In Fig. 5.6 some properties of disaccharides are noted. Disaccharides are formed by a condensation reaction between two monosaccharides, usually hexoses (Figure 5.14).

The bond between two monosaccharides is called glycosidic linkage. It usually forms between the 1st and 4th carbon atoms of adjacent monosaccharide units (1,4-glycosidic bond). This process can be repeated countless times, resulting in the formation of giant polysaccharide molecules (Fig. 5.14). Once the monosaccharide units combine with each other, they are called leftovers. Thus, maltose consists of two glucose residues.

Among the disaccharides, the most common are maltose, lactose and sucrose:

Glucose + Glucose = Maltose, Glucose + Galactose = Lactose, Glucose + Fructose = Sucrose

Maltose is formed from starch during its digestion (for example, in animals or during seed germination) under the action of enzymes called amylases. The breakdown of maltose into glucose occurs under the action of an enzyme called maltose. Lactose, or milk sugar, is found only in milk. Sucrose, or cane sugar, is most abundant in plants. Here it is transported in large quantities through the phloem. Sometimes it is deposited as a reserve nutrient since it is metabolically quite inert. Industrially, sucrose is obtained from sugar cane or sugar beets; It is precisely this “sugar” that we usually buy in the store.

Reducing sugars

All monosaccharides and some disaccharides, including maltose and lactose, belong to the group of reducing sugars. Sucrose is a non-reducing sugar. The reducing ability of sugars depends in aldoses on the activity of the aldehyde group, and in ketoses on the activity of both the keto group and the primary alcohol groups. In non-reducing sugars, these groups cannot enter into any reactions, because here they participate in the formation of a glycosidic bond. Two common reactions to reducing sugars - the Benedict reaction and the Fehling reaction (Section 5.8) - are based on the ability of these sugars to reduce the cuprous ion to cuprous. Both reactions use an alkaline solution of copper(ΙΙ) sulfate (CuS0 4), which is reduced to insoluble copper(Ι) oxide (Cu 2 O).

Please tell me what reducing sugars are and what sugars belong to them? and got the best answer

Answer from Sveta Panchenko[guru]
The term “reducing sugars” refers to a group of sugars that, in a chemical reaction, have a reducing effect on the corresponding reagents. The quantitative ratio of glucose and fructose depends on the type of bribe, on the amount of enzymes secreted by bees and on the duration of storage. In honey that has not been subjected to heat treatment, the enzymes do not lose their activity, and new sugar molecules are formed during storage. The prolonged action of enzymes on the sugar components of honey leads, along with other phenomena, to the “stratification” of honey. Crystallized glucose precipitates, and liquid fructose collects above it. The following table lists the carbohydrates found in honey.
all other information is here:
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Reducing sugars
All monosaccharides and some disaccharides, including maltose and lactose, belong to the reducing (reducing) group.
Sugars, i.e. compounds capable of entering into a reduction reaction. Sucrose is the only non-reducing sugar among common sugars. Two common reactions to reducing sugars - the Benedict reaction and the Fehling reaction - are based on the ability of these sugars to reduce the divalent copper ion to monovalent. Both reactions use an alkaline solution of copper(II) sulfate (CuSO4), which is reduced to insoluble copper(II) oxide (Cu20).

Answer from 2 answers[guru]

Hello! Here is a selection of topics with answers to your question: Please tell me what reducing sugars are and what sugars belong to them?

Answer from NATALIE[guru]
The term “reducing sugars” refers to a group of sugars that, in a chemical reaction, have a reducing effect on the corresponding reagents. Fructose, glucose, sucrose.

One of the main quality indicators of syrup, along with the dry matter content, is the presence of reducing substances in it.

The reducing substances of the syrup are called part of dry substances that is capable of oxidation reaction with salts of polyvalent metals. The aldehyde and ketone (carbonyl) groups of various sugars (glucose, fructose, maltose, lactose, etc.) are capable of such a reaction. Sucrose does not contain free carbonyl groups and is not a reducing sugar.

Due to the fact that the reactivity depends on many factors and especially on the number of carbonyl groups relative to the molecular weight of the sugar, and also because the oxidation reactions of carbonyl groups with polyvalent metals do not proceed stoichiometrically, this ability is not the same for different sugars. For example, for the reducing disaccharides maltose and lactose it is significantly less than for the reducing monosaccharides glucose and fructose.

