In our experiment, about 192 data were obtained with 8 samples analyzed after 24 hours, 2 days and 3 days of milking and of which 08 physico-chemical and biochemical parameters were studied.
The pH of the milk samples in this study, evaluated just after milking, ranged from 6.21 to 6.65 with an average of 6.43± 0.15. Several authors found very close pH values for camel milk.
Yam et al., (2014) and
Meribai (2018) and
Bouguerra (2021) reported pH values directly after milking ranging from (6.4-6.7), (6.58-6.65) and (6.46-6.77), respectively. However, our results are higher than those reported by
Benyagoub and Ayat (2016) who found an average pH of 5.67. In addition,
Sboui et al., (2009) found that fresh camel milk is more acidic and less dense than cattle (6.6) and human milk (7.01).
The variability observed in the pH results of the different authors may be due to several factors such as geographical location, climate, diet and water availability in addition to other factors such as breed, stage of lactation, age and number of calves (
Gorban and Izzeldin, 1997;
Al haj and Al Kanhal, 2010).
According to
Sharma (2006), pH is an index to measure the actual acidity of the milk and to detect abnormal milk from camels with mastitis. While the relatively high vitamin C content of camel milk is the cause of low pH compared to cow’s milk (
Saley, 1993).
The slow decrease in pH, observed during the test period, can be explained by the fact that acidity has little influence on pH, the relatively slow decrease. This experimental finding, reported by many authors
(Farah et al., 1989; Ramet, 1994;
Abu-Tarboush, 1996) is explained by the fact that camel milk has a greater buffer power compared to the milk of other species.
After 24 hours of storage, we recorded a pH value of 5.98±0.30. Statistical analysis did not reveal a significant difference between pH measured immediately after collection and pH measured after 24 hours of storage at room temperature. This result corroborates that of
Kaskous (2019) which confirms that after 24 h an ambient temperature the storage of raw milk samples did not have any significant changes in its quality. After 3 days of storage the pH was 4.45±0.30, very close to that of
Sodini et al., (2002) which who recorded a pH of 4.6 after the same storage period. At 3 days, the pH of our samples was 3.95±0.25.
Sodini et al., (2002) reported that after 72 h of incubation, the pH of camel milk had not yet reached the final acidification point.
Fguiri et al. (2017) reported that lowering the pH during storage is due to lactose fermentation into lactic acid.
This work shows Dornic acidity values, measured 24 hours after milking, of about 17.51±1.35°D. It is comparable to that obtained by
Abidi (2001);
Mahboub et al., (2010); Chethouna (2011) and
Siboukeur (2005) in Algeria and
Sboui et al., (2009) in Tunisia that reveal Dornic D acidity values of 19°D, 21.3±1.44°D, 18°D, 18.2±2.93°D and 17.2°D, respectively.
Other authors have shown titrable acidity values below 17°D, including
Ghennam et al., (2007), Alloui-Loumbarkia et al. (2007) in Algeria and
Kamoun (1994) in Tunisia with 15.6°D, 15.12°D and 15.6±1.4°D. In addition, the variation in acidity is also due to variations in animal feed, environmental conditions and lactation (
Abu-Tarboush, 1996).
It was noted that the acidity of camel milk slowly increased at ambient temperature. Dornic acidity increased from 17.51±1.35°D on the first day to 73.3±3.53°D after 3 days of storage.
Ghennam et al., (2007); Chethouna (2011);
Siboukeur (2005) and
Bezzalla and Gouttaya (2013) reported different results after the 7
th day of storage, 93.6°D, 92.5°D, 78°D and 98°D, respectively. The increase in milk acidity is attributed to a high concentration of lactic acid formed during lactic fermentation by milk bacteria (developed acidity). This tends to slow down acidification due to the particular tampon of camel milk compared to cow milk
(Farah et al., 1989; Ramet, 1994;
Abu-Tarboush, 1996).
