Abstract
This study investigated the effect of animal origin and altitude on some physicochemical properties of milk and on the concentration of some minerals. The studied parameters were pH, conductivity, specific gravity, moisture, ash, total dissolved solids (TDS), sodium, potassium, and calcium. The milk samples were collected from camels (8), goats (5), and sheep (6). The samples were obtained from two altitudes: 14 and 2,110 m above sea level. At the low altitude, the conductivity was significantly different between the milks of the three ruminants and the moisture, TDS, specific gravity, and calcium were significantly different between the camel and sheep milks. Regarding the animals living at the high altitude, the moisture, TDS, specific gravity, and the ash were significantly different between the camel and sheep milks and between the sheep and goat milks. Concerning the effect of altitude on the studied parameters of the milk, it had variable significant effects on the studied parameters according to the animal origin. The animal origin and the altitude had significant effects on the milk conductivity, ash, and specific gravity.
1 Introduction
The physicochemical properties of milk include the pH, conductivity, specific gravity, ash and water, total dissolved solid (TDS) percentages, viscosity, and the optical characteristics such as the refractive index and the optical activity. With regard to the chemical composition of milk, it is majorly composed of proteins, minerals, and vitamins [1,2]. Studying the physicochemical properties of milk is very important for the dairy industry. They are known to affect all the industrial processes including the mixing and homogenization, fluid flow, sterilization, freezing, and the determination of the quality of the milk industry products [3].
Different factors are well known to affect the physicochemical properties of milk such as the origin of the milk, breed and genotype, health, age and size of the lactating animal, environment, nutrition of the lactating animal, and stage of lactation [4,5]. Different studies stated that the animal origin is the major factor behind the different physicochemical properties of milk [6,7]. Animal breed and genotype is strongly involved in the determination of lactation yield and the physicochemical properties of milk [8,9,10].
High altitude areas are characterized by low barometric pressure, hypoxia, cold weather, and increased UV radiation. The climate characteristics of the high altitude affect the physiology and genetics of the living humans and animals. The effects of living at high altitude include polycythemia, increase of intracellular oxidative enzymes, hyperventilation, hypertension, and induction of genetic changes [11].
The nutritional value of human and animal milk includes its concentration of proteins, lipids, carbohydrates, vitamins, minerals, and energy. The milk nutritional value is affected by animal health, nutrition, breed and genotype, climate conditions, and altitude [12,13]. Milk composition has different impacts on human health such as the unmodified cow milk which is deficient for the nutrition of infant and its proteins causes allergy with prevalence ranging from 2 to 7%. On the other hand, goat milk is considered as a good source for infant nutrition. Milk allergy is well known to be the cause because of its proteins and lactose. However, fermented dairy products possess anti-inflammatory activities in humans not suffering from milk allergy [14,15]. Full fat milk has no threatening effects on the cardiovascular health and it is an important source of fat-soluble vitamins such as vitamin D and vitamin K [16].
The aim of this study was to investigate the effect of animal origin and farm altitude on some physicochemical properties and the concentration of three major minerals in milk samples. The studied parameters were the pH, conductivity, specific gravity, moisture, ash, TDS, sodium, potassium, and calcium.
2 Materials and methods
2.1 Study design
Because this study compared between two groups (low and high altitudes) and between three groups (camels, goats, and sheep), it can be classified as descriptive, cross-sectional, and case–control research design. The major disadvantages of the cross-sectional and case–control studies are that their causal effects and risk factors cannot be determined and their conclusions cannot be generalized. Noteworthy, the cross-sectional and case–control study design advantages include the following: they describe the variables and their distribution pattern, and they open doors for survey studies [17]. With regard to the descriptive research designs, they describe the distribution of a small number of variables without emphasizing any causal effects. The advantages of the descriptive studies are that they are easy to conduct, inexpensive, they are useful in evaluating the burden of diseases and environmental problems, and they are useful for the governmental planning sectors. The major disadvantage of the descriptive studies is the difficulty in drawing a reliable conclusion [18].
2.2 Ethical clearance
This study was academically, legally, and ethically approved from the department of chemistry at King Khalid University and the samples were collected from the farmers after obtaining an oral informed consent.
