The study showed that there was no significant (P>0.05) differences in the results of fat, total solids, lactose and protein content of milk samples collected from the three sources in Gadarif town. This generally indicates the similarity of the milk animals and their management. The chemical composition of milk can be influenced by several factors such as animal species and genetics, environmental conditions, lactation stage, and animal nutritional status (et al. 2009; Kalac and Samkova 2010).
This study revealed that fat content of raw milk samples collected from groceries was 3.5±1.2% (Table 1), which was around the findings reported by Mohamed and El Zubeir (2007) who found that the means fat content of milk in Omdurman and Khartoum North were 3.75±1.07 and 3.46±1.17%, respectively. However Ahmed and El Zubeir (2007) reported higher values; 4.54±0.59% and 4.50±0.47%; for milk samples collected from farms in Khartoum State during winter and summer, respectively. The maximum values reported during this study supported Bashir and El Zubeir (2013) who reported 5.08±1.05% fat content for milk of Baggara cattle (5.08±1.05%) in South Kordofan State. Also Elsheikh et al. (2015) found that milk samples collected from Khartoum North and Omdurman were 4.72±0.67% 5.02±0.60%, respectively. Moreover Warsama et al. (2017) showed significantly (P≤0.001) higher fat (5.03%) content of cows’ milk samples obtained during winter in Khartoum State. The reported variations could be attributed to difference in cows’ breeds, location and feeding strategy. Similarly Shuiep et al. (2016) reported that variations between milk fat content could be due to different management, feeding regimes, production systems and breed of cattle. They indicated that the local cows are significantly (P<0.05) capable to produce higher milk fat throughout their lactations. On the other hand, Mirzadeh et al. (2010) found that fat content was 3.90±0.97% in Iran, while Eckles and Combs (2004) reported that the average percent of fat in milk was 3.8% in India and concluded that the milk fat is the most valuable constituent of milk and should be considered as the food value of the milk. Also Pavell and Gavan (2011) reported that nutrition, climatic conditions and regional differences can be regarded as important sources of variation in the composition of milk.
The solids not fat (SNF) of milk samples collected from farms (7.7±1.1%) showed lower values than those obtained from sale points (8.1±1.7%) and groceries (8±1%) as sown in Table 1. Similarly Pavel1and Gavan (2011) reported 8.70% for SNF content of milk during summer period in lactating dairy cows. Mirzadeh et al. (2010) in Iran reported that the average SNF content in raw milk produced by dairy cow at different lactations was 8.67±0.69%. However higher values were reported by Bille et al. (2009); Czerniewicz et al. (2006); Landi et al. (2011). Moreover Bashir and El Zubeir (2013) reported 9.19±0.78% for SNF content of milk of Baggara cattle in Sudan. The solids not fat of milk samples collected from different sources (11.52%) in Khartoum State also revealed non significant differences (Warsama et al. 2017). The SNF content of milk from local cows and crossbred cows was found to be influenced significantly (P≤0.05) by stage of lactation and parity order (Shuiep et al. 2016). They concluded that the variation of breed, feeding and management could be the reasons. The SNF content of the milk (8.09 to 9.03%) generally follow the variation of the fat content, the higher the fat content the higher was the SNF but lower the density (Bille et al. 2009). In Ethiopia, Gemechu et al. (2015) found that the total solids were 12.87%
The average protein content of milk samples (3±0.4%) collected from the three sources in Gadarif town (Table 1) was comparable to that reported by Ahmed and El Zubeir (2007) who found the mean value of protein content was 3.73±0.587% in dairy farms located in Khartoum State. Also Elsheikh et al. (2015) found protein content was 3.58±0.38% for milk samples collected from Khartoum and 3.57±017% for the samples obtained from Khartoum North. The result of protein content of milk samples were also in line to those (3.5±0.9%) obtained by Warsama et al. (2017) in Khartoum State and those collected from Baggara cattle (3.62±0.31%) in South Kordofan State (Bashir and El Zubeir 2013). Similarly et al. (2016) found 3.57% in milk collected from Faisalabad. However Mohamed and El Zubeir (2007) found that the mean value of protein content in milk collected from Khartoum North (3.08±0.59%) was higher than that of Omdurman (2.93±0.47%).