Even sugar molecules that are similar in structure, having one carbonyl (aldehyde) group in the molecule and the same molecular weight, such as maltose and lactose, have slightly different reducing abilities. For these reasons, the content of reducing substances is usually expressed conventionally in invert sugar.

Typically, the mass of reducing substances contained in a syrup containing maltose or other reducing disaccharides is slightly greater than the mass of reducing substances obtained as a result of analysis and expressed in invert sugar. Only in the particular case when the reducing substances of the syrup consist exclusively of equal amounts of glucose and fructose, their actual content in the syrup corresponds to the result of the analysis.

For calculations we will use the following notation:

G C - mass of sugar, kg;

G p - mass of molasses, kg;

G and - mass of invert syrup, kg;

a is the proportion of syrup solids, fractions of a unit;

a C, a p, a and - respectively, the proportion of dry substances of sugar, molasses and invert sugar (the value of a c is close to one and for standard sugar is more than 0.9985, therefore in calculations it is taken equal to one);

k 2 - the amount of molasses dry matter per 1 kg of sugar dry matter,

k 3 - the amount of dry matter of invert syrup per 1 kg of dry matter of sugar,

rv - the proportion of reducing substances incorporated with raw materials in the dry substances of the recipe mixture, syrup, etc.;

rv p and rv i - respectively, the proportion of reducing substances molasses and invert syrup.

The mass of reducing substances incorporated with raw materials

rv = G p a p rv n + G and a and rv i. (1-3)

The share of reducing substances included with raw materials is

(1-4)

Substituting the values ​​of G p and G into equation (1-4) and from equations (1-1) and (1-2) and taking a c = 1, we obtain

(1-5)

In technical calculations it is often necessary to calculate the value of k 3 . The calculation is made using the following formula:

(1-6)

Production control. Granulated sugar is checked for compliance with GOST requirements for water content and color. In addition, the smell, taste and content of mechanical impurities are organoleptically checked.

Molasses is checked for compliance with GOST requirements for dry matter content, color and acidity. The content of dry substances is determined by a refractometer, adjusted for containing reducing substances, which is determined by the polarimetric method.

In finished syrups, the content of dry and reducing substances is controlled. The content of dry substances is determined approximately - by boiling point and a refractometer, the content of reducing substances - by titration of an alkaline copper solution or photocolorimetric.

Introduction

Sugar. Reducing sugars

Invert syrup

Reducing sugar

The importance of sugars for the body

Methods for determining sugar in confectionery products

experimental part

Preparation of copper alkaline citrate solution (Benedict's reagent)

Carrying out analysis

Discussion of the research results

1. Determination of the content of reducing sugars in marmalade

2. Determination of the content of reducing sugars in marshmallows

3. Determination of the content of reducing sugars in caramel

conclusions

Bibliography

Annex 1

Introduction

Iodometry is a method of volumetric analysis, in which newer than which are the reactions: + 2e? 2I?

I? ?2 e? I2

The iodimetry method can be used to determine both oxides teli and reducing agents.

Determination of oxidizing agents. The iodimetry method can be used to determine those oxidizing agents that quantitatively oxidize I ?to free I2. Most often, permanganates, bichromates, copper (II) salts, and jelly salts are determined for (III), free halogens, etc. The indicator in the iodimetry method is a starch solution. This is a sensitive and specific indie cator that forms a blue adsorption compound with iodine.

Definition of reducing agents. From the number restored This method most often determines sulfites, sulfides, tin(II) chloride, etc. The working solution is a solution of iodine I2. The iodimetry method is widely used in chemical analysis. This method determines arsenic (III) compounds; copper (II) in salts, ores; many organic drugs - formaldehyde, analgin, ascorbic acid, etc.
Purpose of the work: determination of reducing sugars in various confectionery products. Tasks:

Development of a technique for the quantitative determination of reducing sugars in a working solution.

To establish compliance with the normal contents of reducing sugars in confectionery products contained in GOST

The main raw materials for the production of confectionery products are sugar, invert syrup, flour, fats, and milk. In addition, fruits and berries, nuts, cocoa beans, honey, spices and many other products are used in the production of confectionery products.

