The indicated number indicates the total amount of peroxides formed during the oxidation of both unsaturated and saturated fatty acids. The formation of hydroperoxides in the case of saturated fatty acids occurs at a lower rate in comparison with unsaturated ones. However, in this case, a free peroxide radical is formed:

When interacting with other fatty acids, the free peroxide radical is stabilized, “tearing off” a hydrogen atom from them:

The resulting new radical interacts with oxygen according to the previous scheme:

The free peroxide radical can be converted to aldehydes by isomerization with the formation of an unstable dialkyl peroxide:

The resulting hydroperoxides can also actively convert to ketones:

It has also been proven that hydroperoxides can interact with double bonds of unsaturated fatty acids to form epoxides:

It is the set of all the above compounds with different molecular weights that determines the presence in the stored milk fat of such taste defects as "greasy", "oleic", "fishy", "mushroom", etc.

The strongest oxidation activators are metal ions.

Method principle: the quantitative determination of peroxides in oil is based on the reaction of iodine liberation by peroxides from potassium iodate in an acidic medium (an example of cyclic peroxide):

The released iodine is titrated with a thiosulfate solution.

Determination technique : in a conical flask or flask with a ground-in stopper with a capacity of 200 cm 3, weigh about 2-3 g of oil on an analytical balance. The sample is dissolved in 20 cm 3 of a mixture of glacial acetic acid and chloroform (2: 1), 5 cm 3 of a saturated solution of potassium iodide is added, the vessel is closed with a stopper and placed in a dark place for 10 minutes, after which 50 cm 3 of distilled water is added and the released iodine 0.002 N. thiosulfate solution (starch indicator). A control determination (without oil) is also carried out at the same time. The peroxide number (PN) (the number of grams of iodine released by the peroxides contained in the oil) is calculated by the formula

,

where V To- the amount of 0.002 n. thiosulfate solution consumed during titration of the control sample, cm 3;

V 0 - the amount of 0.002 n. thiosulfate solution consumed during the titration of the prototype, cm 3;

k is the correction factor for the thiosulfate solution;

0.0002538 - titer 0.002 N. thiosulfate solution for iodine (1 cm 3 of the solution corresponds to 0.0002538 g of iodine);

m - weight of oil, g.

1. Analysis of carbonyl compounds

The secondary oxidation products include alcohols, carbonyl compounds, esters, acids, as well as compounds with mixed functions, such as hydroxy acids, epoxy compounds, etc. All secondary oxidation products appear as a result of certain transformations of hydroperoxides, and some of the secondary products are formed directly during decomposition hydroperoxides, and some - as a result of further reactions.

Method principle : analysis of carbonyl compounds is carried out by photocolorimetry of alkaline solutions of 2,4-dinitrophenylhydrazones absorbing at 430 and 460 nm.

Determination technique: in a volumetric flask of 25 cm 3, place 1.5 cm 3 of a 4.3% solution of trichloroacetic acid (TCA), add 2.5 cm 3 of a 0.05% solution of 2,4-dinitrophenyl-hydrazine in benzene and 2 , 5 cm 3 solution of lipids in benzene. The mixture is heated for 30 minutes at a temperature of 60 0 C, after cooling, add 5 cm 3 of a 4% solution of KOH in ethanol and measure the optical density of the solutions at 430-460 nm. The control is a lipid-free reagent mixture. Calculate the concentration of saturated С 1 (in mmol / kg) and monounsaturated С 2 (in mmol / kg) carbonyl compounds according to the formulas:

,

,

where m is a sample of lipids, g.

Use solvents free of carbonyl compounds.

To eliminate errors, due to the carbonyl compounds formed during the analysis during the decomposition of peroxides, peroxides are preliminarily removed in oxidates by adding acetic acid and potassium iodate to the sample, kept for 20 minutes in the dark, diluted with water and titrated with thiosulfate.

