Food. Application Note Food_02. Application Note. Version: Created on 12/9/2008 1:37:00 PM Created by Petra Schaupp-Morocutti

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1 Application Note Version: Application Note _02 Page 1 of 20

2 Contents Introduction... 3 Rotational viscometers, rheometers and test types... 4 What is a rotational viscometer, what is a rheometer?... 4 Test types... 4 Applications... 8 Chocolate... 8 Jam Starch Ketchup Cheese Salad dressing Ice cream Suitable Rheometers Application Note _02 Page 2 of 20

3 Introduction sustains us. Its rheological properties make us able to bite it, chew it and swallow it, while appealing to our senses. These properties are referred to as the texture of the food. Rheological characterization of food becomes increasingly important for evaluating the quality of both the raw materials and the end product and predicting its behavior during processing. In practice, the following information is important regarding the rheological behavior of food: - The consistency or structural strength at rest - The flow behavior - The time-dependent and temperature-dependent behavior Knowledge of the consistency is important in order to predict the dispersion or gel stability, expected stability in storage and tendency to sedimentation. Knowledge of the flow behavior and behavior over time is essential for predicting the processability and filling behavior. Here, the structure of the material and its structural changes during technological processes must be known. Using this knowledge a process can be designed and calculations for the technological equipment can be carried out. The structure also gives the product the sensory properties required by the consumer, such as the flavor and body of a beverage or creaminess of an ice cream. It provides insight into the stickiness of a sweet or the feeling when swallowing. To guarantee a consistent quality there are a number of different test types which are available. Application Note _02 Page 3 of 20

4 Rotational viscometers, rheometers and test types What is a rotational viscometer, what is a rheometer? In contrast to rheometers, viscometers provide information on the viscous behavior of the sample. Rheometers determine additional properties such as elasticity, stiffness and structural regeneration under different conditions (pressure and temperature). Rheometer measuring systems have two parts. These are typically normed cylinders consisting of a measuring cup and measuring bob. Cone/plate or plate/plate measuring systems (ISO 3219 and DIN and DIN 53019) are also widely used. Measuring systems available on the market are grouped as follows: 1. Absolute measuring systems (such as concentric cylinders, cone/plate and plate/plate measuring systems) which have a defined shear gap and provide constant shear conditions. These systems are described in ISO 3219 (1993) and DIN (Version 2004; previously Version 1976 in DIN 53018). 2. Relative measuring systems (such as vanes, spindles, in the form of disks, pins or balls) which have an infinite shear gap and therefore do not provide constant shear conditions. For this reason, the viscosity results given by relative measuring systems are not absolute values. shear rate controlled test, abbreviated as CSR. The torque M provides the shear stress τ. There is a second method for determining the viscosity in which the torque (shear stress) is set and the resulting speed (shear rate) is measured. From these two values the viscosity η is calculated. This controlled test measurement method is called shear stress, abbreviated as CSS. Using both measurement methods it is possible to determine individual viscosity values or a complete viscosity curve. The viscosity curve describes the viscosity dependence of the sample in a defined shear load range. Samples which begin to flow only after a certain amount of load has been applied are said to have a yield point. This can be determined using the two different methods: CSS and CSR. In the CSS method the yield point can be read off as the point at which the τ-axis is crossed. In the CSR method the yield point can be calculated approximately using a mathematic regression model (e.g. Bingham, Casson, Herschel-Bulkley). The CSS mode is the more accurate method as it determines the real point of flow. Fig. 2: Cylinder measuring system Cone/plate measuring system Plate/plate measuring system Test types 1. Rotational tests With simple viscometers one or different speeds are manually set in steps and the resulting torque T is measured, either in percent or per mille of the maximum. The shear rate γ can be calculated from the speed n. This measurement method is called a Fig. 3: CSR setting Application Note _02 Page 4 of 20

5 Fig. 4: CSS setting Fig. 5: Flow curve with and without yield point Definitions: Shear stress F = A v Shear rate ( ) h (Shear) viscosity N m τ [ Pa] 2 = m 1 1 γ = D = = [ ] m = s s s τ = γ Pa = 1/s η [ Pas] Application Note _02 Page 5 of 20