In shaping the consumer properties of confectionery products, a large role is given to products that give them structure, appearance, taste and color: gelling agents, emulsifiers, foaming agents, dyes, flavorings.

consumer confectionery reducing sugar

Sugar. Reducing sugars

The product is a pure carbohydrate - sucrose, characterized by a pleasant sweet taste and high digestibility. It has great physiological value, has a stimulating effect on the central nervous system, contributing to the aggravation of the organs of vision and hearing; is a nutrient for the gray matter of the brain; participates in the formation of fat, protein-carbohydrate compounds and glycogen. Excessive sugar consumption leads to obesity, diabetes, and caries. The daily norm is 100 g, per year - 36.5 kg, but it should be differentiated depending on age and lifestyle.

Invert syrup

Invert syrup serves as a substitute for molasses, as it has anti-crystallization properties. Invert syrup is obtained by heating an aqueous solution of sugar and acid, during which the inversion process occurs, which consists in the splitting of sucrose into fructose and glucose. Acids used for inversion are: hydrochloric, citric, lactic, acetic.

Reducing sugar

All monosaccharides, in the case of syrup glucose and fructose, and some disaccharides, including maltose and lactose, belong to the group of reducing (reducing) sugars, i.e. compounds that can enter into a reduction reaction.

Two common reactions for reducing sugars - the Benedict reaction and the Fehling reaction - are based on the ability of these sugars to reduce the divalent copper ion to monovalent. Both reactions use an alkaline solution of copper(II) sulfate (CuSO4), which is reduced to insoluble copper(I) oxide (Cu2O).

The Fehling reaction is most often used to prove the reducing properties of sugars; it involves the reduction of copper (II) hydroxide to copper (I) oxide by monosaccharides. When carrying out the reaction, Fehling's reagent is used, which is a mixture of copper sulfate with Rochelle salt (potassium, sodium tartrate) in an alkaline medium. When copper sulfate is mixed with alkali, copper hydroxide is formed.

CuSO4 + 2NaOH -> Cu(OH)2? + Na2SO4

In the presence of Rochelle salt, the released hydroxide does not precipitate, but forms a soluble copper(II) complex compound, which is reduced in the presence of monosaccharides to form copper(I) protoxide. In this case, the aldehyde or ketone group of the monosaccharide is oxidized to a carboxyl group. For example, the reaction of glucose with Fehling's reagent.

CH2OH - (CHOH) 4 - SON + Cu(OH) 2 ===>

The importance of sugars for the body

Fructose.

Fructose is less abundant than glucose and also oxidizes quickly. Some fructose is converted into glucose in the liver, but it does not require insulin for its absorption. This circumstance, as well as the significantly slower absorption of fructose compared to glucose in the intestine, explains its better tolerance in patients with diabetes.

Glucose is the constituent unit from which all the most important polysaccharides are built - glycogen, starch, cellulose. It is part of sucrose, lactose, maltose. Glucose is quickly absorbed into the blood from the gastrointestinal tract, then enters the cells of organs, where it is involved in the processes of biological oxidation. Glucose metabolism is accompanied by the formation of significant amounts of adenosine triphosphoric acid (ATP), which is a source of a unique type of energy. ATP plays the role of a universal battery and energy carrier in all living organisms. In medicine, adenosine preparations are used for vascular spasms and muscular dystrophy, and this proves the importance of ATP and glucose for the body.

While the body is awake, glucose energy replenishes almost half of its energy costs. The remaining unclaimed portion of glucose is converted into glycogen, a polysaccharide that is stored in the liver.

Methods for determining sugar in confectionery products

Since monitoring the sugar level in the body is necessary, there are a number of different methods for determining the amount of both total and reducing (inverse) sugars in confectionery products,
which is an important part of quality control for the production of these products. Iodimetric method

The method is based on the reduction of an alkaline solution of copper with a certain amount of a solution of reducing sugars and determining the amount of copper oxide (1) formed or unreduced copper using an iodometric method.

The method is used for all types of confectionery products and semi-finished products, except flour confectionery products, semi-finished products for cakes and pastries and oriental sweets.

The method is used when disagreements arise in quality assessment.