Materials, reagents and equipment: 4.3% solution of trichloroacetic acid (TCA); 0.05% solution of 2,4-dinitrophenylhydrazine in benzene; 4% KOH solution in ethanol; a solution of lipids in benzene; ethanol, oil; a mixture of acetic acid with chloroform (2: 1); potassium iodide, alcohol solution; thiosulfate, 0.002 N. solution; starch 0.5% solution; conical flasks with ground-in stoppers for 250 cm 3; measuring cylinders; pipettes; burette; analytical balance, photoelectric colorimeter, bath, volumetric flasks.

Peroxide number ( I p) is the amount of peroxides, expressed in milliequivalents of active oxygen, contained in 1000 g of the drug.

MINISTRY OF HEALTH OF THE RUSSIAN FEDERATION

GENERAL PHARMACOPEAN ARTICLE

Peroxide numberOFS.1.2.3.0007.15

Introduced for the first time

Peroxide number ( I p) is the amount of peroxides, expressed in milliequivalents of active oxygen, contained in 1000 g of the drug. The peroxide value can be determined by one of two methods.

The tests are carried out while protecting the solutions from exposure to ultraviolet light.

Method 1

About 5.0 g (accurately weighed) of the drug is placed in a 250 ml conical flask with a ground-in stopper. Add 30 ml of a mixture of glacial acetic acid and chloroform (3: 2), shake until the drug is dissolved, add 0.5 ml of a saturated solution of potassium iodide and close the flask with a stopper. Shake for exactly 1 min, add 30 ml of water and titrate with sodium thiosulfate with a 0.01 M solution, adding the titrant slowly with constant vigorous shaking until the solution is light yellow. Then add 5 ml of starch solution and continue titration with constant shaking until discoloration of the solution. A control experiment is carried out under the same conditions. If the amount of titrant in the control experiment exceeds 0.1 ml, the determination is carried out with a freshly prepared saturated solution of potassium iodide.

Peroxide number ( I p) is calculated by the formula:

where V is the volume of sodium thiosulfate solution 0.01 M, consumed for titration in the main experiment, ml;
V 0 - the volume of sodium thiosulfate solution 0.01 M, consumed in the control experiment, ml; where V- the volume of sodium thiosulfate solution 0.01 M, consumed for titration in the main experiment, ml;

a- weight of the medicinal product, g;

c- molar concentration of sodium thiosulfate solution.

Note . Preparation of starch solution. 1.0 g of soluble starch is triturated with 5 ml of water and the mixture is poured into 100 ml of boiling water containing 10 mg of mercury (II) iodide.

Method 2

The exact weighed portion of the drug, depending on the expected peroxide value (table), is placed in a conical flask with a ground-in stopper with a capacity of 250 ml. Add 50 ml of a mixture of glacial acetic acid and trimethylpentane (3: 2), shake until the drug dissolves, add 0.5 ml of a saturated solution of potassium iodide and close the flask with a stopper. Shake for exactly 1 min, then add 30 ml of water and titrate with sodium thiosulfate with a 0.01 M solution, adding the titrant slowly with constant vigorous shaking, until the solution is light yellow. Then add about 0.5 ml of starch solution of 0.5% and continue titration with constant shaking until the solution becomes discolored.

Table - Weighing of the medicinal product depending on the expected peroxide value

At peroxide values ​​of 70 and above, after adding each portion of the titrant, the solution is kept for 15-30 s with stirring or a small amount (0.5-1.0% (m / m)) of an emulsifier (for example, polysorbate 60) is added.

For peroxide values ​​above 150, it is recommended to use a sodium thiosulfate solution of 0.1 M. A control experiment is carried out under the same conditions. If the amount of titrant in the control experiment exceeds 0.1 ml, the determination is carried out with a freshly prepared saturated solution of potassium iodide.

The peroxide value is calculated using the formula given in method 1.

DETERMINATION OF ACID AND PEROXIDE NUMBERS OF VEGETABLE OILS

Kovalenko M.N., 5th year student of the EHF

Scientific adviser: Panova L.P., Ph.D., associate professor.

In the modern world, food quality control is one of the most important tasks of chemical analysis. It is carried out at all levels of development and production: research, development of new products, control of raw materials, production process and finished products.

