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| Mackey, Andrea C., Margaret M. Hard, and Mary V. Zaehringer. 1973January. Measuring Textural Characteristics of Fresh Fruit and Vegetables - Apples, Carrots, and Cantaloupes. A Manual of Selected Procedures. Technical Bulletin 123. Agricultural Experiment Station, Oregon State University Corvallis, OR. | to Top |
- Full scale, 10 divisions = 100 kg
Each division = 10 kg - Maximum force = maximum height in inches x 2500 pounds
Work in pound-inches per inche=force per inch x area under the curve in square inches x F
Compression strength of carrots may be determined with the Instron Universal Testing Machine (Howard and Heinz, 1970). It is recommended that carrots be measured at a point of uniform diameter, since greater force is required to compress material of greater diameter.
PRESS JUICE
APPLES
Peel and core apples using a stainless steel corer and knife.
Method for succulometer cell attached to the Instron
1. Place a 50-g sample of apple slices cut less than 1/8 inch thick in the succulometer cell, arranging them so the curved edges of the slices are toward the curved edges of the succulometer. keep the slices level and away from the juice funnel
2. Place a previously weighed beaker under the spout to collect the juice.
3. Bring the crosshead down until the piston is close to the sample.
4. Set the dials to allow the crosshead to descend 8 cm.
5. Using a pressure of 500 kg (FSL at 50), allow the piston to press the slices down about 7 cm or until a lag-stop is heard; turn the machine off.
6. Allow the piston to rest on the sample for 3 minutes.
7. Run the piston down again until a lag-stop is heard; turn off the machine and allow the piston to rest on the sample for an additional 3 minutes.
8. Remove the test cell and allow any remaining juice to drain into the beaker.
9. Weigh the beaker. Weight of beaker _ juice - weight of beaker = weight of juice.
Method for succulometer cell attached to the Texturepress
1. adjust the scrrew on the Texturepress located at the back of the cell so that all gauges will be correctly aligned.
2. Insert 5000-pound test ring.
3. Adjust the flow control valve for a 60-second stroke. Calibrate, using a range of 100. Adjust the range to 50.
4. Select a representative sample of apple that has been pared, cut in eighths, and sliced into 1/4 - inch slices. Weigh 50 g and place the pieces in the cell at random. Push apple away from the spout area.
5. Place a circle (2.5 of N. 2 Whatman filter paper over apple slices in thcell area. Attach the cell piston. Install the sample cup in the hydraulic press with the spout to collect the juice.
6. Turn the exterior part of the pressure adjust knob full counterclockwise. Place the direction control valve in the down position.
7. Allow the piston to contact the apple sample in the cup. Slowly turn the exterior part of the pressure control knob clockwise to increase the pressure to 300 pounds or until foam instead of juice appears.
8. Maintain this force until the peak has been reached on the texture-gram.
9. Raise the power ram.
10. Remove the test cell and drain the remaining juice into the beaker. Weigh. Weight of beaker + juice - juice - weight of beaker = weight of juice collected.
11. Rinse and dry the test cell after each sample is processed.
Note: While learning this technique, it is best to use two operations-one to operature the pressure gauge. The second to collect the juice and watch the pen on the texturegram until the procedure is under control. The texturerecorder is used simply to check that the pressure is raised gradually and does not register beyond 95.
CARROTS
A hydraulic laboratory press may be used to press juice from carrots. Using approximately 10 to 12 g of carrot slices, wrap closely in Saran wrap to prevent moisture loss, and free overnight. Thaw the sample and subject to a pressure of 15,000 pounds per square inch. the expressed juice may be frozen immediately in dry ice and used later for freezing point determination or other analysis.
TURGOR PRESSURE
The determination of turgor pressure is a two-step process. The formula is:
Diffusion Pressure Deficit
APPLES
1. To obtain the figure for DPD, make up a series of sucrose solutions, from 0.1 to 1.0 molar, each solution differing by 0.1M
2. Measure 25 mL of each solution into small screw-cap vials. Each series should include a vial containing 25 mL of distilled water.