Permanganate method

The method is based on the reduction of iron (III) salt with copper (I) oxide and subsequent titration reduction of reduced iron oxide (I) with permanganate.

Polarimetric method

The method is based on measuring the rotation of the plane of polarization of light by optically active substances.

The method is used to determine the mass fraction of total sugar in chocolate, pralines, cocoa drinks, chocolate spreads, sweet bars, chocolate semi-finished products without additives and with the addition of milk.

experimental part

Preparation and standardization of a solution C(Na2S2O3) = 0.1 mol/dm3

Reagents:

Weight of Na2S2O3×5H 2O

Sample of K2Cr2O7

M HCl solution

% Starch solution

Distilled water

Volumetric flask 100cm3;

Measuring cylinder with a capacity of 25 cm3;

Conical titration flask 250 cm3

Pipette 10 ml

25 ml burette

Progress:

A working solution of sodium thiosulfate is prepared by weighing, based on the given concentration of the solution and its volume. To prepare 200 ml of a 0.1 m sodium thiosulfate solution, weigh out 5 g of sodium thiosulfate in a weighing bottle on a technical scale. The sample taken is dissolved in 200 ml of distilled water and 0.02 g of soda is added. The solution is stored in a dark glass bottle.

Determination of the exact concentration of sodium thiosulfate solution is carried out using 2-3 precise portions of potassium dichromate using the semi-micro method (25 ml burette, 0.1 ml division). The weight of potassium dichromate is calculated taking into account the volume of the volumetric flask, pipette, burette and the concentration of the prepared sodium thiosulfate solution. Considering that the titration of an aliquot of a solution of potassium dichromate should use 10 ml of 0.1 M sodium thio sulfate and the ratio of the volumetric flask and pipette

: 10, calculate the mass of potassium dichromate: (K2Cr2O7) = C(Na2S2O3) × V(Na2S2O3) × M(1/6 K2Cr2O7) × 100/10 = 0,1× 10 49×10 = 490 mg = 0.49 g.

The exact weight of potassium dichromate is in the range of 0.47-0.51 g. The test tube with potassium dichromate is weighed on an analytical balance, the dichromate is poured through a funnel into a 100 ml volumetric flask and the test tube with potassium dichromate is weighed. Based on the difference in weighing, a portion of potassium dichromate is found. Using distilled water, wash the potassium dichromate from the funnel into the flask, shake the contents of the flask until the potassium dichromate is completely dissolved

and only after that add water to the mark. The solution is mixed well. A 10 ml pipette is washed with potassium dichromate solution

and take 1/10 of it into a 250 ml titration flask, add 5 ml of a 10% KI solution and 5 ml of a 2 M HCl solution. The flask is covered with a watch glass and left for 5 minutes in a dark place. Then add 50 ml of water to the solution and titrate with sodium thiosulfate solution, adding it drop by drop and mixing the solution well. When the color of the solution turns from brown to pale yellow, add 50 drops of starch solution

(2-3 ml) and continue titration until the blue color of the solution turns pale green, almost colorless. In the second and subsequent titrations, starch is added as close to the end of the titration as possible. The volume of sodium thiosulfate solution is measured with an accuracy of ±0.005 ml. Titration of an aliquot of the potassium dichromate solution is carried out 3-4 times and the average value of the volume of sodium thiosulfate (Vavg) is calculated, the relative deviation from the average is not more than 0.5%. Based on experimental data, the titer of sodium thiosulfate is calculated from potassium dichromate.

Calculation part

V1=9, 6 ml=10, 3 ml=9, 8 mlsr=9.9 ml

M(1/6 K2Cr2O7)=49 g/mol

M(Na2S2O3 × 5H2O)=248 g/mol(Na2S2O3)=158.11 g/ml(K2Cr2O7)= C(Na2S2O3) × V(Na2S2O3) × M(1/6 K2Cr2O7) × 100/10=0.1 ×10 ×49 ×10=490 mg =0.49 g

T (Na2S2O3/ K2Cr2O7) = , g/ml(Na2S2O3) = , mol/l(Na2S2O3) = , g/ml(Na2S2O3/ K2Cr2O7) = =0.005050 g/ml(Na2S2O3)= =0.1030 mol/ l(Na2S2O3) = = 0.01629 g/ml

Preparation of copper alkaline citrate solution (Benedict's reagent)

Reagents:×5H20

Citric acid C6H8O7CO3

Distilled water

Equipment

Volumetric flask 250 cm3

Beaker

Progress.

