| Livestock Research for Rural Development 29 (6) 2017 | Guide for preparation of papers | LRRD Newsletter | Citation of this paper |
Milk is considered as nature’s single most complete food and is one of the most valuable and regularly consumed foods. Physicochemical parameters of raw milk are of great importance in the assessment his quality. But, in Algeria, little studies have been conducted to assess the physicochemical quality of raw milk produced specially by cows after importation. This study was conducted to evaluate the physicochemical quality of raw milk of Prim’holstein breed from Mitidja region in Algeria. During March and April, 64 samples of raw milk were taken on 32 Holstein cows. Gerber acid-butyrometric and Bradford methods were used to calculate the milk fat and protein content, respectively. The density was measured using a thermo-lactodensimeter at 20°C and dry matter was obtained by drying by evaporation of milk.
Physicochemical results showed fat 31.0±1.9 g/L, protein 29.1±0.6 g/L, density 1.03±0.002, dry matter 118±6 g/L, and defatted dry matter 87.0±0.8 g/L. Statistical analysis of data revealed that there is a significant correlation between fat and protein (p˂0.05) and dry matter with fat and defatted dry matter (p˂0.001). These results show that the physicochemical quality of raw milk of Prim’holstein breed imported in Algeria is lower than in the country of origin.
Key words: density, dry matter, fat, protein
Milk is definitely one of the important valuable and commonly consumed foods and is considered as nature’s single most complete food (O'Mahony 1988). Algeria did not satisfy yet its requirements out of milk produced locally which is derived primarily from the bovine species. Therefore, Algeria uses annually to import milk powder and high producing cows to make up the deficit (Kaouche-Adjlane 2015).
In Algeria, the number of cattle was estimated at 1.682.400 head of which 882.280 were dairy cows (MARD 2009). The imported race of dairy cattle includes the Montbeliarde, Friesian and Prim’holstein breed. It represents 26% of the total number and contributes about 70% of total production of cow’s milk (MARD 2014, 2009).
Dairy cattle in Algeria is difficult to manage because the insufficient contribution in fodder cultures is far from satisfying the food needs for the national livestock in quantity and quality (Kaouche-Adjlane 2015). The races introduced for the improvement of the production are confronted with ecological conditions completely different from those of their origin countries. Imported for their genetic strong potential, they see their performances decreasing, since most of their metabolism is used for their adaptation to the environmental factors (Nedjraoui 2003), but still higher than the local breeds.
It is clear that the physicochemical parameters of milk are of great importance in the assessment of the quality of raw milk. In Algeria, little studies have been conducted to assess the physicochemical quality of raw milk produced specially by cows after importation. In our study, we performed an analysis of the physicochemical quality of raw milk from Holstein cows raised in an environment and conditions of different farms of its origin.
During March and April 2010, raw milk samples (n = 64) of 60 ml were collected from 32 dairy Holstein cows primiparous, from two farms in the Mitidja plain of Blida region (northern Algeria). The average age of calving of these cows was 30.1 months.
Each cow was concerned by two samples of milk at one week of interval and each sample was obtained after a mixture of the two samples, one (30 ml) was performed during the morning milking and the second (30 ml) for the evening milking. The morning milking was performed at 4h 30 and the evening milking at 16 h30.
The samples were conditioned in plastic bottles, sterile, labeled and in which was added 30 cg potassium dichromate (K2Cr2O7) in order to ensure the preservation of milk and prevent the alteration of its chemical components. Thereafter, the samples were directly sent to the laboratory.
Raw milk samples (n = 64) were the subject of a physicochemical analysis to measure the fat content, proteins, dry matter, defatted dry matter and density.
The dosage of proteins was realized according to Bradford (1976). The collected fractions were treated by a Coomassie blue solution and ortho-phosphoric acid that specifically bind to proteins. The technique is based on the dilution of the milk samples and the reading by the spectrophotometer at 595 nanometers.
Gerber acid-butyrometric method (AFNOR 2001) was used for separation and reading of the milk fat. The principle of the technique is the dissolution of milk components, except fat, with sulfuric acid under the influence of centrifugal force and with the addition of a small quantity of isoamyl alcohol (1 ml). The fat was separated into a clear and transparent layer.
The density was measured using a thermo-lactodensimeter at 20°C. If thermo-lactodensimeter is used at a temperature other than 20°C, a correction was applied using the following method: corrected density = density read + (milk temperature - 20°C) * 0.2
Dry matter is the product resulting from the drying by evaporation of a volume of milk. Its content was estimated by evaporation in a water bath at 70°C and then drying the sample (10 ml) five hours in the incubator at 103±2°C (AFNOR 1980).
To calculate directly the dry matter content (DMC), there is a practical relationship between the dry matter of milk, its density and fat. The most famous equation relating the dry matter density and fat is that of Fleischmann (Vuillaume 1942):
DMC= [2666 * (density-1)] + (1.2 * fat)
The content of dry matter defatted (DMD) was measured by: DM D = DM - fat.
The correlation between analyzed parameters in milk sample was studied by the correlation test. The R software version 3.0.1 (R Core Team 2013) was used to calculate the test. Significance was considered when the probability value was p˂0.05.