6 2. Oscillatory tests In an oscillatory rheometer the moving part of the measuring system oscillates, creating vibrations which are transferred to the sample. This provides information on the viscoelastic behavior of the substance. The oscillation is usually carried out at very low deformations to stay in the elastic range. In contrast to rotational tests, oscillatory tests have the advantage that the samples are not destroyed during testing. Fig. 6: Movement in rotational tests (left figure) and oscillatory tests (right figure) Amplitude sweep: An oscillatory test simultaneously determines both the viscous behavior, e.g. described by the loss modulus G, and the elastic behavior, e.g. described by the storage modulus G. A variety of measuring systems allow both liquids and solids to be measured. This makes it possible to use one single instrument to investigate substances ranging from fluids such as water to cured sealing compounds, resins and even solid plastic. Fig. 7a: Setting for an amplitude sweep Depending on the type of oscillatory test the frequency, deformation and temperature can be varied. In an amplitude sweep the amplitude is varied and the frequency kept constant. This test provides information on the limit of the linearviscoelastic (LVE) range and the structural character of the sample. The following characters are defined: Gel or paste character with > ' and liquid character with ' >. The structural strength of a substance is expressed by the value. Fig. 7b: Possible result (amplitude sweep) Frequency sweep: Application Note _02 Page 6 of 20

7 In a frequency sweep the frequency is varied and the amplitude kept constant. The strain is determined from a prior amplitude sweep test to ensure the measurement is carried out within the LVE range. Measurements at high frequencies represent the short-term behavior of a sample. The long-term behavior (storage stability) is described by measurement data at low frequencies. Fig. 8a: Setting for a frequency sweep Temperature test: For temperature tests a constant frequency and constant strain are set. The temperature is changed at a defined heating or cooling rate. Temperature tests can be used to determine the glass transition temperature and melting temperature. Fig. 8b: Possible result (frequency sweep) Definitions: Fig. 9: Temperature test on a semicrystalline plastic Shear stress Shear deformation or shear strain Shear modulus Storage modulus (elastic portion) Loss modulus (viscous portion) Damping factor or loss factor F = A N m τ [ Pa] s = h m m 2 = γ = [] 1 = 100% τ = γ Pa = 1 G [ Pa] G [Pa] G [Pa] tan ' = Pa Pa δ = [] 1 Application Note _02 Page 7 of 20

8 Applications Chocolate The flow behavior of food plays an important role in the production process and in achieving acceptance from the consumer. The yield point influences the way the chocolate levels out during manufacturing and how it melts in the mouth and on the consumer s hands. Chocolate makers are very interested in the spatial distribution of the cocoa butter molecules. The chocolate should melt on the tongue at temperatures between 29 and 33 C. If not, it tastes waxy or is too soft at room temperature. For quality control of chocolate melts at 40 C a flow curve approximation model is used. The analysis according to Windhab is recommended for the measuring range γ = 2 to 50 1/s by the IOCCC (International Office of Cocoa, Chocolate and Sugar Confectionary). The results are the yield point, a specific shear rate value in the range of shear induced restructuring and the equilibrium viscosity at high shear rates. The viscosity of the chocolate melt is influenced by a number of ingredients. As the amount of fat in the chocolate increases, for example, the viscosity and yield point value decrease. Consistent quality can be guaranteed by checking the flow behavior and viscosity. Application Note _02 Page 8 of 20

