Geographical Variation in the Mineral Profiles of Camel Milk from Xinjiang: Implications for Nutritional Value and Species Identification

Abstract

To investigate the geographical and species differences regarding mineral element content of camel milk, this research used camel milk from the Tacheng, Altay, and Ili regions of Xinjiang and cow milk, goat milk, and horse milk from the Tacheng region as subjects. The contents of 22 mineral elements were measured using inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The results showed that the contents of macro elements Ca, P, K, and Na in camel milk were significantly higher than those in other milk sources (p < 0.01). The contents of trace elements such as Se, Sr, and Ni were very significantly higher than those in other milk sources (p < 0.01). The content of 12 mineral elements in camel milk was very significantly higher than in other types of milk (p < 0.01). Principal component analysis (PCA) and factor analysis emphasized the relationship between element distribution and different milk sources, and the linear discriminant analysis (LDA) model could identify the species type of milk. Geographical analysis indicated that trace elements such as Sr, Ni, and Cr were highly significantly enriched in Tacheng camel milk (p < 0.01). The established LDA model achieved traceability of the geographical origin of Xinjiang camel milk. This research reveals the mineral nutritional advantages of camel milk and its geographical differentiation patterns, providing theoretical support for exploring the functional properties of camel milk and for identifying species and regions through minerals. It is important to promote the upgrading of the specialty dairy product industry.

1. Introduction

Dairy products, as an important source of dietary nutrition for humans, have consistently been a research hotspot in food science due to their nutritional value and health benefits. In recent years, with China’s continuous economic development and the steady increase in per capita disposable income, per capita dairy consumption levels have also risen accordingly. As one of the important milk sources in desert and semi-desert regions, camel milk, favored by consumers for its rich nutritional components and good digestibility has gradually gained global attention for its unique nutritional composition and potential health benefits [1,2]. Camel milk contains not only abundant protein, unsaturated fatty acids, amino acids, and vitamins, but its mineral element profile also exhibits significant characteristics [3]. The protein content in camel milk is comparable to that of cow milk, typically ranging from 3.0% to 3.4% [4]. Its lipid profile is characterized by a high content of long-chain unsaturated fatty acids, particularly polyunsaturated fatty acids (PUFA), which account for a significant proportion of the total fatty acids [5]. It has been reported that camel milk contains higher levels of cysteine and tryptophan compared to cow milk, while differences are also observed in other amino acids such as lysine [5]. It is particularly superior to cow milk and goat milk in the content of trace elements such as zinc and iron, while its balance ratio of calcium and magnesium is closer to human physiological needs [6]. Furthermore, besides its unique nutritional components, the enzymatic hydrolysates of camel milk possess distinct biological functions that can assist in and alleviate various diseases [7]. Studies indicate that camel milk has healthcare effects including anti-inflammatory and immunomodulatory effects, as well as the ability to alleviate diabetes, liver injury, colitis, and kidney disease [8,9,10], providing a scientific basis for its development as a high-value-added health food.

Although research on the nutritional value of dairy products is relatively comprehensive, systematic horizontal comparison of mineral element composition across different types of milk, such as camel, horse, and cow milk, remains insufficient. Meanwhile, growing consumer demand for personalized nutrition and functional foods is driving the dairy market toward diversification and health-oriented products. In this context, a detailed analysis of the mineral characteristics of camel milk and their correlation with human health could address gaps in fundamental research and offer valuable insights for product development and nutritional applications. This research aims to systematically compare the differences in mineral element content between camel milk and traditional dairy products (cow milk, goat milk, horse milk), as well as the variations in mineral element content of camel milk across different geographical regions. The study employs modern analytical techniques, including inductively coupled plasma mass spectrometry (ICP-MS) and inductively coupled plasma optical emission spectrometry (ICP-OES), to characterize these differences. It focuses on revealing the distribution patterns of mineral elements in camel milk and their nutritional significance. The findings will provide a scientific basis for further exploring the functional properties of camel milk and optimizing the structure of dairy product consumption while also offering a theoretical foundation for the sustainable development of camel milk resources and precision nutrition strategies.

2. Materials and Methods

2.1. Experimental Time and Location

Animal experiments were approved by the Animal Welfare and Ethics Committee of Xinjiang Agricultural University (2024018).

The milk samples utilized in this study were collected between 15 and 19 May 2024, from three distinct geographical locations in Xinjiang, China: Yumin County (82°59′ E, 46°12′ N), Tacheng City; Fuhai County (87°30′ E, 47°00′ N), Altay Prefecture; and Huocheng County (80°52′ E, 44°02′ N), Ili Prefecture. These sites are separated by more than 400 km and exhibit diverse topographical and ecological conditions, including variations in soil mineral composition, water sources, and climate, which are known to influence the mineral content of milk from grazing livestock.

