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Test Cells for Objective Textural Measurements1
Test Cells for Objective Textural Measurements! Peter W. Voisey Engineering Research Service Research Branch Canada Dea:>artment of Agriculture Ottawa
Abstract New test cells for estimating textural properties of a range of food products by objective techniques are described. The performance of these cells is demonstrated in relation to the Kramer shear and a back extrusion cell. The new cells offer the advantage of simple designs which can be manufactured inexpensively. Thus, if any wear or damage occurs in experimental work and in particular during routine quality control the cells or critical components can be replaced economically. The cells subject the products to compression shear and extrusion which are the processes used in the popular Kramer shear cell. Initial work has shown that the results from the new cells are well correlated with Kramer shear data. Thus for some purposes the new cells can be used to advantage.
Resume On decrit des nouvelles cellules d'essai pour l'evaluation des proprietes de texture d'une variete de produits alimentaires par des techniques objectives. La performance de ces cellules est comparee it celIe de la presse it cisaillement Kramer et it une cellule it extrusion. Les nouvelles cellules ont l'avantage de conceptions simples qui peuvent etre realisees it bon marche. Ainsi, en cas d'usure ou d'endammagement au cours de travaux experimentaux ou lors du controle de qualite routin;er les cellules ou leurs parties essentielles peuvent etre remplacees it bas prix. Les produits sont soumis dans les cellules it un cisailJement et it une extrusion sous pression tout comme pour la populaire presse it cisail1ement Kramer. Les travaux du debut ont indique que les rpsultats obtenus avec les nouvelles cellules ont une bonne correlation avec ceux de la presse Kramer.
Introduction Currently different approaches are used in the study of the textural characteristics of foods. The rheological and mechanical properties are being investigated to examine the relationships between these fundamental characteristics and consumer reactions. Instruments have been developed to imitate the action of the human mouth while others are empirical in concept where the food is deformed in some arbitrarily selected but practical and convenient way to measure the products reaction to applied force. The empirical type test is the most widely used in both research, product development and quality control. Test specimens are compressed, stretched, sheared or extruded in single or combined operations and provided the force-deformation relationships are correlated with sensory analysis they can be used routinely as an objective estimate of texture. Common requirements to all empirical measurements of texture are a mechanism to deform the product, instruments to record the force and deformation during the test and finally a test cell to contain or hold the sample while it is being deformed. There are a wide range of deformation mechanisms available 1. Contribution No. 200 from Engineering Research Service.
93
such as the universal test machine (Bourne et. al. 1966; Voisey et. al. 1967) and the Kramer shear press (Food Technology Corp., Reston, Virginia) . Different apparatus ranging from simple mechanical devices to sophisticated electronic systems have been use~ to record force and deformation and have been descrIbed elsewhere. Any deformation mechanism and recording apparatus with the required ranges, accuracy and control of test conditions is suitable for texture measurements' thus the selection of the test cell becoines the' most critical decision in assembling a texture measuring system. The most widely used test cell is the multiblade Kramer shear cell (Model CS-1 Food Technology Corp.) . This cell together with a hydraulically actuated deforming mechanism "The Kramer Shear Press" was introduced by Kramer et. al. (1951 a, b) and Kramer (1957). The test cell is a square box with a grid in the bottom and 10 parallel blades which are forced into the box and through the grid (Fig. 1). During this process the product is compressed, sheared and extruded. The cell has the practical advantage that a wide variety of products can be placed in the box for testing. The cell and shear press have become "a basic tool for the food technologist" (Kramer, 1961; Anon. 1968) and its versatility is indicated by the range of products tested. These have included fruits such as apricots (I.. uh and Dastur 1966), cherries (Franks ct. al. 1969), grapefruit segments (Mannheim and Bakal 1968), peaches (Kanujoss and Luh, 1967) and strawberries (Lovell and Flick 1966). Vegetables have also been tested including Lima beans (Kramer and Hart 1954; Neuman et. al., 1960; Binder and Rockland 1964) ; green beans (Fox and Kramer, 1966) and peas (Kramer and Aamlid, 1953; Angel et. al. 1965) . In recent years meat has been tested extensively with the multiblade Kramer shear cell, such as pork (Thomas ct. al. 1966; Tuomy et. al. 1966; Tuomy and Helmer 1967) ; beef (Gilpin et. al. 1966; Wangen and Skala 1968); turkey (Stadelman et. al. 1966; Marion and Goodman 1967; Tuomy ct. al. 1969) and meat products (Baker ct. al. 1969). The results from the Kramer Shear Cell have been compared with other test techniques such as the Warner-Bratzler shear test for meat tenderness (Pangborn ct. al. 1965; Sharrah ct. al. 1965 a, b; Palmer ct. al. 1965). During its development and subsequent widespread use several other test cells have been manufactured for use with the shear press for specific food products. Compression attachments have been used to test unrestrained samples of products such as onion bulbs (Ang et. al. 1960), cakes (Funk ct. al. 1965; Can. Inst. Food Techno!. J. Vo!. 3, No.3, 1970
Brown and Cabik 1967) and butter cakes (Gruber and Cabik 1966). A series of attachments were described by Hartman et. al. (1963) including puncture probes, a "\Varner-Bratzler meat shear fixture, a mechanism to similate the action of teeth, clamps for testing materials in tension and a grate that was forced into a. box containing the product. Several of these attachments were demonstrated with canned tomatoes, snap beans and peas (Ang et. al. 1963). A tensile testing attachment has also been described for testing cakes (Funk et. al. 1965). A single blade cell (Model CA-1 Food Technology Corp.) is also available and has been used to test asparagus (Werner et. al. 1963), and strawberries (Johnson et. al. 1965). A test cell based on the design of Christel (1938) for subjecting chicken breast muscle to multipl-e punctures has also been described by Peterson and Lilyblade (1969). There are thus a wide range of test cells that have been used with the shear press which is currently available from the manufacturer with seven test cells: standard multiblade shear cell (CS-1) ; thin multiblade shear cell (CS-2); single blade shear cell (CA-1); meat shear cell (CW-1); compression test set (TC-1); succulometer cell (CR-1) and a universal cell (CE-1). However, the most popular cell has remained the standard multiblade shear cell because it can handle a wide range of products. It should be noted that all the above cells can be used in any deformation mechanism providing it has sufficient load capacity. Universal test machines based on an electric motor driving a screw (Voisey et. al. 1967) overcome the problem of selecting and maintaining constant deformation speeds that occur with hydraulic systems such as used in the Kramer Shear Press. A different approach to the design of a texture testing cell was suggested by Bartman et. al. (1963) where the product was compressed into a square box by a loosely fitting plunger until it was extruded through the gap between the plunger and the sides of the box. This principle was tested by Ang et. al. (1963)
Fig. 1 Kramer muItibIade shear cell. J. lost. Can. Technol. Aliment. Vol. 3. No 3. 1970
with tomatoes, beans and peas. Bourne (1968) changed the design to use a circular cylinder and piston to investigate the extrusion principal to test peas. This technique has been called the "back extrusion cell" (Kramer and Hawbecker 1966). If it is accepted that the texture of food can be measured objectively by subjecting the product to compression shear and extrusion then the design requirements for a test cell can be formulated in general terms as follows. 1. The cell should be simple in design so that it can be manufactured economically. 2. The cell must be rugged and if any wear or damage occurs the worn parts should be easy to replace. 3. The Lell should conveniently accommodate a wide range of products and be available in the range of sizes to handle different sample sizes. 4. The cell should be easy to clean after testing a sample to maintain hygenic conditions and reduce operating labour to a minimum. 5. During deformation the food should be subjected to compression, shearing and extrusion in separate and distinct phases is possible so that these can be evaluated individually on the force-deformation records. 6. Since the texture of many foods depends on temperature it should also be possible to control the cell temperature. The purpose of the work here is to discuss the design of the multiblade Kramer shear cell, the back extrusion cell and introduce three new cell designs. Operating techniques and typical results for a range of products are shown to demonstrate the advantages and disadvantages of each cell.
Experimental Methods and Apparatus The tests were conducted in a universal compression machine (Model TM-M Instron Canada Ltd., Clarkson, Ontario). To record the force a load cell (:Model FLIU-3SG Strainsert Ltd., Bryn Mawr, Philadelphia) was attached to the moving cross head of the machine. This load cell has a capacity of 454 Kg in tension or compression. The moving component of each test cell was mounted on the load cell and the fixed component attached rigidly to the base of the machine. The load cell was rigid and its deflection under load could be ignored in determining deformation from the relationships between crosshead and recorder chart speeds. A compression speed of 10 cm/min was used for each cell tested. This was an arbitrary selection based on the fact that the rate of rise of force did not exceed the response time of the recorder pen (0.25 sec for full scale). A constant chart speed of 10/min min was used for all tests. The load cell was calibrated using a proving ring and the calibration range selected for each cell and product tested to achieve an adequate recorder pen deflection. Using these techniques it was assumed that force and deformation were recorded with an accuracy of -+- 0.5%. An integrator was connected in parallel with the recorder to record the 94
For testing, the products were drained except in the case of baked beans and cream style corn where this was not practical. The sample sizes used were arbitrarily selected as either the contents of the can or the quantity required to fill the various test cells depending on the product and the relative volumes of the can and test cell. Back Extrusion OeU The dimensions of the back extrusion cell were based on the findings of Bourne (1968). An aluminum cylinder with inside dimensions of 5.2 em diameter and 12.8 em high was mounted on a base (Fig. 2A). The piston driven into the cylinder was 4.4 cm diameter and 1.0 em thick leaving an annulus of 0.4 em between the piston and cylinder. The cylinder was arranged so that it could be quickly detached from a locating boss at the bottom to facilitate cleaning. The piston was lowered into the cylinder by the compression machine until it was 1.2 em from the cylinder bottom. Kramer Shear OeU The standard multiblade shear cell (Model CS-1 !i'ood Technology Corp.) was used (Fig. 1). Plate Extrusion Oell An aluminum box with internal dimensions 5.10 x 4.25 x 11.50 em high was closed at the bottom by a removable plate (Fig. 3A). The plate was made of precision ground steel 0.475 em thick with 31 holes 0.6 em diameter equally distributed over the area covered by the internal dimensions of the box. The holes were drilled and then reamed to final size to maintain accuracy. The plate was removable for cleaning by withdrawing a pin holding a frame which clamped the plate against the bottom of the cell. This greatly facilitated cleaning the tested material from the cell. Sufficient space was allowed below the plate from the extruded product to drop out of the cell. A plunger 4.95 x 4.10 em made of flat aluminum plate was used to force the product through the cell. A 0.075 em clearance between the plunger and the interior walls of the cell prevented the possibility of them contacting and introducing an error in the measurement. The edges of the plate were bevelled at 20· to prevent the slight amount of test material extruded through the clearance being trapped between the plunger and cell walls. The plunger was attached to a rod mounted on the moving crosshead of the test machine and driven into the cell until it was 1 em above the surface of the extrusion plate. Fig. 2
Back extrusion cells. A. the cell used in the experiment; B. and C. possible variations in proportions; D. a water jacketed cell showing a range of piston disc diameters on the right.
