3 experimental part

Key indicators of raw milk

1. Key indicators for cow's and goat's milk

The main raw materials used in the production of soft cheese were cow and goat milk obtained at the CJSC Breeding Plant
"Prinevskoye in the Leningrad Region. Raw milk composition studies were carried out in the laboratory of the Applied Biotechnology Department of ITMO University in accordance with regulatory documents using generally accepted research methods.
In accordance with regulations, milk must be obtained from healthy farm animals in an area that is free from infectious and other diseases common to humans and animals (Annex 2).
According to organoleptic indicators raw milk must meet the requirements of GOST [35,36]. The results of the study of raw cow's milk according to organoleptic indicators are presented in the table 7.
Table7 - Organoleptic characteristics of cow's milk

Name of indicator	Feature
Taste and smell	Clean, pleasant, slightly sweet
Consistency	Homogeneous liquid without residue or flakes
Colour	White to light cream

The results of the organoleptic examination of raw goat milk are shown in the table below 8.

Table8 - Organoleptic characteristics of goat milk

Name of indicator	Feature
Appearance and consistency	Homogeneous liquid without sediment or protein flakes
Taste and smell	It is clean, with no extraneous odours or flavours that are uncharacteristic of fresh goat's milk. A slight foul taste and smell is allowed, and also a slight, specific goat's milk flavour
Colour	White to light cream

Analysis of the data presented in Tables 5 and 6 leads to the conclusion that both cow's and goat's milk samples meet the requirements for raw milk according to organoleptic indicators and can be used in further research.

In production of soft cheese raw cow's milk is used in accordance with technical documentation [23], highest and first grades that meet the following requirements: the level of bacterial contamination by reductase test - not lower than class II, rennet fermentation test - not lower than class II, the number of mesophilic aerobic and facultative anaerobic microorganisms - not more than 5-10 ⁵CFU/cm [127].
The results of studies on the physico-chemical properties of raw cow's and goat's milk are presented in the tables and 910.
Table9 - Quality indicators for raw cow's milk

Indicator	Raw cow's milk	GOST 31449-2013
Mass fraction of protein, %	3,07±0,04	at least 2,8
Mass fraction of fat, %	3,39±0,05	at least 2,8
Acidity, ºT	17±1	16-20
Density, kg/m^3	1031±1,30	at least 1027
TCO, %	8,9±0,15	at least 8,2

Table10 - Quality indicators for raw goat milk

Indicator	Raw goat milk	GOST 32940-2014
Mass fraction of protein, %	3,13±0,05	at least 2,8
Mass fraction of fat, %	3,31±0,03	at least 3,2
Acidity, ºT	17±1,00	14-21
Density, kg/m^3	1029±0,64	1027-1030
TCO, %	8,79±0,17	at least 8,2

The chemical composition of goat milk is similar to that of cow's milk, but the quantity of milk differs considerably.

Goat's milk, like cow's milk, belongs to the casein-predominant product group, and it is also known that the ratio of casein to whey proteins in these types of raw milk is similar, being 75:25 and 80:20 respectively [7].
The protein composition of goat's milk differs from that of cow's milk in such properties as fractional composition, structural, physico-chemical and immunological properties (Table 11).
Table11 - Fractional composition of raw milk proteins [7]

Protein fractions	Milk, g/100 ml
	goat	cow
^αS-Casein1	-	1,37
β-Casein	2,28	0,62
γ-Casein	-	0,12
β-Lactoglobulin	0,26	0,30
α-Lactalbumin	0,43	0,07
Immunoglobulins	-	0,06
Serum albumin	-	0,03

As can be seen from the table, β-casein is the main11, casein fraction of goat milk as well as female milk, while caseins of cow's milk proteins are mostly αS-caseins₁. In goat's milk there is practically

αS-₁ and γ-caseins contained in cow's milk are absent [161, 171]. The main whey protein in goat milk is α-lactalbumin and in cow's milk β-lactoglobulin. However, casein and whey proteins, including β-lactoglobulins and α-lactalbumin, differ not only in their fractional composition, but also, worth noting, in their structural and physicochemical properties [167, 187184,].
The experimental data show that the cow's and goat's milk obtained in the conditions of ZAO Prinevskoe farm corresponds to the highest grade, i.e. it can be used in the research and production of soft cheese.

2.