2.2. Milk Sample Collection and Preservation

For the current experiment, conducted in Yumin County, Tacheng City, Xinjiang, eight samples of Bactrian camel milk (Camel Milk group), cow milk (Cow Milk group), goat milk (Goat Milk group), and horse milk (Horse Milk group) were collected. All samples were obtained from lactating animals that were grazing without supplementary feed and were within 90–120 days of lactation.

Additionally, eight samples of Bactrian camel milk were collected under the same conditions (grazing without supplementary feed, lactation period 90–120 days) in Fuhai County, Altay Prefecture, and Huocheng County, Ili Prefecture (referred to as Altay and Ili, respectively). After collection, the milk samples were aliquoted into 5 mL sterile cryovials, immediately placed in liquid nitrogen for preservation, transported to the laboratory, and stored at −80 °C for subsequent analysis.

2.3. Measured Indicators and Methods

2.3.1. Instruments and Equipment

The analysis and sample preparation procedures involved in this study required the use of a series of high-precision instruments (

Table 1. Main Instruments.

Instrument Type	Model	Manufacturer
Inductively Coupled Plasma Mass Spectrometer (ICP-MS)	ICP-MS6880	Shanghai Meixi Instrument Co., Ltd. (Shanghai, China)
Inductively Coupled Plasma Optical Emission Spectrometer (ICP-OES)	SH-ICP1100	Qingdao Shenghan Chromatography Technology Co., Ltd. (Qingdao, China)
Balance	360EP&ES	Shanghai Meixi Instrument Co., Ltd. (Shanghai, China)
Microwave Digestion System	MID14	Shanghai Zhuoguang Instrument Co., Ltd. (Shanghai, China)
Pressure Digestion Vessel	CEM55ml	Zhengzhou Zhuocheng Instrument Technology Co., Ltd. (Zhengzhou, China)
Constant Temperature Drying Oven	JC-9070A/JC-9070AE	Qingdao Jingcheng Instrument Co., Ltd. (Qingdao, China)
Ultrasonic Water Bath	SCQ-HD300A	Shanghai Shengyan Ultrasonic Instrument Co., Ltd. (Shanghai, China)
Homogenizer	Daxluot-96	Shanghai Daluo Scientific Instrument Co., Ltd. (Shanghai, China)
Muffle Furnace	JC2-12-10A	Qingdao Jingcheng Instrument Co., Ltd. (Qingdao, China)

).

2.3.2. Reagents and Chemicals

Reagents: nitric acid (HNO₃), guaranteed reagent (GR) grade, Knowles Reagent; all water used in the experiment was GR grade. Element standards: single-element standard solutions (1000 mg/L) of Ca, P, K, Na, Mg, Zn, Fe, Sr, Cu, Ba, Ni, Mn, Cr, Se, As, Mo, V, Sb, Cd, Be, Co, and Ti, purchased from the National Analysis Center for Nonferrous Metals and Electronic Materials.

2.3.3. Sample Pretreatment

The milk samples were thawed and shaken thoroughly. A 0.5 g aliquot of the milk sample was weighed and placed into a microwave digestion vessel, and 6 mL of nitric acid solution was added. After capping and standing for 1 h, the vessel was placed in the microwave digestion system for gradient digestion (First stage: temperature 120 °C, holding time: 5 min; Second stage: temperature 150 °C, holding time: 5 min; Third stage: temperature 190 °C, holding time: 20 min). After digestion and cooling, the vessel was removed. The inner cap was rinsed with a small amount of water, and the digestion vessel was placed in an ultrasonic water bath for ultrasonic degassing for 5 min. The solution was then diluted to volume with pure water for analysis. A blank test was performed simultaneously.

2.3.4. Preparation of Standard Solutions

Elements Cr, V, Se, Co, Ni, As, Mo, and Sb were detected by inductively coupled plasma mass spectrometry (ICP-MS). Different volumes of element standards were accurately pipetted and diluted to 50 mL with 1% nitric acid to prepare standard curves with six concentration gradients: V, Cr, As, Se, Co, Ni, Be, Cd, Ti: 0, 1.00, 5.00, 10.00, 30.00, 50.00 μg/L; Mo, Sb: 0, 0.100, 0.500, 1.00, 3.00, 5.00 μg/L. Elements Ca, K, Mg, Na, Zn, Fe, Cu, Mn, Sr, and P were detected by inductively coupled plasma optical emission spectrometry (ICP-OES). Similarly, they were diluted to 50 mL with 1% nitric acid to prepare standard curves with six concentration gradients: Sr: 0, 0.0500, 0.200, 0.500, 0.800, 1.00 mg/L; Ca, K, Mg, Na, P: 0, 5.00, 20.0, 50.0, 80.0, 100 mg/L; Fe and Zn: 0, 0.250, 1.00, 2.50, 4.00, 5.00 mg/L; Ba, Mn, and Cu: 0, 0.0250, 0.100, 0.250, 0.400, 0.500 mg/L.