total energy (area under force-deformation curve) used in each test. A range of canned products was selected at random from a commercial supplier to provide at least two cans of each product from the same production lot to test each type of cell. The products (Table 1) were chosen to provide a range of fruits and vegetables having different textural characteristics. 93
Table 1 List of canned produ.i-ct::.s....:t=es:.:te.:.:d:.:._~~--.._ Fruits Vegetables Miscellaneous Cherries Diced Harvard beets Spaghetti in tomato Deep browned beans sauce Grapefruit Yellow cling sliced in tomato sauce peaches Diced carrots Apricots Mixed vegetables Pineapple chunks Spinach French style green Raspberries Strawberries beans Tomatoes Cream style com Peeled cooked whole new potatoes Peas. Can. Inst. Food Tecbnol. J. Vol. 3, No.3, 1970
Fig. 3
A. plate extrusion cell; B. wire extrusion cell.
Wire Extrusion Cell This cell and plunger (Fig. 3B) had the same dimensions as the plate extrusion cell. The plate at the bottom however was replaced by five equally spaced parallel stainless steel wires 0.3 cm diameter along the 4.25 cm long side of the cell. The wires could be withdrawn from the cell to facilitate cleaning. The plunger was driven into the cell until within 1 cm of the wires. This is similar in design principle to the "Universal Cell" currently available for the Kramer Shear Press (:Uodel CE-1, Food Technology Corp.). This cell however, is cylindrical and uses a slotted bottom disc which must be machined. Because of the circular shape the slots are not uniform in length and the distribution of forces over the product are influenced by this factor. Wire Shear Cell Thi s cell is an extension of a design already established for testing Cottage Cheese (Voisey, et. al. 1966; Voisey and Emmons 1966). An aluminum box with internal dimensions 6.7 x 6.7 x 7.2 cm high and a closed bottom had 10 equally spaced slots machined on opposite sides (Fig. 4). A frame carrying 10 equally spaced 0.15 cm diameter wires was arranged so that the wires could pass through the slots in the cell and thus shear through the product. The slots were 0.3 cm wide so that the wires could not contact the cell during its passage through the product. The wires were driven into the cell until they just cleared the bottom of the cell. Ten wires were arbitrarily selected on the basis that with Cottage cheese three wires increased the precision of measurement achieved with one <>r two wires. (Voisey and Emmons, 1966).
Results and Observations Back Extrusion Cell From practical considerations the circular piston and cylinder are simple and inexpensive to manufacture and with a removable bottom the cell can be cleaned rapidly. If any wear or damage takes place the component can be readily replaced. One problem observed was that great care must be exercised in installing and aligning the piston and cylinder in J. Inst. Can. Technol. Aliment. Vol. 3, No 3, 1970
Fig. 4
Wire shear cell.
the machine to maintain a uniform extrusion annulus around the circumference of the piston. Typical results (Fig. 5) show how the force on the piston initially increases non linearly with deformation as the product is packed into the cylinder. In most cases the force then increases almost linearly as the product was compressed. As shearing and extrusion started the rate of increase of force with deformation decreased but large fluctuations started in most cases and there was a tendency for a plateau to occur. However, for the majority of products the force on the average continued to increase during extrusion. This was because compression of the product trapped below the piston continued throughout the test until the piston stopped. Thus for many products the maximum force must depend on the final clearance between the piston and cylinder. Bourne (1968) however concluded that the clearance was not important provided the piston did not appr?ach the bottom of the cylinder too closely when testmg peas. In view of the results here it is obvious that the clearance is critical and should be kept constant for meaningful comparisons. It is also apparent that the compression and shear-extrusion phases cannot be analyzed separately on the records for many of the products tested. For some purposes this may be a disadvantage. Kramer Shear Cell The Kramer shear cell is expensive ($550 U.S.) 96
because it requires a multiplicity of machining operations during manufacture. Since it is now made of aluminum instead of the stainless steel originally used it is very susceptible to damage. Any dents or wear of the sharp edges of the 10 moving blades (20 edges) or the slots in the bottom of the cell (20 edges) mean that parts of the cell must be replaced with interchangeable parts from the manufacturer. The cell is difficult to assemble during testing because the 10 blades must be aligned and fed into the slots in the lid. Cleaning the cell is also difficult because of the many confined spaces and the fact that the bottom grid cannot be removed. Thus operation of the cell becomes time consuming and tedious particularly when testing large numbers of samples such as in routine quality control operations. In the Kramer shear press damage to the cell, due to a foreign object such as a stone can be limited. .\. pressure relief valve in the hydraulic system is used to limit the force on the moving blades to a selected level. However, the force selected must be high enough to shear the product and this is generally sufficient to damage the cell. If the cell is used in other deformation machines, the cell is unprotected unless an additional control is built into the force recording system or a mechanical device such as a slip clutch incorporated in the drive mechanism. These however, are additional complications. For the majority of products tested the force initially increased non linearly as the product packed into the cell and then almost linearly as the sample was compressed (Fig. 5). This continued until a peak was reached, this coincided with the commencement of extrusion. In the majority of cases the force BACK (XTAUSIOH
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immediately decreased except for some of the softer foods where a plateau occurred indicating steady state conditions in the extrusion phase. An additional useful measurement was observed which is not normally used with the Kramer shear cell. Because the load cell used could record both tension and compression the force required to pull the blades out of the cell could be recorded. This was accomplished by moving zero force to 20% of the recorder chart. A typical example for baked beans (Fig. 6) shows how the force to pull the blades increases as they are pulled through the lid thus wiping off the product extruded up between the blades. A peak occurs as the beans are compacted between the blades against the adhesive forces between the beans and blades. The previously compressed and extruded beans are then compressed again producing a second peak at which point the forces are sufficient to overcome the adhesion. This technique may thus be useful for evaluating adhesive properties of food. Since this measurement could only be made with the Kramer shear cell a full evaluation of the method is not given here. It should be noted (Fig. 6) that within a given product the force deformation curves were not necessarily consistent. For some samples a double peak occurred. Plate Extrusion Cell 'l'he cell is made of standard stock sizes of aluminum bar which can be welded or bolted together and manufacturing costs are minimal. The critical part, the extrusion plate can be easily replaced with economy if worn or damaged. The cell is easily cleaned when the plate is removed however, cleaning the product from the holes in the plate is time consuming unless a high pressure spray can be used. The force increased non linearly during compaction of the samples in the cell (Fig. 5) and then almost linearly during compression. When the force was sufficient to shear and extrude the sample there was either a plateau or the force fluctuated rapidly about a mean force that was for practical purposes constant. This indicates that steady state conditions prevailed during extrusion. 'l'he test material could escape through the uniformly distributed holes in the plate
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Summary of typical records obtained with the different cells. Blank spaces indicate that it was not practical to test the particular product with the cell.
Fig. 6
Typical record for the Kramer shear cell showing the force required for the blades to enter the cell and then withdraw when testing baked beans. Can. Inst. Food Technol. J. Vol. 3, No.3, 1970
Table 2
Summary of Data2 for Products Tested Showing Force and Energy Used to Compress, Shear and Extrude the Samples (Mean of Two Samples).
..'---
Test Cell: Parameter2 : Product3 : Cherries Grapefruit Peaches' Apricot Pineapple Raspberries Strawberries Beet root Baked beans Carrots Mixed vegetable Spinach French beans Tomatoes Com Potatoes Peas Spaghetti 1. 2. 3.