9 300 Pa Hoher Fettgehalt CC 27; d=0 mm τ Schubspannung Hoher Fettgehalt [IOCCC] tau0 = 17 Pa; eta_inf = 2,2 Pa s τ Schubspannung Mittlerer Fettgehalt 10 2 Pa s 10 3 Pa Hoher Fettgehalt [IOCCC] tau0 = 17 Pa; eta_inf = 2,2 Pa s η Viskosität τ Schubspannung Mittlerer Fettgehalt [IOCCC] τ /s 50 Scherrate γ. Anton Paar GmbH CC 27; d=0 mm τ Schubspannung Mittlerer Fettgehalt [IOCCC] tau0 = 23 Pa; eta_inf = 2,9 Pa s τ Schubspannung Niedriger Fettgehalt CC 27; d=0 mm τ Schubspannung Niedriger Fettgehalt [IOCCC] tau0 = 24 Pa; eta_inf = 4,2 Pa s τ Schubspannung η /s 10 2 Scherrate γ. τ tau0 = 23 Pa; eta_inf = 2,9 Pa s η Viskosität τ Schubspannung Niedriger Fettgehalt [IOCCC] tau0 = 24 Pa; eta_inf = 4,2 Pa s η Viskosität τ Schubspannung Anton Paar GmbH Application Note _02 Page 9 of 20

10 Jam The viscosity of jam must be known. For good pumping and filling of the jam the viscosity should be low at high shear rates. For the consumer the viscosity is also of great importance: if the viscosity at rest is too low the jam will run off the bread. Jam, like other food, often contains large particles. Removing these particles is time-consuming and also leads to falsified results when determining the flow behavior. For samples with large particles the typical measuring systems such as parallel plate, cone/plate or cylinder geometries are unsuitable due to their small measuring gap. To make it possible to measure samples with large particles there is a ball measuring system. This moves the ball of the measuring bob rotating in a circular path through the sample. The entire measurement is completed in just one circuit, which ensures that each measuring point is recorded in fresh, nondeformed material Pa Pa s 10 3 Marmelade 1 η Viskosität η 10 2 τ τ Schubspannung Marmelade η τ Viskosität Schubspannung , /s 100 Scherrate γ. Application Note _02 Page 10 of 20

11 Starch Starch is not only important for nutrition, it is often used in the food industry due to its physical properties. The gelification of starch is widely used to improve the appearance, stability, texture and quality of the food. Monitoring of the gelitinization process is difficult due to the different phases at different temperatures. Therefore, a special test geometry and an electrical temperature chamber with rapid heating and cooling rates have been developed. This enables an accurate measurement of the gelification. If higher pressures are required, a pressure cell can be used. Viscosity curves differ widely depending on the starch type. At 35 C starch is not soluble in water, so the measuring geometry must keep the starch granules in suspension. When heated, the granules begin to swell and this increases the viscosity considerably. Depending on the starch type, the viscosity maximum and therefore also a volume maximum is reached at a specific temperature. At this point the starch granules are destroyed and the viscosity decreases. When the starch cools down, the viscosity increases again due to the gelification of the starch. 1 Pa s 0,8 150 C ,7 110 η 0,6 0, T 0,4 70 0,3 60 0,2 0, min 20 Zeit t Application Note _02 Page 11 of 20

12 Ketchup During the manufacturing process, ketchup should be easy to mix and fill into bottles. However, the consumer demands a ketchup which flows easily out of the bottle but then remains on the chips, without running off. To simulate the flowing and leveling behavior after pouring out and the structural regeneration after filling and leaving the bottle, a step test is carried out. This consists of three intervals. The first interval determines the behavior at rest. The second interval determines the structural decomposition and the third the structural regeneration. The settings in the first and third intervals are a constant angular frequency and a constant deformation within the linear viscoelastic range. The second interval consists of rotation at a constant shear rate that simulates shearing during pouring out or filling. Despite its higher viscosity at rest, Ketchup 1 has a lower viscosity during shearing (pouring out of the bottle) than Ketchup 2. The structural regeneration of Ketchup 1 takes longer than that of Ketchup 2. This means that Ketchup 1 runs for a longer period of time and therefore has a thinner layer thickness than Ketchup Pa s Pa 10 2 Ketchup 1 Speichermodul 10 2 ' 10 η ' η Ketchup 2 Verlustmodul Viskosität Speichermodul 1 ' η Verlustmodul Viskosität , s 300 Zeit t Application Note _02 Page 12 of 20

