Content
  Introduction
  1 General characteristics of fruit juices 5
  1.1 production Technology and classification of juices 5
  1.2 Composition and nutritional value of juices 8
  1.3 Main indicators of the quality of fruit juices 9
  1.4 Titratable acidity and methods for its determination 11
  1.4.1 Titrimetric method 12
  1.4.2 Potentiometric Method 12
  2 Practical part 17

  INTRODUCTION
  Vegetables, fruits and berries are of great importance in human nutrition. However, to keep them fresh for a long time, unfortunately, is simply impossible. In this case, juices come to the rescue, which are able to preserve the nutritional value of these products.
  Unfortunately, the juices that are sold in our stores today are hardly natural. All of them undergo serious industrial processing. In addition, almost all of them contain too much sugar.
  Many vegetable juices differ from the fruit and berry juices in the composition of organic acids. In fruit juices, apple, citric and tartaric acids are predominant, while in vegetable juices they are succinic, acetic, formic and oxalic.
  The aim of this course work is to determine the titratable acidity of apple juice of various manufacturers - and comparison of the results with normalized.
  1 GENERAL CHARACTERISTIC OF FRUIT JUICES
  1.1 production Technology and classification of juices
  Juices are obtained from fruits and vegetables by mechanical action and canning by physical means (except for ionizing radiation).
  Currently, the following types of juices are produced: fruit; blended; concentrated; for baby and diet food; fruit nectars; vegetable; juice-containing fruit and vegetable drinks.
  Juice technology includes the following operations:
  1 inspection of raw materials;
  2 washing;
  3 secondary inspection and washing;
  4 crushing;
  5 getting juice;
  6 straining;
  7 lightening.
  1 Inspection of raw materials is necessary to remove non-standard fruits or berries, as well as possible impurities - branches, leaves, stalks, etc. This operation is carried out on a conveyor belt.
2 Raw materials are washed in drum or fan washers; berries (strawberries, raspberries) are washed from sand or earth, immersed in mesh baskets in water and rinsed in the shower.
  3 Both operations are repeated.
  4 Crushing of raw materials is carried out in order to destroy at least 75% of the pulp cells.
  a) When processing enzymes, the crushed mass is heated to a temperature of 45 ° C and an extract of the enzyme preparation is added in an amount of 2-3%. The mixture is stirred, incubated for 6-8 hours, and then pressed. Since plant tissue becomes loose under the action of enzymes due to the destruction of the protoplasm of a significant part of the cells, the yield of juice upon pressing is significantly increased.
  b) Electric treatment can be used for any kind of fruit, berries or vegetables, passing raw materials through the plasma electroplaser not only in crushed (pome fruits and stone fruits), but also in general (grapes and other berries). In this case, the yield of juice can be increased to 80-82% in apples and grapes (respectively) and up to 60-65% in plums.
  5 Obtaining juice (pressing). The effectiveness of this operation largely depends on the design of the press and the pressure regime. The squeezed raw materials after pressing are loosened and pressed again. The best results are obtained on hydraulic pack presses.
  6 Filtering the juice is carried out to separate it from coarse impurities: pieces of pulp, twigs, seeds. For this operation, stainless steel sieves with 0.75 mm openings are used.
  7 Clarification of juice is the most complex technological process, based on the following physical or biochemical methods:
  a) clarification by heating to a temperature of 80 ... 90 ° C for 1-3 minutes to coagulate colloidal substances, followed by rapid cooling to 35 ... 40 ° C and separation of suspended particles in separators (centrifuges);
  b) clarification by gluing - thoroughly mixing a solution of tannin with juice, holding until complete sedimentation and compaction of the resulting flakes, decanting the juice;
  Preparation of prefabricated juice in large bottles.
  Squeezed and filtered juice, heated to a temperature of 95 ° C, is immediately poured into washed and scalded glass bottles with a capacity of 10-15 dm3 and sealed with sterilized lids. The bottles are cooled in air and stored in a warehouse for at least 2–3 months. During this time, the juice self-clarifies, it is carefully decanted, heated and poured into small containers, after which it is pasteurized.
  Processing clarified juices.
Juices clarified by heating, gluing or enzyme preparations, as well as self-clarified, are filtered on the installations of any systems, filter presses or precoated filters.
  Juice classification:
  1 Fruit juices are obtained from benign, ripe, fresh, or freshly stored fruits by cooling or other means. Juices can be made from one or several types of fruits, they can be transparent (clarified), clouded (not clarified) and with flesh.
  2 Blended juices are obtained by adding to the main juice up to 35% juice of other types of fruits and berries (sometimes raw materials are mixed before pressing juice from it). The purpose of blending is to improve the organoleptic properties, nutritional and biological value of the drink. They produce natural juices with sugar, as well as with pulp and sugar.
  3 Concentrated juices are obtained from non-fermented juices, from which organic moisture is partially removed (mainly by evaporation, less often by freezing and reverse osmosis) with the capture of aromatic substances and returning them to the finished product
  a) Concentration by evaporation is carried out in evaporators. The lower the evaporation temperature and the shorter the duration of the operation, the higher the quality of the juice obtained, therefore, it is advisable to carry out the evaporation in vacuum apparatuses.
  b) Concentration by freezing is based on cooling the juice below the freezing temperature. Part of the water freezes and in the form of crystals is separated from the concentrate by separation. The lower the freezing temperature, the higher the solids content in the finished product. At low temperatures, the juice undergoes minimal changes. By freezing get juice with a solids concentration of 45-50%. Freezing is used to produce concentrated citrus juices.
  c) Concentration using membranes - reverse osmosis - can improve the quality of the finished product due to the low process temperature. The essence of the method lies in the fact that on both sides of the membrane are two liquids with different concentrations of dissolved substances. Osmotic pressure occurs at the membrane boundary, and water moves from the low concentration solution to the high concentration solution until the concentrations are equal. If pressure is applied to a solution with a high concentration, then the water will flow in the opposite direction
4 Juices for baby food are prepared only from high-quality fruit and berry raw materials. They can be natural, with sugar, with pulp and sugar, blended. Juices are recommended for children from 6 months of age.
  5 Juices for diet nutrition are produced from fruits and berries with a low content of sucrose. They are intended for patients with diabetes. Xylitol and sorbitol are used to sweeten juices. In recent years, the production of two- and multicomponent juices with pulp for general consumption and special purposes - for children and diet food has increased.
  6 Fruit nectars are obtained by mixing fruit juice, one or more types of concentrated juices, or the edible portion of benign fresh fruits with water, sugar, or honey, brought to a puree state. Nectars are preserved in various physical ways, in addition to processing by ionizing radiation. Mass fraction of fruit juice is 25-50%, depending on the type of fruit.
  7 Juice drinks.
  a) Fruit drink is obtained by mixing fruit juice or concentrated fruit juice, or a mixture of juices, or brought to a puree state of the edible part of benign fresh fruit with water. Sugar, citric acid are added to the drink and canned by physical or chemical methods. In the manufacture of drinks using natural volatile aromatic components of fruit juice of the same name, artificial flavors, sweeteners, sweeteners, natural opacifiers and stabilizers.
  1.2 Composition and nutritional value of juices
  From the point of view of plant biology, juices in composition are the contents of cell vacuoles. Sugars are dissolved in vacuole: glucose with fructose and various polysaccharides; fruit acids (malic, citric, etc.); minerals; vitamins; amino acids; volatile production. The nutritional value of juices consists in their high content of easily digestible carbohydrates (glucose, fructose, sucrose, etc.), a complex of water-soluble vitamins (ascorbic, folic, nicotinic and pantothenic acids, P-active substances, carotene, thiamine, riboflavin, etc.), mineral salts, pectin substances, organic acids, aromatic compounds. Thus, juice is the source of a number of easily digestible substances that are beneficial for the body.
Fruit juices are of great importance in our diet and, therefore, for our health. They serve not only as a source of vitamins and mineral salts, but also contain organic acids, pectins, aromatic substances, and essential oils.
  Many of the fruits contain organic compounds such as gums, which are a complex of potassium, magnesium and calcium salts, sugar-gum acids. Gums successfully make up for the lack of minerals needed by the body. Complex carbohydrates contained in fruit juices - polysaccharides, including pectin compounds, after swelling when interacting with water, remove poisons and pathogenic microbes, and also help to eliminate cholesterol. Fruit juices are also great refreshing drinks.
  The nutritional value of juices has led to their widespread use for the prevention and treatment of diseases, to the allocation of juice therapy as an independent discipline.
  1.3 Main indicators of the quality of fruit juices
  In addition to organoleptics, the main qualitative indicators of juices, which are often taken into account in commercial operations, are density (mass to volume ratio), soluble solids content (RSV), expressed in degrees Brix (° Brix), as well as Ratio.
  The Brix indicator characterizes the total soluble solids content (GOST 51433-99). This indicator can be used to judge the degree of juice concentration (numerical expressions of density are usually given with reference to the measurement temperature, for example, 20 ° C).
  A specific density value corresponds to a certain soluble solids content.
  Ratio is used to assess the palatability of juices, concentrated juices, nectars and juice drinks. It characterizes the ratio between total sugars expressed in terms of Brix and acids expressed in% in terms of the total titratable acidity of the product. Products with a balanced ratio of sugars and acids have a Ratio indicator lying in the range from 12 to 15.
  The composition of physico-chemical indicators used in the analysis of the quality of various groups of drinks from juices has differences.
  1. Fruit juices direct pressed. The main physical and chemical indicators of juices:

