Texture viscosity measurements

Because the quality and health aspects of foods cannot be measured by a single index, it necessarily follows that the subject of control methods in the canned food industry is very broad, and includes chemical, physical, organoleptic, and bacteriological tests, only the first of which is discussed here. The measurement of color, odor, optical clarity, texture, viscosity, and chemical composition has been used to evaluate canned foods, but in many cases the methods that are applicable to one product are either not applicable to another, or can be used only after considerable modification. 

Many studies have been devoted to the relationship between measured viscosity measured instrumentally and perceived fluid texture. In many cases, the systems... 

The inherent viscosity measurements of the polymers were made at 40°C using a Ubbelohde viscometer. Solutions of 0.5 g/dl in TCE were used for the measurements. The thermal transitions of the polymers were measured using a Perkin-Elmer DSC-II at the heating and cooling rates of 10°C/min under a nitrogen atmosphere. The peak maximum positions were taken as those of the transition points. Optical textures of the polymer melts were observed on the hot-stage (Mettler FP-2) of a polarizing microscope (Leitz, Ortholux). 

An 18-20% hydrolyzed polyacrylamide was used in all tests. In all 300 ppm polymer solutions a radioactive C14 tagged polyacrylamide was used. At higher polymer concentrations (600 and 1200 ppm) a commercial product called Calgon Polymer 454 was added to the base 300 ppm radioactive solution. A special study was conducted to develop a radioactive polymer which has properties identical to the commercial product. Several experiments were run on both polymers to check these properties such as, viscosity measurements, friction reduction flow tests, and flow tests in porous media. These special studies showed that performance of the radioactive product was equivalent to that of the commercial product. A typical result of these tests is shown in Figure 1. The small differences in the polymer flow resistance factors are due to small differences in the textures of different sandpacks, rather than to differences in the chemical structures of the polymers. Friction reduction, viscosity, and retention experiments showed even closer agreements between properties of the radioactive and commercial product. 

Acoustic Wave Sensors. Another emerging physical transduction technique involves the use of acoustic waves to detect the accumulation of species in or on a chemically sensitive film. This technique originated with the use of quartz resonators excited into thickness-shear resonance to monitor vacuum deposition of metals (11). The device is operated in an oscillator configuration. Changes in resonant frequency are simply related to the areal mass density accumulated on the crystal face. These sensors, often referred to as quartz crystal microbalances (QCMs), have been coated with chemically sensitive films to produce gas and vapor detectors (12), and have been operated in solution as Hquid-phase microbalances (13). A dual QCM that has one smooth surface and one textured surface can be used to measure both the density and viscosity of many Hquids in real time (14). 

Chapter HI relates to measurement of flow properties of foods that are primarily fluid in nature, unithi.i surveys the nature of viscosity and its relationship to foods. An overview of the various flow behaviors found in different fluid foods is presented. The concept of non-Newtonian foods is developed, along with methods for measurement of the complete flow curve. The quantitative or fundamental measurement of apparent shear viscosity of fluid foods with rotational viscometers or rheometers is described, unithi.2 describes two protocols for the measurement of non-Newtonian fluids. The first is for time-independent fluids, and the second is for time-dependent fluids. Both protocols use rotational rheometers, unit hi.3 describes a protocol for simple Newtonian fluids, which include aqueous solutions or oils. As rotational rheometers are new and expensive, many evaluations of fluid foods have been made with empirical methods. Such methods yield data that are not fundamental but are useful in comparing variations in consistency or texture of a food product, unit hi.4 describes a popular empirical method, the Bostwick Consistometer, which has been used to measure the consistency of tomato paste. It is a well-known method in the food industry and has also been used to evaluate other fruit pastes and juices as well. 

Bourne, M.C. 1982. Food Texture and Viscosity Concept and Measurement. Academic Press, New York. 

As all cyclic polyamines presented up to now were assigned to be columnar hexagonal based on their high viscosity, the typical texture or X-ray measurements devoid of the (110) or any higher reflection, Heiney and Smith [109] reinvestigated Lehn s [5] polyamine 1. Scattering experiments were carried out using laboratory... 

Figure 8-22 Rate of Shear Dependence of the Viscosity of Two Newtonian Fluids. Source From R Sherman, Structure and Textural Properties of Foods, in Texture Measurement of Foods, A. Kramer and A.S. Szczesniak, eds., 1973, D. Reidel Publishing Co.

McCarthy, K. L. and Seymour, J. D. 1993. A AmdamenCal approach for the relationship between the Bostwick measurement and Newtonian fluid viscosity. J. Texture Stud. 24(1) 1-10. 

Sohd fat index, melting points, penetration, and viscosity are normally used to measure factors affecting consistency and texture (5, 35, 112, 113). Color is most frequently measured by the Lovibond procedure (5). 

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