13 Cheese The consistency as a function of the temperature is an important property of cheese products. For example, cheese spread should be spreadable straight from the refrigerator but at room temperature it should have a structure that prevents it from flowing too much. For a good feeling in the mouth, the cheese spread should have the structure of a soft solid when at body temperature. Whether the material characteristics meet the above-mentioned requirements can be investigated using an amplitude sweep. In this test the deformation (strain) is increased logarithmically while keeping a constant angular frequency. The amplitude sweep is carried out at a number of temperatures. Due to the extended gel structures and high consistency at room temperature, a parallel plate measuring system is recommended. A constant normal force should be applied to the sample to ensure it has a good grip on the measuring plate. As this type of sample tends to flow out of the gap, even at very low shear rates, oscillatory tests are preferable. In addition, oscillatory tests reveal information about both the viscous and elastic behavior Pa Spreading Cheese 5 C Storage Modulus 10 4 ' ' Loss Modulus Spreading Cheese 20 C Storage Modulus ' Loss Modulus Spreading Cheese 36 C ' Storage Modulus Loss Modulus % 100 Strain γ Application Note _02 Page 13 of 20

14 Salad dressing Salad dressings and vinegar often contain suspended herbs and vegetable pieces. This has the advantage that the consumer does not have to shake the container to distribute the particles and also improves the appearance of the product. For manufacturers the challenge is to select the right additives in order to modify the viscoelastic behavior so that the particles do not separate out while ensuring that the salad dressing or vinegar remains liquid enough to pour out and distribute on the salad. Amplitude sweeps and frequency sweeps are well suited for checking these properties. Additives change the Newtonian flow behavior into a shear thinning one. The pure viscous character becomes a weak gel character, e.g. the storage modulus G lies slightly above the loss modulus G. This property keeps the particles in suspension and prevents sedimentation. In a frequency sweep the frequency is varied and the amplitude kept constant. The deformation is first determined in an amplitude sweep and must be within the linear viscoelastic range. Measurements at high frequencies represent the short-term behavior of a sample. The long-term behavior (stability in storage) is described by the measuring data at low frequencies Pa 10 0 mpa s Essig modifiziert ' η* Speichermodul ' Verlustmodul η* Betrag(Viskosität) Essig nicht modifiziert Speichermodul ' Verlustmodul η* Betrag(Viskosität) ,1 0, /s 100 Kreisfrequenz ω Application Note _02 Page 14 of 20

15 Ice cream The temperature-dependent rheological behavior is an important property of ice cream. For example, an ice cream should have a low rigidity at low temperatures. This enables good scoopability. On the other hand, ice cream should be creamy and feel good in the mouth after melting at higher temperatures. As it melts in the mouth, the consumer does not like to have a feeling of too much coldness, requiring a slow melting phase. Due to extended crystal structures in ice cream and its stiff consistency at low temperatures, using a parallel plate measuring system is recommended. In order to prevent slip the geometries should be profiled. To keep the temperature gradients at an optimally low level, the measuring cell P-PTD200 with Peltier temperature control and actively heated Peltier controlled hood H-PTD200 is used. Besides temperature controlling the lower plate, the temperature of the measuring area around the sample is controlled from above. Without the Peltier hood the results for G and G are considerably lower in the low temperature range, i.e. the real average temperature of the sample is higher than shown. The resulting curve is also less steep for G and G during the melting process, meaning this process is also simulated inaccurately and does not reflect reality. Temperature tests on ice cream should be carried out using oscillation. In these tests angular frequency is kept constant and the very low deformation is within the linear viscoelastic range. The temperature is steadily increased from low to high values Pa ' C 5 Temperatur T Eiscreme mit Haube ' Eiscreme ohne Haube ' Application Note _02 Page 15 of 20

16 Suitable rheometers Physica MCR 51 A robust ball bearing rheometer for quality assurance and production control. Ideal for high viscosity applications where low torque capability is not required. Physica MCR 101 Air bearing rheometer (basic configuration) for quality assurance and product development. The torque range and angle of deflection are ideal for structured materials (pastes, creams, lotions, suspensions, emulsions). Physica MCR 301 Air bearing rheometer for product development and research. The torque range and angular resolution are ideal for all samples from low viscous liquids up to solids. Physica MCR 501 Air bearing, high-end rheometer for research and development. The widest torque range for the most demanding rheological measurements on all samples from liquids to solids. TruGap TM and DSO are standard for increased accuracy and reproducibility. Expanded housing and frame for customized extension modules. Optimized motor and air bearing system to eliminate external influences and ensure the highest accuracy. Application Note _02 Page 16 of 20

