Dynamic mechanical properties of food
Testing the non-destructive dynamic mechanical properties can be performed with stress and/or strain controlled rheometers to characterize a material's viscoelastic properties. These properties, which define a material's viscous (fluid-like) and elastic (solid-like) response to deformation, are often used to instrumentally measure organoleptic properties of materials. Food companies often look at measurement of dynamic mechanical properties to complement or replace more time consuming taste panels.
Various rheological additives are used in the food and beverage industry to impart texture and to influence dynamic mechanical properties such as mouth feel, or the tendency of a material to stick to the roof of the mouth (an elastic property). Whether it is products like tomato ketchup, soups, synthetic drinks, whipped creams, etc. chemical additives are often used to modify the dynamic mechanical properties and the resulting consumer perceptions.
Brochures:
Application Notes:
Application Note: Download free book "Rheological Methods in Food Process Engineering" Full edition provided with kind permission of James F. Steffe
Application Note: Characterizing gelation time and strength A Bohlin rheometer can be used to accurately quantify the gelation times of foods. The formulation can be optimized with regard to gelant dosing in the minimum of time.
Application Note: Determining stand up characteristics of caramel and chocolate The Bohlin rheometer can be used to assess the dynamic mechanical properties of foods very simply, making it an ideal tool to assist formulation without the need for extensive production trials.
Application Note: Overcoming slippage when characterizing concentrated suspensions Slippage can occur in fibrous suspensions, concentrated particulate suspensions and materials susceptible to shear induced melting.
Application Note: Determination of butter spreadability and fat components The spreadability of butter and margarine products can be easily assessed by measurement of its dynamic mechanical properties at different temperatures.
Application Note: A note on slippage during rheological measurements on concentrated dispersions Measurements at low shear rates or shear stresses can reveal much information on both the application behavior and the microstructure of materials.
Application Note: The rheological properties of mayonnaise The dynamic mechanical properties of materials such as mayonnaise give an indication of this reproducibility and can be correlated with, for example, storage stability, ease of pumping and sensory perception (i.e. mouthfeel).
Application Note: The use of modern rheometers in characterizing the behavior of foods Many foodstuffs are concentrated dispersions of solid particles in a liquid medium (e.g. tomato ketchup), or liquid droplets in a liquid medium (e.g. mayonnaise). The dynamic mechanical properties of these products has to be very reproducible in order to satisfy customer needs.
Application Note: Rheological evaluation of margarine spreads The dynamic mechanical properties of margarine spreads are important both with regard to 'usability', i.e. how easily they spread and aesthetically, whether there is an unacceptably visible phase separation.
Application Note: Formulating soup mixtures to resist settling of solid components The yield stress can be used to calculate whether a sample is likely to settle in-situ, or whether it will be difficult to start pumping or stirring. Good rheological product design will dramatically enhance processing and end use.
Application Note: Compilation of all the above food related application notes Compilation of Bohlin application notes for the Food industry
Application Note: Characterizing ice cream using a rheometer The dynamic mechanical properties of ice cream can be critical for good customer perception and acceptance of the product. The ease of scooping the product when it is removed from the freezer, the mouth feel and the creaminess are three aspects discussed in this application note.
Web seminars available for play back:
Web seminar: Interpretation of the Viscoelastic Spectrum - Part 1 - 13th Feb 2006 This first seminar will discuss the universal viscoelastic spectrum. The spectrum can be divided into three regions. In general, the significance of these regions gives valuable information in terms of the size of a flow unit, molecular interactions, and identifies small molecular segments within the flow units.
Web seminar: Interpretation of the Viscoelastic Spectrum - Part 2 - 27th Mar 2006 This part discusses the temperature- frequency dependence of the material functions of a polymer melt. What can be learned about the structure, molecular weight, molecular weight distribution, long and short chain branching, entanglements, etc. What are some of the reasons a UVS can not be measured.
Web seminar: Interpretation of the Viscoelastic Spectrum - Part 3 - 11th April 2006 This part discusses the relationships between the frequency dependence of the material functions in terms of the dispersed phase. The structure-rheology relationships for data that exists within the three zones of the viscoelastic spectrum. If the temperature dependence of the material can be measured what additional information can be obtained about structure. What are some of the reason a UVS can or can not be determined on liquid dispersions?
Web Seminar: Instabilities in Viscoelastic Flows: Destabilizing Forces, Stability Criteria, and Implications for Rheometry and Processing - 14th Feb 2006 Significant progress has been made over the past 15 years in understanding instabilities in viscoelastic flows, especially rheometric flows such as flow between concentric cylinders and torsional flow between a cone and plate or between parallel plates. We review the criteria for determining when these flows will become unstable due to fluid elasticity (in the absence of fluid inertia), discuss the generalization of these criteria to more complex processing flows, and consider how fluid inertia and thermal sensitivity may also affect flow stability. These stability criteria are important in avoiding rheometric artifacts and in determining materials processing windows.
Web Seminar: Measuring and interpreting the yield stress of colloidal dispersions - 17th Jan 2006 Many concentrated dispersions and emulsions show a yield stress, i.e. they behave as soft solids below some critical value of the applied stress but flow when the critical stress, the yield stress, is exceeded. The yield stress is an important property in many practical applications. For example it is essential that products like tomato paste, toothpaste and skin cream have a yield stress so that gravity does not cause them to flow. For a dispersion or emulsion to show a yield stress the particulate phase has to be able to support a certain level of stress, which in turn means that the particles have to interact with each other to sufficient degree. Either the particles or droplets have to be close-packed, or they have to repel each other strongly at a distance, or they have to be aggregated such that the particles form a continuous network. In the case of such "particulate gels", there is evidence that the yield stress is proportional to the inter-particle contact force. There are various protocols that may be used to measure the shear yield stresses using a rheometer - these will be discussed, as will the nature of the flow above the yield stress.
Web Seminar: Viscometry: Recognizing Measurement Artifacts - 17th June 2005 How do you know the viscometry measurements you are making are real? Does the data include measurement artifacts that you are not aware of? This seminar will explain how to recognize invalid data, and give advice on how to perform correct measurements. In particular, the measurement of low viscosity fluids, sample slippage, the effects of thixotropy and high shear rate testing are discussed.
Web Seminar: How to Establish Automated Test and Analysis Procedures Using the Bohlin Rheometer Software - 10th May 2005 The latest version of control and analysis software (version 6.40) for the range of Malvern Bohlin rheometers incorporates many significant new features, including more flexible data analysis set-up and automation. A new Template Wizard provides easy set-up and storage of analysis routines, and operators can add multiple analyses to the menus for re-use. This seminar will explain new software features whilst leading the viewer through the Template Wizard and model fitting capabilities.