2.3 The study samples
Nineteen fresh milk samples were collected from three lactating animals: camels (Camelus dromedaries) (8), goats (Capra aegagrus hircus – Nagdi breed) (5), and sheep (Ovis aries – Rufidi breed) (6). The samples were collected from farms located at 14 m above sea level (four camel milk samples, two goat milk samples, and three sheep milk samples) and at 2,110 m above sea level (four camel milk samples, three goat milk samples, and three sheep milk samples). The farms were in Abha (Asir region) and Aldarb (Jazan region) at the south western part of Saudi Arabia (Figure 1). The altitudes were determined using the Google earth software [19].
Sample collections sites. The milk samples were collected from two farms located at two different altitudes: 14 m above sea level and 2,110 m above sea level. The figure was created from the Google earth program at: http://srtm.csi.cgiar.org.
The samples were collected during October–December 2019, the animals were fed on similar diet and their milk cycle was the same. However, some samples were excluded because of the small number and the different diet and milk cycle.
The analysis of all the studied parameters was done twice for the purpose of excluding the hand and machine errors.
2.4 Measurement of the pH
The determination of the pH of the milk samples was carried out using a calibrated pH meter (HI 8,314 HANNA, Italy). About 30 mL of each milk sample were used for the determination of its pH value and the pH meter was calibrated by two buffers with pH 9 and pH 7.
2.5 Measurement of conductivity
About 20 mL of each milk sample were used to measure its conductivity value using a calibrated conductometer (Metrohm, 712 conductometer, Switzerland).
2.6 Determination of the moisture percentage
Five grams of each milk sample were weighed (A), heated at 70°C for 1 h, and at 105°C for 6 h. Heating at 70°C was a modification for the original method of Bradley [20], so as to avoid strong boiling of the milk samples. After that, the milk was weighed (B) and the moisture percentage was determined by the following equation:
2.7 Determination of TDS percentage
To measure the TDS of the milk samples, 5 g of each milk sample (A) was heated for 1 h at 70°C and for 6 h at 120°C [20]. The water evaporated milk was weighed (B) and the TDS were calculated according to the equation:
2.8 Determination of the ash percentage
To determine the ash percentage, the starting milk sample was the sample of the moisture determination. The moisture-determined sample was heated to 600°C in a furnace oven and the ash percentage was calculated by dividing the weight of the ash (C) by the weight of the milk sample (A) as follows [21]:
2.9 Calculation of the specific gravity
The ratio of the milk density to the water density is known as the specific gravity of the milk. The specific gravity of the milk samples was determined by weighing 50 mL of each milk sample (A). The density of the milk was calculated by dividing the weight of the milk sample by the volume (50). The density of the milk was divided by the density of the water (1) to obtain the specific gravity of the milk samples [22].
2.10 Measurement of calcium, potassium, and sodium
Two steps were followed to measure the concentration of the calcium, potassium, and sodium according to the method of Singh et al. [23]. The mineral analysis was divided into digestion and measurement steps.
The digestion step was carried out using the microwave (Anton Paar Multiwave ECO). About 0.5 mL of each milk sample was mixed with 4 mL of concentrated nitric acid and 2 mL of hydrogen peroxide. The mixture was introduced into the microwave and the temperature was set at 125°C and the power was 800 W for 1 h as follows: increase of the power to 800 W for 5 min, application of constant pressure for 40 min at 800 W, and cooling for 15 min. Finally, the digested samples were diluted with 1% nitric acid to 25 mL using volumetric flasks.
The three minerals were measured in the digested milk samples using the JENWAY flame photometer (PFP7 Flame Photometer).
For the creation of the standard curves, the following standards were prepared; the standards of the calcium were 12.5, 25, 50, 100, and 200 part per million (ppm), potassium standards were 2, 4, 8, 16, and 32 ppm, while the standards of sodium were 1.25, 2.5, 5, and 10 ppm. The emission wavelengths of the calcium, potassium, and sodium were 622 nm (orange), 766 nm (violet), and 589 nm (yellow), respectively.
Quality control samples were prepared using any sample (C ppm). A spike concentration (S ppm) was added to the sample as follows: 50 ppm of calcium, 16 ppm of potassium, and 5 ppm of sodium. The concentration of the prepared quality control samples was determined (Q ppm). The recovery percentage was calculated by the following equation:
The standards, quality control samples, and the milk samples were introduced to the flame photometer and the emitted wavelength was measured. The concentration of the quality control samples and the samples was determined from the created standard curves. The results of the samples were approved if the R 2 of the standard curves was more than 0.98 and if the recovery percentage of the quality control samples was more than 75%.
