Report on performance of a task

To present results of work in the form given in tab. 4.2 Table 4.2

 

Research technique	Mass fraction in milk (%)
Lactoses	Calcium
1. Refraktometrichesky 2. Polarimetric 3. Kompleksonometrichesky.

 

Control questions

1. Characteristic of lactose as main carbohydrate of milk.

2. Mineral substances of milk: macro - and minerals.

3. Methods of definition of lactose in milk.

4. Kompleksonometrichesky method of definition of calcium, his chemical essence.

Laboratory work № 5

Studying of a method of determination of content in vitamin C milk (ascorbic acid) and enzymes

 

Work purpose: to determine the content of vitamin C and enzymes in various samples of milk.

Task 1.To carry out high-quality reaction to vitamin C.

2. Quantitative definition of vitamin C 2, 6-dikhlorfenolindofenoly (on Tilmansa)

Short theoretical data

Vitamins. Milk contains all vital vitamins, but some in insufficient quantities. Content of vitamins depends on a season of year, breed of animals, quality of forages, storage conditions and processing of milk. Fat-soluble A, D, E, K vitamins and (V-carotene are steady against heating and begin to collapse at a temperature over 120 °C (vitamin A), but aren't steady against effect of air, ultraviolet rays and acids. Vitamin A gives to butter yellow color. Vitamin E is antioxidant of fats and protects vitamin A from oxidizing destruction. Water-soluble vitamins, except for vitamins C and B12, are steady against heating. They maintain heating in the alkaline environment worse. RR vitamin almost completely remains after thermal treatment and in the course of milk storage. Most collapses at pasteurization and storage vitamin C. Vitamin C (ascorbic acid). She participates in an oxidizing voskstanovitelnykh the processes happening in an organism. The lack of a viktamin With in food can cause a scurvy. Raw milk contains 0, 3 - 2, 0 mg of % of vitamin C. Vitamin C sinktezirutsya by hem microflora, his content in milk depends from the inkdividualnykh of features of an animal. Usually it raises in the winter and goes down in the summer.

At milk storage the amount of ascorbic acid decreases. Light affects destructively ascorbic acid therefore at a milk hrakneniye in transparent bottles of loss of vitamin C make 50% and more. Better vitamin B bottles from dark glass and paper packages remains. It is important to consider it at production of vitaminizirovankny milk and dairy drinks.

Enzymes (Latin fermentum - ferment) - the biological katalizaktor accelerating chemical reactions in live organisms. Under a deykstviye of enzymes large molecules of proteins, carbohydrates, fats rasshchepklyatsya on smaller. Enzymes accelerate reactions in tens of thousands and millions of times. Deykstviye of enzymes it is strictly specific, i.e. each enzyme catalyzes only one chemical reaction. Enzyme corresponds to the subkstrat (substance which chemical transformation he catalyzes).

Enzymes work at a certain temperature, рН Wednesdays; their activity depends on availability of chemicals - activators and inhibitors. Opktimalny temperature, i.e. temperature at which the maximum of activity of enzymes is observed for most of them is equal to 40 - 50 °C. At further temperature increase activity of enzyme snizhaktsya. At a temperature of 60-80 °C of squirrels, the forming enzyme, denaturikrut, and enzyme is inactivated (loses the activity). The thermal denaturation of enzymes has important practical znachekny: pasteurization of raw materials promotes destruction of enzymes and predokhranyat foodstuff from enzymatic damage.

The important factor influencing activity of enzymes is рН Wednesdays. Enzymes differ on optimum for their action to znachekniya рН. At too sour or alkaline reaction of the environment the enzyme denaturation proiskhokdit, and it loses the activity.

By the chemical nature enzymes represent proteinaceous substances. They can be simple and complex proteins. Enzymes nakzyvat on that substance which they affect, adding the termination " az" to a name root: lipase, lactase, peptidaza and so forth.

In milk enzymes are in a free state, and also are connected with casein micelles and covers of fatty balls.

Devices and equipment

Conic flasks with a capacity of 250, 100, 50 ml; scales; pipettes on 5, 10, 25 ml; burette; microburette; a funnel, the folded filter, solution with a mass fraction of metaphosphoric or hydrochloric acid of 2%; saturated solution of oxalic acid; saturated solution of chloride of sodium, 2, 6-dikhlorfenolindofenol; methylene blue, a reduktaznik, a water bath, 0, 1% solution of a fenolftaleinfosfat of sodium in ammoniac buffer mix.

Work performance order

Essence of a method: the chemical method of definition of vitamin C 2, 6-dikhlorfenolindofenoly (Tilmans's paint) is based by the specific indicator on properties of this indicator to change the coloring depending on reaction of the environment. In acidic environment the indicator gets pink coloring, in alkaline and neutral - blue. Being restored, the indicator becomes colourless. Decolouration of the indicator in the presence of vitamin C is explained by easy oxidability of vitamin.

Carrying out experience: To part 5 ml of milk by 3 times with water. At cultivation to measure milk a pipette, to pour the distilled water from the burette. To bring 1 ml of 2% in a conic flask with a capacity of 50 ml hydrochloric acid of 5 ml of the received milk solution, to bring water to the total amount of 15 ml. Carefully shaking up, contents of a flask titrut from the microburette 0, 001 N solution of a 2, 6-dikhlorfenolindofenol, flowing him drops before emergence of the weak-pink coloring remaining 0, 5-1 min. To make two parallel definitions of one portion of the divorced milk and to find average size.

To determine the content of vitamin C by a formula:

х = мг %,

where u - the amount of working solution 2, 6 dikhlorfenolindofenol which has gone for titration, ml; k - the amendment on a solution 2, 6 caption dichlorine-fenolindofenola; V- the volume to which the milk hinge plate at addition to her of water and hydrochloric acid is brought, by ml; V₁ - the volume of the analyzed liquid taken for titration, ml; q - milk hinge plate; 0, 88 - amount of vitamin C, corresponding 1 ml 0, 001 N of solution 2, 6 dikhlorfenolindofenol, mg.

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