2.3.5. Instrumental Conditions

Inductively coupled plasma mass spectrometry (ICP-MS) operating reference conditions: RF power: 1500 W; Plasma gas flow: 15 L/min; Carrier gas flow: 0.80 L/min; Sampling depth: 8~10 mm; Auxiliary gas flow: 0.40 L/min; Helium gas flow: 4~5 mL/min; Nebulizer chamber temperature: 2 °C; Points per peak: 1~3; Sample uptake rate: 0.3 r/s; Replicates: 2~3.

Inductively coupled plasma optical emission spectrometry (ICP-OES) operating reference conditions: Power: 1150 W; Plasma gas flow: 15 L/min; Auxiliary gas flow: 0.5 L/min; Nebulizer gas flow: 0.65 L/min; Analysis pump speed: 50 r/min.

2.3.6. Data Processing

Experimental data were collated using Microsoft Office 2019 (Microsoft, Redmond, WA, USA). Results are expressed as mean standard deviation. Differences between samples were analyzed using SPSS Statistics Software Version 27.0 (IBM, New York, NY, USA) through one-way analysis of variance (ANOVA) and Duncan’s multiple range test. Statistical significance was set at p < 0.05, and extreme significance was set at p < 0.01. The images in the text were created using OriginLab Origin 2024 (Version 2024, OriginLab Corporation, Northampton, MA, USA). Factor analysis, principal component analysis (PCA), and linear discriminant analysis (LDA) were employed to explore the underlying structure and patterns within the mineral content data. PCA was used to reduce dimensionality and visualize natural groupings among samples based on mineral composition, while LDA was applied to maximize separation among pre-defined milk type groups and identify the most discriminant minerals. Factor analysis aided in interpreting latent variables influencing mineral profiles.

3. Results

3.1. Mineral Analysis of Different Species

3.1.1. Comparative Analysis of Macro Element Contents

We compared the macro element composition of camel, cow, goat, and horse milk, and the results revealed distinct nutritional profiles among them (

Table 2. Macro Element Contents in Camel Milk, Cow Milk, Goat Milk, and Horse Milk (μg/g).

Items	Camel Milk	Cow Milk	Goat Milk	Horse Milk
K	1696.15 ± 170.49 Bb	1528.34 ± 419.58 Bb	1648.83 ± 176.02 Bb	707.60 ± 59.23 Aa
Ca	1480.22 ± 82.17 ABa	1201.19 ± 212.00 BCb	1578.72 ± 206.39 Aa	1085.39 ± 243.87 Cb
P	1189.11 ± 140.55 Cc	943.88 ± 229.82 Bb	1280.24 ± 76.10 Aa	659.82 ± 100.56 Ba
Na	663.65 ± 76.67 Cc	524.62 ± 236.20 ABb	403.69 ± 54.43 Bb	150.95 ± 7.24 Aa
Mg	92.57 ± 11.50 Bbc	97.97 ± 16.44 Ab	120.63 ± 19.41 Aa	79.83 ± 8.60 Bc
Ca/P	1.25 ± 0.11 Bb	1.29 ± 0.12 Bb	1.24 ± 0.20 Bb	1.63 ± 0.14 Aa
Na/K	0.39 ± 0.04 a	0.38 ± 0.20 a	0.25 ± 0.04 b	0.21 ± 0.02 b

Note: Data are shown as mean ± standard deviation. Different superscripts indicate statistically significant differences among groups. Different lowercase superscript letters indicate significant differences (p < 0.05), while the same or no letters indicate no significant difference (p > 0.05). Different uppercase superscript letters indicate highly significant differences (p < 0.01).

). The K level was highest in camel milk, followed by goat milk and cow milk, while horse milk had the lowest K content, which was very significantly lower than other milks (p < 0.01). The Na content in camel milk was the highest (p < 0.01), while horse milk had the lowest Na content. The Ca content differed significantly among species, with goat milk having the highest concentration and horse milk the lowest (p < 0.01). P and Mg concentrations showed a similar pattern, with the highest in goat milk and the lowest in horse milk (p < 0.05).