3. Use five apples. Each apple constitutes one replication.
4. Using a No. 2, stainless steel, sharp cork borer, cut small cylinders of apple flesh. Weigh 3 g. quickly, and place iin one of the vials. Continue until apple pieces have been placed in each of the vials. By boring close together, enough cylinders can be obtained from one apple.
5. Use the remaining apple pulp for freezing point determination. Blend in a Semi-Micro Blendor for 1 to 2 minutes. Centrifuge at high speed and filter the juice through Whatman No. 4 filter paper. use 10 mL for freezing point determination. This can be done while the apple cylinders equilibrate with the sugar solutions.
6. Allow the apple cylinders to remain in the sugar solutions until the moisture has equilibrated (18 to 24 hours).
7. The Abbe refractometer has a scale showing percent solids as sucrose. Read the percent solids of the sugar solutions. Read the percent solids of the solutions in which the apple tissue is immersed.
8. Subtract, to find the different in percent solids. When the percent of solids is found to be higher in the apple-bathing solutions, it indicates that the apple tissue absorbed moisture from the bathing solution. A lower percent of solids in the apple-bathing medium indicates that moisture diffused from the apple, thus diluting the solution.
9. If these data are plotted, a parabolic curve results, from which it is difficult to read the molarity of the sugar solution at which no change would take place. The point at which the percent solids of the bathing solution would show zero change is found by calculating a best-fitting line. This line is plotted, using the molarity of the sugar solutions as the abscissa and the change in percent solids as the ordinate.
10. That concentration of sucrose at which no change in percent solids takes place is the diffusion pressure deficit.
11. The figure for diffusion pressure deficit is converted to atmospheres in order to calculate turgor pressure.
CARROTS
1. To obtain the figure for DPD, remove a core through the diameter at the center of the carrot, using a sharp, stainless steel cork borer, No. 2 size.
2. Slice the core as thinly as possible with a razor blade.
3. Blot the slices gently, combine five or six and weigh quickly.
4. Place each group of slices in sucrose solutions ranging from 0.1 to 0.6 molar. Each series should include a vial containing distilled water.
5. Allow to equilibrate for 24 hours.
6. Remove the slices form the solutions.
7. As each set of slices is removed from a vial, blot lightly to remove excess liquid, and weigh. The difference between the initial weight and the final weight = weight change.
8. Calculate best-fitting lines.
9. Plot the lines, using molarity of the sucrose solutions as the abscissa and the change in weight as the ordinate.
10. That concentration of sucrose at which no weight change takes place is the diffusion pressure deficit. This is converted to atmospheres in order to calculate turgor pressure.
11. Osmotic pressure is calculated from the freezing point of the carrot juice. Obtain the juice as described under Press Juice.
12. Thaw the frozen juice until just liquid, about 10 minutes, so that the thermocouples of a recording potentiometer or a thermistor may be inserted.
13. Determine freezing point as described.
MELONS
1. To obtain a figure for DPD, take 10 cores, approximately 4 cm long, using a stainless steel core borer, No. 5.
2. Blot all surfaces very lightly with absorbent paper.
3. Weigh each core quickly and place in one of several vials containing sucrose solutions ranging in concentration from 0.1 to 0.7 molar. Each series should include a vial containing distilled water.
4. Close the vials and allow to equilibrate.
5. Remove the cores, blot lightly to remove excess liquid, and weigh quickly.
6. The difference between the initial weight and the final weight = weight change.
7. Calculate best-fitting lines.
8. Plot the lines, using the molarity of the sugar solutions as the abcissa and the change in weight as the ordinate.
9. The concentration of sugar at which water neither enters nor leaves the tissue, as indicated by zero change in weight, is the DPD. This figure is converted to atmospheres for use in the formula for calcualting turgor pressure.
10. Osmotic pressure is determined from the freezing point depression of the melon juice. obtain the juice from melon slurry.
