological measurements was observed (Fig. 3b); the experimental data fitted into an exponential equation: G00 ¼ 2  106 e
0:5547Xw (r2 ¼ 0:72, p < 0:05). It is worthy here to note that the g values were very close with the respective g values for each individual sample (Table 3). It appears therefore that the viscosity data

follow the Cox–Merz rule (Cox & Merz, 1958), as expected for Newtonian fluids. According to this rule the complex viscosity from small-deformation oscillation measurements and the steady shear viscosity from rotational measurements superimpose closely at equivalent numerical values of angular frequency (x, rad s
1 ) _ s
1 ) for non-interacting molecular and shear rate (c, dispersions. The temperature effects on honey viscosity are shown in Fig. 2; as expected, the viscosity was reduced with increasing temperature. The temperature dependence of g is adequately described using the Arrhenius relationship (Fig. 2, inset); the correlation coefficients (r2 ) for each sample are given in Table 3 and were all greater than 0.91. The observation that the temperature dependence of viscosity follows the Arrhenius relationship has been also reported by other researchers for honey (Al-Malah, Abu-Jdayil, Zaitoun, & Ghzawi, 2001; Bath & Singh, 1999; Bhandari et al., 1999; Sopade et al., 2002) as well as for other sugar-rich liquid foods such as fruit juice concentrates and sugar syrups (Khalil, Ramakrishna, Nanjundaswamy, & Patwardhan, 1989; Manohar, Ramakrishna, & Udayasankar, 1991). The activation energies (Ea ) for flow estimated from the slope of the linear relationship of logðgÞ vs. ð1=T Þ are presented in Table 3 for all samples and varied between 69.1 and 93.75 kJ mol
1 . Activation energy reflects the sensitivity of viscosity to temperature changes; higher Ea means that the viscosity is relatively more sensitive to a temperature change. There was an inverse linear relationship between Ea and moisture content (r2 ¼ 0:61, p < 0:01). Although the Arrhenius formalism seems to adequately describe the temperature dependence of honey viscosity, it gives relatively high values for the activation energy, which are more typical of chemical reactions. Similar observations concerning the

16

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21

Table 3 Rheological parameters of 33 Greek honeys Sample No.

Viscosity (Pa s) (20
C)

Ea (kJ mol
1 )

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33

9.9 10.5 10.7 61.1 55.5 63.6 42.8 44.4 46.8 39.0 37.6 39.8 38.5 38.4 86.3 200.0 73.2 80.3 67.4 59.0 154.0 160.0 67.6 118.0 79.8 77.9 73.8 28.8 26.2 12.6 13.2 28.6 26.8

72.69 73.62 74.09 89.09 88.13 88.74 82.79 83.79 84.15 80.88 80.55 82.29 79.39 80.36 86.20 93.75 84.00 85.23 87.33 84.21 89.77 89.56 89.65 93.33 90.22 89.74 88.59 78.87 79.61 83.06 75.40 89.75 90.17

(r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2 (r2

¼ 0:97) ¼ 0:97) ¼ 0:97) ¼ 0:97) ¼ 0:97) ¼ 0:97) ¼ 0:97) ¼ 0:97) ¼ 0:97) ¼ 0:96) ¼ 0:96) ¼ 0:97) ¼ 0:95) ¼ 0:96) ¼ 0:96) ¼ 0:96) ¼ 0:96) ¼ 0:96) ¼ 0:97) ¼ 0:96) ¼ 0:96) ¼ 0:96) ¼ 0:98) ¼ 0:98) ¼ 0:97) ¼ 0:97) ¼ 0:97) ¼ 0:96) ¼ 0:96) ¼ 0:99) ¼ 0:98) ¼ 0:99) ¼ 0:99)

G0 (Pa) (x ¼ 10 rad s
1 ) (20
C)

G00 (Pa) (x ¼ 10 rad s
1 ) (20
C)

Complex viscosity (Pa s) (20
C)