The calcium-to-phosphorus (Ca/P) and sodium-to-potassium (Na/K) ratios, key indicators of mineral balance and bioavailability, varied considerably across the four milk sources (Table 2). The Ca/P ratio remained relatively consistent across different species (approximately 1.24–1.29), except for horse milk, which had a significantly higher Ca/P ratio (p < 0.01). Horse milk had the lowest Na/K ratio, while camel milk had the highest (p < 0.05). Combined with Figure 1, the distribution characteristics and differences in Ca/P and Na/K among different milk sources can be observed. Panel A shows the differences in Ca/P: the value for horse milk is significantly higher than those for camel, cow, and goat milk, indicating a substantial difference in its mineral ratio. In contrast, the Ca/P ratios for camel, cow, and goat milk are relatively close with smaller differences, manifested as overlapping boxes, indicating similarity in Ca/P among these milk sources. Panel B shows the differences in Na/K: camel milk has higher values with a wider distribution, indicating some variability; cow milk has an outlier in Na/K, indicating an elevated ratio in one sample. Goat milk and horse milk have lower Na/K ratios with more concentrated distributions and less overall variability, showing greater consistency in Na/K for these milk sources. The statistical characteristics of these differences also provide a basis for subsequent comparative analysis.

3.1.2. Comparative Analysis of Trace Element Contents

The trace element contents differed markedly among camel, cow, goat, and horse milks, each exhibiting a distinct elemental profile (

Table 3. Trace Element Contents in Camel Milk, Cow Milk, Goat Milk and Horse Milk.

Items	Camel Milk	Cow Milk	Goat Milk	Horse Milk
Zn (μg/g)	3.99 ± 0.67 a	2.58 ± 0.41 b	4.61 ± 1.99 a	4.43 ± 1.11 a
Fe (μg/g)	3.77 ± 1.57 b	3.57 ± 0.48 b	6.92 ± 4.41 a	3.43 ± 0.58 b
Sr (μg/g)	2.00 ± 0.45 Bab	1.85 ± 0.39 Bb	1.11 ± 0.28 Ac	2.30 ± 0.37 Ba
Ba (ng/g)	509.60 ± 235.70	402.38 ± 69.43	447.11 ± 151.20	547.61 ± 208.33
Ni (ng/g)	158.45 ± 44.11 Aa	102.71 ± 29.99 Bb	99.06 ± 22.48 Bb	79.45 ± 14.06 Bb
Se (ng/g)	132.14 ± 46.26 Aa	29.19 ± 7.50 Bb	37.47 ± 14.05 Bb	30.22 ± 6.88 Bb
Cu (ng/g)	118.27 ± 58.21	182.69 ± 87.16	142.07 ± 67.35	192.63 ± 83.28
Cr (ng/g)	93.11 ± 37.96 Aa	37.14 ± 5.45 Bb	37.47 ± 7.19 Bb	32.26 ± 4.34 Bb
As (ng/g)	87.79 ± 48.56 Aa	30.73 ± 11.09 Bb	22.54 ± 15.27 Bb	22.55 ± 13.08 Bb
Mo (ng/g)	77.73 ± 43.80 Aa	21.11 ± 5.63 Bbc	44.88 ± 22.79 ABb	17.73 ± 4.79 Bc
Be (ng/g)	67.64 ± 49.03 Aa	8.02 ± 5.97 Bb	2.07 ± 0.65 Bb	1.47 ± 0.74 Bb
Co (ng/g)	66.00 ± 43.42 Aa	9.82 ± 5.13 Bb	2.84 ± 0.60 Bb	1.51 ± 0.09 Bb
Cd (ng/g)	65.96 ± 42.69 Aa	10.31 ± 4.73 Bb	3.02 ± 0.50 Bb	2.21 ± 0.31 Bb
V (ng/g)	65.21 ± 42.10 Aa	11.01 ± 4.69 Bb	4.46 ± 0.78 Bb	3.44 ± 0.65 Bb
Sb (ng/g)	64.76 ± 41.89 Aa	10.82 ± 4.59 Bb	4.59 ± 0.51 Bb	3.43 ± 0.21 Bb
Mn (ng/g)	46.98 ± 10.83 a	24.51 ± 10.96 b	43.54 ± 12.93 a	47.15 ± 17.32 a
Ti (ng/g)	33.15 ± 20.59 Aa	6.80 ± 4.23 Bb	1.06 ± 0.42 Bb	0.30 ± 0.11 Bb

Note: Data are shown as mean ± standard deviation. Different superscripts indicate statistically significant differences among groups. Different lowercase superscript letters indicate significant differences (p < 0.05), while the same or no letters indicate no significant difference (p > 0.05). Different uppercase superscript letters indicate highly significant differences (p < 0.01).

