Recent Changes

Friday, November 21

  1. msg New wiki classroom message posted New wiki classroom This is an update to wikispaces.
    New wiki classroom
    This is an update to wikispaces.
    8:37 pm
  2. msg Introductions message posted Introductions Use the news feed to introduce yourself, start discussions, and manage your Classroom.
    Introductions
    Use the news feed to introduce yourself, start discussions, and manage your Classroom.
    8:34 pm

Monday, July 15

Thursday, October 25

  1. page LECTURE SUMMARY edited ... Oopss…are you following me up to this point? OK, I know, this is slightly more complicated….ju…
    ...
    Oopss…are you following me up to this point? OK, I know, this is slightly more complicated….just slightly. As usual, as you read more and more, you will understand more. Measurement of viscoelastic properties of food materials can be considered an advanced rheological method (and an expensive one, too…a rheometer can cost at least quarter a million, or more!!). It is meant for R&D rather than for routine QC/QA. But this may change in future, when the rheometer is more affordable, perhaps.
    {summary-objectives.gif}
    ...
    Food Texture Measurement**Measurement
    Texture is such an important physical attribute of food. In fact, when assessing the overall organoleptic quality of a food, texture must be considered together with flavor and appearance. Given the importance of texture as one of the quality attribute, I take the challenge again to put together this lecture online.
    Lecture outline
    ...
    Food Testing Overview – an overview of various probes/fixtures for different types of testings and food samples (also from Instron).
    Standard Testing Procedures for Baked Products -- This is a collection of procedures for testing the texture of common bakery products with the TA.XT2 Texture Analyzer. These procedures are used at the American Institute of Baking's Experimental Bakery Lab in Manhattan, Kansas.
    ...
    texture evaluation.
    Evaluating gel strength -- In the designing of a new product, once a gel system has been selected the next step is to test a large number of samples to obtain data points which can, in turn, be used to develop specifications for the gel system. Both the strength of the gel and how it affects the final product should be measured. This article, from Food Product Design website, describes the common methods (mainly empirical) to test gel strength. *
    The sensory perception of texture and mouthfeel -- Texture and mouthfeel are fundamental sensory properties of foods and beverages. The formulation of specific textures and mouthfeels has been very challenging for product developers and manufacturers. This is due to the limited understanding of the physiology of texture and mouthfeel perception, and of consumer preferences for tactile and kinesthetic characteristics. This article provides an update on the latest advances in the understanding of oral texture and mouthfeel perception. Download the article from the link below. *
    (view changes)
    7:54 am
  2. page LECTURE SUMMARY edited ... The scaling of time in rheology is achieved by means of the ‘Deborah number’, De. This is defi…
    ...
    The scaling of time in rheology is achieved by means of the ‘Deborah number’, De. This is defined as De = t/T, where T is a characteristic time of the material (unique for each material) and T is a characteristic time of the deformation process. High De (De >> 1) corresponds to solid-like behavior and low De (De << 1) to liquid-like behavior. A material can, therefore, appear solid-like either because it has a very long t or because the deformation process we are using to study it is very fast. In my example above, diving slowly into the pool involve slow deformation of the water (long T), therefore resulting in small De (water behave like a liquid). Diving from the top of Penang bridge, however, involve fast deformation of the water (very small T), because you hit the water so fast. In this case, De value is high and the water behaves like a hard solid (and did you know that water, in the form of high pressure water jet, is used as a cutting tool -- cutting foods, glass, and even metal!). [note: t in both cases is constant].
    Viscoelastic properties are measured by using a rheometer. The test is known as small-amplitude oscillatory tests (SAOS). SAOS measurements enable quantification of elastic and viscous components of a material simultaneously. Basically, a small oscillation (sinusoidal) stress (or strain) is applied on the sample and the respective deformation and the phase relationship between viscous and elastic components is measured. This is non-destructive test, i.e., the structure of the material is not destroyed during the test. The stress and the strain is very small, just sufficient to measure the viscoelastic properties of the material. Usually, the stress or the strain applied is within the so-called “linear viscoelastic region”.
    ...
    and loss modulus**,modulus, G” (pronounced
    Another parameter from SAOS test is phase angle. Viscoelastic materials have a phase angle between 0 and 90°. A material with a phase angle approaching 90° will be dominated by viscous behavior; likewise, a sample with a phase angle closer to 0° will behave more elastically.
    Oopss…are you following me up to this point? OK, I know, this is slightly more complicated….just slightly. As usual, as you read more and more, you will understand more. Measurement of viscoelastic properties of food materials can be considered an advanced rheological method (and an expensive one, too…a rheometer can cost at least quarter a million, or more!!). It is meant for R&D rather than for routine QC/QA. But this may change in future, when the rheometer is more affordable, perhaps.
    {summary-objectives.gif}
    LECTURE 8 - Food Texture Measurement**
    Texture is such an important physical attribute of food. In fact, when assessing the overall organoleptic quality of a food, texture must be considered together with flavor and appearance. Given the importance of texture as one of the quality attribute, I take the challenge again to put together this lecture online.
    Lecture outline
    Importance of texture in food quality perception by consumers
    Advantages of instrumental texture analysis
    Definition of food texture
    Types of instrumental texture test
    Instrumental Texture Profile Analysis
    Examples of common empirical test