  - mass fraction of titratable acids;


  2. Recovered fruit juices. The main physical and chemical indicators of juices:
  - mass fraction of soluble solids;
  - pH;
  - mass fraction of ethyl alcohol;
  - mass fraction of oxymethyl furfural;
- mass fraction of pulp (for juices with pulp).
  3. Concentrated fruit juices. The main physical and chemical indicators of juices:
  - recommended mass fraction of soluble solids; recommended mass fractions of titratable acids;
  - mass fraction of sediment;
  - mass concentration of oxymethylfurfural;
  - mass fraction of sulfur dioxide (for grape juice).
  4. Fruit nectars. The main physical and chemical indicators of juices:
  - mass fraction of soluble solids;
  - pH;
  - mass fraction of sediment and pulp;
  - mass fraction of vitamin C (for fortified);
  - mass fraction of oxymethyl furfural.
  5. Fruit juice drinks. The main physical and chemical indicators of juices:
  - mass fraction of sediment;
  - mass fraction of carbon dioxide (for carbonated);
  - mass fraction of vitamin C (for fortified).
  1.4 titratable acidity and methods for its determination
  When controlling the production of food concentrates, acidity is one of the main indicators characterizing the good quality of raw materials and finished products. Acidity also refers to the main factors by which the direction of biochemical and physicochemical processes of food-concentrate and vegetable-drying production is judged.
  In control practice, the acidity is determined as total, or titratable, and active, i.e. concentration of hydrogen ions - pH.
  Under the general acidity is meant the content in the product of all acids and substances that react with alkali. Total acidity is expressed in the following quantities:
  in percent by weight (weight) of any acid prevailing in this product (milk, citric, malic, etc.);
  in “degrees”, i.e. in the volume of alkali with a molar concentration of the equivalent of 0.1 mol / l, which went into the neutralization of acidic compounds in 100 g of product
  To express acidity in weight percent of a certain acid, the volume of alkali with a molar concentration of the equivalent of 0.1 mol / L spent on the neutralization of acidic compounds in 100 g of the product is multiplied by a milliequivalent of the corresponding acid. The total acidity can be determined by titration with an alkali solution of aqueous solutions of the product in the presence of an indicator until its color changes or by potentiometric electrometric titration.
  1.4.1 Titrimetric method
  The method is based on titration of the test solution with sodium hydroxide solution in the presence of phenolphthalein indicator.
25 ml of the test solution are pipetted into a conical flask for titration, 2-3 drops of phenolphthalein solution are added and titrated with sodium hydroxide solution with continuous stirring until a pink color is obtained that does not disappear for 30 s.
  1.4.2 Potentiometric method
  The potentiometric analysis method is based on measuring the electrode potential, the value of which is determined by the concentration (more precisely, the activity) of the potential-determining component of the solution.
  To calculate the electrode potential (E, B), the Nernst equation is used:
  E \u003d E ^ 0 + RT / nF × ln (a_oxide) / a_rest, (1)
  where E0 is the standard potential, V; R is the universal gas constant (8.313 J); T is the absolute temperature, K; F is the Faraday number (96,490 C); n is the charge of the potential-determining ion, a is its activity.
  After introducing the numerical values \u200b\u200bof the quantities R and T, (the temperature is assumed to be 298 K (25 ° C), and taking into account the coefficient of transition from natural logarithms to decimal (2,3026), we obtain the equation:
  E \u003d E ^ 0 + 0.059 / n × lg a_oxid / a_vosst (2)
  The potentiometric analysis method is divided into direct potentiometry (ionometry) and potentiometric titration.
  Direct potentiometry is based on measuring the potential of the indicator electrode and calculating the concentration of the determined ions according to the Nernst equation.
  Potentiometric titration is based on determining the equivalence point from potentiometric measurements. As in other titrimetric methods, potentiometric titration reactions must proceed strictly stoichiometrically, have a high speed and go all the way.
  For potentiometric titration, a chain is assembled from the indicator electrode in the analyzed solution and the reference electrode. Calomel or silver chloride are most often used as reference electrodes.
  Electrodes
  An indicator electrode is called an electrode whose potential determines the activity of the analyzed ion in accordance with the Nernst equation.
  In this course work as an indicator electrode used a glass electrode:
  Figure 1 - Glass electrode
  1 - glass pH-sensitive membrane; 2 - 0.1 M HCl solution, saturated with AgCl; 3 - silver wire; 4 - glass tube; 5 - isolation; 6 - down conductor.
  A reference electrode is an electrode whose potential is constant and independent of the concentration of ions in the solution. The salt bridge serves to prevent mixing of the analyzed solution and the solution of the reference electrode.
A silver chloride electrode was used as a reference electrode:
  Figure 2 - Silver chloride electrode
  1 - hole for pouring an electrolyte solution; 2 - silver wire coated with a layer of AgCl; 3 - KCl solution; 4 - capillary.
  Equivalence Point Definition
  The equivalence point (titration end point) in the titrimetric analysis is the moment of titration, when the number of equivalents of the added titrant is equivalent to or equal to the number of equivalents of the analyte in the sample.
  Methods for determining the equivalence point: using indicators, potentiometry, using pH meters, conductivity, color change, deposition, isothermal calorimetric titration, thermometric titration, thermometric titrimetry, spectroscopy, amperometry.
  In potentiometric titration near the equivalence point, a sharp change (jump) in the potential of the indicator electrode occurs if at least one of the participants in the titration reaction is a participant in the electrode process.
  Figure A shows the titration curve of hydrochloric acid (HCl) with sodium hydroxide (NaOH). It almost exactly reproduces the theoretical curve for titration of a strong acid with a strong base. As can be seen, at the equivalence point, a sharp jump in the EMF occurs, caused by a sharp change in the potential of the indicator electrode. From this jump, you can determine the equivalence point and then calculate the content of hydrochloric acid.
  To find the equivalence point, a differential curve is often constructed in the coordinates dE / dV - V (Fig. B). The maximum of the obtained curve indicates the equivalence point, and the abscissa reading corresponding to this maximum gives the volume of titrant spent on titration to the equivalence point. The determination of the equivalence point from the differential curve is much more accurate than from the simple dependence E - V.
  Since the derivative of the function with a maximum at the maximum point is zero, the second derivative of the potential with respect to volume (d2E / dV2) at the equivalence point will be zero. This property is also used to find the equivalence point (Fig. B).
