1.3. Determination of titrated acidity of plant raw materials and extracts
Materials and reagents pipettes vol. of 20 and 50 ml, conic bulbs vol. of 250 ml, measuring flasks vol. 250 ml, a funnel, burette for titration, technical balance, a chemical glass, 1 % solution of phenolphthalein, 0,1 N KOH solution (potassium caustic), distilled water, filtering paper.
For research weigh 25 g of crushed product on technical scales to within 0,01g. The charge transfers with the hot distilled water through a funnel from chemical glass to a measuring flask vol. of 250 ml and add the distilled water to half of flask. Leave for 30 minutes, periodically mixing. Then cool a flask to a room temperature and add the distilled water to a label, mix a flask further and filter through the filter or cotton.
Take the 50 ml of obtained filtrate to the conic flask of 250 ml with a pipette; add 3-5 drops of 1 % solution of phenolphthalein and titer by 0,1N KOH solution till the pink color appearance.
In case of determination the titrated acidities in liquid products (juice, brine, etc.) Take 25 ml of a liquid in a measuring flask 250 ml and add the distilled water to a label. Carefully mix contents of a test tube and take 50 ml in a conic flask for titration.
Experimental data processing
Calculation of a mass fraction, % titrated acidities Xtc calculation carried out by such formula:
,
Where V1 – quantity of the 0,1M solution of alkali used for titration, ml; K - recalculation factor on acid: apple - 0,0067; lemon - 0,0064; acetic - 0,0060; lactic - 0,0090; wine - 0,0075; V0 - volume to which it is finished charge, ml; V2 - volume of the solution taken for titration, ml; m - charge (volume for liquid products) of tested product, g (cm3).
Analysis of obtained results
Student according to the tasks will give a comparative description of methods for determining the acidity of the raw material and finished products.
Test questions
1 Give the definition to the acidity of medium
2 Give the definition to the total or titrated and active acidity and alkalinity.
3 What are the different indicators? How they are used in determining the alkalinity and acidity of foods?
4 How to prepare the pH meter for work?
5 What methods for determining the pH do you know?
Laboratory work 2
Starch, yeast and flour acidity determination.
Titrated acidity.
Aim of work: To study titration method for analysis of examples of insoluble substances of biological origin.
Main tasks
1. To determine the starch acidity by the titrimetric method.
2. To determine the yeast acidity by the titrimetric method.
3. To determine the flour acidity by the titrimetric method.
Basic theoretical information
Acidity of starch is caused by the presence in it phosphate and sulfuric acid used for the obtaining the starch from corn and during bleaching the potato starch. When starch is storing in adverse conditions, its acidity increases.
Starch is widely used as a nutrient media at the biotechnological industries. Humidity of starch is under 20%. Ash content may reach 0.35-1,2% of dry weight. Starch must not content Cl and free inorganic acids Normal values of acidity for different sorts of starch described in table 2.1.
Table 2.1