The world food industry is increasing its production potential every year, constantly introducing new products. In this regard, there is a need for fast and high-quality methods of quality control of the products obtained. Control of the quality and safety of food products becomes even more important in connection with the growing import of food products.

Federal Law No. 90 established the following standards for edible vegetable oils.

Vegetable oils are unstable, and therefore, during storage, it is necessary to observe strict regimes, especially in relation to sunlight and oxygen, which are catalysts of oxidative processes. Often, the regimes and warranty periods of storage of vegetable oils are violated. Under the influence of unfavorable factors, hydrolysis occurs, as a result of which glycerin and free fatty acids are formed. The acid number determines the amount of free fatty acids contained in 1 g of fat, and is expressed by the amount of mg of caustic potassium (KOH) required to neutralize them. High molecular weight fatty acids are tasteless and odorless, and therefore, with an increase in their amount in the product, no noticeable change in organoleptic characteristics is observed. As a result of the action of air oxygen, primary and secondary oxidation products accumulate in fats. It is their presence that determines the appearance of a characteristic unpleasant taste and odor in fats. The amount of peroxides and hydroperoxides characterizes the peroxide value.

The purpose of our study is to determine the indicators of oxidative deterioration of vegetable oils. We have determined such indicators as acid number (GOST R 52110), peroxide number (GOST 51487).

In retail, 6 samples of vegetable oil from domestic and foreign manufacturers were selected. Of these, 2 samples are sunflower oil, 2 are olive oil, 1 is soybean oil, 1 is sesame oil. The following results were obtained.

The peroxide number exceeds the standard in three samples. Possible reasons for exceeding the peroxide value are poor-quality raw materials or non-compliance with storage conditions, as well as bottling of oil already with signs of oxidative deterioration.

Of the six samples of vegetable oils, the excess of the acid number, which characterizes the depth of hydrolytic processes, was found in two samples. This excess can be explained by non-observance of the temperature regime of oil storage. In the two studied samples, a simultaneous discrepancy with the quality in terms of acid and peroxide numbers was established. Four samples of vegetable oil were potentially hazardous to human health based on only two physicochemical indicators.

The results of our research: only three samples can be recommended for sale without concern for the health of Russian consumers. Considering that vegetable oil is a product of everyday use, and its inadequate quality can harm the health of Russians, we suggest that the problem of the quality of vegetable oils be brought up for discussion by a wide range of experts - employees of certification bodies and testing laboratories, physicians, chemists, biochemists, ecologists, commodity experts, technologists of the oil and fat industry.

INFLUENCE OF HEAVY METALS ON MULTIPLE FORMS OF CULTURAL SOYBEAN CATALASE

Kochkurova I.A., Chernyshuk D.K., Belyakova O.P., Galaktionova S.V., 2nd year students of the "Chemistry" department of the natural-geographical faculty.

Scientific advisers: L.E. Ivachenko, Ph.D., associate professor; Lavrentyeva S.I., Ph.D., Head. laboratory of the Department of Chemistry.

FSBEI HPE "Blagoveshchensk State Pedagogical University"

The existing deficiency of vegetable protein in most countries of the world is causing an increasing demand for soybean grain and its processed products. Recently, special attention has been paid to the study of the soybean genome. The study of polymorphism of soybean proteins abroad began in the last century. The factual material accumulated in this area in our country has not previously been subjected to versatile generalization and systematization. The most readily available gene activity products are isozymes. Isozyme analysis allows you to modify and expand traditional methods based on the use of protein markers .

The chemical composition of soybean seeds is influenced by the agro-ecological conditions for growing soybeans. The introduction of fertilizers into the soil, acid rain, human activity and other factors lead to an increase in the salts of heavy metals in soils, the effect of which on the plant is poorly understood. Environmental factors play an important role in the sustainability of plant productivity and the quality of the crop. Extreme temperature, drought, waterlogging, increased solar radiation, environmental pollution are stress factors. In the course of evolution, plants have developed a defense system against oxidative stress. Inactivation of free radicals is carried out by enzymatic and non-enzymatic antioxidant compounds, such as the enzyme catalase (K1.11.1.6.). In terms of structure and properties, it is capable of oxidizing a number of substrates with the participation of hydrogen peroxide. Catalase dehydrates the hydrogen peroxide molecule. The hydrogen removed from the substrate is transferred to the second hydrogen peroxide molecule, forming water and oxygen.