In the simple and convenient Gran method, the equivalence point is determined from the graph in the coordinates dV / dE-V. Before and after the equivalence point, the Gran curve is linear, and the equivalence point itself is located as the intersection point of these lines (Fig. D). The advantages and convenience of the Gran method are especially noticeable in the analysis of dilute solutions, allowing you to determine the equivalence point with sufficient accuracy due to the linearity of the graph.
  In potentiometry, various types of potentiometric titration are used:
  Redox titration;
  Precipitation titration;
  Complexometric titration;
  Acid-base titration.
  Acid-base potentiometric titration is based on the occurrence of a neutralization chemical reaction. As an indicator, we can use any electrode with a hydrogen function: hydrogen, chinhydron, glass. The most commonly used glass electrode. The method allows the quantitative determination of components in a mixture of acids if the constants of their dissociation differ by at least three orders of magnitude; polybasic acids (bases), since it is possible to achieve the separation of the end points of multistage titration (several jumps are observed on the titration curve).
  Instruments used in potentiometry
  In potentiometric analysis, the main measuring instruments are various types of potentiometers. They are designed to measure the EMF of the electrode system. Since the EMF depends on the activity of the corresponding ions in the solution, many potentiometers can also directly measure pX - the negative logarithm of the activity of the X ion. Such potentiometers, complete with the corresponding ion-selective electrode, are called ionomers. If the potentiometer and electrode system are designed to measure the activity of only hydrogen ions, the device is called a pH meter.
  2 PRACTICAL PART
  2.1 Methodology for the determination of titratable acidity of juices
  GOST R 51434-99 FRUIT AND VEGETABLE JUICES Method for determination of titratable acidity
  Application area
  This International Standard applies to fruit and vegetable juices and other similar products and establishes a method for determining titratable acidity, expressed as molar concentration, mass concentration or mass fraction of titratable acids.
  The range of measurement of molar concentration is from 40 to 300 millimoles N / dm, mass concentration is from 2 to 21 g / dm, mass fraction is from 0.2% to 2.1%.
  Method essence
The method is based on potentiometric titration with a standard titrated sodium hydroxide solution to a pH of 8.1.
  Measuring instruments, laboratory equipment, reagents and materials
  General purpose laboratory balance in accordance with GOST 24104 with the largest weighing limit of 500 g, fourth accuracy class;
  pH meter or universal ionomer at the price of division up to 0.05 pH;
  Measuring glass electrode for pH meter, a reference electrode or a combined glass electrode, replacing a glass electrode and a reference electrode;
  Magnetic stirrer with stepless speed control;
  Pipettes according to GOST 29169, version 2, 1st accuracy class, with a capacity of 25 cm3;
  The burette in accordance with GOST 29251 type 1, execution 1, 2nd accuracy class, with a capacity of 25 cm3, division price of 0.05 cm3;
  Low glass according to GOST 25336 with a capacity of 150 cm3;
  Conical flasks in accordance with GOST 25336 with a capacity of 300 cm3;
  Water for laboratory analysis according to GOST R 52501 is not lower than the third quality category;
  Sodium hydroxide (hydroxide) according to GOST 4328, standard titrated solution () \u003d 0.1 mol / dm3;
  Buffer solutions pH 4.01 and 9.18.
  Sampling and preparation
  Sampling according to GOST 26313.
  Sample preparation - according to GOST 26671.
  Concentrated products are diluted with water to a specified value of relative density in accordance with the regulatory or technical document for a specific type of product. The relative density of the diluted product sample is determined according to GOST R 51431 and the found value is indicated in the test report.
  If the sample contains a significant amount of carbon dioxide, it is removed by shaking the sample in a closed conical flask with periodic opening of the flask or by vacuum or ultrasonic treatment of the sample until all gas has been removed.
  Preparation and testing
  PH meter calibration
  Buffer solutions of pH 4.01 and 9.18 are prepared according to the instructions for the pH meter and the accuracy of the pH meter is checked at a temperature of 20 ° C.
  Testing
  Two parallel determinations are made.
  Pipette 25 cm of undiluted juice or a sample of juice diluted so that no less than 8 cm of titrant is consumed for subsequent titration. For the analysis of products with high viscosity and (or) with a high content of pulp particles (for example, for pulp), an appropriate sample of the sample is taken and diluted with water so that the above condition is met.
The sample in a glass at a temperature of 20 ° C is started to be stirred with a magnetic stirrer and titrated from the burette with a sodium hydroxide solution to a pH of 8.1. The volume of the solution used for titration is measured. If the pH meter is equipped with temperature compensation, the test may be performed at a temperature in the range of 10 ° C - 30 ° C.
  Processing and presentation of results
  Titratable acidity of CH +, millimole H + / dm3 of product, calculated by the formula
  C_ (H ^ +) \u003d (1000 × V_1 × c) / V_0, (9)
  where V1 is the volume of the sodium hydroxide solution used for titration, cm3;
  c is the exact concentration of sodium hydroxide solution, mol / dm3;
  V0 is the sample volume of the sample taken for titration (usually 25 cm), cm3;
  Calculations are carried out to the first decimal place. The result is rounded to the nearest integer.
  Mass fraction of titratable acids,%, calculated on tartaric, malic or citric acid is calculated by the formula
  X_1 \u003d (V_1 × V_2 × c × M) / V_0 × 0.1, (10)
  where V2 is the volume to which the sample is brought, cm3;
  m is the mass of a sample of the product, g;
  M is the molar mass g / mol equal to:
  tartaric acid () \u003d 75.0;
  malic acid () \u003d 67.0;
  anhydrous citric acid () \u003d 64.0.
  Calculations are carried out up to the second decimal place. The result is rounded to the first decimal place.
  The relative discrepancy between the results of two determinations obtained by analyzing the same product sample by one operator using the same equipment for the minimum possible time interval should not exceed the standard for operational control of convergence of 1% (P \u003d 0.95). Subject to this condition, the arithmetic mean of the results of two parallel determinations of titratable acidity is taken as the final measurement result.
  The relative discrepancy between the results of two determinations obtained by analyzing the same product sample in two different laboratories should not exceed the norm of operational control of reproducibility of 2% (P \u003d 0.95).
  The limits of the relative error in determining the content of titratable acidity under the conditions regulated by this standard do not exceed ± 1.5% (P \u003d 0.95).
  2.2 Measurement results
  In this course work was used acid - base potentiometric titration, using the device "Laboratory ionomer i-500", glass and silver chloride electrodes.
  The objects of analysis are the apple juices of the brands: Fruit Orchard, Pridonya Gardens, FrutoNyanya.
Titration was carried out in two parallels in accordance with GOST R 51434-99 FRUIT AND VEGETABLE JUICES Method for determination of titratable acidity