2.11 Statistical analysis
The Least Significant Difference (LSD) post hoc test of the Analysis of Variance (ANOVA) of the SPSS statistical program was used for the analysis of the results. The difference between the mean values of the parameters was considered significant if the p-value was ≤0.05. Multivariate analysis of the general linear model was carried out to investigate the influence of the animal origin and altitude on the measured parameters.
Moreover, the samples were classified according to the results of the studied parameters compared to their classification according to the origin and altitude. The samples were clustered using the agglomerative clustering of the SPSS.
3 Results
3.1 pH
The pH values of the milk samples were insignificantly affected by the animal origin and the altitude (Tables 1 and 2, and Figure 2).
The results of the studied parameters (mean ± SD) in the milk samples from different origins and altitudes
| Parameter | Sheep milk | Goat milk | Camel milk | |||
|---|---|---|---|---|---|---|
| High altitude | Low altitude | High altitude | Low altitude | High altitude | Low altitude | |
| Number of samples | 3 | 3 | 3 | 2 | 4 | 4 |
| pH | 6.54 ± 0.11 | 6.24 ± 0.37 | 6.54 ± 0.07 | 6.23 ± 0.26 | 6.64 ± 0.07 | 6.39 ± 0.16 |
| Conductivity mS/cm | 4.54 ± 0.51 | 5.29 ± 1.11 | 5.56 ± 0.15 | 6.93 ± 0.60 | 5.98 ± 0.85 | 9.55 ± 1.46 |
| Moisture% | 73.57 ± 7.90 | 74.20 ± 0.00 | 84.3 ± 4.42 | 81.5 ± 0.14 | 88.17 ± 2.75 | 88.75 ± 1.06 |
| TDS% | 26.50 ± 7.85 | 25.80 ± 0.00 | 14.07 ± 6.43 | 18.43 ± 0.25 | 12.24 ± 3.70 | 11.21 ± 1.09 |
| Ash% | 4.67 ± 0.96 | 0.51 ± 0.00 | 3.51 ± 0.65 | 0.58 ± 0.15 | 2.64 ± 0.12 | 0.32 ± 0.07 |
| Specific gravity | 1.04 ± 0.000 | 1.03 ± 0.000 | 1.027 ± 0.001 | 1.013 ± 0.004 | 1.025 ± 0.002 | 1.015 ± 0.007 |
| Calcium (Ca) (ppm) | 574.5 ± 10.39 | 543.17 ± 37.53 | 568.5 ± 0.50 | 521.75 ± 0.35 | 568.5 ± 0.41 | 564.87 ± 30.64 |
| Potassium (K) (ppm) | 1129.8 ± 237.9 | 1404.7 ± 309.3 | 1610.8 ± 472.3 | 1147 ± 509.8 | 2149.5 ± 172.9 | 1532.3 ± 413.5 |
| Sodium (Na) (ppm) | 348.17 ± 98.3 | 408 ± 125.5 | 253.8 ± 133.1 | 246.5 ± 140.0 | 500.0 ± 66.4 | 519.8 ± 102.8 |
The pH, ash percentage, specific gravity, calcium, and potassium were increased in the high altitude while the conductivity decreased in all the milk types. The moisture percentage and sodium decreased in the high altitude in the camel and sheep milk samples whereas it increased in the goat milk. The TDS increased by the increase of the altitude increase in the camel and sheep milk. Regarding the goat milk, the TDS decreased by the increase of the altitude. The potassium concentration increased in the high altitude milk samples from the camels and goats while it decreased in the sheep milk. The results showed that the milk samples are rich in potassium rather than the calcium.