The density of camel milk recorded in this study was 1.01±0.02 after 1 day. This is very close to those recorded by
Mahboob (2010);
Siboukeur (2007);
Abidi (2001);
Kamoun (1995);
FAO (1995); with 1.03±0.01, 1.02, 1.02, 1.03 and 1.02, respectively. The latter is strongly related to the frequency of watering (
Siboukeur, 2007), sufficient watering leads to an increase in the water content of the milk and a decrease in the total dry matter content, which explains its low density.
The dry matter content of 129.27±11.31 g/l is comparable to that found by
Sboui (2009) and
Kamoun (1995) in Tunisia and
Siboukeur (2007) and
Ghennam et al., (2007) in Algeria, respectively 119.43 g/l±15.34, 116 g/l±11.11, 11 g/l ±10.58 and 129.98g/l±4.75.
Kaskous, (2019) and
Bengoumi et al., (1994), report that the lactation stage has an effect on the solids content of milk; in fact, the solids content in milk increases continuously as the lactation stage progresses. This increase is, according to the same authors, related to the increasingly high fat and protein content of milk.
Analysis of the ash content of camel milk reveals a value of 7±0.578g/l which is not far from the results reported by other authors. It ranges from 7.5 g/l (
Sboui, 2009) to 7.28 g/l±0.68 (
Siboukeur, 2007). According to
Yagil (1985), the ash content of camel milk varies widely with dietary intake. As a result, the mineral composition of camel milk depends mainly on the diet and the state of dehydration (
Fay, 1997).
Attia et al., (2000) found that camel milk rich in salted micelles is richer in ash than cow’s milk. This variation appears in consecutive amounts of milk produced (
Elamin and Wilcox 1992) and in the lactation stage (
Farah, 1993).
The average milk fat content in this study is approximately 50.09±5.97 g/l. It is comparable to that reported by
Ghennam et al., (2007) for the Algerian chamelle (50.50±8.37 g/l). However, it is higher than that described by
Siboukeur (2007) in Algeria,
Kamoun (1995) and
Sboui (2009) in Tunisia, respectively 28±6 g/l, 35±7 g/l and 37.5±8.95 g/l. It is proved that outside of the breed, milking time affects the fat content. In fact, milk processed in the morning is relatively low in fat compared to milk processed during other hours of the day (
Kamoun 1994).
Food also plays an important role in the evolution of fat content, the study conducted by
Mathieu (1998) showed that when the feed/concentrate ratio in the diet is lower, the amount of volatile fatty acid products increases in the rumen, which has a positive influence on the percentage of fat in camel milk.
In addition, the lactation stage affects the fat content; it increases from the 8
th day of lactation during the first months and then goes down to a high level at the end of lactation (
El Hatmi et al., 2004).
A low fat content of camel milk compared to other milks and its high content of unsaturated and long-chain fatty acids give it beneficial effects for consumers with cardiovascular problems (
Bouguerra, 2021).
Jilo and Tegegne (2016);
Singh et al., (2017); Rahmeh et al., (2019) report that, compared to other ruminants, camel milk fat cells lack agglutinin, making them easily digestible.
According to
Hassan et al. (2007);
Bekele et al., (2011), several factors affect the fat content of camel milk such as weather conditions, stage of lactation, diet, presence of water, country and milking method. Indeed,
Bekele et al., (2011) stated that diet and watering can significantly affect the fat content of camel’s milk, as thirsty camels produce milk high in fat.
In addition,
Gorban and izzeldin (1997) states that the fat content of camel’s milk can also be affected by the type of forage, including the nature of carbohydrates, thus modifying the ratio of volatile fatty acids in milk.
The mean total protein content of the raw milk tested is 2.31±0.21%. It is comparable to that obtained by
Abu-lahia (1994) (2.78±0.12%) and
El Amin (1992) (2.81%). Other authors found results above these values, such as
Mal et al., (2006); Mal et al., (2007), Bakheit et al. (2008) and
Al haj and Al Kanhal, (2010) with 3.73%, 3.89%, 3.4% and 3.1±0.5% respectively.