In connection with the above, the goal of our study was to study the effect of heavy metals on multiple forms of catalases in cultivated soybeans at different stages of the growing season.

The object of the study was the soybean variety Sonata ( Glycinemax (L.) Merrill), obtained from the State Scientific Institution "All-Russian Research Institute of Soybeans" of the Russian Academy of Agricultural Sciences.

Soybean seeds of the Sonata variety were grown in greenhouse conditions on the soil from the fields of the village. Sadovoe, Tambov region from July to September. In the first experiment, lead sulfate was used at concentrations of 12 mg / kg (2 times higher than the OEC) and 2.75 mg / kg (2.5 times higher than the OEC), in the second, zinc sulfate in concentrations of 46 mg / kg (2 times higher than the APC) and 15 mg / kg (10 times higher than the content of metals in the soil). Each experiment was carried out in twenty replicates and lasted 8 days until the emergence of soybean seedlings, 17 days before the appearance of the first trifoliate leaf and 41 days before the flowering period. At each stage of the growing season, the material was collected and stored frozen. The control consisted of samples grown on soil without the introduction of heavy metals at each stage of the growing season.

For biochemical analysis, extracts of soluble proteins were prepared from the test material (500 mg) by homogenization in mortars in the cold and centrifugation. Electrophoretic spectra of the studied enzymes were detected by electrophoresis on columns of 7.5% polyacrylamide gel with subsequent staining of the zones. Since the standard criterion for characterizing multiple forms of enzymes is their relative electrophoretic mobility (Rf), the heterogeneity of soybean varieties was assessed by the identified forms of catalases according to their Rf. Forms are numbered from more highly mobile to low-moving forms. Each form of catalase was assigned its own abbreviation in accordance with the values ​​of their Rf from K1 to K14.

As a result of the studies carried out, fourteen forms of catalases have been identified for the first time. The analysis showed that at the first stage of the growing season there is no high-molecular form with Rf = 0.04, which was first detected at the stages of the first trifoliate leaf and flowering in control and experimental samples grown both with the introduction of lead sulfate and zinc sulfate (Fig. 1) ...

I II III I II III

Fig. 1. Schemes of enzymograms of catalases of soybean varieties Sonata grown on a nutrient medium with the addition of salts of heavy metals: A - lead sulfate in concentrations: 1 - 12 mg / kg; 2 - 2.75 mg / kg; B - zinc sulfate in concentrations: 3 - 46 mg / kg; 4 - 15 mg / kg; K - control (without introducing HM) at different stages of the growing season: I - soybean seedlings, II - the first trifoliate leaf, III - flowering. Arrow - direction of electrophoresis (from cathode to anode).

An increase in the concentration of lead sulfate in the soil leads to a slight decrease in the forms of catalases in soybean seedlings. Moreover, it should be noted that the appearance of low-molecular forms with Rf = 0.66 and Rf = 0.84, which were not established in the control. In the samples of soybeans at the stage of the first trifoliate leaf, the number of multiple forms of catalases did not change with an increase in the concentration of lead sulfate. However, it is important to note that, as in soybean seedlings, in the presence of high concentrations of this salt in the soil, low-molecular forms with Rf = 0.84 and Rf = 0.94 appear. concentrations of 12 mg / kg and 2.75 mg / kg, the number of multiple forms of catalases doubles, which is possibly associated with an increase in metabolic processes at this stage of the growing season. This, in turn, helps to increase the adaptive potential of soybeans under experimental conditions.