To determine the acidity of the wine as accurately as possible, you have to “conjure” a little. Armed with a burette, pipette, litmus test and special titration fluid, you will get a fairly accurate result. In addition, after some simple manipulations, you will know exactly how much sugar will be needed next time to get a drink of the acid you need.

To make good wine, it is important that the juice has a certain acidity. A sufficiently acidic juice ferments better, resulting in a reduced risk of mold and the development of harmful bacteria. Normal is the acidity of the wine in the range from 6 to 10%.

The basis for determining the acidity of juice is the property of acids to combine with alkalis. Consequently, the acidity of the juice can be determined by the amount of alkali that was required to neutralize the acid.

The process of determining the acidity of juice is called titration (from "titer" - the amount of alkali in 1 ml of solution) and consists in adding a certain concentration of titrated solution to the juice of an alkali solution.

As a rule, a solution of sodium hydroxide is used as this remedy. The end of the reaction is determined by a litmus test, which turns red in acid and turns blue in alkali.

How to determine the acidity of wort for wine at home

Before determining the acidity of wine at home, prepare the following inventory:

• 10 ml pipette;
• burette - a glass tube with a glass faucet with a volume of up to 50 ml, on which divisions are applied corresponding to a volume of 0.1 ml; for convenience, the burette should be mounted vertically (best with a tripod);
• porcelain cup;
• a glass rod;
• titration liquid, i.e. 5.97 g of dry sodium hydroxide, dissolved in 1 liter of distilled water, 0.25 liter in volume (stored in a glass bottle with a ground stopper);
• litmus test.

The process of determining the acidity of a wort for wine is as follows. The title fluid is poured into a clean, dry burette. Then open the tap to let the air out of the burette. This must be done, otherwise the result will be incorrect. The upper liquid level is set at zero division of the burette. After this, the pipette is filled with juice to zero division (10 ml) and poured into a cup.

Since fruit and berry juices are highly colored, they are pre-diluted with distilled water (at the rate of 20-50 ml per 10 ml of juice) and mixed well. If it is not, you can use ordinary water, but boiled 4-6 times. The fact that the juice is diluted with water does not affect its acidity at all. The same amount of acid remains in the diluted juice, it just becomes less colored, which greatly facilitates the obtaining of the result.