77 g of copper sulfate is dissolved in 25 cm3 dist. water.

5 g of citric acid are dissolved separately in 13 cm3 dist. water.

9 g of anhydrous sodium carbonate are also separately dissolved in 125 cm3 of hot dist. water.

The citric acid solution is carefully poured into the sodium carbonate solution. After the release of carbon dioxide ceases, the mixture of solutions is transferred to a volumetric flask with a capacity of 250 cm3, a solution of copper sulfate is poured into the flask and the contents of the flask are adjusted to dist. water to the mark, mix

During the experiment, aldehyde groups are oxidized, and copper cations are reduced. Benedict's reagent tends to form hydrated oxides, so the reaction product is not always red in color: it can also be yellow or green. If the sugar content is low, then a precipitate forms only upon cooling. If there are no reducing sugars, the solution remains clear. Solutions with a sugar content of 0.08% give a noticeable positive result, while for Fehling's reagent this value is 0.12%

Preparation of the working test solution.

A weighed portion of the crushed test product is taken so that the amount of reducing sugars in 1 cm3 of solution is about 0.005 g

The weight of the sample is calculated using the formula

where b is the optimal concentration of reducing sugars g/cm3 capacity of the volumetric flask, cm3 is the expected mass fraction of reducing sugars in the product under study, %

According to GOST 6442-89 Marmalade can contain no more than 20% reducing sugars by weight of the product.

According to GOST 6441-96 Pastille confectionery products can contain from 10% to 25% of reducing sugars by weight of the product.

According to GOST 6477-88, caramel can contain no more than 20% reducing sugars by weight of the product.

The sample in a glass is dissolved in distilled water heated to 60?-70?C

If the product dissolves without a residue, then the resulting solution is cooled and transferred to a 250 cm3 volumetric flask, adjusted to the mark with the same water and mixed well.

If the product contains substances that are insoluble in water, then after transferring the sample into a volumetric flask, place it in a water bath for 10-15 minutes, then filter, cool and adjust with distilled water to the mark.

Carrying out analysis

25 cm3 of an alkaline copper citrate solution, 10 cm3 of the test solution and 15 cm3 of distilled water are pipetted into a conical flask with a capacity of 250 cm3. The flask is connected to a reflux refrigerator and brought to a boil for 3-4 minutes and boiled for 10 minutes. During boiling, we observe a qualitative reaction of glucose with copper hydroxide: since glucose contains five hydroxyl groups and one aldehyde group, it is classified as an aldehyde alcohol. Its chemical properties are similar to those of polyhydric alcohols and aldehydes. The reaction with copper(II) hydroxide demonstrates the reducing properties of glucose. Add a few drops of Benedict's solution to the glucose solution. No copper hydroxide precipitate is formed. The solution turns bright blue. In this case, glucose dissolves copper (II) hydroxide and behaves like a polyhydric alcohol. Let's heat the solution. The color of the solution begins to change. First, a yellow Cu2O precipitate forms, which over time forms larger red Cu2O crystals. Glucose is oxidized to gluconic acid.

CH2OH - (CHOH) 4 - SON + Cu(OH) 2 ===> CH2OH - (CHOH) 4 - COOH + Cu2O?+ H2O

The flask is quickly cooled to room temperature.

Add 10 cm3 of KI solution 30% and 25 cm3 of H2SO4 solution with a concentration of 4 mol/dm3 to the cooled liquid. Sulfuric acid is poured in carefully to prevent it from splashing out of the flask due to the released carbon dioxide. After this, the released iodine is immediately titrated with a solution of sodium thiosulfate until the liquid turns light yellow.

Then add 2-3 cm3 of 1% starch solution and continue to titrate the dirty blue liquid until a milky white color appears. Record the amount of thiosulfate that was used for titration. The experiment is repeated 3 times.

The control experiment is carried out under the same conditions, for which 25 cm3 of an alkaline copper citrate solution and 25 cm3 of distilled water are taken.