11. Thaw approximately 20 g of the frozen slurry at room temperature for about 10 minutes.
12. Centrifuge at high speed (4500 rpm) and filter through Whatman No. 4 filter paper.
13. Use 10 mL of the filtered juice for determining the freezing point.
Freezing Point
A recording potentiometer or an apparatus employing a thermistor and a moisture ohmeter may be used for nothing the freezing point.
Freezer
The temperature at which freezing of the fruit or vegetable juice takes place can be determined by placing the juice with the inserted thermocouples into a freezer. The freezing point is indicated by a plateau in the temperature readings.
Thermistor and moisture ohmeter. 1. Construct a calibration curve, using glycerol solutions maintained at different temperatures in ice, salt and water baths. Insert the thermistor and a thermometer into the glycerol solution and obtain microampere readings and temperture readings simultaneously.
2. To find the freezing point of the juice, insert the thermistor into the juice.
3. Place this assembly in a container of ice and salt, 8 to 10 parts ice to 1 part salt.
4. Stir the liquid surrounding the test tube of juice during cooling.
5. Take readings of electric current in microamperes at zero and at 15-second intervals until a constant reading equal to the freezing point is obtained.
6. Determine the temperature of freezing by reference to the calibration curve relating microampere readings to temperature.
For determining specific gravity, it is necessary to obtain the weight of the apple in air and when submerged in water. Either of the following methods yields satisfactory results.
Equipment
1. Wire basket with a lid.
2. Large container nearly ful of distilled water (plastic wastebasket can be used).
3. Toledo scale, capacity 5 kg.
Directions
1. Mark a bar of wood approximately 1 inch x 1/2 inch x 18 inches with red lines about 2 1/2 inches from the end. Place it on the right-hand weighing pan of the Toledo scale, securing it under the metal pice at the side.
2. Place the chain of the wire mesh basket between the red lines and suspend the wire basket freely in the container of distilled water, taking care to eliminate air bubbles. A rubber policeman may be used to rub away air bubbles. leave the basket in water during all weighings.
3. Place a box on the left-hand weighing pan and put sufficient sand in it to bring the pointer exactly to the 100-g mark on the scale.
4. Place the apple on the right-hand weighing pan. Record the scale reading for the weight in air.
5. Place the apple in the submerged basket, taking care to eliminate air bubbles around the apple and under edges of the lid. Record scale reading for weight in water.
1. Metal plunger made of stainless steel wire. Mark a red line on the plunger 9 cm from the bottom.
2. Tin can 22 cm high with a diameter of 17.5 cm; mark a red line inside the can 15.5 cm from the bottom.
3. Toledo scale.
Directions
1. Weigh the apple in air.
2. Fill the can to the red line with water at room temperature.
3. Place the can with water and plunger on the scale and weigh.
4. Place each apple with blossom and stem ends horizontal to water level. Place the plunger ooover the apple, pushing it under water until the red line of the plunger is in line with the red line on the can. Record the weight.
5. The following formula is used.
Weigh the melons in air to 0.1 g. precision. Submerge in 2500 mL water at 22C and measure the water displaced by each melon. Take two measurements on each melon.
The Magness Probe is suitable fgor measuring resistance to penetration (Magness and Taylor, 1925; Szczesniak, 1963). fit a rubber stopper with a hole in the center over the probe so that only 1/4 inch will penetrate the apple. Hold the apple firmly against the rear wall of the counter.
Test for skin toughness
1. Push the probe, 7/16 inch diameter, firmly against the apple at its largest circumference.
2. Make two tets on opposite sides of each apple and record the readings to the first decimal place.
Test of flesh
1. Remove small circles of skin approximately 1/2 inch in diameter at opposite sides of the same apple near the largest circumference.,br> 2. Push the 7/16 inch diameter probe firmly into the flesh and record the reading.
The following directions are offered to simplify and facilitate the operation of the instruments used in the determination of shear compression.