An increase in the concentration of zinc sulfate in the soil does not affect the number of multiple forms of catalases in soybean seedlings. Interestingly, instead of forms with Rf = 0.23 and Rf = 0.48, forms with Rf = 0.17 and Rf = 0.3 appear, both at a concentration of 46 mg / kg and 15 mg / kg. It is important to note that the form with Rf = 0.3 is present in all samples obtained from soils with an increased content of this salt. This fact probably indicates an increase in the adaptive potential of soybeans in the presence of zinc sulfate. An increase in the concentration of zinc sulfate in the soil does not affect the number of multiple forms of soybean catalases at the stage of the first trifoliate leaf. However, when salt is added at a concentration of 15 mg / kg, the disappearance of the form with Rf = 0.13 and the appearance of the form with Rf = 0.17 should be noted. And when 46 mg / kg of zinc sulfate is introduced into the soil, a form with Rf = 0.56 appears instead of a form with Rf = 0.42. Also, in the presence of increased salt concentrations, a form with Rf = 0.23 appears, which is absent in the control. At the stage of flowering in soybeans in the presence of zinc sulfate in the studied concentrations, a slight increase in multiple forms of catalases is observed. Moreover, forms with Rf = 0.07 were found; 0.23; 0.3 and 0.84, not typical for control. Forms with an average electrophoretic mobility can be called minor and they do not show visible changes.

Thus, as a result of the research, it was found that the number of multiple forms of soybean catalases of the Sonata variety does not depend on the growing season, but depends on the concentration of heavy metal salts in the soil. It was shown that lead sulfate causes a decrease in the number of multiple forms of catalases in soybean seedlings, which leads to a decrease in the adaptive potential of soybeans. During the flowering period, in the presence of HM salts, the number of catalase forms, on the contrary, increases, which is associated with the intensification of metabolic processes towards an important stage in the development of soybeans - bean formation.

Studies have shown that the analysis of catalase enzyme patterns at different stages of the growing season in the presence of HM salts makes it possible to control the adaptive potential of cultivated soybeans.

INFLUENCE OF HEAVY METAL SALTS ON THE PEROXIDASE ACTIVITY OF SOY

Kuznetsova V.A., postgraduate student; Mikhailova M.P., 5th year student.

Scientific adviser: Ivachenko L.E., Ph.D., Associate Professor of the Department of Chemistry.

FSBEI HPE "Blagoveshchensk State Pedagogical University"

One of the most important problems in plant ecology is the study of the response of plants to the action of salts of heavy metals (HM), which at high concentrations have a toxic effect on a wide variety of physiological processes. This problem is not only of practical importance associated with the increasing pollution of the environment with HM, but also with the study of the mechanisms of plant adaptation. Among heavy metals, the most common toxicants are Cd and Pb, while Cu and Zn are also trace elements.

For a number of reasons, plants absorb HMs and, unlike animals, are able to accumulate them in large quantities. With the accumulation of HMs in plant organs, their content can be tens and even hundreds of times higher than the content in the environment. The ability of plants to accumulate HM is realized at different levels of organization: cellular, tissue, and organ. Entering cells, HMs react with functional groups of proteins and other compounds, which may be one of the detoxification mechanisms, but at the same time leads to numerous metabolic disorders, causing oxidative stress, which underlies the high toxicity of HMs. The strength of binding of heavy metal ions with functional groups of biopolymers can differ, which may be one of the reasons for the different toxicity of HMs. Therefore, in our studies, we selected the widespread TM Cd, Pb, Cu, Zn, firstly, having different affinity for the functional groups of biopolymers, and secondly, accumulating in different cell compartments. That is why the problem of the accumulation of metals in a plant is decisive in the study of their toxic effect and resistance mechanisms.

Due to effective mechanisms of detoxification of metals, plants continue to grow when their content in the environment is increased. The protection of organisms from damaging external factors that disrupt cellular and organismal homeostasis and often threaten their existence by oxidative stress is provided by a number of special cellular systems. Among the totality of processes of adaptation syndrome (stress), natural antioxidants play an important role. This role is played by the enzyme peroxidase, which is involved in the protection of cells from stressors. The broad specificity of peroxidase to substrates of various natures is of particular interest. Peroxidase is a heme-containing glycoprotein. Its catalytic properties are strictly specific to hydrogen peroxide, but this enzyme exhibits broad specificity to other substrates of very diverse structure. The only iron ion present in peroxidase has the ability not only to activate hydrogen peroxide, but also to impart to it the ability to enter into oxidation reactions of various substrates. Organic peroxides, including peroxides of unsaturated fatty acids and carotene, can also serve as a source of active oxygen during the catalytic action of peroxidase. The substrates oxidized by peroxidase in the presence of peroxide include most phenols, as well as benzidine, adrenaline, aniline, aromatic acids, ascorbic acid, nitrites, and a number of other compounds.