    As I have explained in the class, a large determinant of the quality of a food is its texture , i.e., what sensation does the food impart to the nerves and muscles in the mouth as the food is bitten, chewed and swallowed. It is this critical importance of food texture to optimal food quality that warrants studies of food texture and an appropriate method to measure the textural attributes of foods. How do we define the term “texture” in the context of food quality? Briefly, texture is a sensory attribute, perceived by the senses of touch, sight and hearing. Well, in that case, the only direct method of measuring texture is by means of one or more of these senses, agree? Hmm…actually sensory evaluation by using trained sensory panels is one of the methods that can be used to study food texture. Sensory evaluation of texture is not covered in this lecture. Here, we will discuss about instrumental method of measuring texture.
    A more general definition of texture is that “it is the composite of all physical characteristics sensed by the feeling of touch that are related to deformation under an applied force and are measured objectively in terms of force, distance, and time” (Bourne, 1982). This concept is the basis for most instrumental method to study texture. Compared with sensory panels, which are costly and time consuming, instrumental methods can save time, reduce costs, and provide more consistent, objective results. However, since it is difficult for machines to imitate biting and chewing, the need for sensory panels as a correlative test method will continue for the foreseeable future.
    A common principle used in instrumental texture measurement is to cause a probe to come into contact with the sample of food. The sample is deformed and the extent of the deformation and the resistance offered by the sample is noted and used as an index of the texture of the food. Various types of instruments or devices have been developed and generally, the instrument can fall into one of three categories: empirical methods, imitative methods, and fundamental methods. All three of these approaches have their merits and specific applications. Which one is chosen should depend on the problem being faced and the questions being asked. Two of the most popular machines for texture testing of food are Instron Universal Testing Machine and Texture Analyzer (Stable Micro System).
    When we talk about instrumental food texture measurement, Texture Profile Analysis (TPA) is perhaps one of the most popular one (TPA is classified as an imitative test). I’m not about to give a history lesson here, but….hmmm…perhaps very briefly. The scientists in General Foods Corporation (USA) were the forerunner in this area. It all began with the introduction of General Foods Texturometer, designed to simulate mastication by means of a mechanical chewing device. The instrument operates by partially compressing the sample twice (imitating the first two bites taken of a food – you don’t just swallow the food, right?). Several parameters are obtained from the resulting force-time plots (hardness, fracturability, cohesiveness, and chewiness), and these have been found to correlate highly with sensory ratings. The values of the various parameters make up what is known now as instrumental texture profile analysis (and the rest is history…).
    Finally, in this lecture I gave a few examples of typical empirical tests based on compression, puncture/penetration, cutting & shearing, extrusion, etc. In the online lecture, I explained these tests briefly with some examples of results from actual food sample. Check out the additional resources listed below to learn more about food texture measurements.
    ADDITIONAL READINGS
    The following articles are strongly recommended if you want to learn more about Texture Profile Analysis:
    Bourne, M.C. (1978). Texture profile analysis. Food Technology, 32(7), 62-66.
    Breene,W.M. (1975). Application of texture profile analysis to instrumental food texture evaluation. Journal of Texture Studies, 6, 53-82.
    Pons, M. & Fiszman, S.M. (1996). Instrumental texture profile analysis with particular reference to gelled system. Journal of Texture Studies, 27, 597-624.
    Szczesniak, A.S. (1963). Classification of textural characteristics. Journal of Food Science, 28, 385-389.
    Here are some interesting resources I found from internet on the subject of food texture and associated topics. Enjoy!
    Practical definitions of standard TPA terms – self-explanatory – also, you will find a list of references on food texture. In addition, if you are using TA.XT2 Texture Analyzer (Stable Micro System) to do your TPA, procedures to calculate the parameters are also given. *
    Benefits of Food Texture Analysis – this article is from Instron website. You may also view or download some of the literatures provided for further study. *
    Food Testing Overview – an overview of various probes/fixtures for different types of testings and food samples (also from Instron).
    Standard Testing Procedures for Baked Products -- This is a collection of procedures for testing the texture of common bakery products with the TA.XT2 Texture Analyzer. These procedures are used at the American Institute of Baking's Experimental Bakery Lab in Manhattan, Kansas.
    Making sensory tests instrumental -- Correlating sensory data with instrumental testing helps designers optimize the eating pleasure to make products more successful. This article, from Food Product Design website, explains the various facets of sensory and instrumental texture evaluation.
    Evaluating gel strength -- In the designing of a new product, once a gel system has been selected the next step is to test a large number of samples to obtain data points which can, in turn, be used to develop specifications for the gel system. Both the strength of the gel and how it affects the final product should be measured. This article, from Food Product Design website, describes the common methods (mainly empirical) to test gel strength. *
    The sensory perception of texture and mouthfeel -- Texture and mouthfeel are fundamental sensory properties of foods and beverages. The formulation of specific textures and mouthfeels has been very challenging for product developers and manufacturers. This is due to the limited understanding of the physiology of texture and mouthfeel perception, and of consumer preferences for tactile and kinesthetic characteristics. This article provides an update on the latest advances in the understanding of oral texture and mouthfeel perception. Download the article from the link below. *

