Determination of starch acidity

Starch acidity is caused by presence at it of phosphates and the sulfuric acid used during reception of starch from corn and during bleaching of potato starch. In case of starch storage in adverse conditions its acidity increases.

Starch acidity express in degrees. One degree of starch acidity answers 1 sm 3 0,1 n a solution of sodium hydroxide spent for neutralisation of acids in 100 g of solid of starch. Norms of sizes of starch acidity for its different kinds and grades:

The corn:

The higher 20,0

The first 25,0

Amylopectinous 23,0

The potato:

"Extra" 6,0

The higher 10,0

The first 14,0

The second 20,0

Determination course:

In a conic flask vol. of 250-300 ml place 20 g the starch weighed to within 0,01 г, add of 100 ml from the measured cylinder of the distilled water and add 5-8капель of phenolphtalein. Titrate the suspension with 0,1 n solution of sodium hydroxide from metric burette before occurrence of pink colouring. In connection with adsorption ability of starch to phenolphtalein, before the titration termination add 5-6 more drops of phenolphtalein. In parallel in the same conditions titrate with 100 sm of the distilled water.

Starch acidity, in degrees, define under such formula:

Where V₁ - quantity 0,1 n solution of sodium hydroxide used for titration of test, cm³; V₂ - quantity 0,1 n solution of sodium hydroxide used for titration of 100 cm³ of distilled water, cm³; m - weight of starch charge, g; B - a water mass fraction in starch, %.

Example

3,4 cm³ of potato starch used for titration in weight 20 g 0,1 n a solution sodium hydroxide and 0,2 cm³ are used for titration of the distilled water of 100 cm³ 0,1 n a solution sodium hydroxide.

Moisture contents in starch - 20 %

Starch acidity:

The structure of yeast includes fat acids, basically - palmitinic and stearinic acids. In a storage time of yeast, owing to ability to live of microorganisms produces acids, therefore their acidity increases. Acidity express in milligrammes of acetic acid on 100 g yeast.

Devices, laboratory ware and reactants: technical scales, a porcelain cup, metric burette, 0,1 n solution sodium hydroxide and the indicator phenolphtalein.

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Дата добавления: 2015-11-14