The study showed the lactose content of milk samples collected from sale points were 4.4±0.8 (Table 1), it was in accord to Ahmed and El Zubeir (2007) findings for lactose content of milk samples collected during summer and winter in Khartoum State, which were 3.95±0.561% and 4.06± 0.618%, respectively. Also Elsheikh et al. (2015) found that the mean of lactose content in milk samples from Omdurman was 4.72±0.4% and those obtained from Khartoum showed a mean of 4.86±0.24%. Similarly the mean of milk lactose from Baggara cattle in South Kordofan State, Sudan was 4.89±0.33% (Bashir and El Zubeir 2013). Nateghi et al. (2014) found that the lactose content of milk during summer was 4.61%. The lactose of the milk samples collected from different sources and during different seasons showed high significant differences (Warsama et al. 2017). The lactose content was found in a range of 5.21 to 5.15% and 5.33 to 5.02%, in local and crossbred cows, respectively (Shuiep et al. 2016). This might be due to the fact that the lactose content of milk is affected by different locations and feedstuff that animals utilized (Kittivachra et al. 2007). On the other hand, Eckles and Combs (2004) reported that lactose has an important relation to the manufacture. However there is some evidence that lactose is the least cariogenic of the common dietary sugar. In addition, various other components of milk have been considered to be protective against dental caries (Bánóczy et al. 2009).
There was no significant difference between the results of milk sources in Gadarif town as this study revealed that the freezing point in sale points were -0.524±-0.007° C (Table 2). Similarly Ahmed El Zubeir (2007) reported that the freezing point of raw milk were -0.519±-0.0251° C and -0.533±-0.013° C in the samples collected during summer and winter, respectively and the average was -0.535±0.033° C. Marshall (1992) stated that a freezing point of -0.517° C is considered normal for milk and milk that freezes at or below this value is presumed to be free of added water.
In the present study the mean density was 0.026±0.005 g/cm3 (Table 2), which was lower than those reported by Abd Elrahman et al. (2009); Bashir, and El Zubeir (2013); Elsheikh et al. (2015); Warsama et al. (2017) who found the average density of milk was about 1.031 g/cm3. This indicated addition of water or subtraction of fat as was shown in Table 1 that lower values were found for fat, lactose and solids not fat. Similarly El Zubeir et al. (2008) reported lower levels for the chemical content (fat, protein, lactose, SNF, and total solids) of the pasteurized milk compared to the raw milk samples obtained from different milk producing companies in Western Cape, South Africa.
The added water in the milk samples collected from the farms was estimated as 10.6±11.6% (Table 2). When comparing the present results, it was observed that the level of the added water was relatively high. This may be due to adulteration by adding water to milk in Gadaref town. Elsheikh et al. (2015) reported the adulteration by water in some of the milk collected from Omdurman and Khartoum towns. Also the percentage of the added water was very high in the processed milk compared to the samples from herd raw bulk milk in South Africa (El Zubeir et al. 2008). Also Tasci (2011) stated that addition of water and ice affected the physical and chemical quality of milk by adulterant proportion different constituents of milk in Western Cape, South Africa. Similarly Faraz et al. (2013) reported 97 and 93% of the milk samples in canteens of educational institutes and public places of Faisalabad had added water.
The raw milk samples tested during this study (Table 3) showed that 22 (27.5%) of the samples were found positive for aflatoxin M1 with the highest occurrence in the samples obtained from sale points and farms (15% and 11.5%, respectively). Moreover all strong positive (level 1; 0.05 to 0.1) contaminated samples were obtained from the farms (22.72%). Aflatoxin M1 (AFM1) is a hydroxylated metabolite of aflatoxin B1 (Zinedine et al. 2007). Hence the high level of contamination in raw milk samples from the farms might be due to the contamination of dairy cow rations with aflatoxins B1 (Ali et al. 2014; Elteib et al. 2012). Higher occurrence were also reported in India, the range of contamination with AFM1 was 28- 164 µg/l and that 99% of the contaminated milk samples exceeded the European Communities recommended limit (Shipra et al. 2004). Also Kang'ethe and Lang'a (2009) detected 99% of milk samples were contaminated with aflatoxin in Kenya. Bokhari et al. (2017) in KSA, tested 160 milk samples and found that 74.47% of milk samples were contaminated with aflatoxin. Ali et al. (2014) concluded that the levels of AFM1 in the raw milk samples indicated that the feeds offered to the cows were contaminated with aflatoxin B1 in such a level that might cause a serious public problem. Aflatoxins are absorbed in the gastrointestinal