The variations between the mean values of the studied parameters in the different study groups using the LSD post hoc test of ANOVA test
| Parameter | p-value | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| Goat− | Camel− | Sheep+ | Goat+ | Camel+ | |||||
| Sheep− | Sheep− | Goat− | Sheep− | Sheep+ | Goat− | Sheep+ | Goat+ | Camel− | |
| pH | 0.95 | 0.33 | 0.33 | 0.09 | 0.97 | 0.10 | 0.61 | 0.59 | 0.15 |
| Conductivity mS/cm | 0.024 | <0.001 | 0.001 | 0.31 | 0.224 | 0.087 | 0.09 | 0.61 | <0.001 |
| Moisture% | 0.14 | 0.01 | 0.14 | 0.88 | 0.02 | 0.51 | 0.003 | 0.32 | 0.89 |
| TDS% | 0.18 | 0.02 | 0.19 | 0.88 | 0.02 | 0.37 | 0.008 | 0.67 | 0.83 |
| Ash% | 0.91 | 0.74 | 0.66 | <0.001 | 0.03 | <0.001 | 0.002 | 0.087 | 0.001 |
| Specific gravity | <0.001 | 0.001 | 0.41 | 0.004 | <0.001 | <0.001 | <0.001 | 0.42 | 0.005 |
| Calcium (Ca) (ppm) | 0.29 | 0.20 | 0.035 | 0.09 | 0.74 | 0.03 | 0.72 | 1 | 0.81 |
| Potassium (K) (ppm) | 0.44 | 0.64 | 0.23 | 0.36 | 0.12 | 0.17 | 0.002 | 0.07 | 0.03 |
| Sodium (Na) (ppm) | 0.12 | 0.20 | 0.012 | 0.51 | 0.30 | 0.94 | 0.09 | 0.01 | 0.8 |
+High altitude milk.
−Low altitude milk.
The significance level of the compared mean values of the studied parameters was set at the level of 95% (p-value ≤ 0.05).
Significant effects of animal origin and altitude on the studied parameters. According to the multivariate analysis, the conductivity, ash, and specific gravity were significantly affected by the milk origin and altitude.
3.2 Conductivity
The conductivity mean values were decreased in the high altitude milk samples. However, the significant decrease was reported in the camel milk samples only. Concerning the effect of animal origin at the two altitudes, it insignificantly affected the conductivity at low altitude while it significantly affected the conductivity at high altitude (Tables 1 and 2, and Figure 2).
3.3 Moisture%
The moisture percentage was insignificantly decreased in the high altitude camel and sheep milk samples while it insignificantly increased in the high altitude goat milk samples. When comparing the camel and sheep milk samples, their moisture percentages were significantly different at high and low altitudes while the moisture percentage of the goat and sheep milk samples was significantly different at high altitude only (Tables 1 and 2, and Figure 2).
3.4 TDS%
The TDS% insignificantly increased in the high altitude camel and sheep milk samples while it insignificantly decreased in the goat milk samples from high altitude. There was significant variation between the camel and sheep milk samples in the low and high altitude while the significant variation between the goat and sheep milk in the low altitude only (Tables 1 and 2, and Figure 2).
3.5 Ash percentage
The high altitude significantly increased the ash percentage in the camel, goat, and sheep milk samples. There were significant variations between the mean ash percentage of the milk samples from the camels and sheep and between the goats and sheep living at the high altitude (Tables 1 and 2, and Figure 2).
3.6 Specific gravity
The high altitude significantly increased the specific gravity in the camel, goat, and sheep milk samples. There were significant variations between the specific gravity of the milk samples from camels and sheep and between goats and sheep living at the low and high altitudes (Tables 2 and 3, and Figure 2).
The effects of the milk animal origin and altitude on the studied parameters using the multivariate analysis
| Parameter | Significance | |
|---|---|---|
| Origin | Altitude | |
| pH | 0.33 | 0.15 |
| Conductivity mS/cm | <0.001 | <0.001 |
| Moisture% | 0.05 | 0.87 |
| TDS% | 0.19 | 0.67 |
| Ash% | <0.001 | <0.001 |
| Specific gravity | <0.001 | 0.003 |
| Calcium (Ca) (ppm) | 0.11 | 0.07 |
| Potassium (K) (ppm) | 0.25 | 0.048 |
| Sodium (Na) (ppm) | 0.10 | 0.27 |
3.7 Minerals
Standard curves. The R 2 values of the standard curves of the calcium, potassium, and sodium were 0.9923, 0.9995, and 0.9867, respectively.
Recovery percentages of the quality control samples. The recovery percentages of the quality control samples for the calcium, potassium, and sodium were 76.92, 89.9, and 86.4%, respectively.
Calcium. The calcium concentration in the camel and sheep milk samples was insignificantly increased in the high altitude compared to its concentration in the milk samples from the low altitude. The altitude significantly increased the concentration of calcium in the goat milk samples. The concentration of the calcium in the camel milk and goat milk samples from the low altitude was significantly different (Tables 1 and 2, and Figure 2).