After this, a cup with diluted juice is placed under the burette, carefully open the tap and release 1 drop of alkaline solution. The contents of the cup are thoroughly mixed with a glass rod and it is applied to juice on a litmus test. If it remains red, then the acid has not yet neutralized. Another 1 drop of an alkaline solution is dripped into the cup and the contents are again checked with litmus paper, and so on until the litmus paper turns blue, that is, until all the acid has connected to the alkali. It is known that 1 ml of alkali corresponds to 0.1% acid in juice.

In addition, acid should be present in the wine - about 6–7 g per 1 liter. You can reduce acidity by adding water before fermentation in fruit juice.

The acidity of wine is determined by the content of titratable acid in grams per liter of wine (ppm) and can range from 2.5 to 9 g / l.

It should be remembered that the acidity of light wines can be 5.5–7 g / l of acid per 1 l, tablespoons - from 7 to 9 g / l, dessert - 9-11 g / l.

Demina Diana

The analysis of apple juices for organoleptic indicators and total acidity

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Regional scientific and practical conference

“Youth to science and technology”

Determination of acidity and organoleptic characteristics of apple juice from various manufacturers

Izhevsk 2017

1. Introduction
2. Theoretical part

1. Juice History
2. Juice classification
3. Juice Composition

1. Practical part

1. The experimental technique
2. Results and its discussion

IV. conclusions

V. List of references

VI Appendix

I. Introduction

Any person entering a store will definitely see a shelf, or even a shelf, where packages of juices and nectars are full of colors, eyes are scattered from such abundance! Probably everyone has their favorite taste, favorite brand. We noticed that very often in the cafeteria, students buy exactly the juice. I wonder why? Some even specifically defend the whole line just for the sake of the treasured box. Is it just for quenching thirst? Most likely not, there is water in that case.

It became of interest to us whether the juice consumed by the students of our lyceum complies with GOST. These may be: acidity, organoleptic properties of the used juices. My classmates supported me in research activities and eagerly answered questions.

Purpose:   Determine the organoleptic properties, the acidity of the leading juice according to the survey.

To achieve this goal, the following were decidedtasks :

* Conduct a survey on the favorite juices of students of the Lyceum №25;

* Conduct an organoleptic analysis of juice leaders;

* Master the method of titration;

* Conduct titration to determine the acidity of the leading juice;

* Summarize the results of experiments.

Subject of study:  apple juice of various manufacturers;

Object of study:  juice acidity;

Research Methods:  theoretical (analysis of educational, popular science literature, Internet resources), experimental (titration method, chemical experience in determining organoleptic properties), static (processing of obtained data);

1. Theoretical part

1. Juice History

The first written information about juices from various fruits and berries belongs to ancient Greek writers. It is known that the Greeks and Romans used the fruits of fruit trees not only for food, but also stocked in the form of juices as a medicine for some diseases. Especially popular among the Greco-Romans were raspberry juices, rich in mineral salts (iron, potassium, copper), pectin (up to 0.9%) and fiber (4-6%), vitamins C (25 mg%), B, B2 , PP, folic acid, carotene. Juices were also known in Ancient China and in Ancient Russia. For example, our ancestors especially appreciated the fruits of sea buckthorn, which in the wild grew in the valleys and floodplains of the rivers in the south of the European part of Russia, in Western and Eastern Siberia, the Caucasus and Central Asia. Due to the high nutritional, especially taste, qualities of sea-buckthorn, in Siberia the berry was called "Siberian pineapple". Sea buckthorn juice was considered an indispensable tool in the prevention and treatment of hypovitaminosis. For long-term storage, the juice obtained from fresh berries and fruits, our ancestors subjected to heat treatment, subsequently adding honey to the resulting drink.

In ancient times, the collected berries and fruits were ground with sugar, thereby prolonging the life of substances useful to the body for several months. Fruit and berry juices were also less popular in Soviet times. About 550 million liters of juice per year were produced in the Soviet Union. Basically, the juice assortment was represented by apple and tomato nectars and juices, poured into glass jars with a capacity of 1 and 3 liters, using pasteurization technology (hot filling).

In 1992, the expansion of the Russian market began on the part of imported juice products in “fashionable” aseptic carton packaging, and the development of a new Russian juice industry. The 90s were also marked by the appearance on the holiday tables of Russians of juices from “overseas” fruits, such as oranges and pineapples. In the 2000s, the juice market of modern Russia experienced rapid growth. After the 1998 crisis, many foreign firms left the Russian market, thereby freeing up space for the development of national industries.

2.1. Juice classification

There are several definitions of what juice is:

1. Juice is a liquid food product obtained by squeezing edible ripe fruits of vegetable or fruit crops.

2. Juice - the intercellular fluid of plants.

3. Juice is a liquid or suspension naturally found in fruits, berries, vegetables.

What juices are there?

Unclarified juice  - juice with suspensions.

Clarified juice   - juice from which suspensions are removed to a visual transparent state.

Pulp juice   - juice with pulp particles, the mass fraction of which does not exceed 55%.

Fruit juice   - juice obtained from benign ripe, fresh and kept fresh thanks to the cooling of fruits, unfermented, but capable of fermentation, intended for direct consumption in food or for industrial processing.

Direct-squeezed fruit juice  - fruit juice obtained directly from fruits by squeezing, or by centrifugation, or by rubbing.

Reconstructed Fruit Juice  - fruit juice obtained by restoring concentrated fruit juice with drinking water in a ratio that ensures the preservation of the physicochemical, microbiological, nutritional and organoleptic properties of juice from fruits of the same name, while restoring the aroma by adding concentrated natural volatile aroma-forming substances or without restoring the aroma, and with or without addition of the same name direct-squeezed fruit juice, fruit puree.

Vegetable juice   - juice obtained from the edible part of benign vegetables, unfermented or lactic fermented, intended for direct consumption or for industrial processing.