3.01 0.40 0.33 4.46 2.88 4.87 3.02 2.39 3.91 2.87 2.22 2.79 2.10 6.51 7.83 10.70 3.40 4.91 3.50 2.98 19.10 10.20 5.58 4.30 5.64 4.40 5.90 3.75 0.94 0.33 0.15 0.31 2.35

99 80 111 665 526 708 476 467 469 424 418 429 928 265 980 1682 772 988 708 624 1177 1701 683 1074 839 803 773 376 108 106 100 208 64

9.0 7.7 10.4 62.2 51.4 66.2 43.1 42.2 42.4 38.4 37.8 38.8 34.1 35.9 88.6 164.4 69.7 89.3 64.0 56.4 115.0 167.0 67.5 105.0 75.8 78.9 69.8 34.0 20.5 10.4 9.9 20.4 26.8

magnitude of Ea derived from viscosity data of three Jordanian honey samples (Ea 95.6–97.7 kJ mol
1 , temperature range 20–50
C) have been made in a previous study by Al-Malah et al. (2001). 3.3. DSC thermal behaviour The effect of moisture content (m.c.) on the DSC thermal traces of four representative native honey samples is demonstrated in Fig. 4a. The glass transition temperature shifted to lower temperatures with increase of moisture content due to the plasticization effect of water. Water is a very effective plasticizer for hydrophilic components, such as low molecular weight carbohydrates (Levine & Slade, 1988); this effect has been related to the ability of water molecules to weaken hydrogen bonds, dipole–dipole, and intra- and inter molecular interactions (Matveev, Grinberg, & Tolstoguzov, 2000). The glass transition temperatures of the honey samples are summarized in Table 4, varying between )34.6 and )47.2
C for a moisture content range of 13.0–18.9 g/100 g. These values are similar to those

found by other researchers; i.e. a range from )40 to )46
C for honey samples with 15.8–18.0% moisture content (Sopade, Bhandari, Halley, D’Arcy, & Caffin, 2001; Sopade et al., 2002), from )37.5 to )42.5
C for samples with m.c. about 17.5% (Cordella et al., 2002), and from )42.5 to )50.7
C for samples with undetermined m.c. (Kantor, Pitsi, & Thoen, 1999) have been reported. It is generally accepted that differences in the composition of carbohydrate solutions could contribute to the variation in the Tg ; i.e. the glass transition temperature is a function of both moisture content and the type of solute (Slade & Levine, 1991). Recently, the Tg value responses to the modification of chemical composition of honey has been used, concomitantly with other thermal events detected by DSC, to develop a new method for adulteration detection in this product (Cordella et al., 2002); these authors have found that adulterations of honey by industrial sugar syrups can be detected calorimetrically up to a minimum of 5–10% addition. The plasticizing action of water is also obvious at comparative DSC traces of diluted and concentrated honey samples using a native sample (16), as illustrated

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21

(a)

17

(a)

(b) (b)

Fig. 4. DSC thermal scans for four honey samples with different moisture content (a) and for sample 16, and diluted and concentrated sample 16 (b); arrows indicate the position of the onset temperature considered as glass transition. Fig. 3. Effect of moisture content on viscosity (g) (a) and loss modulus (G00 ) (b) of Greek honeys.

in Fig. 4b. With increasing moisture content of honey from 10.2 to 26.9 g/100 g the Tg decreased significantly from )25.0 to )69.5
C. Similar trends in Tg for diluted honeys samples have been reported by Kantor et al. (1999). These authors have also noticed onto the DSC scans water crystallization from honey/water mixtures with less than approximately 85% honey content. Their DSC traces showed the presence of a typical endothermic peak in the range )20 to 0
C linked to the free water of the sample; with decreasing honey content this peak moved towards 0
C and the enthalpy of melting increased. In the present study, the sample with the highest moisture content (26.9%) corresponds to 84% honey content. For all the examined samples there was no evidence of water or sugar crystallization (Fig. 4). This could be attributed to the effectiveness of quenchcooling with liquid nitrogen in preventing freezing of water during Tg measurement and the absence of Ôfreewater’ from the native honey samples. The minor tran-

