SOP: Grading of Low-Methoxyl Pectin

GIFSQ — Global Institute for Food Safety & Quality

Principle

The jelly strength of low-methoxyl pectin is influenced not only by its pectin content and pH, but also by the calcium-to-pectin ratio, which depends on the manner of preparation of the low-methoxyl pectin and on its methoxyl content. Grading is carried out in gels with a sugar content of 35%, and the jelly strength is then measured by the sag method.

Apparatus required

• 3-quart saucepan, previously tared
• Jelly glasses, previously prepared for making jellies for sag measurement

Reagents

a. Sodium citrate (Na₃C₆H₅O₇·2H₂O) solution: 6% in water.

b. Citric acid (C₆H₈O₇·H₂O) solution: dissolve 60 g of citric acid in water and make to 100 ml.

c. Calcium chloride (CaCl₂·2H₂O) solution: dissolve 22.05 g of calcium chloride dihydrate in 1 litre of water.

Procedure

Measure 425 ml of water into the previously tared 3-quart saucepan

↓

Add 10 ml of sodium citrate solution and 5 ml of citric acid solution

↓

Mix 6 g of standardized low-methoxyl pectin with 30 g of sugar and pour into the saucepan

↓

Heat the mixture to boiling with constant stirring; add 150 g of sugar and again bring to boiling

↓

When the mixture is boiling, add 25 ml of calcium chloride solution and boil the mixture to a final weight of 600 g

↓

Pour the jelly into the jelly glasses previously prepared for making jellies for sag measurement; store at 24–26°C for 18–24 hr and then test by the sag method

↓

If the pH of the finished jelly is not 3.0 ± 0.05, make changes in the quantity of citric acid added to get the required value

Notes

• The percentage of sag for normal firmness of this type of gel is 20–21%, as against 23.5% for high-methoxyl pectin jellies.
• A pectin prepared by the acid precipitation method, with a uniform methoxyl content of 3.2 ± 0.3% and an intrinsic viscosity of 3.4 ± 0.5, will be satisfactory for gel purposes. For films and fibres, the lower limit of viscosity is about 3.5.
• Higher methoxyl content requires additional calcium ion for gelation, while higher viscosity requires less calcium. By varying calcium ion concentration, pectinic acids outside the mentioned range can be applied for formation of gels.

References

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

Hills, C.H., J.W. White & G.L. Baker, Proc. Inst. Food Technol., 47 (1942) — cited in the book.

Lange, D., W. Bock & K. Taufel, Ernährungsforsch, 6, 65 (1961) — cited in the book.

Joseph, G.H., Low Methoxyl Pectin, California Fruit Growers’ Exchange, Ontario, California (1947) — cited in the book.

Owens, H.S. et al., ibid. — cited in the book.