). The contents of Zn, Fe, Sr, Se, As, Mo, Be, Co, Cd, V, Sb, Mn, and Ti in camel milk were significantly higher than those in cow milk (p < 0.05), with the contents of Se, As, Mo, Be, Co, Cd, V, Sb, Mn, and Ti in camel milk being much higher than those in the cow milk group (p < 0.01). The Ni content in camel milk was also higher than that in the other three animal milks. Compared to goat milk and horse milk, camel milk still exhibited significant advantages in trace elements such as Se, As, Mo, Be, Co, Cd, V, Sb, Mn, and Ti (p < 0.01), but showed smaller differences from goat milk in elements like Zn, Fe, and Ba (p > 0.05). It is particularly noteworthy that cow milk had the highest Cu content, significantly higher than that in the other three animal milks (p < 0.05), while camel milk had a relatively low Cu content. Additionally, horse milk had the highest Ba content, and the Fe content in goat milk was significantly higher than that in camel milk and cow milk (p < 0.05). Overall, camel milk has distinct advantages in the content of various essential trace elements (such as Se, Mo, Co, etc.), showing high nutritional potential.

3.1.3. Principal Component Analysis of Minerals in Milk from Different Species

Principal component analysis (PCA) was performed on the mineral elements in the four types of milk. Using the criterion of eigenvalues greater than 1 for selection, five principal components were extracted (

Table 4. Component Matrix of the Top 5 Factors and Cumulative Variance Contribution.

Items	Factors
	PC1	PC2	PC3	PC4	PC5
Se	0.984	−0.001	−0.015	−0.008	−0.036
Sb	0.982	−0.148	0.035	−0.004	0.043
Cd	0.982	−0.149	0.042	−0.008	0.046
Co	0.981	−0.15	0.036	−0.007	0.042
V	0.981	−0.15	0.039	−0.01	0.051
Be	0.975	−0.127	0.029	0.047	0.05
Cr	0.975	−0.113	−0.021	0.004	0.105
As	0.941	−0.119	0.09	0.056	0.015
Mo	0.88	−0.158	−0.215	0.271	−0.036
Ni	0.798	−0.187	−0.125	−0.261	0.247
Ti	0.601	0.029	0.049	−0.302	−0.496
P	0.297	0.878	0.151	−0.164	−0.111
Mg	−0.124	0.843	0.192	0.158	−0.025
K	0.324	0.834	−0.198	−0.027	−0.181
Ca	0.274	0.793	0.372	−0.26	0.082
Zn	0.089	0.786	−0.324	−0.055	0.117
Mn	0.285	0.568	−0.127	0.371	0.258
Sr	0.14	0.2	0.823	−0.23	0.336
Fe	−0.077	0.263	−0.748	−0.116	0.441
Cu	−0.225	−0.189	0.373	0.58	−0.056
Ba	0.234	0.285	0.164	0.526	0.304
Na	0.538	0.394	−0.166	0.303	−0.54
Variance%	10.177	4.321	1.867	1.27	1.16
Cumulative variance%	46.259	65.901	74.387	80.162	85.433

). Principal component 1 (PC1) had an eigenvalue of 10.177, accounting for 46.259% of the variance, with Se, Sb, and Cd as the main influencing elements. Principal component 2 (PC2) had an eigenvalue of 4.321, accounting for 19.642% of the variance, with P, Mg, and Ca as the main influencing elements. Principal component 3 (PC3) had an eigenvalue of 1.867, accounting for 8.486% of the variance, with Sr as the main influencing element. Principal component 4 (PC4) had an eigenvalue of 1.270, accounting for 5.775% of the variance, with Cu and Ba as the main influencing elements. Principal component 5 (PC5) had an eigenvalue of 1.160, accounting for 5.271% of the variance, with Sr as the main influencing element. The cumulative variance contribution rate of the five components was 85.433%. In the scatter plot based on standardized scores of the first three factors (Figure 2), milk samples from different sources formed distinct clusters according to species differences.

3.1.4. Linear Discriminant Analysis (LDA) of Minerals in Milk from Different Species

Linear discriminant analysis (LDA) was performed based on 22 mineral elements in the milk samples, using a cross-validation procedure to evaluate the stability of the model. Three canonical discriminant functions explained 100% of the variance, with function 1 explaining 48.4% of the total variance, function 2 explaining 37.5% of the total variance, and function 3 explaining 14% of the total variance. The first two functions explained 86% of the variance. The LDA scatter plot revealed clear separation among milk samples from different species in the space defined by the first two discriminant functions (Figure 3). Camel milk samples were scattered, indicating greater intra-species variation, while the other milks were more concentrated, indicating smaller intra-species variation. This phenomenon revealed that the combination of mineral elements possesses high explanatory power for milk source classification. Thus, a discriminant model was constructed and validated using leave-one-out cross-validation, demonstrating the feasibility of this approach in distinguishing samples from different milk sources (

Table 5. LDA Results for Milk Samples from Different Species.