    (view changes)
    7:52 am
  3. page LECTURE SUMMARY edited ... What is Yield Stress and Why Does it Matter? -- The presence of a significant yield stress wil…
    ...
    What is Yield Stress and Why Does it Matter? -- The presence of a significant yield stress will impart various qualities to a fluid that may or may not be desirable. Read more about this important phenomenon.
    I mentioned about inline viscosity measurement above and also in my handout. If you are interested to learn more about the applications of this in-line viscometers in actual food processing, here are two examples: (i) chocolate processing (ii) tomato processing. *
    ...
    the food products**products
    Making Use Of Models: The Power Law (or Ostwald) Rheological Model - A brief article explaining the application of the Power law model.
    {summary-objectives.gif}
    LECTURE 7
    Lecture outline
    · Definition of viscoelasticity
    · Definition of Deborah number
    · Viscoelastic parameters
    Before I summarise this lecture, let me revise some of the important points we have covered so far. Basically, I have defined basic terms such as stress and strain, shear stress and shear rates, etc. In addition, I talked about flow behavior of fluids, classifications of flow behavior, and the measurements and interpretation of flow curves. One of the important parameter we have discussed is viscosity. It should be clear to you now that we have been discussing about liquid foods, or foods that appear like a liquid – or a material that can flow. So, for a liquid, we measure viscosity. We know, however, some foods are solid, such as hard cheese, hard candy, or even an ice cube. What about foods such as jelly, bread, cakes, dough, noodle, tofu, soft cheese, etc.? These are materials which have some solid-like and some liquid-like properties – or we call them “viscoelastic materials”.
    Viscoelastic materials are both elastic (having solid-like) and viscous (having liquid-like). Their rheological properties depend on the relative degrees of elasticity and viscosity and are also dependent on the time-scale of the deformation. Now, you have to understand the concept of “time-scale of deformation”. In the lecture, I gave water as an example –- water can behave like a solid or like a liquid –- depending on the time-scale of deformation. Imagine you are sitting next to the swimming pool and just dive in slowly….aahh…nice ha! Now, try to dive from the top of the Penang bridge (please don’t do this!), the water now will feel like a hard rock solid when you hit it!! Why? In the first instance, the time-scale of deformation is slow (long – equivalent to low frequency), and in the second instance the time-scale of deformation is fast (short – equivalent to high frequency).
    The scaling of time in rheology is achieved by means of the ‘Deborah number’, De. This is defined as De = t/T, where T is a characteristic time of the material (unique for each material) and T is a characteristic time of the deformation process. High De (De >> 1) corresponds to solid-like behavior and low De (De << 1) to liquid-like behavior. A material can, therefore, appear solid-like either because it has a very long t or because the deformation process we are using to study it is very fast. In my example above, diving slowly into the pool involve slow deformation of the water (long T), therefore resulting in small De (water behave like a liquid). Diving from the top of Penang bridge, however, involve fast deformation of the water (very small T), because you hit the water so fast. In this case, De value is high and the water behaves like a hard solid (and did you know that water, in the form of high pressure water jet, is used as a cutting tool -- cutting foods, glass, and even metal!). [note: t in both cases is constant].
    Viscoelastic properties are measured by using a rheometer. The test is known as small-amplitude oscillatory tests (SAOS). SAOS measurements enable quantification of elastic and viscous components of a material simultaneously. Basically, a small oscillation (sinusoidal) stress (or strain) is applied on the sample and the respective deformation and the phase relationship between viscous and elastic components is measured. This is non-destructive test, i.e., the structure of the material is not destroyed during the test. The stress and the strain is very small, just sufficient to measure the viscoelastic properties of the material. Usually, the stress or the strain applied is within the so-called “linear viscoelastic region”.
    SAOS measurements allow determination of viscoelastic parameters: storage modulus, G’ (pronounced G-prime) and loss modulus**, G” (pronounced G-double prime). G’ is simply a measure of the elastic component and G” is a measure of the viscous component of the material. In other words, G’ and G” are parameters representing the relative degrees of elastic and viscous behavior of viscoelastic materials. Therefore, a sample with a larger G’ component will behave elastically (solid-like), while a material with a higher G” will be more viscous (liquid-like).
    Another parameter from SAOS test is phase angle. Viscoelastic materials have a phase angle between 0 and 90°. A material with a phase angle approaching 90° will be dominated by viscous behavior; likewise, a sample with a phase angle closer to 0° will behave more elastically.
    Oopss…are you following me up to this point? OK, I know, this is slightly more complicated….just slightly. As usual, as you read more and more, you will understand more. Measurement of viscoelastic properties of food materials can be considered an advanced rheological method (and an expensive one, too…a rheometer can cost at least quarter a million, or more!!). It is meant for R&D rather than for routine QC/QA. But this may change in future, when the rheometer is more affordable, perhaps.