KRAMER SHEAR Force Energy
BACK EXTRUSION Force Energy
PLATE EXTRUSION WIRE EXTRUSION Force Energy Force Energy
WIRE SHEAR Force Energy
6 12 6 8 38 1 3
45 73 36 36 127 7 11
15 31 11 24 120 4 8
68 143 71 113 35.'5 21 34
6 6 7 11 46
34 46 46 55 187
12 17 10 20 118
35 37 39 40 241
180 74 178 254 100 38
30 31 10 28 17 16 4
31 46 J4 43 61 20 13
56 26
73
19 21 7 24 23 12 7 11 36 29
109 121 37 105 109 55 55 32 243 126
93 94 36 99 132 48 31
531 269
176 258 68 145 256 8.5 65 69 295 258
23 28 8 31 43 15 13
Jl6 128
159 200 52 136 87 77 27 43 300 142
31 54
123 121
12
5
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32
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43
3
25
5
24
33 70 21 44 294
81 154 57 105 556
12
28
50 93 22 7.'5 137 34 20
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Blanks in the data imply that it was not practical to test the product by the method. Force in Kg energy in cmKg. For a full description see Table 1.
and was not trapped under the plunger. The product was therefore compressed only enough to initiate shearing and extrusion. Wire Extrusion Cell The cell is manufactured in the same way as the plate extrusion cell and therefore is also inexpensive. If the wires are fixed in the bottom of the cell clean· ing is relatively tedious. This can be overcome if the wires have sufficient strength by withdrawing them as shown (Fig. 3B). If any of the wires, which are the only critical parts are damaged they can be replaced at practically no cost. The results for this cell were not as consistent as with the plate extrusion (Fig. 5). While the majority of curves are similar several indicated that compression continued after extrusion started because material was trapped under the plunger. The force therefore continued to increase until a peak was reached which coincided with the maximum penetration of the plunger. It is assumed that this is caused by the relatively large diameter wire selected which presented smooth surfaces to the product preventing an efficient shearing action whereas in the plate extrusion cell sharp edges were used. Wire Shear Cell This cell while economic to manufacture is the most costly of the three new cells because of greater amount of machining is required. Compared to the wire and plate extrusion types it is relatively fragile. However, the critical parts, the shearing wires can be easily replaced. Cleaning is also more tedious. Previous work with Cottage cheese (Voisey and Emmons 1966) indicated that the force increased as the cheese curds were compressed and reached a plateau as the curds were cut by the wire. Similar behaviour was shown by several of the products tested J. Inst. Can. Techno!. Aliment. Vol. 3, No 3, 1970
indicating steady state conditions as the wires cut the sample (Fig. 5). However, for most of the products the force increased throughout the deformation indicating that the product was not all being cut by the wires and compression continued throughout the test. This was most marked for products containing fibrous materials. A summary of the forces and energies recorded for each cell for the various products (Table 2) is given to indicate the order of these measurements. It should be noted that within each product the force and energy required to operate the different cells covers a considerable range. Thus if a deformation machine with only a particular load capacity if available then a test cell producing loads within that range can be selected to accomplish the measurement. The ranking of the different products by each cell in this experiment cannot be considered meaningfUl because of the large differences between the sample sizes used. Effect of Sample Size Bourne (1968) found that sample size did not affect the results from the back extrusion method using a circular cylinder to test peas. Szczesniak (1969) has shown that sample size does influence results from the Kramer shear cell and that the effect varies with different products. The effect of sample weight on results from the wire and plate extrusion and the wire shear cells using peas and washed and drained baked beans as the test material was investigated. The results (Fig. 7) indicate that variation in sample weight does not affect the force measurements seriously but the sample weight should be considered important. There was a marked effect however on energy measurements. The energy used was directly proportional to sample weight. This should be obvious since the more material in the cell the 98
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The effect of sample weight on force and energy measure ments from plate extrusion, wire extrusion and wire shear cells.
more work that must be done to compress shear and extrude the product. This points out that if energy measurements are used, for the convenience of a direct electronic digital readout, then control of sample size becomes extremely critical. It is reasonable to assume that this would be a requirement for any texture test cell.
Discussion The results indicate that each cell is not ideally suited for testing all the products used in the experiment. Each cell also has practical advanta~es and disadvantages which must be considered. The cells all subject the product to compression and then shearing combined with extrusion. Thus it can be assumed from a general viewpoint that each cell can detect similar textural properties. The relationships between force and deformation for each cell are different in varying degrees with each product tested. The interpretation of these curves is therefore a critical part of the technique. Reliability of any interpretations made can only result from extensive experience in relating the measurements to sensory analysis. This has not been attempted here. The limited number of products tested can only serve to introduce possible applications of the three new cell designs. However, it can be assumed that the elastic and shear strength properties of certain products can be estimated by all the cells. Extensive work is still required to determine the full potential of each new cell design. The cells described use a bulked sample, that is a selected weight or volume of the product to be tested, 9!J
A. plate extrusion and B. wire extrusion cells of different sizes and proportions.
not individual pieces such as a pea or a carrot slice. It is generally assumed that this provides an averaging effect. This is the case but if a single peak occurs in the force-deformation curve as in the Kramer shear cell, then this is a single unique result related to the shearing properties of the food. This single point may be biased by the sampling method, instrument errors or the manner in which the cell deforms a particular bulked sample. On the other hand if a plateau occurs indicating that the product is being sheared and steady state conditions prevail as the material is extruded then an average result, the mean height of the plateau, should in theory provide a more accurate estimate of the shear strength. Another aspect is that for research and in particular quality control applications a digital output eliminates the analysis of an analogue records on strip-charts. The instrumentation required to achieve this when a plateau is the parameter of interest can be made simpler than peak detection systems and still achieve a high degree of accuracy. Temperature control has not been used extensively with texture test cells except in viscosity measure· ments or when testing fats with various devices. The simplest approach is probably to use a water jacket. This can be installed on all the cells describrd but it is easier to manufacture a jacket for a cylindrical cell. A typical example of a back extrusion cell is shown (Fig. 2D). Water can be circulated from a constant tempprature bath and the specimen brought to the required temperature before testing. In selecting a cell to test a particular product both practical and measurement accuracy aspects must be considered and satisfied. Assuming the ease of cleaning and susceptibility to damage and initial and maintenance costs of a cell are satisfactory then it should be possible to design the cell using proportions suitable for the application. For example~ Can. Inst. Food Technol. J. Vol. 3, No.3. 1970
Table 3
Variations that can be used in the design and proportions of the test ceIIs1
Kramer Shear Area Height Number of blades Blade thickness Blade spacing Clearance between blades and grid
Back Extrusion Area Height Piston diameter Piston thickness Piston taper
Plate Extrusion Area Height Plate thickness Number of holes Spacing of holes Hole taper
Wire Extrusion Area Height Number of wires Diameter of wires Spacing of wires Shape of wires (round, square, etc.)
Wire Shear Area Height Number of wires Diameter of wires Spacing of wires Shape of wires (round, square, etc.)
1 Common parameters to all ceIIs are: a) compression speed; b) penetration of moving part of cell.
sample size may be dictated by the cost of preparing the material and in some cases it may be desirable to reduce this to a minimum. The sizes of the component parts or particles of the sample will also dictate the proportions of the cell parts that shear the product. It is therefore a distinct advantage if the cell can be "tailor made" for the particular product. For example a cell that will test products having an aggregate size in the order of peas may not be suitable for testing new potatoes. In general terms it can therefore be stated that the design principle of a cell may be universally applicable to a range of products but the cell proportions must change. The Kramer Shear Cell proportions can be varied by making it larger or smaller, changing the number and thickness of the blades and varying the clearance between the blades and the slots in the bottom grid. However, any change requires an entirely new cell. This is expensive, for example the half-scale multiblade cell (Model OS-2 Food Technology Corp.) currently costs $9:>0 U.s. Thus it is not economic to have a range of cells. On the other hand the proportions of the back extrusion, plate extrusion, wire extrusion and wire shear cell can be changed because they are cheaper to produce and the size of the critical components can be changed. There are a number of variables available with each of these cells. As pointed out by Bourne (1968) the piston diameter can be changed to vary the width of the extrusion annulus. This only involves removing a metal disc from a shaft (Fig. 2D). The cylinder can be made short and large in diameter or tall and small in diameter (Fig. 2B) or a range of cylinder diameters arranged to fit the same removable base (Fig. 2B). The thickness of the piston disc can be varied to change the length of the extrusion passage. If the circumference of the piston is bevelled the length of the extrusion passage could be reduced to almost zero since the extruded material could then expand into the space available. The tapered annulus formed could be either pointing up or down to provide either an expanding or contracting passage. The plate and wire extrusion cells can be made in a range of sizes (Fig.S). The nurnbel' of holes, the spacing between holes and the thickness of the extrusion plate can be changed within each size to suit each product. The holes can be tapered in either direction to provide either an expanding or contracting passage. Similarly for a given size of wire extrusion J. Inst. Can. Techno!. Aliment. Vo!. 3, No 3, 1970
or wire shear cell the number, spacing and diameter of the wires can be selected to suit the application. Another alternative would be to use square or rectangular wires oriented in different ways so that different shear edges were presented to the test material. Interchangeahility of texture test cells becomes important if the same test is to be made using several cells. This can be achieved in relation to the mechanical aspects of the cell. The sizes of the various components can be specified to close tolerances. The cost of achieving this depends greatly on the cell design and should be reduced to a minimum. In the plate and wire extrusion and wire shear cells the critical shearing components and their spacing are based on drilling operations, ground steel plate and wire diameters. These are relatively inexpensive. The back extrusion cell can be manufactured almost entirely by turning in a lathe which can be done at reasonable cost and still maintain close tolerances. The cylinders can be made from stock tubing to further reduce costs. The simplicity of design of the three new cells and the back extrusion cell indicates that they can be manufactured locally and the low cost means that a range -of cells can be kept on hand to test different products. Standardization of the mechanical aspects of the cells is of prime importance because of the number of variables possible. While individual researchers will obviously wish to tailor their own cells it would be logical to base this on some previously agreed standard. There is insufficient data available to lay down these standards at present. However it is proposed that the proportions be based on the area of the cell measured at the horizontal plane that is covered by the test sample. To emphasize the flexibility of the cell designs and the need for standardization of the dimensions those that can be varied are tabulated (Table 3). It should be noted that most of the variables can be made proportional to the area of the cell.