The aim of our study was to study the effect of heavy metal salts on the peroxidase activity of wild and cultivated soybeans.

Soybean seeds of the Sonata variety ( Glycine max (L.) Merrill) and the wild form KA-1344 (Glycine soja Sieb. et Zucc.) received from the State Scientific Research Institute of Soybeans of the Russian Academy of Agricultural Sciences (Blagoveshchensk). Soybeans were germinated in greenhouse conditions in the soil with the addition of salts of heavy metals. In the first experiment, zinc sulfate was added to the soil at concentrations of 46 mg / kg (2 times higher than the ODC) and 15 mg / kg (10 times higher than the metal content in the soil). In the second experiment, cadmium sulfate was added at concentrations of 2 mg / kg (2 times higher than the ODC) and 0.2 mg / kg (10 times higher than the metal content in the soil). In the third experiment, copper sulfate was introduced at concentrations of 6 mg / kg (2 times higher than the ODC) and 1.6 mg / kg (10 times higher than the metal content in the soil). In the fourth experiment, lead sulfate was introduced at concentrations of 12 mg / kg (2 times higher than the ODC) and 2.75 mg / kg (10 times higher than the metal content in the soil). Each experiment was carried out in 20 replicates and lasted 17 days until the appearance of the first trifoliate leaf and 41 days before the flowering period. At each stage of the growing season, the material was collected and stored frozen. Samples grown on soil without heavy metals were used as control at each stage of the growing season. The peroxidase activity was determined by the colorimetric method, the protein content was determined by Lowry.

A B

Rice. Effect of heavy metal salts on the specific activity of peroxidases

cultural (A) and wild (B) soybeans

(1 - control, 2 - ZnSO 4 (15 mg / kg), 3 - ZnSO 4 (2 ODK), 4 - CdSO 4 (0.2 mg / kg), 5 - CdSO 4 (2 ODK),

6 - CuSO 4 (1.6 mg / kg), 7 - CuSO 4 (2 ODK), 8 - PbSO 4 (2.75 mg / kg), 9 - PbSO 4 (2 ODK).

As a result of the studies, it was found that the specific activity of peroxidases at the studied stages of the growing season (control without adding HM salts) changes insignificantly (Fig.).

When sprouting soybeans of the Sonata variety with the introduction of zinc sulfate in the soil at concentrations of 15 mg / kg and 46 mg / kg, the peroxidase activity increases insignificantly compared to the control at the stage of formation of the first trifoliate leaf and increases significantly during the flowering period (Fig.). It should be noted that cadmium salts at concentrations of 0.2 mg / kg and 2 mg / kg during the formation of a trifoliate leaf cause a slight increase in the activity of peroxidases, as well as during the flowering period in the presence of high concentration cadmium salts. At the stage of flowering, in the presence of a minimum concentration of this salt in the soil, the activity of the enzyme increases. The introduction of copper and lead salts into the soil at the studied concentrations insignificantly increases the activity of peroxidases in comparison with the control at the stage of formation of the first trifoliate leaf and significantly increases during the flowering period in the presence of copper salts and lead salt at a concentration of 2.75 mg / kg, which can be explained by the action of severe oxidative stress.

During the germination of wild-growing soybeans with the addition of zinc sulfate and cadmium salts to the soil in the studied concentrations, the peroxidase activity increases insignificantly compared to the control (Fig.) At the stage of formation of the first trifoliate leaf and during the flowering period, with the exception of samples grown on soil containing zinc sulfate at a concentration of 46 mg / kg at the stage of the first trifoliate leaf, where the enzyme activity was minimal. With the introduction of copper sulfate of various concentrations, the activity of peroxidases significantly increases in comparison with the control at all stages of the growing season. Lead salts at a concentration of 2.75 mg / kg increase the activity of peroxidases in comparison with the control during the formation of a trifoliate leaf and during the flowering period, and the use of this salt at a concentration of 12 mg / kg leads to a slight increase in peroxidase activity compared to the control.