Potassium. The concentration of the potassium increased in the high altitude milk samples from goats and camels with significant increase in the camel milk samples. There were insignificant variations between the potassium concentrations in the milk samples from camels and goats in the high and low altitudes while there was significant variation between the milk samples of camels and sheep living at the high altitude. The potassium concentration in the milk samples was very high compared to the calcium and sodium (Tables 1 and 2, and Figure 2).
Sodium. The altitude insignificantly affected the concentration of the sodium in the different milk samples. However, the concentration of the sodium decreased in the high altitude in the camel and sheep milk samples while it increased in the goat milk samples. Significant variation between the sodium concentrations was reported between the milk samples from camels and goats living at high altitude (Tables 1 and 2, and Figure 2).
3.8 Multivariate analysis
The multivariate analysis showed that the animal origin significantly affected the conductivity, moisture, specific gravity, and ash percentage. The altitude influenced significantly the conductivity, specific gravity, and ash beside the potassium (Table 3).
3.9 Clustering analysis
According to the milk origin and altitude, the samples were classified into six groups. The six groups were (1) high altitude camel milk, (2) low altitude camel milk, (3) high altitude goat milk, (4) low altitude goat milk, (5) high altitude sheep milk, and (6) low altitude sheep milk. The clustering of the milk samples according to the results of the studied parameters was to some extent different than that of the milk origin and altitude. For example, the second level from the top of the dendrogram (Figure 3) clustered the sample number 4, 3, 9, and 5 in one cluster while they were from three different groups according to the milk origin and altitude (1, 2, and 3).
The agglomerative clustering of the milk samples according to the results of the studied parameters compared to the animal origin and altitude classification. The milk samples were grouped into six groups according to the origin and altitude as follows: 1 for camel milk from high altitude;, 2 for camel milk from low altitude,; 3 for goat milk from high altitude;, 4 for goat milk from low altitude,; 5 for sheep milk from high altitude,; and 6 for sheep milk from low altitude.
Comparison between the findings of this study and the reviewed literature without considering the altitude effect
| Parameter | This study | Previous studies | |||||
|---|---|---|---|---|---|---|---|
| Sheep | Goat | Camel | Sheep | Goat | Camel | Reference | |
| pH | 6.39 ± 0.21 | 6.39 ± 0.23 | 6.54 ± 0.16 | 6.38 ± 0.08 | 6.13 ± 0.11 | [24] | |
| Conductivity (mS/cm) | 4.92 ± 0.88 | 6.11 + 0.76 | 7.62 ± 2.02 | 10.8 ± 2.07 | [2] | ||
| Moisture% | 73.62 ± 4.55 | 83.26 ± 1.38 | 88.39 ± 1.38 | 80.7 | [25] | ||
| TDS% | 26.15 ± 4.98 | 15.73 ± 5.05 | 11.43 ± 2.19 | 14.25 ± 1.16 | 13.65 ± 1.40 | [24] | |
| 12.9 ± 1.01 | [2] | ||||||
| 19.3 | [25] | ||||||
| Ash% | 2.59 ± 2.39 | 2.37 ± 1.69 | 1.56 ± 1.28 | 0.73 ± 0.07 | 0.73 ± 0.03 | [24] | |
| 1.04 ± 0.13 | [2] | ||||||
| <0.9 | [25] | ||||||
| Specific gravity | 1.035 ± 0.01 | 1.021 ± 0.01 | 1.019 ± 0.01 | 1.04 ± 0.00 | 1.03 ± 0.00 | [24] | |
| Calcium (Ca) (ppm) | 563 ± 21.8 | 549.8 ± 25.6 | 567.5 ± 16.8 | 644 ± 76.6 | [2] | ||
| 850–1980 | [26] | ||||||
| 1,950–2,000 | 1,320–1,340 | 1,140–1,160 | [27] | ||||
| 1,060–1,920 | [28] | ||||||
| Potassium (K) (ppm) | 1258 ± 303 | 1482 ± 389 | 1,864 ± 511 | 1,400–2,420 | [26] | ||
| 1,360–1,400 | 1,510–1,820 | 1,440–1,650 | [27] | ||||
| 1,350–2,350 | [28] | ||||||
| Sodium (Na) (ppm) | 378 ± 106 | 250 ± 118 | 516 ± 78.4 | 380–580 | [26] | ||
| 440–580 | 410–594 | ≥590 | [27] | ||||
| 340–500 | [28] | ||||||
The results of the literature were compared to the results of the sheep, goat, and camel milk of this study irrespective of the altitude they lived in.