Conclusions The performance of three new cells and the back extrusion cell in relation to the Kramer Shear Cell has been demonstrated. The data presented indicates that these cells can be used to estimate textural propreties of some products instead of the Kramer Shear Cell. Each cell has practical advantages and the one 100
selected depends on the product to be tested. There is a definite advantage if a plateau occurs in the force-deformation relationship since this may provide a more reliable index of shearing strength than a single peak. This behaviour occurs with all the cells for particular products. It is probable that each cell can be made to achieve this type of result by changing the proportions of the shearing-extrusion components. Extensive work to be published later has shown that results from the back extrusion and three new cell designs are highly correlated with Kramer shear tests for peas and baked beans. This is to be expected since all the cells subject the samples to essentially the same basic mechanical operations, that is, compression, shear and extrusion. An obvious conclusion that is worth repeating here is that in any empirical test using the test cells all test conditions must be kept constant. This is the only way meaningful comparisons can be made by the techniques described. If any condition is changed such as sample size, cell size, deformation speed ,etc., the effect of this should be investigated. It is necessary to standardize the proportions and dimensions of the test cells so that interlaboratory comparisons can be made or quality control applications can be standardized. While it is too early at present to lay down a set of formal standards it would appear that this aspect should be investigated before the different cells become widely used. The different cell designs cannot replace the Kramer shear cell for all products. For example they are not suitable for testing meat because extremely high forces are involved. It should be noted that the forces required to compress, shear and extrude even the soft products tested were high, for example canned pineapple required up to 300kg. The force required will also depend on the size of test cell used. Thus the deformation mechanism should have high load capacity. Manufacturing arrangements are currently being made to produce the plate and wire extrusion cells as one integrated unit with interchangeable bottoms so that one cell body and plunger can be used for both types of tests. It is estimated that the cost will be about $100.
Acknowledgement The author wishes to acknowledge the valuable technical assistance of M. Kloek, Engineering Research Service.
References Ang, J. K., F. M. Isenberg and J. D. Hartman. 1960. Measurement of firmness of onion bulbs with a shear press and potentiometric recorder. Proc. Amer. Soc. Hort. ScI. 75: 500. Ang, J. K., J. Hartman and F. M. Isenberg. 1963. New applications of the shear press in measuring texture in vegetables and vegetable products. II. Correlation of subjective estimates of texture of a number of whole and cut vegetables and objective measurements made with several sensing elements of the shear press. Proc. Amer. Soc. Hort. ScI. 83: 734. Angel, S., A. Kramer and J. N. Yeatman. 1965. Physical methods of measuring quallty of canned peas. Food Techno!. 19: 96. Anon. 1968. Texture test systems designed to measure quality of foods. Can. Food Ind. 39: 53. Baker, R. C., J. Darfler and D. V. Vadehra. 1969. Type and level of fat and amount of protein and their effect on the quallty of
101
chicken frankfurters. Food Techno!. 23: 100. Binder, L. J. and L. B. Rockland. 1964. Use of automatic recording shear press In cooking studies of large dry llma beans (Phaseolus Lunatus). Food Techno!. 18: 127. Bourne, M. C., J. C. Moyer and D. B. Hand. 1966. Measurement of food texture by a universal testing machine. Food Techno!. 20: 17.. Bourne, M. C. and J. C. Moyer. 1968. The extrusion principle in texture measurement of fresh peas. Food Techno!. 22: 1013. Brown, S. L. and M. E. Zablk. 1967. Effects of heat treatments on the physical and functional properties of liquid and spray-dried egg albumen. Food Techno!. 21: 87. Buck, E. M. and D. L. Black. 1967. The effect of stretch-tension during rigor on certain physical characteristics of bovine muscle. J. Food Sci. 32: 593. Buck, E. M. and D. L. Black. 1968. Microscopic characteristics of cooked muscles subjected to stretch tension during rigor. J. Food ScI. 33: 464. Christel, W. F. 1938. Texturemeter. A new device for measuring the texture of peas. Canning Trade. 60(34): 10. Fox, M. and A. Kramer. 1966. Objective tests for determining quality of fresh green beans. Food Techno!. 21: 88. Franks, O. J., M. E. Zablk and C. L. Bedford. 1969. Sensory and objective comparisons of frozen, IQF, dried and canned montmorency cherries In pies. Food Techno!. 23: 77. Fry, J. L., P. W. Waldroup, E. M. Ahmed and H. Lydick. 1966. Enzymatic tenderization of pOUltry meat. Food Techno!. 20: 102. Funk, K., M. E. Zabik and D. M. Downs. 1965. Comparison of shear press measurements and sensory evaluation of angel caKes. J. Food ScI. 30: 729-736. Gilpin, G. L., O. M. Batcher and P. A. Deary. 1965. Influence of marbling and final Internal temperature of quallty characterIstics of broiled rib and eye of round steaks. Food Techno!. 19: 152. GrUber, S. M. and M. E. Zabik. 1966. Comparison of sensory evaluation and shear-press measurements of butter cakes. Food Techno!. 20: 118. Hartman, J. D., F. M. Isenberg and J. K. Ang. 1963. New appllcatlons of the shear press in measuring texture in vegetables and vegetable products. 1. Modifications and attachments to increase the versatllity and accuracy of the press. Proc. Amr. Soc. Hort. Sci. 82: 465. Johnson, C. F., E. C. Maxie and E. M. Elbert. 1965. Physical and sensory tests on fresh strawberries subjected to Gamma radiation. Food Techno!. 19: 119. Kanujoso, B. W. T. and B. S. Luh. 1967. Texture, pectin, and syrup viscosity of canned cllng peaches. Food Techno!. 21: 139A. a. Kramer, A., K. Aamlld, R. B. Guyer and H. Rogers. 1951. New shear-press predicts quallty of canned limas. Food Engng. 23: 112. b. Kramer, A., G. J. Burkhardt and H. P. Rogers. 1951. The shearpress, a device for measuring food quality. Canner. 112: 34. Kramer, A. and K. Aarnlid. 1953. The shear-press, an instrument for measuring the quality of foods. III. Application to peas. Proc. Amer. Soc. Hort. Sci. 6: 417. Kramer, A. and W. J. Hart. 1954. Recommendations on procedures for determining grades of raw, canned, and frozen llma beans. Food Techno!. 8: 55. Kramer, A. 1957. Food Texture rapidly gaged with versatile shear press. Food Engng. 29: 57. Kramer, A. 1961. The shear-press, a basic tool for the food technologist. Food Scientist 5: 7. Kramer, A. and J. V. Hawbecker. 1966. Measuring and recording rheological properties of gels. Food Techno!. 20: 209. Lovel!. R. T. and G. J. Fllck. 1966. Irradiation of gulf coast strawberries. Food Techno!. 20: 99. Luh, B. S. and K. D. Dastur. 1966. Texture and pectin changes in apricots. J. Food Sci. 31: 178. Mannheim, H. C. and A. Baka!. 1968. An Instrument for evaluating firmness of grapefruit segments. "Food Techno!. 22: 83. Marion. W. W. and H. M. Goodman. 1967. Influence of continuous chilling on tenderness of turkeys. Food Techno!. 21: 89. Miller, W. O. and K. N. May. 1965. Tenderness of chicken as affected by rate of freezing, storage time and temperature, and freeze drying. Food Techno!. 19: 147. Newmann, H. J., L. R. Frame, L. Morgan and R. L. Olson. 1960. Use of the Kramer shear-press In forcastlng harvest dates for Fordhook llma beans. Food Techno!. 15: 225. Palmer, H. H., A. A. Klose, S. Smith and A. A. Campbell. 1965. Evaluation of toughness differences in chickens In terms of consumer reaction. J. Food Sci. 30: 898. Pangborn, R. M., N. Sharrah, H. Lewis and A. W. Brant. 1965. Sensory and mechanical measurements of turkey tenderness. Food Techno!. 19: 86. Peterson, D. W. and A. L. Lllyblade. 1969. Relative differences in tenderness of breast muscle in normal and two dystrophic mutant strains of chickens. J. Food Sci. 34: 142. a. Sharrah, N., M. S. Kunze and R. M. Pangborn. 1965. Beef tenderness: Sensory and mechanical evaluation of animals of different breeds. Food Techno!. 19: 131. b. Sharrah, N., M. S. Kunze and R. M. Pangborn. 1965. Beef tenderness. Comparison of sensory methods with the Wa~ner Bratzler and LEE-Kramer shear press. Food Techno!. 19: 136. Stadelman, W. J., G. C. Mostert and R. B. Harrington. 1966. Effect of aging time, sex, strain and age on resistance to shear of turkey meat. Food Techno!. 20: 110. Szczesniak, A. S. 1969. The Whys and whats of objective texture measurements. J. Can. Inst. Food Techno!. 2: 150. Thomas, N. W., P. B. Addis, H. R. Johnson, R. D. Howard and M. D. Judge. 1966. Effects of environmental temperature and humidity during growth on muscle properties of two porcine breeds. J. Food Sci. 31: 309. Can. Inst. Food Techno!. J. Vo!. 3, No.3, 1970
Toumy, J. M., J. Felder and R. L. Helmer. 1966. Relation of pork loin weight to shear-force values, panel scores, fat In lean meat, and cut out percentages. Food Techno!. 20: 174. Toumy, J. M. and R. L. Helmer. 1967. Effect of freeze drying on the quallty of the longissimus dorsi muscle of pork. Food Techno!. 21: 167. Toumy, J. M., H. T. Schlup and R. L. Helmer. 1969. Effect of cooking temperature and time on the tenderness of precooked freeze-dried turkey white meat. Food Techno!. 23: 60. Voisey, P. W., M. Kloek and A. W. Thomlison. 1966. An apparatus for comparing to textural quality of foods. Eng. Res. Service, Ottawa Bul!. 6262. Voisey, P. W. 'and D. B. Emmons. 1966. Modlflcatlon of the curd
J. lust. Can. Techno!. Aliment. Vo!. 3, No 3, 1970
firmness test for Cottage cheese. J. Dairy ScI. 49: 93. Voisey, P. W., D. C. MacDonald and W. Foster. 1967. An apparatus for measuring the mechanical properties of food products. Food Techno!. 21: 43A. Wangen, R. M. and J. H. Skala. 1968. Tenderness and maturity In relation to certain muscle components of White Leghorn fow!. J. Food ScI. 33: 613. Werner, G., E. E. Meschter, H. Lacey and A. Kramer. 1963. Use of the shear press In determining the flbrousness of raw and canned green asparagus. Food Techno!. 17: 81. Received May 7, 1970
102
Abstract New test cells for estimating textural properties of a range of food products by objective techniques are described. The performance of these cells is demonstrated in relation to the Kramer shear and a back extrusion cell. The new cells offer the advantage of simple designs which can be manufactured inexpensively. Thus, if any wear or damage occurs in experimental work and in particular during routine quality control the cells or critical components can be replaced economically. The cells subject the products to compression shear and extrusion which are the processes used in the popular Kramer shear cell. Initial work has shown that the results from the new cells are well correlated with Kramer shear data. Thus for some purposes the new cells can be used to advantage.