As a result of the study, it was shown that the introduction of HM into the soil plays an important role in the metabolism of soybeans. Thus, in the flowering phase of cultivated soybeans, an increase in peroxidase activity was noted when the studied HMs were introduced, with the exception of cadmium sulfate in a high concentration and copper sulfate in a minimum. Analysis of wild-growing soybeans revealed that HM salts increase the peroxidase activity, or it remains at the control level at all stages of the growing season, with the exception of zinc sulfate in maximum concentration at the stage of formation of the first trifoliate leaf.

Thus, with the introduction of HM salts into the soil during the cultivation of cultivated and wild-growing soybeans, a regularity was established: if in the phase of the first trifoliate leaf the specific activity of peroxidases is higher, then in the flowering stage it decreases and, conversely, which is possibly associated with the antioxidant reaction of peroxidases under conditions oxidative stress of soy.

EARTH SCIENCES GEOLOGY 05-111 General ... sciences Karhn candidate biologicalsciences KBN candidate veterinarysciences kvn military candidate sciences sciences ...

When fat is oxidized, a large amount of peroxide compounds and atomic oxygen are released. These substances are stronger oxidants than iodine. Oxygen displaces iodine from potassium iodide. The presence of free iodine is determined using starch. To determine the amount of free iodine, the amount of sodium sulfate used to neutralize it is determined.

The peroxide number is the number of grams of iodine isolated from potassium iodide by the peroxides contained in 100 g of fat.

Preparation of the material for the reaction. Poultry adipose tissue is crushed with scissors, melted and filtered.

Formulation of the reaction: A sample of the studied rendered fat (weighing 1 g) is weighed in a conical flask with an error of not more than 0.0002 g and dissolved in 20 ml of a mixture of glacial acetic acid and chloroform (1: 1). 0.5 ml of a freshly prepared saturated solution of potassium iodide is added to the solution and kept in a dark place for 3 minutes. Then 100 ml of distilled water is added to the solution, to which 1 ml of 1% starch solution is added in advance. The released iodine is titrated with 0.01 N. sodium sulfate solution until the blue color disappears. In parallel, under the same conditions, a control determination is carried out, in which the same amounts of reagents are taken, but without fat.

The peroxide number of fat X (%) is calculated by the formula:

where K is the correction to the titer 0.01 N. sodium sulfate solution;

V - amount 0.01 N. sodium sulfate solution, consumed for titration of the test solution, ml;

V 1 amount 0.01 N. sodium sulfate solution, consumed for titration of the control solution, ml;

0.00127 - the amount of iodine corresponding to 1 ml of 0.01 N. sodium sulfate solution, g;

m - fat mass, g.

Accounting for the reaction: Fat from chilled and frozen carcasses of all types of poultry is considered fresh: if the peroxide value does not exceed 0.01 g of iodine; chicken fat from chilled carcasses with a peroxide value of 0.01-0.04 g of iodine, goose, duck, turkey - 0.01-0.1 g of iodine, fat from frozen carcasses of all types of poultry with a peroxide value of 0.01-0, 03 g of iodine is considered to be of doubtful freshness; if the indicated values ​​are exceeded, poultry meat is considered stale.

Edible rendered fat obtained from slaughter cattle, depending on the value of the peroxide number, is considered: fresh - up to 0.03; fresh, but not subject to storage - from 0.03 to 0.06; doubtful freshness - from 0.06 to 0.1; stale - above 0.1.

Reaction with neutral red.

The hydrolysis of fats produces a large amount of free fatty acids, and the products of fat oxidation can be volatile fatty acids. The accumulation of these products in fat leads to an increase in its acidity. Neutral red in an acidic environment is oxidized, acquiring a red color. In addition, neutral red can be oxidized under the influence of peroxide compounds, atomic oxygen and a number of other oxidants formed during the oxidation of fats.