The difference between the volume of sodium thiosulfate in cm3 spent in the control experiment and in the determination, multiplied by the correction factor K = 1.2, gives the amount of copper expressed in cm3 of 0.1 mol/dm3 sodium thiosulfate solution, from which the number of milligrams of inverse sugar is found in 10 cm3 of solution of a sample of the test product according to Table 1, provided in GOST 5903-89

The mass fraction of reducing sugars (X) as a percentage is calculated using the formula

Where m is the sample of the product, g is the mass of inverse sugar determined from Table 1, mg is the capacity of the volumetric flask, cm3 is the volume of the test solution taken for analysis, cm3

Discussion of the research results

Determination of the content of reducing sugars in marmalade.

Titration 123 Volume, ml 1716.616 Average value, ml 16.5 The volume of sodium thiosulfate in the control experiment was 31 cm3isk1 = (31-17)1.21= 16.9 cm3isk2 = (31-16.6)1.21= 17.4 cm3isk3 = (31-16)1.21= 18.2 cm3inv1 = 46.14 mg (in accordance with the table in Appendix 1) inv2 = 47.34 mg (in accordance with the table in Appendix 1) inv3 = 49.74 mg (in accordance with the table in Appendix 1) = 6, 25 g = 250 cm3 = 10 cm3

Average = 19.1%

Determination of the content of reducing sugars in marshmallows.

Volume of sodium thiosulfate used for titration

Titration 123 Volume 17.817.717.5 Average value, ml 17.7 isk1 = (31-17.8)1.21= 16 cm3isk2 = (31-17.7)1.21= 16.1 cm3isk3 = (31-17.5)1.21= 16.3 cm3inv1 =43, 53 mg (according to the table in Appendix 1) inv2 = 43.82 mg (according to the table in Appendix 1) inv3 = 44.11 mg (according to the table in Appendix 1) = 5, 25 g = 250 cm3 = 10 cm3

Average = 20.86%

Determination of the content of reducing sugars in caramel

Volume of sodium thiosulfate used for titration

Titration 123 Volume 18,318,518.1 Average value, ml 18.3 isk1 = (31-18.3)1.21= 15.4 cm3isk2 = (31-18.5)1.21= 15.1 cm3isk3 = (31-18.1)1.21= 15.6 cm3inv1 = 41.79 mg (in accordance with the table in Appendix 1) inv2 = 40.92 mg (in accordance with the table in Appendix 1) inv3 = 42.37 mg (in accordance with the table in Appendix 1) = 5, 25 g = 250 cm3=10 cm3

Average = 19.9%

Objects of research Established contents ed. sugars, % Normal content ed. sugars according to GOST,% Marmalade 19.1 No more than 20 Pastille 20.86 From 10 to 25 Caramel 19.9 No more than 20

As a result of the study, it was possible to establish the mass fraction of reducing sugars in various types of confectionery products using the method of iodometric titration. According to the results, the content of reducing sugars in all products provided for analysis corresponds to the state standard, and therefore can be approved for sale.

Bibliography

GOST 6477-88 Caramel. General technical conditions.

GOST 6441-96 Pastille confectionery products.

GOST 6442-89 Marmalade. Technical conditions.

V.P. Vasiliev Analytical Chemistry - M.: Bustard 2004

Skoog D., West D. Fundamentals of analytical chemistry. - M.: Mir, 1979. T. 1,2.

Fundamentals of Analytical Chemistry / Ed. Academician Yu. A. Zolotov. - M.: Higher School, 2002. Book. 12.

Alekseev V.I. Quantitative analysis. - M.: Chemistry, 1972.

Confectionery [Electronic resource]: #"justify">Confectionery [Electronic resource]: #"justify">Appendix 1

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For some types of raw materials, it is necessary to determine the mass fraction of reducing sugars. This indicator is largely determined by food raw materials, which are used in the production of various biologically active additives produced by our company KorolevPharm LLC. Reducing sugars are those sugars that enter into a reduction reaction, that is, they can easily oxidize. This indicator is also needed to determine the total sugar in the product.

Rice. 1 Testing

It is also important for food raw materials such as honey. The low content of such sugars and high content of sucrose indicates that the bees have been fed sugar syrup for a long time. Thus, adulterated honey is identified, which is called sugar honey.