A table model Instron Universal Testing Machine (TM-M) with a CDM compression load cell (capacity 0-500 kg) is used. The gears in the Instron are set so that the crosshead and the recorder move at the same rate of speed, 2 cm per minute. The full scale load (FSL) is set at 10 (100 kg) for Golden Delicious and Red Delicious apples and at 20 (200 kg) for Winesap variety. Apples become softer after storage, so it may not always be necessary to use 200 kg for Winesap.
The Instron is fitted with an adapter to accommodate the Allo C-1 standard compression test cell.
Rinse all parts of the shear compression test cell with distilled water and dry before the first use so that the same amounbt of moisture is present each time it is used.
Calibration
The Instron is calibrated as follows: 1. Turn on main power switch. Allow to warm up 30 minutes.
2. Turn on pen motor switch
3. Set full scale load switch on 20
4. Depress "zero" switch. Turn "zero knob," while holding zero switch down, until the pen is on the zero line on the chart.
5. Release zero switch and lock knob in place. Adjust the "balance" knob until the pen is on zero.
6. Set FSL on 10,5,2, and 1, repeating steps 4 and 5 for each position.
7. With FSL in position 1, load 10 kg on load cell platform. Adjust the pen to 10 on the chart, using the "calibration" knob. Remove weights.
8. Place testing cell on platform. Adjust pen back to zero, using the "balance" knob.
Operation
The Instron is operated as follows:
1. Set FSL at 10 or 20 as needed.
2. Turn on crosshead powder switch. Turn off pen switch.
3. Set dials to allow crosshead to descend a total of 10 cm. Run crosshead down until blades of shear unit can be aligned with grids of testing cell (about 1 1/4 cm).
4. turn on chart switch and pen switch. Depress "down" button at "A" speed. Run crosshead down until blades emerge from bottom of the test cell (about 8 3/4 cm). Depress "up" button at "B" speed. Run crosshead up until blades are free of the grid. Remove blades and rinse in hot water and distilled water. Remove testing cell and collect samples for alcohol-insoluble solids, if desired. Rinse and dry testing cell.
Preparation of sample
Remove two apples from the refrigerator and allow to come to room temperature. Balance each on the stem end and cut into quarters from the blossom to the stem end. Pare each quarter thinly, core, and cut longitudinally into 1/4-inch slices, discarding wedge-shaped pieces. Cut the slices in half crosswise, place in a bowl, and mix well with the hands, stirring and tossing the apples over at least 10 times to obtain a homogeneous sample.
It is convenient to weigh out three 80-g aliquots of apple slices and wrap them in Saran wrap. the first aliquot is used as a "dummy" or "test" run to determine whether a full scale load of 100 kg or 200 kgt is needed. A sample size of 80 g of apple was selected in order to stay within the capacity of the Instron compression load cell used with the table model machine.
Arrange the 80 g. of apple slices in even layers, alternating directions, in the bottom of the test cell box. Assemble the test cell, set in place, and carry out the shear compression test.
Since the Instron has a metric sclae and the planimeter reads in inches, the formulas for a full scale load of 100 kg are:
1. MAXIMUM FORCE. Number of divisions at highest peak on curve x 10 x 2.2046= maximum force in pounds.
2. Work To Shear. Each division = 1.056 inches. at full scale load of 10, force per inch in pounds = 10.56 x 2.2046 = 23.281 pounds. Area under the curve in square inches x 23.281 = work to shear in pound-inches.
Shear compression may also be determined with this instrument. In this cooperative research, the Allo-Kramer Shear Press, model S-2HE, and Recorder Indicator, model E-2EZ, were used on three varieties of apples- Red Delicious, Golden Delicious, and Winesap. The recorder chart advanced 2.725 inches for each full stroke of the power ram. The ram speed was 3.475 inches for 60 seconds after 16 to 18 warm-up strokes at room temperature of 72 to 74F. Other individual instruments or models may differ somewhat, but these factors should be known.
