Comparison of Rheological Behavior of Sweet and Salad Sauces

Abstract

A comparative study of different commercial sauces was carried out from a rheological point of view. The different sauces were divided into sweet and salad, and for each sausage the behavior was studied at different temperatures. The power-law parameters, n and k, for sauces were calculated and their variation with the temperature was studied. On the other hand, the activation energy was calculated for the sweet sauces.

Keywords:

• Viscosity
• Activation energy
• Honey
• Caramel
• Mayonnaise
• Mustard
• Ketchup

Introduction

The increasing social and economic importance of food production, together with the complexity of technology of production, processing, handling, and acceptance of these highly perishable and fragile food materials requires a more extensive knowledge of their physical properties; because of this, the viscoelastic properties play an important role in the handling and quality attributes of both minimally processed foods, such as fruits and vegetables, and fabricated foods such as sauces and frankfurters. One of the important characteristic of viscoelastic behavior is the dependence of the material properties on time, in addition to temperature and moisture content.1 The rheological properties are very important in order to design food processing operations (mixing, pumping, heating, cooling),2 3 4 5 and in aspects such as the product acceptance by the consumer6 and the optimization of process variables.7 8

Most foods are complex multicomponent systems, often containing more than one phase and many of these systems exist in the form of emulsions, for example mayonnaise, ketchup, or syrup. The processing of emulsions is a highly complex operation with many variables influencing the processing performance and the final product form.1 In order to understand and eventually improve the processing performance of food emulsions, a sound understanding of their flow behavior is necessary. Because of their commercial importance, the role of the various components: oil, water, egg yolk, thickening agents (usually gums), salt, and sugar have been studied by food technologists and summarized in some publications.6 7 8 9 10 11

The substances studied in this work are natural and commercial honey, caramel, mayonnaise, ketchup, and mustard. The authors carried out an investigation to study the rheological properties of different kind of sauces at different temperatures. Sauces were divided into two groups based in their kind of flow: Newtonian and non-Newtonian fluids12 using the Herschel-Bulkley model.13

where τ is the shear stress in Pa, k is the consistence index in Pa s ⁿ , γ is the shear rate expressed in s⁻¹, n the behavior index, and τ _o is the yield stress prior to any response expressed in Pa.

Materials and Methods

All sauces were employed in their commercial form. The mayonnaise contained the following ingredients: girasol oil, egg yolk, vinegar, water, sugar, salt, spices, and stabilizer (E-412). The ingredients of the ketchup are: water, tomato paste, sucrose, spirit vinegar, salt, thickener (E-1422), spices, and aromas. The mustard was constituted by: water, spirit vinegar, mustard, sugar, salt, and spices. The ingredients of the caramel were: syrup of glucose, water sugar, and conservator (E-202). The two honeys had only an ingredient: honey. The composition, moisture content, and pH of all sauces are reported in Table 1.

Table 1 Composition, moisture content, and pH of the sauces

Sauce	pH	Moisture content (g/100 g)	Ingredients composition (g/100 g)
Caramel	4.36	31.4	Syrup	53.7
			Water	31.4
			Sugar	14.9
Natural honey	3.85	15.9	Fructose	46.5
			Glucose	25.1
			Water	15.9
			Maltose	2.5
Commercial honey	6.03	30.6	Fructose	38.7
			Glucose	30.7
			Water	30.6
			Maltose	3.0
Mustard	2.95	55.2	Water	55.2
			Vinegar	30
			Mustard	14
			Sugar	0.4
			Salt	0.3
			Spices	0.1
Ketchup	3.32	67.0	Water	67
			Tomato paste	24
			Sucrose	5.3
			Vinegar	3.5
			Salt	0.1
			Spices	0.1
Mayonnaise	3.88	6.0	Girasol oil	80
			Egg yolk	7
			Vinegar	6.2
			Water	6
			Sugar	0.5
			Salt	0.2
			Spices	0.1

Different rheological measurements were carried out for all the sauces using a rotational viscosimeter HAAKE VT550, based in two coaxial cylinders, with a temperature sensor PT100. The viscosimeter is connected to a thermostated bath to maintain constant temperature during the measurement. The shear rate range was varied from 18 to 445 s⁻¹. The temperature was varied from 20 to 40°C.

Results and Discussion

Sweet Sauces

The employed sweet sauces were natural and commercial honey and caramel. To study the rheological behavior of these substances, the shear stress (τ) against shear rate (γ) was represented (Fig. 1). It was observed that the shear stress changed lineally with the shear rate and shear stress decreased when the temperature increased.