Certain types of juices are determined based on

1.   Used raw materials (apple juice, carrot juice, etc.)
2.   Manufacturing technologies (clarified, non-clarified, with pulp)

3. Presence of additives (with sugar, without sugar)

2.3. Juice Composition

Juice is a tasty and valuable nutritious product. The composition of fruit juices includes: water, natural carbohydrates (glucose, fructose, sucrose), organic acids (citric, malic, tartaric), protein, amino acids, vitamins (A, C, B1, B6, B9), minerals (K-potassium , Mg-magnesium, Ca-calcium), antioxidants, dietary fiber. The full composition of juices is presented in table 1.

Table 1

Nutritional value of juices (per 100 g)

The nutritional value of juices has led to their widespread use for the prevention and treatment of diseases. For example, orange juice kills bacteria, boosts immunity, protects against some forms of cancer, grape normalizes metabolism, and is effective for anemia, gastritis, and neurosis. Pumpkin increases the level of hemoglobin in the blood, improves sleep, helps to eliminate toxins from the body.

Natural aromatic substances can be added to juices, as well as sugar, citric and ascorbic acids to adjust the taste. All added substances must be indicated in the composition of the product, which is given on the product packaging.

III. Practical part

3.1 Methodology

Objective: To determine the organoleptic properties, the acidity of the leading juice according to the survey.

3.1.1 opinion poll

To select the objects of research, as well as to reveal some of the questions, a sociological survey was conducted among students of the lyceum (the questionnaire is presented in the appendix). Based on the results of the sociological survey, we selected 6 samples for research (appendix)

3.1.2. Organoleptic quality assessment

According to organoleptic indicators, the juice must comply with the requirements of GOST 6687-89. Before examining the taste of juices, we rinsed our mouth with clean water each time. The interval for studying the smell and taste of each type of juice was 3 minutes. As a result, we obtained the results presented later in the work

With organoleptic control, the taste, aroma and appearance of the drink are evaluated according to table 2,3,4.

table 2

Table 3

Table 4

1. Determination of titratable acidity

3.1.3.1 Preparation of sodium hydroxide solution

To determine the acidity of apple juices, we need, according to the method, a solution of sodium hydroxide of an exact concentration.To do this, we weighed 4 g of sodium hydroxide on a technical scale, placed it in a 1 L volumetric flask, and added distilled water to the level of 1000 ml. The exact concentration of the prepared sodium hydroxide was determined by a solution of hydrochloric acid prepared from fixanal.

The titration results are presented in table 5.

Table 5

Establishment of sodium hydroxide concentration

Titratable acidity is expressed in g /  dm 3 . The magnitude of titratable acidity is determined by the amount of alkali (caustic soda or potassium) needed to neutralize acids.

Titratable acidity is determined by the following procedure.

Fifty ml of juice is transferred into a 250 ml volumetric flask, adjusted to the mark with distilled water. Then, 10 cm³ was pipetted into the flask and titrated with a 0.1 M NaOH solution in the presence of phenolphthalein (3 drops) until a raspberry color that did not disappear within 30 seconds (analysis was performed 2 times).

Mass concentration of titratable acids g / dm3   (acidity), calculated on malic acid, is calculated by the formula  Xk \u003d 100 x V x C x M x V 0 / (1000 x M 1 x V 1)

V - volume of NaOH solution used for titration, cm³

С - molar concentration of titrated NaOH solution, mol / dm³

M - molecular weight of the organic acid to be calculated (malic acid) 67g / mol

V 0 - volume to which the hitch is brought, cm³

M 1   - molecular weight of alkali

V 1   - volume of solution taken for titration, cm³

1. Results and its discussion

To determine the most popular types, we conducted a sociological survey (questionnaire in the appendix) in which 100 people of our lyceum took part. It was found that 70% of the respondents preferred juices, 20% nectars and 10% did not see much difference between nectar and juice. It was found that the leading position was taken by apple juice; 53% of the respondents selected it for orange juice; 44%; the remainder in 3% was divided among themselves by the most different juices and nectars to taste. Of the most preferred brands of juice, the brands Dobryi (35%), J7 (24%), Rich (15%), Favorite (13%), Orchard (8%), My family (5%) were selected. For our research, we chose apple juices from these manufacturers.

Organoleptic quality indicators of the finished drink - appearance, transparency, color, aroma and taste are determined according to GOST 6687

The results of organoleptic indicators are presented in table 6

Table 6

Organoleptic indicators

Of the analyzed juices, organoleptic indicators lead"J7"   This juice has the following characteristics: transparent, intensely yellow, with an apple aroma, the taste is thick, sweet, a pleasant apple taste remains in the mouth. Next come the juices"Kind" : light yellow transparent juice, has a pronounced smell of apples, the taste is saturated, harmonious in the content of acids and sugars and"Orchard" natural color juice, well-defined apple flavor, well-defined apple flavor. Next, the rating scale for taste characteristics took  "Rich"   dark yellow juice with a sour taste and a faint odor, a clear liquid and  "Favorite" transparent juice intensely yellow. Bright apple aroma and taste. Low rated juice"My family" transparent juice of normal yellow color. Taste and smell are not quite natural, there is a taste and smell of apple essence.

We conducted a quantitative analysis of the acidity of the selected juices. The titration method was used. In total, 20 titrations with 6 objects were done.

Acidity is the content of organic and mineral acids, as well as their acid salts determined by titration in accordance with GOST R 51434-99.

The titratable acidity indicator shows how acidic or sweet the drink is. Apple juice is highly acidic and relatively low in sugar. Therefore, to normalize the taste, it is often diluted with water and sweetened with sugar.The titration results are shown in table 7.

Table 7

Titration results

According to titration, the acidity values \u200b\u200bof juices were calculated. Presented in table 8.

Based on the results of titration and comparison with GOST data, (0.3-1.4), we can conclude that all juice samples fit the GOST scale for apple juice. The received data pleased us very much, which means that these juices can be safely used in school meals

Table 8

Titratable acidity

IV. Conclusion

Thus, as a result of the studies we obtained the following results:

1.   Organoleptic quality indicators of apple juicescolor, taste and aroma are normal. The color of different samples from yellow to dark yellow. The taste and aroma of all samples without extraneous smacks and smells. In terms of appearance, the samples turned out to be a transparent liquid.
2. The highest score for organoleptic indicators was juiceJ7
3. The acidity of the juices is normal.