    (view changes)
    7:42 am

Sunday, October 21

  1. page RESOURCES edited ... Texture Analyzers provide food companies with a new means of ensuring consistent quality in fo…
    ...
    Texture Analyzers provide food companies with a new means of ensuring consistent quality in food products. Be sure to join us for an
    educational discussion on this important test methodology known as "Texture Analysis"
    EMULSION & FOAM
    Difference Between Surface Tension and Interfacial Tension
    Measurement of Surface Tension

    CRYSTALLIZATION
    A video clip demonstrating crystallization process.
    (view changes)
    3:53 am

Friday, October 19

Wednesday, October 17

  1. page RESOURCES edited ... to approach some difficult viscosity and texture questions posed by Food Viscosity site member…
    ...
    to approach some difficult viscosity and texture questions posed by Food Viscosity site members.
    The Basics of How to Do Texture Analysis
    {http://www.viscosityjournal.com/forum/The-Basics-of-How-to-Do-Texture-Analysis/ross-clark.jpg} Ross Clark InterviewRoss Clark
    Is mouth feel important for how customers evaluate your products? Are you new to texture
    analysis and what you can do with instruments that measure this property? Do you want a
    quick education in less than an hour?
    Fundamental Approaches to the Measurement of Food Texture
    {http://www.viscosityjournal.com/forum/Fundamental-Approaches-to-the-Measurement-of-Food-Texture/andrew-rosenthal.jpg} Fundamental Approaches to the Measurement of Food TextureDr.Dr. Andrew Rosenthal
    Did you ever wonder how food companies evaluate "chewiness" of meat, the "snap" of a biscuit or cracker, the "springiness" of bread? Dr Andrew Rosenthal from Oxford Brookes University in
    the UK will enlighten listeners on the subject of "Texture Analysis", the science of conducting
    (view changes)
    7:38 am

More