Resume On decrit des nouvelles cellules d'essai pour l'evaluation des proprietes de texture d'une variete de produits alimentaires par des techniques objectives. La performance de ces cellules est comparee it celIe de la presse it cisaillement Kramer et it une cellule it extrusion. Les nouvelles cellules ont l'avantage de conceptions simples qui peuvent etre realisees it bon marche. Ainsi, en cas d'usure ou d'endammagement au cours de travaux experimentaux ou lors du controle de qualite routin;er les cellules ou leurs parties essentielles peuvent etre remplacees it bas prix. Les produits sont soumis dans les cellules it un cisailJement et it une extrusion sous pression tout comme pour la populaire presse it cisail1ement Kramer. Les travaux du debut ont indique que les rpsultats obtenus avec les nouvelles cellules ont une bonne correlation avec ceux de la presse Kramer.
Introduction Currently different approaches are used in the study of the textural characteristics of foods. The rheological and mechanical properties are being investigated to examine the relationships between these fundamental characteristics and consumer reactions. Instruments have been developed to imitate the action of the human mouth while others are empirical in concept where the food is deformed in some arbitrarily selected but practical and convenient way to measure the products reaction to applied force. The empirical type test is the most widely used in both research, product development and quality control. Test specimens are compressed, stretched, sheared or extruded in single or combined operations and provided the force-deformation relationships are correlated with sensory analysis they can be used routinely as an objective estimate of texture. Common requirements to all empirical measurements of texture are a mechanism to deform the product, instruments to record the force and deformation during the test and finally a test cell to contain or hold the sample while it is being deformed. There are a wide range of deformation mechanisms available 1. Contribution No. 200 from Engineering Research Service.
93
such as the universal test machine (Bourne et. al. 1966; Voisey et. al. 1967) and the Kramer shear press (Food Technology Corp., Reston, Virginia) . Different apparatus ranging from simple mechanical devices to sophisticated electronic systems have been use~ to record force and deformation and have been descrIbed elsewhere. Any deformation mechanism and recording apparatus with the required ranges, accuracy and control of test conditions is suitable for texture measurements' thus the selection of the test cell becoines the' most critical decision in assembling a texture measuring system. The most widely used test cell is the multiblade Kramer shear cell (Model CS-1 Food Technology Corp.) . This cell together with a hydraulically actuated deforming mechanism "The Kramer Shear Press" was introduced by Kramer et. al. (1951 a, b) and Kramer (1957). The test cell is a square box with a grid in the bottom and 10 parallel blades which are forced into the box and through the grid (Fig. 1). During this process the product is compressed, sheared and extruded. The cell has the practical advantage that a wide variety of products can be placed in the box for testing. The cell and shear press have become "a basic tool for the food technologist" (Kramer, 1961; Anon. 1968) and its versatility is indicated by the range of products tested. These have included fruits such as apricots (I.. uh and Dastur 1966), cherries (Franks ct. al. 1969), grapefruit segments (Mannheim and Bakal 1968), peaches (Kanujoss and Luh, 1967) and strawberries (Lovell and Flick 1966). Vegetables have also been tested including Lima beans (Kramer and Hart 1954; Neuman et. al., 1960; Binder and Rockland 1964) ; green beans (Fox and Kramer, 1966) and peas (Kramer and Aamlid, 1953; Angel et. al. 1965) . In recent years meat has been tested extensively with the multiblade Kramer shear cell, such as pork (Thomas ct. al. 1966; Tuomy et. al. 1966; Tuomy and Helmer 1967) ; beef (Gilpin et. al. 1966; Wangen and Skala 1968); turkey (Stadelman et. al. 1966; Marion and Goodman 1967; Tuomy ct. al. 1969) and meat products (Baker ct. al. 1969). The results from the Kramer Shear Cell have been compared with other test techniques such as the Warner-Bratzler shear test for meat tenderness (Pangborn ct. al. 1965; Sharrah ct. al. 1965 a, b; Palmer ct. al. 1965). During its development and subsequent widespread use several other test cells have been manufactured for use with the shear press for specific food products. Compression attachments have been used to test unrestrained samples of products such as onion bulbs (Ang et. al. 1960), cakes (Funk ct. al. 1965; Can. Inst. Food Techno!. J. Vo!. 3, No.3, 1970
Brown and Cabik 1967) and butter cakes (Gruber and Cabik 1966). A series of attachments were described by Hartman et. al. (1963) including puncture probes, a "\Varner-Bratzler meat shear fixture, a mechanism to similate the action of teeth, clamps for testing materials in tension and a grate that was forced into a. box containing the product. Several of these attachments were demonstrated with canned tomatoes, snap beans and peas (Ang et. al. 1963). A tensile testing attachment has also been described for testing cakes (Funk et. al. 1965). A single blade cell (Model CA-1 Food Technology Corp.) is also available and has been used to test asparagus (Werner et. al. 1963), and strawberries (Johnson et. al. 1965). A test cell based on the design of Christel (1938) for subjecting chicken breast muscle to multipl-e punctures has also been described by Peterson and Lilyblade (1969). There are thus a wide range of test cells that have been used with the shear press which is currently available from the manufacturer with seven test cells: standard multiblade shear cell (CS-1) ; thin multiblade shear cell (CS-2); single blade shear cell (CA-1); meat shear cell (CW-1); compression test set (TC-1); succulometer cell (CR-1) and a universal cell (CE-1). However, the most popular cell has remained the standard multiblade shear cell because it can handle a wide range of products. It should be noted that all the above cells can be used in any deformation mechanism providing it has sufficient load capacity. Universal test machines based on an electric motor driving a screw (Voisey et. al. 1967) overcome the problem of selecting and maintaining constant deformation speeds that occur with hydraulic systems such as used in the Kramer Shear Press. A different approach to the design of a texture testing cell was suggested by Bartman et. al. (1963) where the product was compressed into a square box by a loosely fitting plunger until it was extruded through the gap between the plunger and the sides of the box. This principle was tested by Ang et. al. (1963)
Fig. 1 Kramer muItibIade shear cell. J. lost. Can. Technol. Aliment. Vol. 3. No 3. 1970
with tomatoes, beans and peas. Bourne (1968) changed the design to use a circular cylinder and piston to investigate the extrusion principal to test peas. This technique has been called the "back extrusion cell" (Kramer and Hawbecker 1966). If it is accepted that the texture of food can be measured objectively by subjecting the product to compression shear and extrusion then the design requirements for a test cell can be formulated in general terms as follows. 1. The cell should be simple in design so that it can be manufactured economically. 2. The cell must be rugged and if any wear or damage occurs the worn parts should be easy to replace. 3. The Lell should conveniently accommodate a wide range of products and be available in the range of sizes to handle different sample sizes. 4. The cell should be easy to clean after testing a sample to maintain hygenic conditions and reduce operating labour to a minimum. 5. During deformation the food should be subjected to compression, shearing and extrusion in separate and distinct phases is possible so that these can be evaluated individually on the force-deformation records. 6. Since the texture of many foods depends on temperature it should also be possible to control the cell temperature. The purpose of the work here is to discuss the design of the multiblade Kramer shear cell, the back extrusion cell and introduce three new cell designs. Operating techniques and typical results for a range of products are shown to demonstrate the advantages and disadvantages of each cell.
Experimental Methods and Apparatus The tests were conducted in a universal compression machine (Model TM-M Instron Canada Ltd., Clarkson, Ontario). To record the force a load cell (:Model FLIU-3SG Strainsert Ltd., Bryn Mawr, Philadelphia) was attached to the moving cross head of the machine. This load cell has a capacity of 454 Kg in tension or compression. The moving component of each test cell was mounted on the load cell and the fixed component attached rigidly to the base of the machine. The load cell was rigid and its deflection under load could be ignored in determining deformation from the relationships between crosshead and recorder chart speeds. A compression speed of 10 cm/min was used for each cell tested. This was an arbitrary selection based on the fact that the rate of rise of force did not exceed the response time of the recorder pen (0.25 sec for full scale). A constant chart speed of 10/min min was used for all tests. The load cell was calibrated using a proving ring and the calibration range selected for each cell and product tested to achieve an adequate recorder pen deflection. Using these techniques it was assumed that force and deformation were recorded with an accuracy of -+- 0.5%. An integrator was connected in parallel with the recorder to record the 94
For testing, the products were drained except in the case of baked beans and cream style corn where this was not practical. The sample sizes used were arbitrarily selected as either the contents of the can or the quantity required to fill the various test cells depending on the product and the relative volumes of the can and test cell. Back Extrusion OeU The dimensions of the back extrusion cell were based on the findings of Bourne (1968). An aluminum cylinder with inside dimensions of 5.2 em diameter and 12.8 em high was mounted on a base (Fig. 2A). The piston driven into the cylinder was 4.4 cm diameter and 1.0 em thick leaving an annulus of 0.4 em between the piston and cylinder. The cylinder was arranged so that it could be quickly detached from a locating boss at the bottom to facilitate cleaning. The piston was lowered into the cylinder by the compression machine until it was 1.2 em from the cylinder bottom. Kramer Shear OeU The standard multiblade shear cell (Model CS-1 !i'ood Technology Corp.) was used (Fig. 1). Plate Extrusion Oell An aluminum box with internal dimensions 5.10 x 4.25 x 11.50 em high was closed at the bottom by a removable plate (Fig. 3A). The plate was made of precision ground steel 0.475 em thick with 31 holes 0.6 em diameter equally distributed over the area covered by the internal dimensions of the box. The holes were drilled and then reamed to final size to maintain accuracy. The plate was removable for cleaning by withdrawing a pin holding a frame which clamped the plate against the bottom of the cell. This greatly facilitated cleaning the tested material from the cell. Sufficient space was allowed below the plate from the extruded product to drop out of the cell. A plunger 4.95 x 4.10 em made of flat aluminum plate was used to force the product through the cell. A 0.075 em clearance between the plunger and the interior walls of the cell prevented the possibility of them contacting and introducing an error in the measurement. The edges of the plate were bevelled at 20· to prevent the slight amount of test material extruded through the clearance being trapped between the plunger and cell walls. The plunger was attached to a rod mounted on the moving crosshead of the test machine and driven into the cell until it was 1 em above the surface of the extrusion plate. Fig. 2
Back extrusion cells. A. the cell used in the experiment; B. and C. possible variations in proportions; D. a water jacketed cell showing a range of piston disc diameters on the right.