V. List of references

1. Analytical chemistry. Chemical analysis methods / under the editorship of OM Petrukhina M 1992
2. Biology: Encyclopedia / ed. M.S. Gilyarova.- M .: Big Russian Encyclopedia, 2003.- p. 384.
3. GOST 6687 -89. Products of processing fruits and vegetables. Methods for determining organoleptic indicators
4. GOST R 51434-99 Fruit and vegetable juices. Method for determination of titratable acidity.
5. Nikiforova, N.S. Handbook of commodity food products. In 2 vol. T. 1: Textbook. for the beginning. prof. education / N.S. Nikiforova, A.M. Novikova, S.A. Prokofiev.-M.: Publishing Center "Academy" .- 2008.-p.128-131
6. Handbook Chemical composition of food products / ed. Skurikhina M: Agropromizdad 1987

Internet resources:

1. The nutritional value of juices. // www.nashedelo.com.ua
2. Juices. // www.life4u.ru
3. Juice therapy. // fito-center.boom.ru
4. Scheme of organoleptic analysis. // (www.cargill.ru)

VI Appendix

1. Questionnaire for interviewing students of the Lyceum

1) What do you like more?

a) Juice

b) Nectar

c) I do not see the difference

2) What juice / nectar do you prefer (one option)?

a) Carrot

b) Apple

c) Pear

d) Pineapple

e) Grape

f) Tomato

g) Orange

h) Grapefruit

i) Cherry

j) Peach

k) Apricot

l) Blueberry

m) Blackcurrant

n) Cranberry

o) Lingonberry

p) Passion fruit

q) Banana

r) Pumpkin

s) Multifruit

t) Its options: _________________________________________

3) What brand of drink do you prefer (one option)?

a) “Good”

b) “Beloved”

c) "Orchard"

d) “I”

e) “J7”

f) "Rich"

g) “Gardens of the bottom”

h) “My family”

i) “Favorite garden”

j) Tone

k) "Frutonyanya"

l) Its options: _________________________________________

2. Information about the investigated juicesApple juice, sugar, citric acid, water

Russia, Moscow Region, Schelkovo, Fruit Ave

1 year

Orchard

Apple juice, sugar, glucose-fruit syrup, citric acid, water

RF, Lipetsk region, Lebedyan, ul. Matrosova, d. 7

6 months

kind

Russia, Moscow region, Schelkovo

3. Results of the survey

1. What do you like more?

2. What juice / nectar do you prefer (one option)?

1. What brand of drink do you prefer (one option)?

Juice acidity adjustment

The wort acidity should be between 0.6% (for dry table wines) and 1% (for dessert wines). It means:

1 liter of juice should contain from 6 to 10 g of acid.This is either malic (apples, cherries) or citric acid (berries).

Fruits and berries (with the exception of apples, rose hips, etc.), most often used for making homemade wines, such as currants, gooseberries or cherries, have high acidity, which must be lowered by adding water to the juice. The amount of added water should be minimal, otherwise the wine will be more susceptible to disease and worse clarified. In practice, it is better to set the acidity for table wines in the range of 7-8 g / l, and for dessert wines - 9-11 g / l. Wine yeast can easily tolerate this acidity, while other harmful microorganisms die or are depressed.

In the case of very acidic juice, for example, from currant, when its acidity is brought to the indicated level, it may be necessary to dilute it three times with water, which is unacceptable, because the wine’s extractivity will decrease and it will have an “empty” taste. Therefore, the rule applies : the addition of water with sugar should not exceed 2 liters per 1 liter of juice.

The acidity of the juice can be determined approximately using the acidity tables of fruits and berries. But these are average values \u200b\u200bfor ripe fruits; in those years when there is more sun, it is lower.

The average percentage chemical composition of the fruit

(according to E. Pianovsky and Z. Vasilevsky)

For those who want to accurately determine the acid content in the juice, ready-made titration kits or pH meters are offered.

Reducing acidity by diluting the juice with water.

The amount of water needed to dilute the juice is calculated as follows.

EXAMPLE: From currant juice with an acidity of 2.4%, i.e. 24 g / l, it is necessary to obtain wine with an acid content of 8 g / l, that is, 3 times less. In this case, each liter of juice with an acid content of 24 g / l must be supplemented with 3 l to obtain the desired acidity of 8 g / l, in other words, 2 liters of water must be added to each liter of juice along with the sugar dissolved in it. If you want to get a sweet wine with the acidity of 9 g / l from the same juice, then the amount of acid must be reduced by 24/9 \u003d 2.7 times, that is, bring the juice to 2.7 liters.

For dessert wine with an acidity of 10 g / l, it is necessary to increase the volume of juice to 2.4 liters.

Chemical Juice Acidity Reduction

If the above limiting dilution of juice with water is not enough to reduce its acidity to 8 g / l, then such juice can be sent to dessert wine by setting its acidity level to 10-14 g / l. In the case when it is necessary to reduce the acidity to a greater extent than is permissible by diluting the juice with water, this can be achieved chemically by neutralizing excess acid with chalk (calcium carbonate). In this case, poorly soluble salts of calcium arise, which precipitate. To reduce acidity by 1 g / l, it is necessary to use 0.35 g of chalk.

EXAMPLE: 10 liters of blackcurrant juice with an acidity of 3% (30 g / l) should be processed into dry wine with an acidity of 8 g / l. After diluting 1 liter of juice with water in a limit ratio of 1 liter of juice to 2 liters of water with sugar, we get 3 liters of wort, which should contain 3 * 8 \u003d 24 g of acid. Since undiluted juice contained 30 g of acid per liter, it is necessary to remove another 30-24 \u003d 6 g of acid from 1 liter of juice. This will require 6 * 0.35 \u003d 2.1 grams of chalk. To 10 liters of juice (which will make 30 liters of wort) add 10 * 2.0 \u003d 21 g of chalk. Mix it thoroughly.

A preparation for the simultaneous removal of tartar and reduce the level of calcium in wines

  - a special-purpose preparation intended for the simultaneous removal of tartar (potassium tartrate) and calcium (calcium tartrate) in wine. This preparation is especially recommended for the processing of wines with a calcium content of 90 to 120 mg / l, since one treatment will completely stabilize the wine against crystalline opacities.