sition at 0
C present in all DSC curves of Fig. 4 was not related to crystallization of free water from the sample but is an artifact due to moisture condensation from the atmosphere; i.e. the magnitude of this transition was found independent of the moisture content of the sample and it represented ice melting of water in amounts less than 0.22% of the amount of water present in anyone of the honey samples examined. With reference to the concentrated sugar solutions, such as honeys, a rapid reduction in temperature also prevents solute nucleation as a result of the lack of sufficient mobility of the sugar molecules to assemble into a crystal lattice. The Tg –water content relationship presented in Fig. 5 reveal more clearly the sensitivity of honey to waterplasticization. Despite the large variation in sugar composition among the samples (Table 2), the experimental data for all honeys fitted successfully well (r2 ¼ 0:99) to the empirical G–T model (Eq. (6)). Estimated values of the G–T parameters were 3.14 for the k and 288.0 K (or 15
C) for the Tg1 , i.e. the glass transition temperature for dry honey solids. Consequently, the

30.90 24.81 25.07 24.75 22.44 14.89 17.11 15.12 20.92 16.91 20.92 13.95 29.71 20.20 17.68 18.98 19.38 19.89 20.41 25.18 24.56 23.17 21.60 24.17 21.52 25.01 17.20 22.68 11.52 11.57 11.57 11.57 11.69 11.75 11.81 11.85 11.68 11.89 11.62 11.80 11.60 11.61 ()47.15) ()45.55) ()37.23) ()38.69) ()39.85) ()40.04) ()35.77) ()34.60) ()38.69) ()36.64) ()37.23) ()43.80) ()43.94) ()44.09) 225.85 227.45 235.77 234.31 233.15 232.96 237.23 238.40 234.31 236.36 235.77 229.20 229.06 228.90 18.9 17.4 13.9 15.4 15.4 16.3 13.0 13.9 14.6 14.1 14.1 16.2 17.9 15.6

214.09 ()58.91) 213.40 ()59.60) 226.73 ()46.27) 226.04()46.96) 222.72 ()50.28) 219.65 ()53.35) 230.53 ()42.47) 223.17 ()49.83) 225.65()47.39) 227.68 ()45.32) 227.42 ()45.58) 209.88 ()63.12) 214.92 ()58.08) 219.96 ()53.04)

r logðgTg Þ (Pa s) Tg , K (
C) (predicted)

0.99 0.99 0.99 0.99 0.99 0.98 0.99 0.99 0.99 0.99 0.99 0.95 0.99 0.99

13.10 14.77 15.26 15.73 16.50 21.72 21.09 20.00 17.75 20.79 17.64 21.59 12.85 18.66

C2 (K) C1 logðgTg Þ (Pa s)

WLF (Tg from DSC experimental data)

2

WLF (Ôuniversal’ constants)

Tg , K (
C) experimental data from DSC Moisture content (g/100 g)

Fig. 5. Relationship of glass transition and moisture content for honey; the solid line gives the G–T plot of the experimental data from DSC measurements.

G–T model could be an important tool for the prediction of Tg . Another usefulness of the above modeling is the determination of Tg1 , a temperature that it could not be measured experimentally, as it is impossible to remove the strongly bound water from honey. Being a molecular phenomenon, the glass transition has been often related to many food properties that comprise mechanical/structural relaxation processes. The WLF equation (Eq. (5)) includes the glass transition temperature as a parameter and has been suggested to be applicable in predicting the temperature dependence of viscosity, a primary property that describes mechanical relaxation of mobile components. This equation has been claimed as a more appropriated model than the Arrhenius relationship in the rubbery domain; i.e. between Tg and about Tg þ 100
C (Roos, 1995; Slade & Levine, 1991). The WLF equation specifies a much stronger temperature dependence of viscosity compared to that predicted by the Arrhenius formalism. In this context, the Tg is considered as a reference temperature: below Tg , the viscosity is very high, whereas above this temperature, the difference between storage and processing temperatures (T
Tg ) is assumed to control the rate of viscosity changes in the product. Generally, the viscosity in the glassy state varies between 107 and 1016 Pa s as has been estimated and/or extrapolated for a range of materials by various procedures (Maltini & Manzocco, 1998; Ollett & Parker, 1990; Peleg, 1992; Slade & Levine, 1993; Soesanto & Williams, 1981; Williams et al., 1955). 3.4. WLF modeling of viscosity

1 2 4 5 9 13 16 17 19 21 26 30 31 33

Sample No.