However, our results remain higher than those published by
Kaskous (2019) at 2.28±0.01%;
Ellouze and Kamoun (1989) at 2.29%; Raghvendar
et al. (2004) at 2.30% and
Omer and Eltinay (2009) at 2.06%.
In general, the percentage of protein in raw camel milk ranges from 2.1 to 4.9% (Bouguerra, 2021); 2.15 to 4.90%
(Konuspayeva et al., 2009) or 2.30 to 3.95%
(Yadav et al., 2015) or 3 to 3.90%
(Jilo et al., 2016).
As with fats, the protein content of our samples appears normal since
Bekele et al., (2011) have reported that the protein content of camel’s milk is not affected when the animal is not deprived of water or food as is the case with our breeding.
The stage of lactation leads to a decrease in protein and fat content according to
Kamoun (1994), these levels subsequently reach a minimum value coinciding with the peak of lactation and then return to a level comparable to that of departure at the end of lactation. Diet plays an important role in the evolution of protein levels. The protein content varies in the same direction as the energy intake. It depends on the proportion of concentrated food in the ration, its size and its distribution (fineness of the hash, number of meals, food mixture) (
Benhedane, 2012).
The vitamin C content of the sample analyzed is 41.89±4.51 mg/l.
Farah et al., (1992); Siboukeur (2005) and
Boudjenah (2012) report similar levels of 37.4 mg/l, 41.4±8.2 mg/l and 45±0.03 mg/l, respectively. The concentration of vitamin C in milk varies with the stage of lactation.
Konuspayeva et al., (2003) conclude that alfalfa-based diets are more favourable on the concentration of ascorbic acid in plasma and leukocytes than grazing-based diets.
Singh et al., (2017); Rahmeh et al., (2019) published vitamin C levels between 24-52 mg/kg and reported that camel milk is 3-5 times richer in vitamin C than bovine milk, which is of great nutritional importance.
The variation in vitamin C content is also related to the number of births. Indeed, milk from primipares contains less ascorbic acid than milk from multipares
(Konuspayeva et al., 2003). Table 2 shows a decrease in vitamin C content to 16.72±3.16 mg/l after 3 days of milking. This decrease is due to the oxidation of vitamin C by oxygen dissolved in milk and under the effect of light that transforms ascorbic acid into deoxyascorbic acid which remains biologically active but very unstable
(Mohamed et al., 2013).
Statistical analysis showed that storage time influenced certain parameters of camel milk. Table 1 and 2 clearly show the significant effect (P<0.001) of storage time on acidity, pH and vitamin C content. The protein content of our samples does not change significantly an ambient temperature until 48 hours and then they changed significantly (P=0.001), on the 3
rd day of storage.
The increase in the acidity of milk stored an ambient temperature, is due, according to
Kaskous (2019) to the fact that beyond 24 hours of storage, the load of lactic bacteria and the extent of fermentations increase by decreasing, the pH of the milk, the latter then becomes inconsumable. The negative pH evolution observed for our samples is confirmed by the results of
Omer and Eltinay (2009) which reported a pH of 6.57 on the day of collection and 5.47 after 3 days vs 6.43 and 4.45 respectively in our study.
The milk fat content of our camels decreased slightly and non-significantly (p=0.30) from 50.09 g/l (24 h) to 48.60 g/l (48 h) to 43.01 g/l (72 h). The same findings were made by
Kaskous (2019). In fact, he reported 2.62% at 24 hours and 2.61% at 48 hours. However,
Omer and Eltinay (2009) reported a significant increase in mean fat contents with 2.72% at 48 hours and 3.06% at 72 hours.
The results of this study showed that milk quality did not change after a 24-hour storage period at room temperature. However, the milk was acidified after 48 hours. This corroborates the results of
Kaskous (2019) which suggests that generally storage at room temperature (24±1.7°C) contributes to the decrease in milk quality and that raw camel milk can be kept at room temperature for 24 hours without noticeable change. Similarly,
Millogo (2015) shows that in practice camel milk is generally stored at room temperature for 24 hours in many countries.
