SU734562A1 - Colorimetric method of determining citric acid in cheese - Google Patents

Description

(54) COLORYMETRIC METHOD FOR DETERMINING LIMO

ACID IN CHEESE

one

The invention relates to the cheese industry.

The content of citric acid in cheese is one of the indications of the degree of development of the aromatherapy microflora and can serve as an indirect assessment of the quality of the finished product. This is important in light of the recent trend towards a transition to instrumental methods of control in cheesemaking.

A method for determining citric acid is currently known, which consists in preparing reagents (trichloroacetic acid, pyridine, acetic anhydride and nitrate solution) for analysis;

preparing the sample of the product under study (dosage of the sample of cheese, grinding and dispersing in warm distilled water, cooling to room temperature, adding trichloroacetic acid, aging for 30 minutes and filtering); obtaining a colored solution (adding pyridine and acetic anhydride to the filtrate., mixing, aging for 30 minutes

In a water bath, cooling to room temperature); optical density measurement; comparing the measurement results with the calibration curve and determining the citric acid content using the formula SLF This method is known as pyridine-acetic anhydride and is based on the oxidation of citric acid by pyridine to acetaldehyde, due to which staining of the solution occurs.

ten

However, this method has not been widely used in production because of the high cost of the reagents used and their toxicity. Toxic is also the product of the reaction of citric acid with pyridine - acetaldegnd.

The aim of the invention is to improve the accuracy of determination.

The goal is achieved by the fact that the colored solution is obtained by adding alcohol

20 vanillin solution to an aqueous solution of citric acid, while the latter is obtained by extraction with sulfuric ether, followed by distillation. The proposed method includes the following operations: the preparation of reagents (sulfuric ether, sulfuric acid ethyl alcohol and vanilla); preparing a sample of the product under study (grinding, dosing a sample of cheese, extracting citric acid with sulfuric ether, distilling the ether at 38 ° C, diluting the dry residue with water and filtering the colored solution (adding vanillin to the filtrate of the alcohol solution, evaporation, adding sulfuric acid to the dry residue ); measurement of optical density; comparison of measurement results with a calibration curve and determination of citric acid content by the formula. The coloring occurs due to the reaction between vanillin and imonic acid in the presence of sulfuric acid. The following formula is used for the formula: where A is the content of citric acid in the product,%; Cx is an indicator determined from the calibration table characterizing the content of citric acid in the solution, mg, V-volume of the colored solution, ml; G is a sample of cheese, g. Example: A portion of Kostroma cheese (5 g) after grinding was placed in a separating funnel per 150 ml and extracted with 3 portions of sulfur, ether (40, 30, 20 m, respectively). United extracts re

After the press 4 6

. 10 12

14

2.0%

-2.36. 2.0%

1.12

0.85

2.0%

0.387

0.183 2.0% 2.0%

Claims (1)

0.061 2% was carried into a 100 ml flask and the contents of the flask evaporated to dryness in a water bath at 38 ° C. 15 ml of distilled water was poured to the dry residue, placed in a refrigerator for 10 minutes and filtered through an ashless filter. The finished filtrate was transferred to a vial “porcelain porcelain dish, added with 10 ml of ethanol and 20 mg of vanillin. The resulting mixture was thoroughly mixed and blown dry in a water bath at 100 ° C. 3 drops of concentrated sulfuric acid were added to the dry residue, heated in a water bath for 15 minutes until a dark purple color appeared. The contents of the cups were dissolved in distilled water, poured into a measuring cylinder, the volume was adjusted to 10 ml, and the optical density of the solution colored in yellow-green color on FEC-56 m at a wavelength of 364 km in cuvettes with a working layer thickness of 1.0 ml was measured. Further, using the calibration curve (see drawing) and the calculated formula, the content of citric acid in the cheese was determined. Similar studies were conducted for cheeses of different degrees of maturity (after the press, after 4, 6, 10.12 and 14 days). To determine the accuracy of the method, the content of citric acid in the same cheeses was determined by the standard method, which is considered the most accurate by the method of specialists and can be used as an arbitration method. The results of the experiment are presented in the table. 57 The data in Table 1 show that the recommended method gives a deviation of 2% from the standard method, i.e. he is quite reliable. The calibration curve for the same instrument is plotted periodically depending on the presence of reagents of the same batch, i.e. with the same degree of purification. An example of building a calibration curve. A series of citric acid solutions of the following concentrations are prepared: 0.2; 0.4; 0.6; 0.8; 1.0 mg, measure, respectively; 2,4,6,8,10 ml of standard acid solution. 1 g of anhydrous or 1.0416 g of citric acid monohydrate is dissolved in a 1 L volumetric flask in a 1 N solution of H2SO4. 100 ml of this solution are brought in another volumetric flask to 1 liter of H2SO4 (1 ml of the solution contains 0.1 mg of acid), placed in a cooking bowl, 3 ml of an alcoholic solution of vanillin are added thereto, mixed thoroughly, and the contents are dried. 3 drops of concentrated sulfuric acid are added to the dry residue and heated to a dark purple color. The resulting precipitate is dissolved in water, brought to a volume of 10 ml, and the optical density of the colored solutions relative to distilled water in FEC is measured at a wavelength of 364 km in cuvettes with a working layer thickness of 1.0 ml. The indications of extricts correspond to mg / ml citric acid content according to the calibration curve (see drawing). The use of the method in practice will allow an increase in the accuracy of determining the content of citric acid in cheese, while it does not require the use of expensive reagents and is more beneficial for the operation of the service perchanal. Claims Colorimetric method for determining citric acid in cells, including preparing initial components, obtaining a colored solution for colorimetry, measuring the optical density and determining the citric acid content by calculation, characterized in that, in order to improve the accuracy of determination, the colored solution is obtained by adding an alcohol solution of vanillin to an aqueous solution of citric acid, the latter being obtained by extraction with sulfuric ether, followed by distillation. Sources of information taken into account in the examination .1. International Standard. Per. N ISO 2963-74. Cheese Control method for determination of citric acid content (prototype).