Raw milk may be defined as poly disperse system, which has a temperature of 38C directly after milking. This extremely heterogeneous system is not very stable; creaming and microbiological deterioration is well known changes which take place during storage. In addition to changes in the microbiological status of raw milk, several physical and chemical alterations occur, including changes in the rennet coagulation time and curd firmness and reduced yields of cheese, as well as increases-casein content and flavor defects (Reimedes, 1987).
Ohri and Joshi (1961) reported that camels milk soured in 8hr when kept at 30oC, compared with cows milk, which soured within 3 h at the same temperature.
Yagil et al. (1984) stored camels milk, womens milk and cows milk at 30oC and refrigerated at 4oC. He found that at room temperature womens milk turned extremely sour within 24 h reaching a pH of 5.5. Cows milk becomes sour within 2 days with pH of 5.7. Camels milk remained un changed for 5 days with a pH of 5.8. Refrigerated unstirred womens milk separated into a fat layer and a sticky liquid layer within 2 days. Within 5 days the milk had coagulated and developed a pungent odour. Unstirred cows milk slowly separated into a coagulum surrounded by milk-serum in 7 days. After 10 days the milk was rancid with a pungent odour. Unstirred camels milk slowly separated within 10 days, but did not coagulate. After 2 months of standing the milk tasted the same as before. After 3 months it had a very unpleasant smell.
The aim of the present study is to evaluate the changes that might happen in the gross composition of Camels raw milk during storage.
MATERIALS AND METHODS
Collection of milk samples: Camels milk samples were collected
from 70 lactating camels, from private camel herds, from different areas. All
camels were in mid lactation (2nd to 5th month of lactation). A box containing
ice was used to provide cold storage during transportation to the laboratory.
The milk samples were divided into three portions under sterile conditions the
1st portion stored at 4oC, the 2nd portion stored at 7oC,
the 3rd portion stored at room temperature (25-30oC). Twenty Samples
were examined for pH, acidity, fat, protein, lactose, total solids and ash contents.
Samples at room temperature were analyzed daily. Samples stored at 7oC
were analyzed at two-week intervals, while samples stored at 4oC
at three-week interval (Those intervals of analysis based on pre-experiments
Sample containers: 1000 mL, autoclave able plastic containers were used for the collection of samples. Containers were sterilized at 120oC for 15 min and kept ready for milk collection from different sites.
Chemicals: All chemicals used were analytical grade.
Preparation of the udder: Healthy and uninfected camels were used for milk collection. The udder was cleaned and washed with disinfectant solution (Safflon; 20% concentration) and was kept on the udder 5-10 min., before collection of samples. 20 mL of the 1st milk leaving the udder was discarded.
Types of analysis conducted: The following parameters were analyzed, pH, acidity, density, ash, moisture, fat, protein, lactose and total solids.
pH determinations: The pH of the milk was determined by a pH meter at 25oC according to APHA (1972).
Acidity, density, gross composition determinations: The acidity, density, total solids, ash, lactose and protein contents were determined according to AOAC (1995) methods.
Fat determination: Fat was determined according to Rose Gottleb method (Person, 1967).
Data analysis: SAS program was used for the data analysis (SAS, 1997).
RESULTS AND DISCUSSION
The presence of many organic compounds in milk helps various types of microorganisms to decompose it and causing different chemical changes.
Table 1 shows the physicochemical characteristics of camel milk stored at 4oC. The mean value of pH at 4oC. on the day of collection (1st reading) as 6.6, accompanied by a slight decrease in 3rd week (2nd reading) and a further decrease to 5.8 at day 42 (3rd reading). Yagil (1982) reported no change in the pH of camel's milk, stored at 4oC after 2 days of collection. Titratable acidity at 4oC rose from 0.2-0.4-0.6% for the 1st, 2nd and 3rd readings, respectively. The mean values of fat during storage at 4oC were 2.4, 2.4 and 2.5% for the 1st, 2nd and 3rd readings, respectively. The observed data indicated no significant change in milk fat content when the milk was refrigerated at 4oC.The mean values of protein were as follows: 2.1, 2.8, 2.7% for the 1st, 2nd and 3rd reading, respectively and that mean a slight changes had occurred during storage at 4oC. Lactose content was the most constituent affected by storage at different temperatures. At 4oC the mean value decreased from 4.4% at the day of collection to 3.26% at the 2nd reading and 2.68% at the 3rd reading. The decrease of lactose during storage could be attributed to the activity of microorganisms. Total solids mean value at 4oC decreased slightly from 9.8-9.5-9.0% at the 1st, 2nd and 3rd readings, respectively. The mean values of ash content increased from 0.94% at the day of collection to 1.0% at the 2nd reading and 1.1% at the 3rd reading. Moisture content increased slightly from 90.2% at the day of collection to 90.4-9.6% for the 2nd and 3rd reading, respectively.
