SOP: Measurement of Jelly Strength with the Lüers–Lochmüller Pektinometer

GIFSQ — Global Institute for Food Safety & Quality

Principle

The jelly is allowed to set in a special container with corrugated sides, and the force required to pull a disc embedded in the jelly upward is measured. The disc is suspended from one arm of a balance; a moving load on the other arm supplies the breaking force.

Apparatus required

• Jelly container with corrugated sides (C)
• Disc (A) held by an arm and suspended on a balance
• Moving load on the other arm of the balance
• Weights for pan (W)
• Indicator (I), showing the extent of compression of the jelly
• Base (B) of the balance

Procedure — Pektinometer test

Place disc (A), held by an arm and suspended on a balance, in the corrugated container (C)

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Pour hot jelly on it and allow to cool for at least one hour in running cold water, so the disc becomes embedded in the jelly

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Apply weights on pan (W) and measure the force needed to break the jelly by the pressure of the submerged disc — the corrugated sides of the vessel prevent the jelly from slipping in the container

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Read the indicator (I) for the extent of compression of the jelly caused by the weight

Procedure — Hamer modification

Suspend a brass disc, 0.5 to 0.75 inch in diameter, in a beaker containing the jelly by means of a wire attached to one beam of an analytical balance

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Keep the beaker containing the jelly on an adjustable platform

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Connect a calibrated capillary tip to a burette containing mercury

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Add mercury to a beaker on the other pan at a constant rate of 16 g per min; as the mercury is added, keep adjusting the height of the platform manually so that the pointer is always at zero

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Note the height of the adjustable platform at frequent intervals until the jelly is broken

Calculation

Gel strength (g/cm²) = weight of mercury ÷ area of the disc

Where,

• Gel strength = gel strength in grams per square centimetre
• Weight of mercury = weight of mercury added up to the breaking of the jelly (g)
• Area of the disc = area of the brass disc (cm²)

The resistance of the jelly to deformation is indicated by the rate of change in the height of the platform.

Notes

• Henglein suggested a breaking value of 200 g, while Gudjons recommended 300 ± 15 g for a standard jelly strength.
• The Hamer modification enables simultaneous observation of the resistance of the jelly to deformation in addition to measuring the force required to pull the disc upward.

Precautions

• The drawbacks of the Hamer modification are that the jelly may slip in the beaker and the manual operation of the platform may introduce an element of arbitrariness.

References

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

Lüers, H. & K. Lochmüller, Kolloid-Zschr., 42, 154 (1927) — cited in the book.

Henglein, F.A., Z. Lebensm-Untersuch. U. Forsch., 90, 417 (1950) — cited in the book.

Gudjons, H., Z. Lebensm-Untersuch. U. Forsch., 90, 426 (1950) — cited in the book.

Hamer, W.J., J. Research, Nat. Bur. Standards, 39, 29 (1947) — cited in the book.