Items	Real Group	Anticipated Group				Whole
		Camel Milk	Cow Milk	Goat Milk	Horse Milk
Original a	Camel Milk	8	0	0	0	8
	Cow Milk	0	8	0	0	8
	Goat Milk	0	0	8	0	8
	Horse Milk	0	0	0	8	8
Discriminant Accuracy/%		100	100	100	100	100
Cross-validation b	Camel Milk	6	1	0	1	8
	Cow Milk	1	4	2	1	8
	Goat Milk	0	1	7	0	8
	Horse Milk	0	0	0	8	8
Discriminant Accuracy/%		75	50	87.5	100	100

Note: ^a Correctly classified 100.0% of original grouped cases. ^b Cross validation is done only for those cases in the analysis. In cross validation, each case is classified by the functions derived from all cases other than that case; correctly classified 78.1% of cross-validated grouped cases.

). The overall accuracy rates for the back substitution test and cross-validation for individual regions were 100% and 78.1%, respectively. The overall model achieved effective classification, demonstrating that the discriminant functions can capture systematic differences between milk sources rather than relying solely on concentration thresholds of single elements.

3.2. Mineral Content of Camel Milk from Different Regions

In the previous subsection, we conducted a preliminary analysis based on the mineral profiles of camel, cow, goat, and horse milk, revealing the influence of species classification on mineral content distribution. However, mineral content is not only significantly regulated by species genetic background and metabolic characteristics but also driven by regional environments. To further clarify the impact of regional differences on minerals in camel milk, this section will systematically compare and analyze the same Tacheng camel milk data from the perspective of geographical regions. Through this multidimensional analysis, we aim to reveal the comprehensive determinants of variation in the camel milk mineral profile, providing a more comprehensive scientific basis for understanding the nutritional properties and adaptive mechanisms of camel milk.

3.2.1. Macro Elements Content of Camel Milk from Different Regions

Significant variations were observed in the macro elements content of camel milk obtained from the Altay, Tacheng, and Ili regions (

Table 6. Macro Elements Contents in Camel Milk from Altay, Tacheng and Ili Regions μg/g.

Items	Altay	Tacheng	Ili
K	1438.30 ± 169.93 ABb	1696.15 ± 170.49 Aa	1424.61 ± 62.87 Bb
Ca	1519.00 ± 104.29	1480.22 ± 82.17	1432.59 ± 161.99
P	1095.20 ± 139.36	1189.11 ± 140.55	1128.57 ± 97.93
Na	643.88 ± 75.88	663.65 ± 76.67	608.03 ± 58.99
Mg	83.75 ± 3.55	92.57 ± 11.50	94.46 ± 13.90
Ca/P	1.40 ± 0.15 a	1.25 ± 0.11 b	1.27 ± 0.09 b
Na/K	0.45 ± 0.04 a	0.39 ± 0.04 b	0.43 ± 0.04 ab

Note: Data are shown as mean ± standard deviation. Different superscripts indicate statistically significant differences among groups. Different lowercase superscript letters indicate significant differences (p < 0.05), while the same or no letters indicate no significant difference (p > 0.05). Different uppercase superscript letters indicate highly significant differences (p < 0.01).

). Among the macro elements, the K content in Tacheng camel milk was significantly higher than that in Altay camel milk (p < 0.05) and very significantly higher than that in Ili camel milk (p < 0.01). Except for calcium, the contents of other macro elements in the Tacheng region were higher than those in the Altay and Ili regions, but the differences were not significant.

Camel milk from the Altay, Tacheng, and Ili regions exhibited distinct regional variations in calcium-to-phosphorus (Ca/P) and sodium-to-potassium (Na/K) ratios (Table 6). The Ca/P ratio in Altay camel milk was significantly higher than that in Tacheng and Ili camel milk (p < 0.05). All three regions showed comparable interquartile ranges, though Ili camel milk demonstrated the most concentrated Ca/P distribution, indicating minimal individual variation. In contrast, both Tacheng and Altay camel milk displayed more dispersed distributions, suggesting greater variability within these regions. Notably, Tacheng camel milk showed significantly higher Ca/P ratios compared to Altay camel milk (p < 0.05), with its concentrated distribution positioned at markedly higher values (Figure 4).

3.2.2. Trace Element Content of Camel Milk from Different Regions

Camel milk exhibited significant regional variations in trace element content among the Altay, Tacheng, and Ili regions (

Table 7. Trace Element Contents in Camel Milk from Altay, Ili and Tacheng Regions.