Table 4 Glass transition temperatures of Greek honeys and estimated parameters of the WLF model

0.99 0.99 0.99 0.99 0.99 0.98 0.99 0.99 0.99 0.99 0.99 0.94 0.99 0.99

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21

r2

18

The viscosity data of 14 honey samples were fitted to the WLF model to test its applicability at temperatures

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21

Fig. 6. Temperature dependence of viscosity for 14 honey samples according to the WLF formalism; the solid line shows the WLF equation using the Ôuniversal’ constants.

from 20 to 60
C (Fig. 6); i.e. between 60 and 125
C above Tg of honeys. In general, as already mentioned, the WLF equation is not intended for use much below Tg , (in the glassy state) or in the very low viscosity regime (<10 Pa s) occurring at temperatures typically 100
C or more above Tg , where Arrhenius kinetics apply (Slade & Levine, 1991; Soesanto & Williams, 1981; Sopade et al., 2002). In a study for the application of WLF relationship in starch hydrolysates, D’Haene and Van Liederkerke (1996) considered the latter limit restrictive and proved that the principles of the WLF-theory can be applied down to viscosity levels of 0.1 Pa s. These viscosity levels are comparable to viscosity values for Greek honeys measured at high temperatures. Our viscosity data were also extended to higher temperatures than usual with success. Moreover, these high temperatures are usually used in honey processing for ease of handling with minimal quality (e.g. hydroxymethylfurfural, HMF) degradation and thus it would be useful the prediction of viscosity changes under these conditions. The WLF equation has been previously found to adequately describe viscosity data of Jordanian (temperature range 20–50
C; Al-Malah et al., 2001) and Australian (temperature range 2–40
C; Sopade et al., 2002) honeys. Very good fits (r2 > 0:95) to the WLF model were obtained for all 14 data sets (Table 4) as showed in Fig. 6. All data sets could be fitted to a single master curve using the WLF model with the fixed Ôuniversal’ constants, C1 ¼ 17:44 and C2 ¼ 51:6 K (Williams et al., 1955). These results concur with the findings of Al-Malah et al. (2001) who also found that the WLF equation, using the Ôuniversal’ constants, adequately described the temperature-dependence of viscosity for

19

three honey samples. The Ôuniversal constants’ of the WLF equation are actually average values, which have been extracted from data on numerous glass-forming liquids and their use is not successful for all materials. For each data set of g vs. T (each honey sample considered individually), the WLF equation with Ôuniversal’ constants was fitted to yield the corresponding values of Tg and gTg . Table 3 shows these predicted values for the glass transition temperature (Tg ) ranging from )59.6 to )42.5
C and for the glass viscosity (gTg ) values which ranged from 1011:5 to 1011:9 Pa s. Although Tg is a parameter that is measured by various techniques, a high viscosity value such as gTg , is not accessible experimentally by any of the existing rheometers and viscometers. The predicted Tg values differed from the corresponding DSC values obtained experimentally by 7–19
C (Table 4). It is well known that the glass transition reflects a range of temperatures rather than a single temperature. Even for single components (e.g. starch) the glass entails changes over a temperature range of 10–20
C (Biliaderis, 1998) and thus the Tg value depends on the technique and experimental conditions used for its determination. Moreover, in a previous study for concentrated fructose (69%) solutions differences up to 21
C between Tg s values obtained by DSC measurements and Tg s values estimated by the application of WLF on viscosity data have been reported (Maltini & Manzocco, 1998). Recently, there have been conflicting reports on how to handle the constants in the WLF model, whether to use the Ôuniversal’ constants or to allow them to vary for a good fit to the experimentally data (Peleg, 1992; Roos, 1995). In a second attempt to apply the WLF model on viscosity data of Greek honeys with varying the C1 and C2 constants and using as reference temperature the Tg values experimentally determined from DSC, the correlation coefficients were the same with the previous analysis using the Ôuniversal’ constants (Table 4). The C1 and C2 constants were in the range of 17.20–25.18 and 13.95–30.90 K, respectively (Table 4). Moreover, the predicted values of glass viscosities varied widely from 1012:9 to 1021:7 Pa s and for most of the samples were extremely high which is probably unrealistic. However, the latter findings are in agreement with a recent study by Sopade et al. (2002) for Australian honeys. In their study, although the temperature dependence of viscosity was badly predicted using the Ôuniversal’ WLF constants, the WLF model was successfully applied if the C1 and C2 were allowed to vary. The estimated values for the Australian honeys have been reported within the range 13.7–21.1, 55.9–118.7
C, and 4 · 107 )4 · 1020 Pa s for C1 , C2 , and gTg , respectively (Sopade et al., 2002). These researchers claimed that the WLF constants should be allowed to vary in order to use them as parameters for comparison of the temperature sensitivity among different samples. The WLF model with