Statement of the reaction. 1 g of the test fat is placed in a porcelain mortar, then 1 ml of a working (0.01%) aqueous solution of neutral red is added there. After that, the contents of the mortar are intensively rubbed with a pestle for 1 minute. An aqueous solution of neutral red does not mix with grease, therefore, the remaining paint must be drained.

Taking into account the reaction. Fresh fat turns yellow or beige, pork and lamb fat can have a greenish tint. Fat of doubtful freshness is brown to pink in color. Tainted fat is bright pink to red in color.

Qualitative reaction to aldehydes.

Aldehydes are one of the main products of fat oxidation, so their presence in fat indicates deterioration.

The essence of a qualitative reaction to aldehydes lies in their ability to form a colored compound with polyhydric phenol in an acidic medium.

Statement of the reaction. In a test tube is placed 2 ml of the test fat, previously melted in a water bath, add 2 ml of hydrochloric acid with a density of 1190 kg / m 3 and 2 ml of a saturated solution of resorcinol in benzene. Then close the tube with a rubber stopper and mix its contents.

Taking into account the reaction. If there are aldehydes in the test fat, the contents of the test tube are colored lilac-red. If the color of the contents of the tube has not changed, then the reaction to aldehydes is considered negative.

Determination of hydrogen sulfide.

The reaction is based on the interaction of lead acetic acid with gaseous hydrogen sulfide, as a result of which a salt of hydrogen sulfide acid is formed - lead sulphide of a dark color:

H 2 S + (CH 3 COO) 2 Pb = PbS + 2CH 8 COOH.

Determination of hydrogen sulfide does not give a good result for all types of meat spoilage. A positive result is usually obtained when the meat is decomposed under anaerobic conditions (in the skin). When meat decays under normal conditions, hydrogen sulfide may not be detected by this reaction.

Reaction progress... Place 25-30 pieces of meat in a short test tube or vial with a wide neck. A strip of filter paper moistened with an alkaline 10% solution of lead acetic acid is fixed near the cork, and the paper should not touch either the meat or the walls of the glass below the cork.

The reaction is read after 15 minutes. If there is no hydrogen sulfide in the meat, then the piece of paper remains white. From hydrogen sulfide, the paper turns brown or dark brown. If there is little hydrogen sulfide in the meat, then only the edge of the paper darkens, and with a large amount of hydrogen sulfide, the plaque on the paper acquires a metallic sheen.

The reagent for hydrogen sulfide is prepared as follows: 10% caustic soda is added to a 10% aqueous solution of lead acetate until a precipitate forms. Store the solution in a tightly closed bottle.

Determination of pH.

For the determination method, see the topic: determination of the meat of sick animals. During the decomposition of meat, alkaline products accumulate in it, as a result of which the concentration of hydrogen ions decreases.

To assess the freshness of meat, the pH value is of relative importance, since it depends not only on the degree of freshness of the meat, but also on the condition of the animal before slaughter. In filtered extracts from fresh meat, the pH is 7-6.2, and for defrosted meat it is 6.0-6.5; in extracts of meat of suspicious freshness - 6.3-6.6 (defrosted - 6.6); in extracts of stale meat -6.7 and higher.

Luminescent analysis.

It is known that meat of different degrees of freshness fluoresces differently when exposed to ultraviolet radiation.

Rice. 2. Luminoscope "Owl"

Statement of the reaction. For the luminescent analysis of meat freshness, the Filin luminoscope is used (Fig. 2). The device is connected to the network. A sample of the investigated meat or meat extract 1: 4 is placed in the working compartment of the device and viewed in ultraviolet light.

Taking into account the reaction. Fresh bovine meat fluoresces with a velvety red color, mutton - a dark brown color.

pork - light brown. When decomposing meat, a glow is noted in the form of yellow dots on a dirty-dark background.

The meat extract from fresh meat fluoresces with a pink-violet light; from meat of dubious freshness - pink-purple with a greenish tint; from stale meat - green-bluish color.