Items	Altay	Tacheng	Ili
Zn (μg/g)	7.25 ± 2.53 Bb	3.99 ± 0.67 Aa	7.20 ± 0.76 Bb
Fe (μg/g)	3.67 ± 1.14	3.77 ± 1.57	3.73 ± 1.40
Sr (μg/g)	2.18 ± 0.56 Bb	2.00 ± 0.45 Bb	1.32 ± 0.23 Aa
Ba (ng/g)	513.74 ± 66.25	509.60 ± 235.70	430.71 ± 89.20
Cu (ng/g)	159.73 ± 34.67	118.27 ± 58.21	136.08 ± 71.44
Ni (ng/g)	92.41 ± 25.77 b	158.45 ± 44.11 a	110.12 ± 36.27 b
Mn (ng/g)	69.19 ± 17.78 a	46.98 ± 10.83 b	52.42 ± 10.37 b
Cr (ng/g)	32.34 ± 5.88 Bb	93.11 ± 37.96 Aa	35.78 ± 5.99 Bb
Se (ng/g)	27.57 ± 3.37 Bb	132.14 ± 46.26 Aa	30.03 ± 4.37 Bb
As (ng/g)	21.25 ± 7.29 Bb	87.79 ± 48.56 Aa	31.65 ± 24.90 ABb
Mo (ng/g)	8.92 ± 1.39 Bb	77.73 ± 43.80 Aa	13.24 ± 2.98 Bb
V (ng/g)	3.28 ± 0.43 Bb	65.21 ± 42.10 Aa	3.62 ± 1.62 Bb
Sb (ng/g)	3.21 ± 0.31 Bb	64.76 ± 41.89 Aa	2.89 ± 0.89 Bb
Cd (ng/g)	2.10 ± 0.26 Bb	65.96 ± 42.69 Aa	2.11 ± 0.62 Bb
Be (ng/g)	1.61 ± 0.61 Bb	67.64 ± 49.03 Aa	1.10 ± 0.49 Bb
Co (ng/g)	1.74 ± 0.34 Bb	66.00 ± 43.42 Aa	1.81 ± 0.29 Bb
Ti (ng/g)	0.25 ± 0.02 Bb	33.15 ± 20.59 Aa	0.35 ± 0.14 Bb

Note: Data are shown as mean ± standard deviation. Different superscripts indicate statistically significant differences among groups. Different lowercase superscript letters indicate significant differences (p < 0.05), while the same or no letters indicate no significant difference (p > 0.05). Different uppercase superscript letters indicate highly significant differences (p < 0.01).

). Tacheng camel milk showed highly significant enrichment in elements such as Sr, Ni, Cr, etc., compared to Altay and Ili camel milk (p < 0.01). Among them, the Sr content in Tacheng camel milk was very significantly higher than that in Altay and Ili camel milk (p < 0.01). The Ni content in Tacheng camel milk was very significantly higher than that in Ili camel milk (p < 0.01), and significantly higher than that in Altay camel milk (p < 0.05). The Cr content in Tacheng camel milk was significantly higher than that in Altay and Ili camel milk (p < 0.05). However, the Se content in Tacheng camel milk was significantly lower than that in Ili camel milk (p < 0.05). The Mo content in Tacheng camel milk was significantly lower than that in Ili camel milk (p < 0.05), and the V content was significantly lower than that in Altay camel milk (p < 0.05).

3.2.3. LDA of Mineral Elements in Camel Milk from Different Regions

Linear Discriminant Analysis (LDA) was performed based on 22 mineral elements in camel milk samples from different regions, using a cross-validation procedure to assess model stability. Two canonical discriminant functions explained 100% of the variance, with Function 1 explaining 90.9% of the total variance and Function 2 explaining 9.1%. These two functions indicated that the differences in elemental composition among camel milk samples from different regions are mainly concentrated in the first discriminant dimension. The LDA scatter plot revealed clear separation among camel milk samples from different regions in the space defined by the first two discriminant functions (Figure 5). Samples from the Tacheng region were more distant from the other two regions and exhibited smaller within-group variation. A discriminant model was applied to classify camel milk by geographical origin, and its effectiveness was validated. The overall discrimination performance demonstrated feasibility (

Table 8. LDA Results for Camel Milk Samples from Altay, Tacheng and Ili Regions.

Items	Real Group	Anticipated Group			Whole
		Altay	Ili	Tacheng
Original a	Altay	8	0	0	8
	Ili	0	8	0	8
	Tacheng	0	0	8	8
Discriminant Accuracy/%		100	100	100	100
Cross-validation b	Altay	2	2	2	8
	Ili	2	6	0	8
	Tacheng	1	0	7	8
Discriminant Accuracy/%		75	50	87.5	100

Note: ^a Correctly classified 100.0% of original grouped cases. ^b Cross validation is done only for those cases in the analysis. In cross validation, each case is classified by the functions derived from all cases other than that case; correctly classified 70.8% of cross-validated grouped cases.