4 Discussion
The high altitude was characterized by increased pH, ash percentage, specific gravity, calcium, and concerning the potassium while it was characterized by decreased conductivity in all the milk types. However, the pH and the potassium concentration difference were insignificant while the ash percentage and the specific gravity differences were significant. The variations of the high and low altitude calcium and potassium were significant in the goat and camel milk samples, respectively. The animal origin had significant effects on the conductivity, moisture%, TDS%, ash%, specific gravity, and calcium and insignificant effects on the pH, potassium, and sodium. However, the multivariate analysis showed fewer significant effects of the milk animal origin and altitude compared to the one-way ANOVA test. The difference between the results of the ANOVA and the multivariate analysis is due to the post hoc test (LSD) of the ANOVA. The differences in the values of the studied parameters can be referred to the different animal origins and farm altitudes. Effect of animal origin on the physicochemical properties of milk samples; Legesse et al. [24] studied camel, goat, and cow milk samples from Ethiopia and found that the pH of the goat and camel milk samples was 6.38 ± 0.08 and 6.13 ± 0.11, respectively, with insignificant difference while the specific gravity values were 1.04 ± 0.00 and 103 ± 0.00, respectively, and also with insignificant variation (Table 4). The TDS% of the goat and camel milk samples were 14.25 ± 1.16 and 13.65 ± 1.40, respectively. The ash percentage of the Ethiopian goat and camel milk samples was 0.73 ± 0.07 and 0.73 ± 0.03, respectively. The conclusion of Legesse et al. study is that there is no variation between camel goat milk except the TDS% which is high in the goat milk compared to the camel milk. However, this study reported insignificant variation between the TDS% of the camel and goat milk samples whereas there was significant variation between the TDS% of the camel and sheep milk samples. In general, the study of Legesse et al. is comparable to the samples from the high altitude because the altitude of the study area of their study is 1,803 m above sea level. A Pakistani research (Zhao et al., 2020) studied buffalo, cow, and goat milk samples with regard to their pH, conductivity, moisture%, TDS%, specific gravity, calcium, potassium, and sodium [2]. The findings of the Pakistani study were to some extent similar to the findings of this study with slight differences except for the conductivity (10.8 ± 2.07 Pakistani compared 6.93 ± 0.60 in low altitude of this study and 5.56 ± 0.15 at the high altitude), TDS% (12.9 ± 1.01 Pakistani study compared to 18.43 ± 0.25 at low altitude and 14.07 ± 6.43 at high altitude), and ash% (1.04 ± 0.13 Pakistani compared to 0.58 ± 0.15 at low altitude and 3.51 ± 0.65 at high altitude of our study). The differences between the Pakistani study and this study may be due to the different geographical and environmental conditions. As mentioned by the authors of the Pakistani study, their mineral results are less than the WHO standards and comparable to some previous studies. Compared to the results of this study, the results of the minerals of the Pakistani study were comparable with regard to the calcium concentration only (644 ± 76.6 in the Pakistani study compared to 521.75 ± 0.35 and 568.5 ± 0.50 in the low and high altitude milk samples, respectively). Sabahelkhier et al. compared the pH, moisture%, TDS%, ash%, and specific gravity of milk samples from camel, goat, sheep, and cow (Table 4) [25]. The results of this study are different from the results of Sabahelkhier et al. with respect to the values of the sheep milk TDS (19.3% in Sabahelkhier study compared to 25.80 ± 0.00 or 26.50 ± 7.85 in this study), and moisture% (80.7% in Sabahelkhier study compared to 74.20 ± 0.00 or 73.57 ± 7.90 in this study), while the ash% of the high altitude milk samples (2.64, 3.51, and 4.67%) are not comparable to the ash% of Sabahelkhier study (<0.9%). The differences between the study of Sabahelkhier et al. and this study may be due to the different breeds, environmental conditions, and altitude. Depending on the review article of Abbas et al., about the physicochemical properties of goat milk, the calcium concentration of this study is very low compared to the previous studies which may be referred to the recovery percentage in our assay (76.92%) and to the differences in the breeds and altitudes (Table 4) [26]. However, the ranges of the calcium, potassium, and sodium in goats milk were (850–1,980 mg/L), (1,400–2,420 mg/L), and (380–580 mg/L), respectively [26]. The results of the potassium and sodium of this study are compatible to the results of the previous studies. In a review article about the nutritional value of milk from different origin, Barłowska et al. reported that the source of the milk determines its nutritional value and its