20

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21

different constants than the Ôuniversal’ ones has been also applied by Kerr and Reid (1994) on viscosity data of sugar (glucose and sucrose) and maltodextrin solutions. Maltini and Manzocco (1998) have applied the WLF formalism in both ways (with Ôuniversal’ and with varying constants) on viscosity data for concentrated solutions of various materials (polymers, fructose, lactic acid, and glycerol); in their study the estimated values for glass viscosities have been found about 1014 cP. Soesanto and Williams (1981), using the Ôuniversal’ constants on viscosity data of highly concentrated (91.9– 97.9%) fructose–sucrose mixtures (1:7), indicated that gTg may not be invariant; i.e. they showed that gTg varies from about 4.5 · 1014 to 1.5 · 1015 mPa s as the mole fraction of sugar varies from 0.4 to 0.7. Finally, Peleg (1992) has reported that for a variety of polymers and amorphous sugars, the magnitude of C1 and C2 may vary considerably from the Ôuniversal’ constants depending on the material studied, the measured property and the selected reference temperature.

4. Conclusions All honey samples exhibited Newtonian flow behaviour and the viscosity in the temperature range of 20–60
C can be predicted using the Arrhenius relationship; the calculated activation energies for flow were inversely related to the moisture content. Steady shear viscosity and the loss modulus values (G00 ) at 10 s
1 or rad s
1 decreased exponentially with increasing moisture content of honey. The glass transition temperature (Tg ) of the honey samples varied between )34 and )47
C (over the entire moisture content range, 13.0–18.9%) and exhibited strong depression with the moisture; the Tg data fitted reasonably well to the Gordon–Taylor empirical equation. The WLF equation was also suitable to model the rheological behaviour of honey viscosity above the glass transition (T
Tg ¼ 60–125
C) using the universal values of the WLF model (C1 ¼ 17:44 and C2 ¼ 51:6 K) where all samples fitted onto a common master curve.

Acknowledgement The authors wish to thank Mr. A. Pavlis for his analytical assistance.

References Abu-Jdayil, B., Al-Majeed Ghzawi, A., Al-Malah, K. I. M., & Zaitoun, S. (2002). Heat effect on rheology of light- and darkcolored honey. Journal of Food Engineering, 51, 33–38. Adobe Photoshop 5.0 User Guide for Machintosh and Windows. (1998). Adobe Systems, Inc., San Jose, CA, USA.