Figure 1. Shear stress vs. shear rate for the sweet sauces at different temperatures: commercial honey (•), natural honey (▪), caramel (▴) at 20°C, and commercial honey (ˆ), natural honey (□), caramel (▵) at 40°C.

Because of this, it is deduced that these sauces present a Newtonian behavior and n have a value of 1. The values of the viscosity, that are equal to the values of consistence index, are obtained with the slope and they are reported in Table 2. Once the values of the viscosity for this kind of sauces were calculated, the activation energy was obtained with the Eq. (2).

where η is the viscosity in Pa s, E_A is the activation energy expressed in J/mol, B is a parameter expressed in Pa s, R is the gas constant in J/mol K, and T is the temperature in K. The values of the E_A are shown in Table 3.

Table 2 Values of coefficients in Herschel-Bulkley fluid model for the sauces

Sauce	T(°C)	k	n
Caramel	20	3.575	1
	25	2.026	1
	30	1.520	1
	35	1.222	1
	40	0.810	1
Natural honey	20	6.476	1
	25	2.994	1
	30	1.319	1
	35	0.761	1
	40	0.438	1
Commercial honey	20	2.572	1
	25	1.418	1
	30	0.802	1
	35	0.450	1
	40	0.227	1
Mustard	20	14.944	0.308
	25	13.420	0.310
	30	12.005	0.312
	35	10.812	0.315
	40	9.938	0.318
Ketchup	20	16.698	0.349
	25	15.120	0.353
	30	14.180	0.359
	35	12.992	0.364
	40	11.790	0.370
Mayonnaise	20	58.556	0.251
	25	52.277	0.264
	30	47.061	0.282
	35	40.995	0.298
	40	36.313	0.308

Table 3 Values of activation energy for sweet sauces

Sauce	B	EA (kJ/mol)
Home honey	3.436×10^−2	0.893
Liquid caramel	1.113×10^−9	53.136
Commercial honey	1.290×10^−16	91.554

Salad Sauces

The employed salad sauces were mayonnaise, ketchup, and mustard. Based on the dependence of the shear stress on the shear rate, the type of solutions was determined. From the typical curves on dependence of the shear stress (τ) on shear rate (γ) it could be seen that all of these substances had a non-Newtonian and pseudoplastic behavior and therefore the shear stress decreases with the temperature (Fig. 2). Another form of studying the Newtonian or non-Newtonian behavior of a fluid would be to represent the viscosity against the shear rate and analyze its behavior.14 In this case, the variation is exponential, and therefore we are working with non-Newtonian fluids; otherwise, the variation should be lineal. This indicates that the viscosity of the three salad sauces must decrease when the temperature increases. Once analyzed their behavior, Herschel-Bulkley model was used to determine the consistence and behavior indexes, k and n, respectively and the variation of the both indexes with the temperature was analyzed. These indexes have a similar and opposed behavior with the temperature for all these sauces. Consequently, n, increases lineally with the temperature (Fig. 3) and k decreases lineally when increasing the operation temperature (Fig. 4). Therefore, they can be fitting to the Eqs. (3) and (4).

where A_i and B_i are fitting parameters expressed in (°C)⁻ⁱ and Pa s ⁿ (°C)⁻ⁱ , respectively, and T represents the temperature in °C. The values of the fitting parameters are shown in Table 4.

Table 4 Fitting parameters of the behavior and consistence indexes with the temperature for salad sauces

	n		k
Sauce	A 0×10^1	A 1×10^3	B 0×10^−1	B 1×10^1
Ketchup	3.285	1.018	2.132	−2.389
Mustard	2.971	0.524	1.980	−2.524
Mayonnaise	1.919	2.952	8.050	−11.150

Figure 2. Shear stress vs. shear rate for the salad sauces at different temperatures: mayonnaise (•), mustard (□), ketchup (▵) at 20°C, and mayonnaise (•), mustard (▪), ketchup (▴) at 40°C

Figure 3. Behavior index vs. temperature for the salad sauces: mayonnaise (▴), mustard (•), ketchup (▪).

Figure 4. Consistence index vs. temperature for the salad sauces: mayonnaise (▴), mustard (•), ketchup (▪).

Conclusions

The obtained results allow concluding that the studied sweet sauces have a Newtonian behavior while the studied salad sauces have a non-Newtonian and pseudoplastic behavior. The value of the activation energy for sweet sauces was determined and it is observed that the value of commercial honey is very much higher than the natural honey. The liquid caramel has an intermediate value. The rheological parameters, n and k, were calculated for the salad sauces. It is concluded that on the one hand, the behavior index, n, increases lineally with the temperature and on the other hand, the consistence index decreases lineally when the temperature increases.