SOP: Texture Profile Analysis Using the General Foods Texturometer

GIFSQ — Global Institute for Food Safety & Quality

Principle

The General Foods Texturometer imitates mastication: an articulator drives a plunger up and down on the sample for two successive cycles (two “bites”), and the force-time curve so obtained yields the texture profile parameters — hardness, cohesiveness, elasticity (springiness), adhesiveness, fracturability (brittleness), gumminess and chewiness — all derived from the same curve. A standard sponge rubber sample standardises the instrument; samples are normally 0.5 inch in height and are compressed to a 0.125 inch clearance (75% compression).

Apparatus required

• General Foods Texturometer: deformation mechanism (electric motor driving an articulator up and down at 12 to 24 strokes per min, plunger motion sinusoidal); force indicating system with strain-gauge beam transducer; flat-bottom brass or acrylic plungers (17–50 mm diameter) and a three-serration plunger; flat plate for solid samples and shallow dish for liquid or semi-liquid products; recorder
• Standard sponge rubber sample, 0.5 inch in height
• Talcum powder (for adhesive samples)

Procedure — Standardisation and sample mounting

Position the articulator arm for a clearance of 0.125 inch (75% compression) between plunger and sample stage at the point of maximum drive

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Refer to the standard sponge rubber sample at intervals during a day’s run of samples

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Wherever possible, trim all samples to 0.5 inch height with an area at least equal to the plunger base; where other heights are used, apply the necessary corrections

Procedure — Texture profile recording

Set the rate of chewing (e.g. 12 chews per min for the strawberry determination) and the distance between the supporting platform and the plunger in its most downward position

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Place the sample on the platform (halves with the cut surface down, slices built up to the required height) and record the force-time curve for two successive compression cycles, the first bite (peak A₁) and the second chew (peak A₂)

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Derive the parameters from the curve as described under Calculation

Calculation

(i) Hardness: the peak force during the first compression, measured as the height of the force peak on the first compression cycle; normalise all hardness values to a one-volt output as (height of first peak)/(volts input).

Where,

• The book’s printed statement of the hardness normalisation is illegible in the extraction; the form above follows the book’s text description.

(ii) Cohesiveness: the ratio of the area under the second peak to the area under the first peak (A₂/A₁), dimensionless; if the food shows adhesiveness, dust it with talcum powder before recording the cohesiveness profile so that the negative adhesion peak does not distort the curve.

(iii) Springiness or Elasticity: measured as the difference between the distance B (from initial sample contact to contact on the second chew) and the distance C (the same measurement made on a completely inelastic standard material such as clay). Springiness = C − B; with the instrument, the value of C is 68.5. The preferred sample height for this measurement is 1.0 inch. Currently springiness is defined as the height that the food recovers during the time that elapses between the end of the first bite and the start of the second bite.

(iv) Adhesiveness: measured as the negative force area beneath the base line (A₃), representing the work necessary to pull the compressing plunger away from the sample; measure using samples 0.5 inch high and input voltage of 5.

(v) Fracturability (or brittleness): characterised by the multipeak shape of the first bite; measured as the height of the first significant break in the peak; conditions: sample height 0.5 inch and input voltage of 1.

(vi) Gumminess: Hardness × cohesiveness; multiply the results by 100 to eliminate decimals.

(vii) Chewiness: Hardness × cohesiveness × elasticity.

Where,

• Measurements are reported in arbitrary instrument units which can be converted into CGS units by the use of standard references.
• An additional parameter, the crushability index (D/A₁), is obtained by subtracting twice the area of decompression of the first bite from the total positive area of the first bite and calculating the ratio; D represents crushing work and A₁ represents elastic work during compression. The crushability index has a correlation with the tenderness in some foods.

Worked illustration — texture of strawberry (17 mm diameter flat brass plunger, 12 chews per min, plunger-to-platform distance 1.2 mm at maximum down position, 6 to 15 individual determinations per lot, averaged): firmness and crispness are expressed as grams force; cohesiveness is a dimensionless ratio of the recorded area for the second and first chew (A₂/A₁); adhesiveness is expressed as grams force multiplied by centimetre chart; juiciness is determined by placing one piece of Whatman No. 41 filter paper under the sample and another piece above the sample, and determining the total wetted area after three consecutive instrument “chews”, expressed in cm².

Precautions

• Standardise the instrument during each day’s run.
• Keep sample heights uniform; correct for any deviation.

References

Szczesniak, A.S. & Smith, B., Journal of Texture Studies, 1, 65 (1969).

Ranganna, S., Handbook of Analysis and Quality Control for Fruit and Vegetable Products, 2nd edition.