Al-Khalifa, A. S., & Al-Arify, I. A. (1999). Physicochemical characteristics and pollen spectrum of some Saudi honeys. Food Chemistry, 67, 21–25. Al-Malah, K. I. M., Abu-Jdayil, B., Zaitoun, S., & Ghzawi, A.-M. (2001). Application of WLF and Arhenius kinetics to rheology of selected dark-colored honey. Journal of Food Process Engineering, 24, 341–357. Anupama, D., Bhat, K. K., & Sapna, V. K. (2003). Sensory and physico-chemical properties of commercial samples of honey. Food Research International, 36, 183–191. AOAC (1990). In K. Helrich (Ed.), Official methods of analysis (15th edn). Arlington, VA: Association of Official Analytical Chemists. Bath, P. K., & Singh, N. (1999). A comparison between Helianthus annuus and Eucalyptus lanceolatus honey. Food Chemistry, 67, 389– 397. Bhandari, B., D’Arcy, B., & Chow, S. (1999). Rheology of selected Australian honeys. Journal of Food Engineering, 41, 65–68. Biliaderis, C. G. (1998). Structures and phase transitions of starch polymers. In R. H. Walter (Ed.), Polysaccharide association structures in Food (pp. 57–168). New York: Marcel Dekker. Biliaderis, C. G., Lazaridou, A., & Arvanitoyannis, I. (1999). Glass transition and physical properties of polyol-plasticized pullulanstarch blends at low moisture. Carbohydrate Polymers, 40, 29–47. CIE (1976). Committee TC-1.3 CIE, Technical note (1974). Journal of Optical Society of America, 64, 896–897. Cordella, C., Antinelli, J. F., Aurieres, C., Faucon, J. P., Cabrol-Bass, D., & Sbirrazzuoli, N. (2002). Use of differential scanning calorimetry (DSC) as a new technique for detection of adulteration in honeys. 1. Study of adulteration effect on honey thermal behavior. Journal of Agriculture Food Chemistry, 50, 203–208. Cox, W. P., & Merz, E. H. (1958). Correlation of dynamic and steady shear flow viscosities. Journal of Polymer Science, 28, 619–622. D’Haene, P., & Van Liederkerke, B. (1996). Viscosity prediction of starch hydrolysates from single point measurements. Starch, 48, 327–334. da Costa, C. C., & Pereira, R. G. (2002). The influence of propolis on the rheological behaviour of pure honey. Food Chemistry, 76, 417– 421. Doner, L. W. (1977). The sugars of honey––a review. Journal of the Science of Food and Agriculture, 28, 443–456. Doner, L. W., & Hicks, K. B. (1982). Lactose and the sugras of honey and maple: reactions, properties, and analysis. In D. R. Lineback & G. E. Inglett (Eds.), Food Carbohydrates (pp. 74–112). West Port, CT: AVI Publishing Company. Gomez Barez, J. A., Garcia-Villanova, R. J., Elvira Garcia, S., Rivas Pala, T., Gonzalez Paramas, A. M., & Sanchez Sanchez, J. (2000). Geographical discrimination of honeys through the employment of sugar patterns and common chemical quality parameters. European Food Research and Technology, 210, 437–444. Gordon, M., & Taylor, J. S. (1952). Ideal copolymers and the secondorder transitions of synthetic rubbers. I. Non-crystalline copolymers. Journal of Applied Chemistry, 2, 493–500. Junzheng, P., & Changying, J. (1998). General rheological model for natural honeys in China. Journal of Food Engineering, 36, 165–168. Kantor, Z., Pitsi, G., & Thoen, J. (1999). Glass transition temperature of honey as a function of water content as determined by differential scanning calorimetry. Journal of Agriculture Food Chemistry, 47, 2327–2330. Kerr, W. L., & Reid, D. S. (1994). Temperature dependence of the viscosity of sugar and maltodextrin solutions in coexistence with ice. Lebensmittel-Wissenschaft und-Technologie, 27, 225–231. Khalil, K. E., Ramakrishna, P., Nanjundaswamy, A. M., & Patwardhan, M. V. (1989). Rheology of banana juice. Journal of Food Engineering, 10, 231–240. Levine, H., & Slade, L. (1988). Principles of ‘‘cryostabilization’’ technology from structure/property relationship of carbohydrate/ water systems––a review. Cryo-Letter, 9, 21–63.