Table 2 shows Physicochemical characteristics of camel milk stored at 7o the mean value of pH at 7oC on the day of collection (1st reading) as 6.6 then decreased to 5.9 at the end of the 1st week (2nd reading) and then decreased slightly by the end of the 2nd week (3rd reading). At 7oC the acidity rose from 0.2-0.3% by the end of the 1st week and to 0.55% at the 2nd week. The mean values of fat during storage at 7oC were 2.4, 2.5 and 2.5%, for the 1st, 2nd and 3rd reading, respectively. That means no significant change in fat content was observed when milk was refrigerated at 7oC. The mean values of protein content at 7oC were 2.1, 2.1 and 2.0% for the 1st, 2nd and 3rd readings, respectively. The mean value of Lactose content at 7oC decreased from 4.4% at the day of collections to 4.1% at the 2nd reading to 3.6% at the 3rd reading. Total solids mean value at 7oC decreased from 9.8% at the day of collection to 9.6% at the 2nd reading and to 9.4% at the 3rd reading. The mean values of ash content were 0.94, 1 and 1.1% at the 1st, 2nd and 3rd reading, respectively. No significant change in the moisture content at 7oC.
Table 3 shows the physicochemical characteristics of camel milk stored at room temp (25-30oC) the mean value of pH at room temperature as 6.6 at the day of collection to 5.6 in the 2nd day (2nd reading) to 5.4 at the 3rd day (3rd reading). At room temperature the acidity rose from 0.2-0.4-0.5% for the 1st, 2nd and 3rd reading, respectively. These results differ from those of Yagil (1982) who reported that souring of camels milk at room temperature, was after 7 days collection, while Ohri and Joshi (1961) reported that camel milk when left to stand at room temp, the acidity rapidly increases after 8 h. These differences in results may be due to differences in milking practices. At room temperature, the mean values of fat were 2.4, 2.7 and 3.1% for the 1st, 2nd and 3rd readings, respectively. The data indicate a significant increase in fat when milk stored at room temperature. The percentage of total protein was 2.1% in the 1st reading, 2.1% in the 2nd reading and 2.2% in the 3rd reading. The percentage of total proteins was insignificantly altered during storage at room temperature. The mean value of Lactose content at room temperature, decreased from 4.4% in the 1st reading to 3.34% at the 2nd reading and to 3.28% at the 3rd reading, respectively. Total solids mean value at room temperature decreased from 9.8% at the day of collection to 9.7% at the 2nd reading, then decreased to 9.3% at the 3rd reading, respectively. The mean values of ash content at room temperature were 0.94, 1.1 and 1.11% from the 1st day of collection, to the 2nd and 3rd day, respectively. The mean value of moisture content was 90.2% at the day of collection to 90.5% at the 2nd day and 90.3% at the 3rd day.
Table 4 represents the storage duration of raw camel milk,
at 4oC, 7oC and room temperature. Eleven samples out of
seventy samples stored at room temperature were spoiled within 2 days, 47 samples
out of seventy samples were spoiled after 3 days and 12 samples out of seventy
were spoiled in 4 days. At 7oC 1 sample out of 70 was spoiled after
11 days, 20 samples out of 70 were spoiled after 14 days, 38 samples out of
70 samples were spoiled after 15 days, 3 samples out of 70 samples were spoiled
after 18 days and eight samples out of 70 samples were spoiled after 22 days.
For samples kept at 4oC, 4 out of the 70 samples tested were spoiled
after 37 days, 50 samples out of 70 samples were spoiled after 42 days, 5 samples
were spoiled after 44 days and 11 samples were spoiled after 46 days. These
results differ from those reported by Yagil (1990) who reported that camel milk
stored at room temperature remains unchanged for 5 days then becomes sour within
the next 2 days. That camel milk stored at 4oC remains unchanged
for 3 months. Camel milk has good keeping quality compared to cow milk. Raw
cow milk as reported by Yagil (1990) became sour within 2 days when left at
room temperature and within 10 days when refrigerated at 4oC.
characteristics of camel milk stored at 4oC
|*Means with same letter are not significantly different
characteristics of camel milk stored at 7oC
|*Means with same letter are not significantly differe
Physicochemical characteristics of camel milk stored at
room temp. (25-30oC)
|*Means with same letter are not significantly different
duration of camel raw milk
Table 5 shows the Storage duration of Camel Milk Compared
with Cow Milk. Ahmed (1995) reported that the keeping quality of the raw cow
milk samples at room, refrigerator and deep freeze temperature was 3.5, 70 h
and >4 weeks, respectively.
duration of camel raw milk compared with cow milk (Mean values)
|*Adapted from Yagil et al. (1984), **Adapted from Ahmad
Generally, there was little change in camel milk during storage at different
temperatures, the obvious change was on odour and taste but it did not coagulate.
This agrees with Sohail (1983) who reported that camel milk is less affected
by storage and the acidity increases slowly. It was comparable to that reported
by Yagi (1990) who reported that camel milk didnt coagulate after 2 months
of standing, at room temperature and that shaking was enough to bring the milk
back into its original form.
Conclusion: From the foregoing results it could be concluded that camel milk is less affected by storage and can be kept for comparatively long periods than cow milk.