total energy (area under force-deformation curve) used in each test. A range of canned products was selected at random from a commercial supplier to provide at least two cans of each product from the same production lot to test each type of cell. The products (Table 1) were chosen to provide a range of fruits and vegetables having different textural characteristics. 93
Table 1 List of canned produ.i-ct::.s....:t=es:.:te.:.:d:.:._~~--.._ Fruits Vegetables Miscellaneous Cherries Diced Harvard beets Spaghetti in tomato Deep browned beans sauce Grapefruit Yellow cling sliced in tomato sauce peaches Diced carrots Apricots Mixed vegetables Pineapple chunks Spinach French style green Raspberries Strawberries beans Tomatoes Cream style com Peeled cooked whole new potatoes Peas. Can. Inst. Food Tecbnol. J. Vol. 3, No.3, 1970
Fig. 3
A. plate extrusion cell; B. wire extrusion cell.
Wire Extrusion Cell This cell and plunger (Fig. 3B) had the same dimensions as the plate extrusion cell. The plate at the bottom however was replaced by five equally spaced parallel stainless steel wires 0.3 cm diameter along the 4.25 cm long side of the cell. The wires could be withdrawn from the cell to facilitate cleaning. The plunger was driven into the cell until within 1 cm of the wires. This is similar in design principle to the "Universal Cell" currently available for the Kramer Shear Press (:Uodel CE-1, Food Technology Corp.). This cell however, is cylindrical and uses a slotted bottom disc which must be machined. Because of the circular shape the slots are not uniform in length and the distribution of forces over the product are influenced by this factor. Wire Shear Cell Thi s cell is an extension of a design already established for testing Cottage Cheese (Voisey, et. al. 1966; Voisey and Emmons 1966). An aluminum box with internal dimensions 6.7 x 6.7 x 7.2 cm high and a closed bottom had 10 equally spaced slots machined on opposite sides (Fig. 4). A frame carrying 10 equally spaced 0.15 cm diameter wires was arranged so that the wires could pass through the slots in the cell and thus shear through the product. The slots were 0.3 cm wide so that the wires could not contact the cell during its passage through the product. The wires were driven into the cell until they just cleared the bottom of the cell. Ten wires were arbitrarily selected on the basis that with Cottage cheese three wires increased the precision of measurement achieved with one <>r two wires. (Voisey and Emmons, 1966).
Results and Observations Back Extrusion Cell From practical considerations the circular piston and cylinder are simple and inexpensive to manufacture and with a removable bottom the cell can be cleaned rapidly. If any wear or damage takes place the component can be readily replaced. One problem observed was that great care must be exercised in installing and aligning the piston and cylinder in J. Inst. Can. Technol. Aliment. Vol. 3, No 3, 1970
Fig. 4
Wire shear cell.
the machine to maintain a uniform extrusion annulus around the circumference of the piston. Typical results (Fig. 5) show how the force on the piston initially increases non linearly with deformation as the product is packed into the cylinder. In most cases the force then increases almost linearly as the product was compressed. As shearing and extrusion started the rate of increase of force with deformation decreased but large fluctuations started in most cases and there was a tendency for a plateau to occur. However, for the majority of products the force on the average continued to increase during extrusion. This was because compression of the product trapped below the piston continued throughout the test until the piston stopped. Thus for many products the maximum force must depend on the final clearance between the piston and cylinder. Bourne (1968) however concluded that the clearance was not important provided the piston did not appr?ach the bottom of the cylinder too closely when testmg peas. In view of the results here it is obvious that the clearance is critical and should be kept constant for meaningful comparisons. It is also apparent that the compression and shear-extrusion phases cannot be analyzed separately on the records for many of the products tested. For some purposes this may be a disadvantage. Kramer Shear Cell The Kramer shear cell is expensive ($550 U.S.) 96
because it requires a multiplicity of machining operations during manufacture. Since it is now made of aluminum instead of the stainless steel originally used it is very susceptible to damage. Any dents or wear of the sharp edges of the 10 moving blades (20 edges) or the slots in the bottom of the cell (20 edges) mean that parts of the cell must be replaced with interchangeable parts from the manufacturer. The cell is difficult to assemble during testing because the 10 blades must be aligned and fed into the slots in the lid. Cleaning the cell is also difficult because of the many confined spaces and the fact that the bottom grid cannot be removed. Thus operation of the cell becomes time consuming and tedious particularly when testing large numbers of samples such as in routine quality control operations. In the Kramer shear press damage to the cell, due to a foreign object such as a stone can be limited. .\. pressure relief valve in the hydraulic system is used to limit the force on the moving blades to a selected level. However, the force selected must be high enough to shear the product and this is generally sufficient to damage the cell. If the cell is used in other deformation machines, the cell is unprotected unless an additional control is built into the force recording system or a mechanical device such as a slip clutch incorporated in the drive mechanism. These however, are additional complications. For the majority of products tested the force initially increased non linearly as the product packed into the cell and then almost linearly as the sample was compressed (Fig. 5). This continued until a peak was reached, this coincided with the commencement of extrusion. In the majority of cases the force BACK (XTAUSIOH
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immediately decreased except for some of the softer foods where a plateau occurred indicating steady state conditions in the extrusion phase. An additional useful measurement was observed which is not normally used with the Kramer shear cell. Because the load cell used could record both tension and compression the force required to pull the blades out of the cell could be recorded. This was accomplished by moving zero force to 20% of the recorder chart. A typical example for baked beans (Fig. 6) shows how the force to pull the blades increases as they are pulled through the lid thus wiping off the product extruded up between the blades. A peak occurs as the beans are compacted between the blades against the adhesive forces between the beans and blades. The previously compressed and extruded beans are then compressed again producing a second peak at which point the forces are sufficient to overcome the adhesion. This technique may thus be useful for evaluating adhesive properties of food. Since this measurement could only be made with the Kramer shear cell a full evaluation of the method is not given here. It should be noted (Fig. 6) that within a given product the force deformation curves were not necessarily consistent. For some samples a double peak occurred. Plate Extrusion Cell 'l'he cell is made of standard stock sizes of aluminum bar which can be welded or bolted together and manufacturing costs are minimal. The critical part, the extrusion plate can be easily replaced with economy if worn or damaged. The cell is easily cleaned when the plate is removed however, cleaning the product from the holes in the plate is time consuming unless a high pressure spray can be used. The force increased non linearly during compaction of the samples in the cell (Fig. 5) and then almost linearly during compression. When the force was sufficient to shear and extrude the sample there was either a plateau or the force fluctuated rapidly about a mean force that was for practical purposes constant. This indicates that steady state conditions prevailed during extrusion. 'l'he test material could escape through the uniformly distributed holes in the plate
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Summary of typical records obtained with the different cells. Blank spaces indicate that it was not practical to test the particular product with the cell.
Fig. 6
Typical record for the Kramer shear cell showing the force required for the blades to enter the cell and then withdraw when testing baked beans. Can. Inst. Food Technol. J. Vol. 3, No.3, 1970
Table 2
Summary of Data2 for Products Tested Showing Force and Energy Used to Compress, Shear and Extrude the Samples (Mean of Two Samples).
..'---
Test Cell: Parameter2 : Product3 : Cherries Grapefruit Peaches' Apricot Pineapple Raspberries Strawberries Beet root Baked beans Carrots Mixed vegetable Spinach French beans Tomatoes Com Potatoes Peas Spaghetti 1. 2. 3.