A. Lazaridou et al. / Journal of Food Engineering 64 (2004) 9–21 Maltini, E., & Manzocco, L. (1998). Experimental and predicted viscosities of model solutions at temperatures above the glass transitions. In proceedings of ISOPOW 7 International Symposium on water management in the design and distribution of quality foods, Helsinki, Filand, pp. 57–60. Manohar, B., Ramakrishna, P., & Udayasankar, K. (1991). Some physical properties of Tamarind Tamarindus indica L. juice concentrates. Journal of Food Engineering, 13, 241–258. Matveev, Y. I., Grinberg, V. Y., & Tolstoguzov, V. B. (2000). The plasticizing effect of water on proteins, polysaccharides and their mixtures. Glassy state of biopolymers, food and seeds. Food Hydrocolloids, 14, 425–437. Ollett, A. L., & Parker, R. (1990). The viscosity of supercooled fructose and its glass transition temperature. Journal of Texture Studies, 21, 355–362. Papadakis, S. E., Abdul-Malek, S., Kamdem, R. E., & Yam, K. L. (2000). A versatile and inexpensive technique for measuring color of foods. Food Technology, 54(12), 48–51. Peleg, M. (1992). On the use of the WLF model in polymers and foods. Critical Reviews in Food Science and Nutrition, 32, 59–66. Perez-Arquille, C., Conchello, P., Arino, A., Juan, T., & Herresa, A. (1994). Quality evaluation of spanish rosemary (Rosmarius officinalis) honey. Food Chemistry, 51, 207–210. Popek, S. (2002). A procedure to identify a honey type. Food Chemistry, 79, 401–406. Popek, S. (2003). Identification of honey types. Nahrung/Food, 47, 39–40. Roos, Y. H. (1995). Phase transitions in foods. New York: Academic Press. Sabatini, A. G., Marcazzan, G. L., Colombo, R., Carpana, E., & Serra, G. (2001). The analytical determination of sugars in honey. Industrie Alimentari, 40(404), 623–627. Singh, N., & Bath, P. K. (1997). Quality evaluation of different types of Indian honey. Food Chemistry, 58, 129–133.

21

Slade, L., & Levine, H. (1991). Beyond water activities: recent advances based on an alternative approach to the assessment of food quality and safety. Critical Reviews in Food Science and Nutrition, 30, 115–360. Slade, L., & Levine, H. (1993). The glassy state phenomenon in food molecules. In J. M. V. Blanshard & P. J. Lillford (Eds.), The glassy state in foods (pp. 35–101). Sutton Bonington, UK: Nottingham University Press. Soesanto, T., & Williams, M. C. (1981). Volumetric interpretation of viscosity for concentrated and dilute sugar solutions. Journal of Physical Chemistry, 85, 3338–3341. Sopade, P. A., Bhandari, B., Halley, P., D’Arcy, B., & Caffin, N. (2001). Glass transition in Australian honeys. Food Australia, 53, 399–404. Sopade, P. A., Halley, P., Bhandari, B., D’Arcy, B., Doebler, C., & Caffin, N. (2002). Application of the Williams–Landel–Ferry model to the viscosity–temperature relationship of Australian honeys. Journal of Food Engineering, 56, 67–75. Sugisaki, M., Suga, H., & Seki, S. (1968). Calorimetric study of the glassy state IV. Heat capacities of glassy water and cubic ice. Bulletin of the Chemical Society of Japan, 41, 2591–2599. Terrab, A., Diez, M. J., & Heredia, F. J. (2002). Characterization of Moroccan unifloral honeys by their physicochemical characteristics. Food Chemistry, 79, 373–379. White, J. W., Jr. (1978). Honey. Advances in Food Research, 24, 288– 354. Williams, M. L., Landel, R. F., & Ferry, J. D. (1955). The temperature dependence of relaxation mechanisms in amorphous polymers and other glass-forming liquids. Journal of the American Chemical Society, 77, 3701–3707. Zaitoun, S., Ghzawi, A. -M., Al-Malah, K. I. M., & Abu-Jdayil, B. (2001). Rheological properties of selected light colored Jordanian honey. International Journal of Food Properties, 4, 139–148.