The 5000-pound proving ring at range 10 was used for all varieties except Golden Delicious, which were very tender, or for apples that had been stored at 45F in which case a 500-pound proving ring at range 50 was used. Two hundred pounds pressure was used on the 5000-pound ring, and 50 pounds on the 500-pound ring was set at values to accommodate the 60-second stroke of the ram. The test cell was the C-IS standard shear compression cell which consisted of a sample holder, slotted lid, and 10 movable blades each 1/8 inch thick.
1. Turn function switch of the texturerecorder to "Standby" position and allow a 30-minute warm-up period. Power switch on. Chart speed low.
2. Rinse texturecorder pen with warm water. Fill with just enough ink to cover the bottom of the reservoir.
3. Establish the descent rate and pressure on the ram of the Texturepress. Release the locking nut on the pressure releaf valve.
Put the direction control in the down position. Turn the power switch to on and the direction control valve to down. The pressure gauge will register. If the reading is too high for the ring being used, immediately turn the pressure control valve counterclockwise. Then slowly turn clockwise to the desired pressure setting and lock this setting in by turning the inner black knob clockwise. The 5000-pound ring should not exceed 420 pounds of pressure, and the 500-pound ring should not exceed 50 pounds pressure.
Return the ram to its upper position by turning the direction control valve to up. Set the direction control valve to the center position when the ram is fully retracted.
Adjust the ram descent speed by rotating the flow control valve. Turn the bottom silver-colored valve clockwise to decrease the speed or counterclockwise to increase the speed. When ram speed is achieved, lock the flow control valve by tightening the small knurled green knob on top.
4. Turn the function switch of the recorder indicator to operate.
5. Raise and lower the ram 15 to 20 strokes or until the descent is one minute.
Install the proving ring and test head. check the transducer carriage so that it is securely in place. Tighten the locking thumb screw.
1. Turn the recorder zero adjust knob one quarter turn clockwise.
2. Turn the range selector knob to the 1% position on the range dial.
3. Adjust the zero adjust stud on the proving ring so that the pen on the recorder travels to the center of the chart paper.
4. Turn the range selector knob to 100% position and rotate the zero adjust knob on the recorder to zero on the chart paper.
5. Turn the range selector knob to the 1% position and adjust the zero adjust stud on the proving ring until the pen rests on the chart paper zero. At this time the range selector knob should be turned quickly from 1% to 100%, with the pen continuing on zero. If this is not possible, repeat the steps for calibrating the recorder indicator.
1. The range selector knob must be on 100% and the recorder indicator pen on zero.
2. Place the gauge block for the designated proving ring between the zero adjust stud and the transducer pickup (number area must be to the front).
3. Push down lightly on the edge of the gauge block to tilt it upwards so that the pen deflects upon five divisions. Remove finger: the recorder indicator pen should return to the position which corresponds to the three-digit number etched on the gauge block.
4. A fine adjustment may be made by adjusting the calibration control on the recorder indicator.
5. A greater adjustment is made by again calibrating the recorder indicator.
6. Slight changes in the zero position may be observed on the more sensitive range settings.,br> 7. Wipe the gauge block with light oil and return it to the container for storage.
1. Use an 80-g sample of 1/4 inch slices of apple. Interlace crosswise over the bars of the shear compression cell.
2. Wet blades before shearing the first sample.
3. Align the blades over the shear cell. If the ram is slightly twisted so the blade element and cell cover do not mesh properly, remove the cell. Straighten by easing the ram down 1/4 inch; then grasp the whole assembly and roate slightly. raise the ram and insert the cell.
4. Place drip pan below the shear compression cell.
A Texture press may be used to determine the force and work required to shear carrot samples. Arrange 50 g of sliced carrot in the shear cell. Set the instrument to a full scale of 2400 pounds. During shearing, the time-force curve is recorded as peaks on a graph. Measure the area under the peak in square inches using a Compensating Polar Planimeter, and ascertain the maximum height of the curve in inches by measuring. The full scale of 5 inches is equal to 2500 pounds. The following formulas apply (F is explained under determination for apples):
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Updated: Saturday, September 20, 2008.
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