Many people know about the benefits of juices for physical health. Realizing this, people try to drink juices daily with meals. After all, fruits, berries and vegetables are of great value in human nutrition. Today, keep fresh, for a long time, these products are not easy, and some of them for a short time. Therefore, the preparation of juices from them, makes it possible to preserve their vitamin value for a longer time.

Composition and acidity of juices

The juice has the most important value as a storehouse of minerals and vitamins, of which mainly the necessary salts of potassium, calcium, iron, magnesium, phosphorus. Acids, essential oils, sugars, tannins and pectin are stored in juices. And in the form of juices, these necessary substances are quickly absorbed in our body. After all, juices are mainly composed of liquid, and without obstacles it penetrates through the walls of the intestine and with it all the useful components of the juices.

It is not necessary to think that vegetable juices are somewhat inferior to fruit and berry juices, therefore, they are in a small assortment in stores, in fact, trade cares about profit, and we must care about health, and not neglect to drink juices that complement it. Grape juice is the easiest to make at home.
  In addition, the juices that we see on store shelves today are not always natural; for long-term storage, preservatives are added to them and additionally processed, sweeteners are added excessively, not always natural. The packaging may not indicate the addition of sugar, because it is replaced with refined glucose.

The composition of vegetable juices differs from fruit juices, the content of organic acids. Fruit juices are rich in the following acids: - citric, tartaric, malic, and vegetable juices: in vinegar, formic, oxalic, and mainly in very useful amber.

Quinic acid is found in such juices: apple, plum, blueberry, apricot, peach, pear. Chlorogenic acid is present directly in apple juice. Isolimonic acid is found in small amounts in juice, blackberries, currants, cherries, cherries.
The most valuable components of fruit and vegetable juices are, of course, minerals. Mineral juices lose fruit juices to vegetable juices. It is in vegetable juices, a large number of sodium and potassium salts, which are responsible for the water-salt metabolism of the body. But they have less sugar than fruit juices. Yes, and their taste is slightly acidic, which allows them to drink to everyone on an empty stomach, because of its neutrality, and it is better to drink acid juices after meals.

On the one hand, vegetable juices have low acidity, this is a plus, but for canning at home, this creates the danger of the development of harmful microflora in the sunset. To eliminate this, acid juices must be added to vegetable juices. Most often, cranberry, apple, redcurrant juice is used for this, or, in extreme cases, citric acid is used. Despite the fact that some vegetables can be stored fresh for about a year, these are carrots, cabbage, beets. Therefore, from such vegetables, juices can be obtained, right before use.

Juice Acidity: Benefits

The acids contained in the fruits make it possible to pasteurize the juices from them at low temperatures. These acids have various beneficial properties. First of all, they prevent the development of harmful microflora, due to which it spoils the juice. They exhibit bactericidal action. Due to their presence, the rapid destruction of many pathogens occurs.

But, unfortunately, the presence of fruit acids has a detrimental irritating effect on the digestive system. Due to the increased action of the gastric glands, it facilitates the digestive activity in the body. In the intestines, mucus is produced, food residues are collected on it, acids are necessary for their better dissolution. In this environment, bacteria that are unnecessary for the digestive system die. The presence of acids helps better blood and lymph circulation. They activate blood circulation and remove ballast substances from the body. Organic acids, malic and citric, have a positive effect on the activity of the digestive glands, and the absorption of food is enhanced. Be careful with highly acidic juices, such as grapefruit juice.

Juices are very useful for diseases caused by low acidity of gastric juice. Juices entering the stomach are able to slightly compensate for the weak release of hydrochloric acid in the stomach.
Juices have always been appreciated as a dietary, medicinal drink that is well absorbed, it is advised to drink it for the prevention and treatment of many diseases.

Freshly squeezed juices

The most useful are freshly prepared and immediately drunk juices. Some juices are highly concentrated, they are advised to dilute with water, but to obtain an enhancement of the therapeutic effect, for this they take not simple boiled water, but mineral water. To obtain a full range of nutrients, juice should be drunk immediately, after receipt, it should not be stored, even in the refrigerator. This does not apply to beet juice, it is necessary before use

insist for 2 hours. Freshly squeezed juices very quickly lose their quality. It must be remembered that after drinking the juice, it is necessary to rinse the oral cavity, or even brush your teeth, this is necessary to protect against the destructive effect on the tooth enamel that acids of all juices have. For children whose tooth enamel is very thin, this is especially dangerous. After juices, teach your children to rinse their mouth with water.

Although combining different juices, fruit and vegetable, you will improve their taste and reduce their acidity, but still freshly prepared juices do not get used to drinking after meals, but a little later, so as not to provoke gas formation and bloating. And it is best to take juices between meals, like all sour fruits.

Contraindications for acidic juices

Usually acidic juices, such as cranberry and apple, lead to heartburn, those who have a stomach ulcer and pancreatic inflammation should not drink them, so as not to cause further complications of the disease, due to increased acidity in the stomach
  Diabetics and obese people should not drink grape juice. This juice is very high in calories and has a high glucose content. Especially it is not indicated for irritable bowel syndrome.

Some juices have a laxative effect, and sometimes a very strong laxative effect. This is harmful for people with irritated bowels, they should not drink juices in glasses or pick up juices of the desired concentration. And remember, out of habit, fresh juices can even do harm than help. Also, diabetics need to be careful with banana juice.

The healing properties of juices

Natural juices are suitable for dietary nutrition. They do not contain heavy fiber, but there are a lot of useful components that are absorbed faster in this form. The body requires a minimum of energy costs, and time for the digestion of juice. For therapeutic sessions, juices are preferable to medications. If you start drinking them regularly, this will add to your health and extend your life.

Juices have a great bracing effect on human life, and are also biogenic stimulants. They significantly increase the immune system and working capacity, have a laxative, diuretic and choleretic effect, enrich the body with vitamins and everything necessary for a good mood with “aroma and taste”.

Juices significantly affect digestive activity, activating the secretion of gastric juice and stimulating the endocrine glands, which remove toxins from the organs, exhibit anti-inflammatory effects, normalize blood pressure and increase vitality.