Recommendations to students on preparation for occupations

Students are allowed to work in laboratory only later

acquaintance with safety regulations and receipt of instructing that is fixed in the special magazine.

The student needs to be prepared beforehand for a work vykpolneniye, to deeply study the corresponding teoreticheksky material on lectures or textbooks, and also on a laboratorkny practical work, to get acquainted with the specifications and technical documentation on a subject.

At the same time the student shall acquire structure and properties of an izuchayekmy object, essence of biochemical and physical and chemical transformations during engineering procedures of its conversion or obtaining; the work purpose, importance of the indicators determined in work and their influence on quality of the processed raw materials, semifinished products and finished goods, the technique of carrying out a rabokta and the principles which are been the basis for determination of that or иного an indicator, the device of the device or installation.

The questions arising by independent preparation for work, the student shall find out from the teacher conducting a laboratory practical work.

At the beginning of the occupation the teacher by poll finds out readiness of students to work.

The students allowed to work start to its vypolnekniya according to the technique stated in a practical work.

Working in laboratory, students are obliged to follow strictly safety regulations, rules of personal and production hygiene.

All data obtained in a work progress (indications of pribokr, calculations, etc.) are brought in a workbook, processed and entered in the summary final table after which analysis the corresponding conclusions are drawn.

On the next occupation the student hands over to the teacher the oformklenny report (in a workbook) on the performed work.

In the report the work purpose, the short description of the device of devices or installation, detailed calculation of the determined sizes, the analysis of the obtained data and the corresponding conclusions shall be specified. The student protects each performed and arranged work at the teacher and pokluchat offsetting.

 

 

Laboratory work №1

Determination of freshness and naturalness of milk

 

Work purpose: to get acquainted with methods of determination of naturalness and freshness of milk.

Task:

1. In the proposed milk samples to determine the titratable acidity, the number of coagulation, the degree of freshness, as well as to conduct heating, and the alcohol test.

2. Based on the received results to make the conclusion about general freshness of samples of milk and its suitability to further conversion.

Short theoretical data

The main indicator of freshness of milk is titrable acidity. In fermentable milk it constitutes 16-18 ⁰T. After a while after milking acidity of milk increases as in it the microorganisms fermenting lactose to lactic acid begin to develop.

Acidity of milk is expressed in ⁰T degrees. Tipsy ⁰T the quantity of milliliters of 0, 1 N of solution of alkali (a caustic natr or caustic potassium) which went for neutralization of 100 ml of milk in case of the indicator of a fenolftalein is understood. Determination of freshness of milk on titrable and extreme acidity gives the chance to judge milk reaction change, but doesn't allow to catch changes of the major components of milk, in particular proteins. So, if to fresh milk to add milk with the increased acidity (27-30⁰T) and it is good to mix, then titrable acidity of mix can not exceed 20⁰T. However such milk doesn't maintain heat treatment, proteins of milk coagulate and can spoil all lot of products.

For the purpose of milk impurity identification with the increased acidity the heating and spirit tests characterizing stability of a proteinaceous phase are carried out. Action of these tests is based on equal sensitivity of proteins of milk to action of high temperatures and alcohols depending on рН. Knowing titrable acidity and having result of heating and spirit tests, it is possible to establish general freshness of milk (tab. 1)

 

Assessment of freshness of milk Table 1

Titrable acidity, °Т	Kipyatilny test	Spirit test	Characteristic Milk
Less than 16 16-20	Changes	No	Milk is received from the patientanimal or it is diluted with water Fresh normal milk
20-23   24-26   26-35   60 andmore	Changesno   Can be curtailed   Is curtailed   Spontaneousfolding	Thin flakes   It is a lot of flakes   Large flakes Dense Clot	Milk stale and processing isn't subject Sour smack, it is impossible to use Sour on taste, it is impossible to use Folding at the room temperature

 

Freshness of milk is expressed in degrees. The degree of freshness of - is the sum of value of titrable acidity and number of folding of milk.

The number of folding of - is the quantity of milliliters of 0, 1 N of solution of sulfuric acid necessary for folding of 100 ml of milk. The degree of freshness of normal milk shouldn't be lower than 60. If in milk there were changes mainly under the influence of putrefactive bacteria, then folding of milk will require less acid. In such milk the degree of freshness will be lower, than in normal.

Falsification of milk is possible in places of his receiving or sending to the state enterprises of the dairy industry.

Milk is considered forged if foreign substances are added to it or a part of fat is removed from it.

At detection of falsification establish that it is added to milk (the nature of falsification) and in what quantity (extent of falsification). For definition of character and extent of falsification it is necessary to know physical and chemical indicators (a mass fraction (m) of solids, SOMO, fat and acidity) milk of the stall and studied tests. Most often milk is forged, adding water, skim milk or water with skim milk (double falsification). The forged milk sharply changes the structure and properties (tab. 2).

Change of structure and properties of milk at his falsification the Table 2

Nature of falsification
Indicator	Water	Fat-free milk (subremoval of cream)	Water + fat-free milk
М.д.fat, % М.д. СОМО, %   М.д.dry substances, % Density, г/см3	1. go down same -² -   -² -	go down Doesn't change or slightlyraises   Go down Raise	go down same -² -   Almost not Changes

 

Equipment, devices and technical means:

Flasks with a capacity of 150-200 ml, pipettes with a capacity of 1, 5 and 10 ml, burettes, test tubes, Petri's cups, areometer dairy, tile; 0, 1 N solution of sulfuric acid, 0, 1 N solution of a caustic natr, sulfuric acid with a density of 1, 81-1, 82 kg/m3; izoamilovy alcohol with a density of 0, 810-0, 813 kg/m3, 1% spirit solution of a fenolftalein, 68% solution of ethyl alcohol.

Work performance order

In a conic flask with a capacity of 150-200 ml measure 10 ml of milk by means of a pipette, add 20 ml distilled water and three drops of 1% - го spirit solution of a fenolftalein. Mix is carefully mixed and titrut 0, 1 N solution of a caustic natr before emergence of the weak-pink coloring which isn't disappearing within one minute. Acidity of milk is equal in Turner's degrees to the quantity of milliliters of 0, 1 N of solution of the caustic natr (heat) spent for neutralization of 10 ml of milk, increased on 10. Divergences between parallel definitions there have to be no more than 1 °Т.

In mass analyses when a large amount of milk is subject to acceptance, define extreme acidity, i.e. acidity, is higher than which milk is considered sub-standard. In this case in a row the test tubes placed in a support are poured on 10 ml 0, 1 N of the solution of alkali containing phenolphthalein and add 5 ml of the studied milk. Contents are mixed and watched coloring change. If solution has become colourless, so acidity of milk above norm.

When conducting heat test in a test tube pour 5 ml of milk and heat to boiling. Milk which titrable acidity higher than 24°T, at boiling is curtailed. Heating test allows to find also in fresh milk milk impurity with the increased acidity as the mixed milk at boiling also turns.

During spirit test in a test tube or Petri's cup pour 1 ml of the studied milk, add 1 ml of 68% ethyl alcohol, mix and monitor emergence of flakes of protein. As alcohol with a strength of 68% causes casein coagulation only at the acidity of milk exceeding 20°T spirit test gives the chance to reveal the extreme acidity of milk allowed by the standard and also to find sour milk in fresh. If acidity of milk is lower 20°T, then protein keeps the colloidal properties and milk doesn't turn. Lack of flakes curled up a squirrel testifies to freshness of milk. Formation of flakes, even hardly noticeable, indicates the lowered stability of proteins of milk.

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