KRAMER SHEAR Force Energy
BACK EXTRUSION Force Energy
PLATE EXTRUSION WIRE EXTRUSION Force Energy Force Energy
WIRE SHEAR Force Energy
6 12 6 8 38 1 3
45 73 36 36 127 7 11
15 31 11 24 120 4 8
68 143 71 113 35.'5 21 34
6 6 7 11 46
34 46 46 55 187
12 17 10 20 118
35 37 39 40 241
180 74 178 254 100 38
30 31 10 28 17 16 4
31 46 J4 43 61 20 13
56 26
73
19 21 7 24 23 12 7 11 36 29
109 121 37 105 109 55 55 32 243 126
93 94 36 99 132 48 31
531 269
176 258 68 145 256 8.5 65 69 295 258
23 28 8 31 43 15 13
Jl6 128
159 200 52 136 87 77 27 43 300 142
31 54
123 121
12
5
4
32
.5
43
3
25
5
24
33 70 21 44 294
81 154 57 105 556
12
28
50 93 22 7.'5 137 34 20
11
;;'.'1 ,~7
Blanks in the data imply that it was not practical to test the product by the method. Force in Kg energy in cmKg. For a full description see Table 1.
and was not trapped under the plunger. The product was therefore compressed only enough to initiate shearing and extrusion. Wire Extrusion Cell The cell is manufactured in the same way as the plate extrusion cell and therefore is also inexpensive. If the wires are fixed in the bottom of the cell clean· ing is relatively tedious. This can be overcome if the wires have sufficient strength by withdrawing them as shown (Fig. 3B). If any of the wires, which are the only critical parts are damaged they can be replaced at practically no cost. The results for this cell were not as consistent as with the plate extrusion (Fig. 5). While the majority of curves are similar several indicated that compression continued after extrusion started because material was trapped under the plunger. The force therefore continued to increase until a peak was reached which coincided with the maximum penetration of the plunger. It is assumed that this is caused by the relatively large diameter wire selected which presented smooth surfaces to the product preventing an efficient shearing action whereas in the plate extrusion cell sharp edges were used. Wire Shear Cell This cell while economic to manufacture is the most costly of the three new cells because of greater amount of machining is required. Compared to the wire and plate extrusion types it is relatively fragile. However, the critical parts, the shearing wires can be easily replaced. Cleaning is also more tedious. Previous work with Cottage cheese (Voisey and Emmons 1966) indicated that the force increased as the cheese curds were compressed and reached a plateau as the curds were cut by the wire. Similar behaviour was shown by several of the products tested J. Inst. Can. Techno!. Aliment. Vol. 3, No 3, 1970
indicating steady state conditions as the wires cut the sample (Fig. 5). However, for most of the products the force increased throughout the deformation indicating that the product was not all being cut by the wires and compression continued throughout the test. This was most marked for products containing fibrous materials. A summary of the forces and energies recorded for each cell for the various products (Table 2) is given to indicate the order of these measurements. It should be noted that within each product the force and energy required to operate the different cells covers a considerable range. Thus if a deformation machine with only a particular load capacity if available then a test cell producing loads within that range can be selected to accomplish the measurement. The ranking of the different products by each cell in this experiment cannot be considered meaningfUl because of the large differences between the sample sizes used. Effect of Sample Size Bourne (1968) found that sample size did not affect the results from the back extrusion method using a circular cylinder to test peas. Szczesniak (1969) has shown that sample size does influence results from the Kramer shear cell and that the effect varies with different products. The effect of sample weight on results from the wire and plate extrusion and the wire shear cells using peas and washed and drained baked beans as the test material was investigated. The results (Fig. 7) indicate that variation in sample weight does not affect the force measurements seriously but the sample weight should be considered important. There was a marked effect however on energy measurements. The energy used was directly proportional to sample weight. This should be obvious since the more material in the cell the 98
BEANS
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The effect of sample weight on force and energy measure ments from plate extrusion, wire extrusion and wire shear cells.
more work that must be done to compress shear and extrude the product. This points out that if energy measurements are used, for the convenience of a direct electronic digital readout, then control of sample size becomes extremely critical. It is reasonable to assume that this would be a requirement for any texture test cell.
Discussion The results indicate that each cell is not ideally suited for testing all the products used in the experiment. Each cell also has practical advanta~es and disadvantages which must be considered. The cells all subject the product to compression and then shearing combined with extrusion. Thus it can be assumed from a general viewpoint that each cell can detect similar textural properties. The relationships between force and deformation for each cell are different in varying degrees with each product tested. The interpretation of these curves is therefore a critical part of the technique. Reliability of any interpretations made can only result from extensive experience in relating the measurements to sensory analysis. This has not been attempted here. The limited number of products tested can only serve to introduce possible applications of the three new cell designs. However, it can be assumed that the elastic and shear strength properties of certain products can be estimated by all the cells. Extensive work is still required to determine the full potential of each new cell design. The cells described use a bulked sample, that is a selected weight or volume of the product to be tested, 9!J
A. plate extrusion and B. wire extrusion cells of different sizes and proportions.
not individual pieces such as a pea or a carrot slice. It is generally assumed that this provides an averaging effect. This is the case but if a single peak occurs in the force-deformation curve as in the Kramer shear cell, then this is a single unique result related to the shearing properties of the food. This single point may be biased by the sampling method, instrument errors or the manner in which the cell deforms a particular bulked sample. On the other hand if a plateau occurs indicating that the product is being sheared and steady state conditions prevail as the material is extruded then an average result, the mean height of the plateau, should in theory provide a more accurate estimate of the shear strength. Another aspect is that for research and in particular quality control applications a digital output eliminates the analysis of an analogue records on strip-charts. The instrumentation required to achieve this when a plateau is the parameter of interest can be made simpler than peak detection systems and still achieve a high degree of accuracy. Temperature control has not been used extensively with texture test cells except in viscosity measure· ments or when testing fats with various devices. The simplest approach is probably to use a water jacket. This can be installed on all the cells describrd but it is easier to manufacture a jacket for a cylindrical cell. A typical example of a back extrusion cell is shown (Fig. 2D). Water can be circulated from a constant tempprature bath and the specimen brought to the required temperature before testing. In selecting a cell to test a particular product both practical and measurement accuracy aspects must be considered and satisfied. Assuming the ease of cleaning and susceptibility to damage and initial and maintenance costs of a cell are satisfactory then it should be possible to design the cell using proportions suitable for the application. For example~ Can. Inst. Food Technol. J. Vol. 3, No.3. 1970
Table 3
Variations that can be used in the design and proportions of the test ceIIs1
Kramer Shear Area Height Number of blades Blade thickness Blade spacing Clearance between blades and grid
Back Extrusion Area Height Piston diameter Piston thickness Piston taper
Plate Extrusion Area Height Plate thickness Number of holes Spacing of holes Hole taper
Wire Extrusion Area Height Number of wires Diameter of wires Spacing of wires Shape of wires (round, square, etc.)
Wire Shear Area Height Number of wires Diameter of wires Spacing of wires Shape of wires (round, square, etc.)
1 Common parameters to all ceIIs are: a) compression speed; b) penetration of moving part of cell.
sample size may be dictated by the cost of preparing the material and in some cases it may be desirable to reduce this to a minimum. The sizes of the component parts or particles of the sample will also dictate the proportions of the cell parts that shear the product. It is therefore a distinct advantage if the cell can be "tailor made" for the particular product. For example a cell that will test products having an aggregate size in the order of peas may not be suitable for testing new potatoes. In general terms it can therefore be stated that the design principle of a cell may be universally applicable to a range of products but the cell proportions must change. The Kramer Shear Cell proportions can be varied by making it larger or smaller, changing the number and thickness of the blades and varying the clearance between the blades and the slots in the bottom grid. However, any change requires an entirely new cell. This is expensive, for example the half-scale multiblade cell (Model OS-2 Food Technology Corp.) currently costs $9:>0 U.s. Thus it is not economic to have a range of cells. On the other hand the proportions of the back extrusion, plate extrusion, wire extrusion and wire shear cell can be changed because they are cheaper to produce and the size of the critical components can be changed. There are a number of variables available with each of these cells. As pointed out by Bourne (1968) the piston diameter can be changed to vary the width of the extrusion annulus. This only involves removing a metal disc from a shaft (Fig. 2D). The cylinder can be made short and large in diameter or tall and small in diameter (Fig. 2B) or a range of cylinder diameters arranged to fit the same removable base (Fig. 2B). The thickness of the piston disc can be varied to change the length of the extrusion passage. If the circumference of the piston is bevelled the length of the extrusion passage could be reduced to almost zero since the extruded material could then expand into the space available. The tapered annulus formed could be either pointing up or down to provide either an expanding or contracting passage. The plate and wire extrusion cells can be made in a range of sizes (Fig.S). The nurnbel' of holes, the spacing between holes and the thickness of the extrusion plate can be changed within each size to suit each product. The holes can be tapered in either direction to provide either an expanding or contracting passage. Similarly for a given size of wire extrusion J. Inst. Can. Techno!. Aliment. Vo!. 3, No 3, 1970
or wire shear cell the number, spacing and diameter of the wires can be selected to suit the application. Another alternative would be to use square or rectangular wires oriented in different ways so that different shear edges were presented to the test material. Interchangeahility of texture test cells becomes important if the same test is to be made using several cells. This can be achieved in relation to the mechanical aspects of the cell. The sizes of the various components can be specified to close tolerances. The cost of achieving this depends greatly on the cell design and should be reduced to a minimum. In the plate and wire extrusion and wire shear cells the critical shearing components and their spacing are based on drilling operations, ground steel plate and wire diameters. These are relatively inexpensive. The back extrusion cell can be manufactured almost entirely by turning in a lathe which can be done at reasonable cost and still maintain close tolerances. The cylinders can be made from stock tubing to further reduce costs. The simplicity of design of the three new cells and the back extrusion cell indicates that they can be manufactured locally and the low cost means that a range -of cells can be kept on hand to test different products. Standardization of the mechanical aspects of the cells is of prime importance because of the number of variables possible. While individual researchers will obviously wish to tailor their own cells it would be logical to base this on some previously agreed standard. There is insufficient data available to lay down these standards at present. However it is proposed that the proportions be based on the area of the cell measured at the horizontal plane that is covered by the test sample. To emphasize the flexibility of the cell designs and the need for standardization of the dimensions those that can be varied are tabulated (Table 3). It should be noted that most of the variables can be made proportional to the area of the cell.