The results of physicochemical analyzes were obtained by averaging the results of the two samples taken with 1 week of interval (Table 1).
The results showed that the milk protein content in the 32 cows varied from 25.9 g/L to 33.9 g/L with a mean of 29.1 ± 0.6 g/L.
Concerning fat, the values varied between 24.0 and 38.0 g/l and the average was 31.0 ± 1.9 g/L. For the milk density, we found an average value of 1.03 ± 0.002 for all cows.
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Table 1. Means and standard deviations of the sample measured parameters (expressed in grams per liter of milk -g/l- except density) (n=64) |
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|
Protein |
Fat |
Density |
DM |
DMD |
DMC |
|
29.1±0.6 |
31.0±1.9 |
1.03±0.002 |
118±5.9 |
87.0±0.8 |
117 |
DM: Dry matter, DMD: Dry matter defatted, DMC: Dry matter calculated
Regarding the DM, the recorded values were between 107 and 127 g/l. The average value calculated was equal to 118 ± 6 g/l.
A very significant correlation was observed between DM and DMC (p˂0.001). DMC values varied between 109 and 126 g/L with an average of 117 g/L.
The results of DMD values was ranging from 79.6 g/l and 96.1 g/l with a mean value of 87.0 ± 0.8 g/l.
Intensity of the correlation between analyzed parameters in milk sample was found significant between the protein and fat (p ˂ 0.05) and highly significant between dry matter and fat and between dry matter and defatted dry matter (p ˂ 0.001) (table 2).
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Table 2. Data of correlation strength among protein, fat, dry matter and defatted dry matter |
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|
Parameters |
Protein |
Fat |
Dry |
Defatted |
|
Protein |
1 |
0.355 * |
0.130 |
-0.1367 |
|
Fat |
1 |
0.615*** |
-0.0693 |
|
|
Dry matter |
1 |
0.744*** |
||
|
Defatted dry matter |
1 |
|||
|
Significance : * p ˂ 0.05, *** p ˂ 0.001 |
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Of all the 32 cows, we revealed an average content of milk fat 31.0 ± 1.9 g /L (24.0 to 38.0 g/L) and proteins 29.1 ± 0.6 g/L (25.9 g/L to 33.9 g/L). These findings are low compared to the values indicated by Alais (1984) of cow's milk with a liter contains an average 37 g fat and 34 g proteins.
Couvreur et al (2006) revealed that the concentration of milk from primiparous Holstein cows in fat and proteins was, respectively, 37.8 g/L and 31.2 g/L. These values are also higher than our results.
Several factors can affect the milk content of fat and proteins and explain the weakness of the latter in our study. The various factors affecting the milk composition has been the subject of many studies. Rates vary depending on: the breed and within-breed variability (Bonaïti 1985), stage of lactation, age, season and feed (Coulon et al 1991, Hoden and Coulon 1991 ; Journet and Chilliard 1985).
According to Legarto et al (2014), feed has a direct effect on the fat and proteins content. Poorly-balanced diet of dairy cows and the reduced level of nitrogen inputs in the ration lead regression of milk fat and protein rate (Remond 1985).
Also, high yielding breeds introduced in ecological conditions different than their country of origin, see their performance decline, since a large part of their metabolism is used for adaptation to environmental factors (Nedjraoui 2003).
The cows calved for the first time after 35 months longer produce fat and proteins. The Holstein cows produce milk with a more up to +0.9 g/kg of fat and +0.5 g/kg of protein (Legarto et al 2014). In our study, the average age of first calving was 30.1 months.
The content of fat and protein is lower in primiparous than multiparous (Legarto et al 2014). In our study, all cows were primiparous.
The average value measured of the milk density recorded in our study was 1.032 ± 0.002. This value is comparable to that indicated by Alais (1984) and Vierling (2008), which is 1.031 and 1.032, respectively.
The milk density increases with the dry matter content and decreases with the fat content (Luquet 1985). Bonnefoye et al (2002) consider that a normal density of milk is between 1.028 and 1.032. Result in line with what we reported in this study.
As regards dry matter DM, the founded values are between 107 and 127 g/L with a mean of 118 ± 6 g/L. This mean value is relatively low compared to that indicated by Alais (1984) (128 g/L) and Veisseyre (1961) (125 and 130 g/L).
However, our results corroborated with the results of Labioui et al (2009) in Morocco which recorded a DM content of 117.5 g/L and are superior to the results presented by Sboui et al, (2009) in Tunisia of the order of 104.9 ± 14.4 g/L.
For the DMC, mainly two equations are used: the formula Fleischmann and formula Halenke and Mëslinger. The formula Fleischmann certainly gives the most accurate results (Muller-Hoessli 1944; Vuillaume 1942). In our study, we found a highly significant correlation between DM and DMC calculated using the method of Fleischmann (p˂0.001). The average of the DM (118 g/L) and DMC (117 g /L) are very close.
For the defatted dry matter, we found an average of 87.0 ± 0.8 g/L, a significantly lower value compared to the value indicated in the normal milk that is 91 g/l (Alais 1984). This is explained by the low rate of milk protein in our study.
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Received 6 February 2017; Accepted 20 March 2017; Published 1 June 2017