Food products mainly contain disaccharides in the form of sucrose, maltose, and lactose. Monosaccharides are represented by glucose, galactose and fructose; trisaccharides are found mainly in the form of raffinose. For food products, according to GOSTs or TUs, the total sugar content or the so-called total sugar, expressed as a percentage of sucrose, is mainly standardized. All of the sugars listed above, except sucrose, have reducing ability.

In the Analytical Laboratory of KorolevPharm LLC at the physical and chemical testing site, this indicator of the quality of raw materials is determined by photocolorimetric method. It is based on the reaction of the interaction of carbonyl groups of sugars with potassium iron sulfide, and then determining the optical density of solutions before and after inversion on a spectrophotometer.

To carry out the test, prepare the following solutions:

1. potassium iron sulfide;
2. methyl orange;
3. sugar standard solution after inversion.

To prepare (1) solution, take a sample of potassium iron sulfide equal to 10 g, place it in a 1000 ml flask, dissolve it and bring it to the mark with water.

To obtain (2) solution, take 0.02 g of methyl orange reagent, dissolve it in 10 ml of boiling water, cool and filter.

We prepare (3) the solution as follows: take 0.38 g of sucrose, dried for 3 days in a desiccator (or refined sugar), weigh it to the nearest 0.001 g, transfer the sample to a 200 ml flask, add 100 ml water and 5 ml hydrochloric acid. Place a thermometer in the flask and place it in an ultrathermostat. We heat the contents of the flask to 67-70°C and hold it at this temperature for exactly 5 minutes. Having cooled the contents to 20°C, add one drop of indicator (2), neutralize with a 25% alkali solution, bring the mixture to 200 ml with water and mix everything thoroughly. The resulting solution contains 2 mg of invert sugar per 1 ml.

To determine the optical density, we prepare a series of dilutions of the standard solution. To do this, take 7 250 ml flasks, place 20 ml of potassium ferricyanide and 5 ml of an alkaline solution with a concentration of 2.5 mol/ml in each of them. Then add the standard solution in quantities: 5.5 ml; 6.0 ml; 6.5 ml; 7.0 ml; 7.5 ml; 8.0 ml and 8.5 ml. This corresponds to 11 mg, 12 mg, 13 mg, 14 mg, 15 mg, 16 mg and 17 mg invert sugar. Then, alternately add 4.5 ml of water from the burette; 4.0 ml; 3.5 ml; 3.0 ml; 2.5 ml; 2.0 ml and 1.5 ml. As a result, the volume in each flask becomes 35 ml. We heat the contents and boil for 60 seconds, then cool and fill the cuvettes with liquid. We measure the optical density of each resulting solution with a light filter at a light transmission wavelength of 440 nm. For the reference solution we use distilled water. We record the measurements three times and calculate the arithmetic mean value for each sample.

Rice. 3. Taking measurements with a spectrophotometer

We draw a graph on graph paper. On the ordinate axis we plot the obtained readings of the optical density of standard solutions with a certain content of invert sugar, and on the abscissa axis these values ​​​​of sugar concentrations in milligrams. We get the graph that we will need later.

To determine the mass fraction of sugars before inversion, prepare a sample in the amount of 2.00 g, place it in a 100 ml flask and dissolve it. Transfer 10 ml of this solution to another similar flask and bring it to the mark (this is the working solution of the substance under study).

Add 20 ml of potassium ferricyanide, 5 ml of alkali (C = 2.5 mol/ml) and 10 ml of the prepared solution into a 250 ml flask. We heat the mixture and boil for exactly 1 minute, then quickly cool and determine the optical density on a spectrophotometer. We take measurements 3 times. We calculate the arithmetic mean of the results.

Knowing the optical density, we use the graph to find the mass of reducing sugars in milligrams and calculate it as a percentage using the formula:

Х1= m1VV2/mV1V3 10

where m1 is the mass of reducing sugar found using the graph, mg.

V is the volume of solution prepared from the test sample, cm3;

V2 is the volume to which the diluted solution is brought, cm3;

M—product mass, g;

V1 is the volume taken to dilute the solution, cm3;

V3 is the volume of the diluted solution that is used for determination, cm3.