Conclusions The performance of three new cells and the back extrusion cell in relation to the Kramer Shear Cell has been demonstrated. The data presented indicates that these cells can be used to estimate textural propreties of some products instead of the Kramer Shear Cell. Each cell has practical advantages and the one 100
selected depends on the product to be tested. There is a definite advantage if a plateau occurs in the force-deformation relationship since this may provide a more reliable index of shearing strength than a single peak. This behaviour occurs with all the cells for particular products. It is probable that each cell can be made to achieve this type of result by changing the proportions of the shearing-extrusion components. Extensive work to be published later has shown that results from the back extrusion and three new cell designs are highly correlated with Kramer shear tests for peas and baked beans. This is to be expected since all the cells subject the samples to essentially the same basic mechanical operations, that is, compression, shear and extrusion. An obvious conclusion that is worth repeating here is that in any empirical test using the test cells all test conditions must be kept constant. This is the only way meaningful comparisons can be made by the techniques described. If any condition is changed such as sample size, cell size, deformation speed ,etc., the effect of this should be investigated. It is necessary to standardize the proportions and dimensions of the test cells so that interlaboratory comparisons can be made or quality control applications can be standardized. While it is too early at present to lay down a set of formal standards it would appear that this aspect should be investigated before the different cells become widely used. The different cell designs cannot replace the Kramer shear cell for all products. For example they are not suitable for testing meat because extremely high forces are involved. It should be noted that the forces required to compress, shear and extrude even the soft products tested were high, for example canned pineapple required up to 300kg. The force required will also depend on the size of test cell used. Thus the deformation mechanism should have high load capacity. Manufacturing arrangements are currently being made to produce the plate and wire extrusion cells as one integrated unit with interchangeable bottoms so that one cell body and plunger can be used for both types of tests. It is estimated that the cost will be about $100.
Acknowledgement The author wishes to acknowledge the valuable technical assistance of M. Kloek, Engineering Research Service.
References Ang, J. K., F. M. Isenberg and J. D. Hartman. 1960. Measurement of firmness of onion bulbs with a shear press and potentiometric recorder. Proc. Amer. Soc. Hort. ScI. 75: 500. Ang, J. K., J. Hartman and F. M. Isenberg. 1963. New applications of the shear press in measuring texture in vegetables and vegetable products. II. Correlation of subjective estimates of texture of a number of whole and cut vegetables and objective measurements made with several sensing elements of the shear press. Proc. Amer. Soc. Hort. ScI. 83: 734. Angel, S., A. Kramer and J. N. Yeatman. 1965. Physical methods of measuring quallty of canned peas. Food Techno!. 19: 96. Anon. 1968. Texture test systems designed to measure quality of foods. Can. Food Ind. 39: 53. Baker, R. C., J. Darfler and D. V. Vadehra. 1969. Type and level of fat and amount of protein and their effect on the quallty of
101
chicken frankfurters. Food Techno!. 23: 100. Binder, L. J. and L. B. Rockland. 1964. Use of automatic recording shear press In cooking studies of large dry llma beans (Phaseolus Lunatus). Food Techno!. 18: 127. Bourne, M. C., J. C. Moyer and D. B. Hand. 1966. Measurement of food texture by a universal testing machine. Food Techno!. 20: 17.. Bourne, M. C. and J. C. Moyer. 1968. The extrusion principle in texture measurement of fresh peas. Food Techno!. 22: 1013. Brown, S. L. and M. E. Zablk. 1967. Effects of heat treatments on the physical and functional properties of liquid and spray-dried egg albumen. Food Techno!. 21: 87. Buck, E. M. and D. L. Black. 1967. The effect of stretch-tension during rigor on certain physical characteristics of bovine muscle. J. Food Sci. 32: 593. Buck, E. M. and D. L. Black. 1968. Microscopic characteristics of cooked muscles subjected to stretch tension during rigor. J. Food ScI. 33: 464. Christel, W. F. 1938. Texturemeter. A new device for measuring the texture of peas. Canning Trade. 60(34): 10. Fox, M. and A. Kramer. 1966. Objective tests for determining quality of fresh green beans. Food Techno!. 21: 88. Franks, O. J., M. E. Zablk and C. L. Bedford. 1969. Sensory and objective comparisons of frozen, IQF, dried and canned montmorency cherries In pies. Food Techno!. 23: 77. Fry, J. L., P. W. Waldroup, E. M. Ahmed and H. Lydick. 1966. Enzymatic tenderization of pOUltry meat. Food Techno!. 20: 102. Funk, K., M. E. Zabik and D. M. Downs. 1965. Comparison of shear press measurements and sensory evaluation of angel caKes. J. Food ScI. 30: 729-736. Gilpin, G. L., O. M. Batcher and P. A. Deary. 1965. Influence of marbling and final Internal temperature of quallty characterIstics of broiled rib and eye of round steaks. Food Techno!. 19: 152. GrUber, S. M. and M. E. Zabik. 1966. Comparison of sensory evaluation and shear-press measurements of butter cakes. Food Techno!. 20: 118. Hartman, J. D., F. M. Isenberg and J. K. Ang. 1963. New appllcatlons of the shear press in measuring texture in vegetables and vegetable products. 1. Modifications and attachments to increase the versatllity and accuracy of the press. Proc. Amr. Soc. Hort. Sci. 82: 465. Johnson, C. F., E. C. Maxie and E. M. Elbert. 1965. Physical and sensory tests on fresh strawberries subjected to Gamma radiation. Food Techno!. 19: 119. Kanujoso, B. W. T. and B. S. Luh. 1967. Texture, pectin, and syrup viscosity of canned cllng peaches. Food Techno!. 21: 139A. a. Kramer, A., K. Aamlld, R. B. Guyer and H. Rogers. 1951. New shear-press predicts quallty of canned limas. Food Engng. 23: 112. b. Kramer, A., G. J. Burkhardt and H. P. Rogers. 1951. The shearpress, a device for measuring food quality. Canner. 112: 34. Kramer, A. and K. Aarnlid. 1953. The shear-press, an instrument for measuring the quality of foods. III. Application to peas. Proc. Amer. Soc. Hort. Sci. 6: 417. Kramer, A. and W. J. Hart. 1954. Recommendations on procedures for determining grades of raw, canned, and frozen llma beans. Food Techno!. 8: 55. Kramer, A. 1957. Food Texture rapidly gaged with versatile shear press. Food Engng. 29: 57. Kramer, A. 1961. The shear-press, a basic tool for the food technologist. Food Scientist 5: 7. Kramer, A. and J. V. Hawbecker. 1966. Measuring and recording rheological properties of gels. Food Techno!. 20: 209. Lovel!. R. T. and G. J. Fllck. 1966. Irradiation of gulf coast strawberries. Food Techno!. 20: 99. Luh, B. S. and K. D. Dastur. 1966. Texture and pectin changes in apricots. J. Food Sci. 31: 178. Mannheim, H. C. and A. Baka!. 1968. An Instrument for evaluating firmness of grapefruit segments. "Food Techno!. 22: 83. Marion. W. W. and H. M. Goodman. 1967. Influence of continuous chilling on tenderness of turkeys. Food Techno!. 21: 89. Miller, W. O. and K. N. May. 1965. Tenderness of chicken as affected by rate of freezing, storage time and temperature, and freeze drying. Food Techno!. 19: 147. Newmann, H. J., L. R. Frame, L. Morgan and R. L. Olson. 1960. Use of the Kramer shear-press In forcastlng harvest dates for Fordhook llma beans. Food Techno!. 15: 225. Palmer, H. H., A. A. Klose, S. Smith and A. A. Campbell. 1965. Evaluation of toughness differences in chickens In terms of consumer reaction. J. Food Sci. 30: 898. Pangborn, R. M., N. Sharrah, H. Lewis and A. W. Brant. 1965. Sensory and mechanical measurements of turkey tenderness. Food Techno!. 19: 86. Peterson, D. W. and A. L. Lllyblade. 1969. Relative differences in tenderness of breast muscle in normal and two dystrophic mutant strains of chickens. J. Food Sci. 34: 142. a. Sharrah, N., M. S. Kunze and R. M. Pangborn. 1965. Beef tenderness: Sensory and mechanical evaluation of animals of different breeds. Food Techno!. 19: 131. b. Sharrah, N., M. S. Kunze and R. M. Pangborn. 1965. Beef tenderness. Comparison of sensory methods with the Wa~ner Bratzler and LEE-Kramer shear press. Food Techno!. 19: 136. Stadelman, W. J., G. C. Mostert and R. B. Harrington. 1966. Effect of aging time, sex, strain and age on resistance to shear of turkey meat. Food Techno!. 20: 110. Szczesniak, A. S. 1969. The Whys and whats of objective texture measurements. J. Can. Inst. Food Techno!. 2: 150. Thomas, N. W., P. B. Addis, H. R. Johnson, R. D. Howard and M. D. Judge. 1966. Effects of environmental temperature and humidity during growth on muscle properties of two porcine breeds. J. Food Sci. 31: 309. Can. Inst. Food Techno!. J. Vo!. 3, No.3, 1970
Toumy, J. M., J. Felder and R. L. Helmer. 1966. Relation of pork loin weight to shear-force values, panel scores, fat In lean meat, and cut out percentages. Food Techno!. 20: 174. Toumy, J. M. and R. L. Helmer. 1967. Effect of freeze drying on the quallty of the longissimus dorsi muscle of pork. Food Techno!. 21: 167. Toumy, J. M., H. T. Schlup and R. L. Helmer. 1969. Effect of cooking temperature and time on the tenderness of precooked freeze-dried turkey white meat. Food Techno!. 23: 60. Voisey, P. W., M. Kloek and A. W. Thomlison. 1966. An apparatus for comparing to textural quality of foods. Eng. Res. Service, Ottawa Bul!. 6262. Voisey, P. W. 'and D. B. Emmons. 1966. Modlflcatlon of the curd
J. lust. Can. Techno!. Aliment. Vo!. 3, No 3, 1970
firmness test for Cottage cheese. J. Dairy ScI. 49: 93. Voisey, P. W., D. C. MacDonald and W. Foster. 1967. An apparatus for measuring the mechanical properties of food products. Food Techno!. 21: 43A. Wangen, R. M. and J. H. Skala. 1968. Tenderness and maturity In relation to certain muscle components of White Leghorn fow!. J. Food ScI. 33: 613. Werner, G., E. E. Meschter, H. Lacey and A. Kramer. 1963. Use of the shear press In determining the flbrousness of raw and canned green asparagus. Food Techno!. 17: 81. Received May 7, 1970
102