tract but not been biotransformed in the liver can also be excreted (Scaglioni et al. 2014). Thus aflatoxin can accumulate through the food chain posing a serious health concern to both humans and animals (Gavrilova et al. 2014; Otim et al. 2005; Patel et al. 2015). However according to the survey conducted throughout North western Italy between 2012 and 2014, the overall AFM contamination rate was 2.2% (36 samples out of 1668 samples) and less than 1% of milk samples of were non-compliant with EU limits (Bellio et al. 2016). However the positive samples with level 2 (0.1 to 0.15) were detected in the samples collected from sale points (15.0%) compared to those collected from farms (5.0%) and groceries (1.25%) as shown in Table 4. This might indicate that the higher concentration of the contaminated milk from the farms was dilated to a lower level in the sale points, because in the sale points and groceries they bulked the milk from different farms. Similarly Sharma et al. (2020) was able to detect AFM1contamination in the milk sold by local traders (14/50) and vendors (16/50) in India. This study suggested the presence of aflatoxin in animal feed, which supported that of Omer et al. (2004); Elteib et al. (2013) who showed the presence of aflatoxin content in groundnut seeds and cakes, respectively. Aflatoxins are generally classified into B1, B2, G1 and G2, which metabolized to aflatoxins M1 and M2 (Boudra et al. 2007). Aflatoxins B1 is a potent mutagenic and carcinogenic agent found in numerous agricultural and dairy products consumed by humans (Madrigal-Santillan et al. 2007). Moreover Aflatoxins are highly carcinogenic and mutagenic in nature (Ehrlich et al. 2003; Ozay et al. 2008; Williams et al. 2004). Aflatoxins contaminated corn and cotton seed meal in dairy rations has resulted in aflatoxins M1 contaminated milk and milk products (Van Eijkeren et al. 2006; Zinedine et al. 2007). Hence regular monitoring of AFM1 is necessary for evaluating their contamination and improvement status. Simultaneously, more precautions could be implemented on hygiene controls in order to limit AFM1 contamination in dairy products (Min et al. 2020).
Furthermore in Khartoum State, higher prevalence was found compared to the present study and the percentage of AFM1 contamination has been found in 42/44 (95.45%) samples with contamination level ranging between 0.22 and 6.90 lg L_1 and average concentration of 2.07 lg L_1 (Elzupir and Elhussien 2010). Also Ali et al. (2014) showed that the average concentration for AFM1 in raw milk samples ranged between 0.1 and 2.52 ppb with 100% exceeding the limits of European countries. The presence of AFM1 was detected in a concentration that ranged between 20ـ 150 ppt and that 88.7% of the processed milk samples were found to be contaminated with aflatoxin M1 compared to 92% of the raw milk samples (Fadlalla et al. 2020). The average concentration for AFM1 in Nigeria revealed 2.04 µg/k (Atanda et al. 2007), although Nigeria set a limit of 1.0 µg kg-1 (Iqbal et al. 2015). However the European communities and Codex Alimentarius recommend limits of 0.05µg/kg and 0.5µg/kg, respectively. (Kemboi et al. 2020) stated that despite their regulation being stricter, the EU is a major destination of trade for most African countries, and hence the EU regulatory and guidance values are used for comparison since they may negatively impact trade and in addition they cover a wide variety of feeds for different species. In China, the situation of AFM1 contamination in milk proved the improvement of surveillance (Xiong et al. 2018; Zheng et al. 2017).
The variations in AFM1 levels among milk samples from farms and distributors (Table 3 and 4) could be attributed to forage and feed quality, cow’s diet, genetic variation in dairy cows, and geographical and seasonal variations (Mohammed et al. 2016; Sahin et al. 2016). On the other hand, the mean concentration of AFM1 in milk samples collected in summer ((96.3%) was significantly (P<0.05) higher than that obtained in winter ((89.0%) in Karachi, Pakistan (Asghar et al. 2018). They added that seasonal variations tend to increase the growth rate of fungi and AFs contamination, ultimately resulting in higher AFM1 contamination in summer when compared to winter. Based on 171 different milk samples, the results showed that all age's categories, especially children were exposed with high risk related to presence of AFM1 in milk in Serbia (Kos 2014). However Ahmad et al. (2019) found that the dietary exposure data of AFM1 among six different groups was indicated that the male children population was the most vulnerable group to AFM1, up to 6.68 ng L−1 per day and the least affected one was the female group above 20 years of age with 1.13 ng L−1 per day. The economic impact of aflatoxins leads directly to crop and livestock losses as well as indirectly to costs of regulatory programmers designed to reduce risks to animal and human health (Martins et al. 2007).