17 Environmental Systems Since temperature has a great influence on the rheological behavior of all samples, precise temperature control is crucial for obtaining reliable rheological data. However, in practical tests inaccurate temperature control is still responsible for a large number of measurement uncertainties and errors. To address these issues, our engineers have taken great care to develop various temperature control systems based on different principles. These systems fulfill the requirement of accurate temperature control in all respects and are still commercially affordable, putting Anton Paar in the lead position with respect to temperature control in rheology. Numerous patents and scientific reports on the performance of the various environmental systems have been published. Some key features include the broadest temperature range available for a standard rheometer (-150 C to 1000 C), proof of performance, i.e. as results of temperature gradient testing, and the availability of certified temperature sensors which allow softwarecontrolled automatic temperature calibration in a broad temperature range. Ball Measuring System The ball measuring system is used to measure the flow properties of samples with very large particles such as building materials and foods. The measuring principle is an excentrically rotating sphere which is available in various diameters. Due to the outstanding motor control of the Physica MCR series, it is possible to record a full flow and viscosity curve in one revolution. Application Note _02 Page 17 of 20

18 Starch Cell C-ETD 160/ST The starch cell is an electrically heated cylinder system with water cooling to provide the high heating and cooling rates required for the measurement of the starch gelation process. The open system can be used up to a temperature of 95 ºC. For high temperature applications, the starch cell can be equipped with a pressure cell, e.g. to simulate the sterilization process of foods. The temperature range of the starch cell is 0 ºC to 160 ºC. A special stirrer is used to prevent sedimentation of the starch before gelation. The analysis in the RheoPlus software calculates values such as peak viscosity, gelation temperature and final viscosity. Peltier Temperature Device P-PTD 200 Lower plate system with Peltier temperature control High heating and cooling rates Temperature range suitable for many applications Precise temperature control Lower plate with a coating with high thermal conductivity for short equilibrium times H-PTD 200 Peltier-controlled hood (US-Patent 6,571,610) To be used in combination with the P-PTD 200 to prevent temperature gradients within the sample Recommended for temperatures more than 10 ºC above or below ambient Can be flushed with inert gas Prevents ice formation at low temperatures Optional Evaporation Blocker to minimize evaporation Application Note _02 Page 18 of 20

19 Cylinder Peltier Temperature Device C-PTD200 Concentric cylinder system with Peltier temperature control High heating and cooling rates Temperature range suitable for many applications No vertical temperature gradients in the sample due to the patented thermal transfer system (US Patent 6,24,770) Application Note _02 Page 19 of 20

20 Available measuring systems and accessories Standard measuring geometries Meas. ø Angle Cone truncation system PP25 25 mm PP50 50 mm CP mm 1 50 μm CP mm μm Special measuring geometries In addition to the standard geometries, Anton Paar also provides special geometries with various diameters, cone angles and cone truncation. Surfaces The standard measuring systems have a polished high quality surface. Measuring systems with various coatings, a profiled and sandblasted surface are available. Standard measuring geometries Cylinder systems ø cup ø bob CC mm mm Other geometries are available on request Also available: cylinder systems with various dimensions, double gap systems, surfaces (PTFE-coated, sandblasted,...) and profiles (vertical profile, helix profile,...). Materials The standard measuring cups are made of aluminum. The surfaces are hard-anodized and therefore extremely resistant to corrosion and mechanical forces. They are available in stainless steel as well. Both cups and bobs made of special materials (titanium, Hastelloy and others) are available on request. Materials The standard material is stainless steel (303 according to AISI).Titanium, Invar, Hastelloy and other special materials are available on request. Application Note _02 Page 20 of 20