industrial uses [27]. According to Barłowska et al. the concentration of calcium in the camel, goat, and sheep is (1,140–1,160 mg/L), (1,320–1,340 mg/L), and (1,950–2,000 mg/L), respectively (Table 4) [27]. The calcium results of this study are less than the ranges of the previous studies as mentioned by Barłowska et al. The potassium and sodium results of this study are within the ranges mentioned by Barłowska et al. [27]. The potassium ranges in the milk of camels, goats, and sheep in the review article of Barłowska et al. were (1,440–1,650 mg/L), (1,510–1,820 mg/L), and (1,360–1,400 mg/L), respectively. The sodium ranges in camel, goat, and sheep milk samples of the mentioned review article were (≥590 mg/L), (410–594 mg/L), and (440–580 mg/L), respectively. The results of the potassium and sodium of this study are comparable to the results mentioned in the review article of Barłowska et al. (Table 4) [27]. Another review article reported that the calcium, potassium, and sodium concentration ranges in goats milk are (1,060–1,920 mg/L), (1,350–2,350 mg/L), and (340–500 mg/L), respectively, while their concentration ranges in the sheep milk are (1,360–2,000 mg/L), (1,740–1,900 mg/L), and (290–310 mg/L), respectively (Table 4) [28]. The results of the minerals concentration in the milk samples prove the effect of the milk animal source. Similar to the finding of this study about the concentration of the milk potassium, all the reviewed previous studies reported high range of potassium concentration compared to the calcium and potassium.
Any region with elevation more than 1,500 m above sea level is considered as high altitude area. High altitude is characterized by low atmospheric pressure, hypoxia, low temperature, high amount of rain falls, and ultraviolet radiation compared to low or sea level altitudes [29,30]. The climate conditions of high altitude areas affect the health, physical, and physiological activities of the living animals which affects the amount and quality of their products [31,32,33]. This study reported significant effects of high altitude because of its climate conditions on the physicochemical properties and mineral content of different sources of milk samples. Previously, different studies reported significant effects of the geographical origin and the seasonal variations on the pH, moisture%, TDS%, proteins%, fats%, lactose%, and density [34,35,36,37,38].
As this study is a descriptive research, its findings cannot be generalized due to the small number of samples in the overall study and in the subgroups. Still, descriptive research studies are very important in opening windows for new survey research studies.
5 Conclusion
The one-way ANOVA test showed that (1) the altitude had significant effects on the conductivity, ash%, specific gravity, calcium, and potassium; (2) the animal source significantly affected the conductivity, ash%, specific gravity, calcium, potassium, moisture percentage, TDS%, and sodium.
The multivariate analysis results revealed fewer significant effects of the altitude and animal origin on the studied parameters as follows: (1) the altitude significantly affected the conductivity, ash%, specific gravity, and potassium (calcium was excluded); (2) the animal origin of the milk had significant effect on the conductivity, ash%, moisture%, and specific gravity (calcium, potassium, TDS%, and sodium were excluded).
The differences in the results of the multivariate analysis and ANOVA test are due to the (LSD) post hoc test of ANOVA.
Acknowledgement
The authors extend thier appreciation to professor Hamed Ghramh for financing this research and for his encouragement.
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Funding information: This study was funded by the Research Center for Material Science at King Khalid University under the grant number KKU/RCAMS/22.
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Author contributions: AA, QN, and AM did the practical work and approved the final copy of the manuscript. BA did the clustering analysis and created two figures. MM and BE designed the research, statistically analyzed the results, and revised and approved the final copy of the manuscript.
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Conflict of interest: The authors declare no conflict of interest
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Consent for publication: The authors agree that the open chemistry Journal has the right to publish this article.
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Ethical approval: This study was academically, legally, and ethically approved from the department of chemistry at King Khalid University and the samples were collected from the farmers after obtaining an oral informed consent.
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Data availability statement: The data of this research are available for the journal.
References
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