). The overall accuracy rates for the re-substitution test and cross-validation for individual regions were 100% and 70.8%, respectively. The results of this research validate the potential of mineral elements as geographical markers.

4. Discussion

Due to variations in genetics, environment, and digestive/absorption mechanisms among different species, the mineral content in milk is significantly influenced by the species. This research found that camel milk is rich in macro elements. The contents of Ca, P, and K were the highest in the camel milk, followed by Na and Mg. The contents of Ca and P in camel milk were very significantly higher than in cow milk and horse milk, and the contents of K and Na were very significantly higher than in horse milk. Studies indicate that the contents of Ca, P, and K in camel milk are higher than in cow milk [11]. The high concentration of electrolytes like sodium and potassium in camel milk is closely related to the extremely arid environment of its habitat [12]. Camels transfer high osmotic pressure minerals through their milk to maintain the fluid balance of their calves under water-scarce conditions [13]. Genomics studies have shown that the strong expression of the AQP1 gene in renal tubular epithelial cells in camels enhances water reabsorption capacity, while the upregulation of Na⁺/K⁺ -ATPase activity in milk may be achieved through epigenetic regulation, ensuring efficient mineral transport into the milk [14]. The enrichment of electrolyte-related mineral elements in camel milk reflects the species’ metabolic adaptation to the desert niche [15]. If the body’s K is high and Na is low, leading to a decrease in blood Na/K, it can cause an increase in blood pressure. The results of this research show that the Na/K ratio in camel milk is significantly higher than in goat milk and horse milk, indicating that camel milk is relatively friendly for patients with blood pressure elevation-related diseases. The Ca and P contents in camel milk were very significantly higher than in cow milk and horse milk. According to research data [16,17], the calcium content in camel milk is 154.57–186.87 mg/100 g. In comparison, the calcium content in cow milk is 112–134 mg/100 g, while that in horse milk is lower, at only 60–80 mg/100 g for liquid milk. The calcium content in mature camel milk is approximately 30–40% higher than in cow milk and more than twice as high as in horse milk. The phosphorus content in cow milk is 59–121 mg/100 g, while in horse milk it is 40–60 mg/100 g. The phosphorus content in camel milk is approximately 20–50% higher than in cow milk and about twice as high as in horse milk. Camels live in arid and high-temperature environments, and their milk needs to provide minerals required for rapid skeletal development in calves. The high calcium and phosphorus content in the milk may be an evolutionary adaptive trait.

Camel milk provides abundant trace elements. The study by Chen L et al. [18] showed that the contents of Zn, Ni, Se, Cu, Cr, and As in camel milk are higher than those in cow milk. We found that, among the trace elements in camel milk, the content of Zn is relatively high, followed by Fe and Sr, while the contents of Ni, Se, Cu, Cr, As, Be, Co, Cd, V, Sb, and Ti were significantly higher than those in other types of milk; the contents of Zn and Fe were higher than those in cow milk. Trace elements not only reflect the nutritional value of milk [19], but also play certain roles in promoting immune function, energy metabolism [20,21], enhancing metabolic processes, and reducing oxidative stress damage in organisms [22,23]. Moreover, they help protect young camels from the influences of arid environments. The high levels of Fe and Cu in camel milk are associated with hemoglobin metabolism and adaptation to oxidative stress in camels, which can enhance the survival ability of calves in hypoxic environments [18]. Zn and Se are crucial for immunity and antioxidation, and camels transmit these elements through their milk to strengthen the resistance of their offspring in harsh environments [24]. The significant loadings of Se, Sb, and Cd in Principal Component 1 (46.259%) suggest that these elements may have a common source or bioaccumulation characteristics [25,26]. The high loadings of Ca, Mg, and P in Principal Component 2 (19.642%) reflect the biological role of macro mineral elements; their content differences may be directly related to mammary gland biosynthesis capacity [27], species metabolic characteristics, and dietary nutritional levels [28]. The cluster analysis results visually presented the differential distribution of milk samples based on species, confirming that mineral fingerprints can serve as effective biomarkers for milk source identification. Chen Lu et al. [18] made similar observations that milk samples were divided into different clusters based on PCA scatter plots.

Among the five macro mineral elements, only the K content in Tacheng camel milk was significantly higher than in Altay camel milk. The Na/K ratio in Tacheng camel milk was 0.37, significantly lower than in Altay (0.43) and Ili (0.52). This electrolyte balance characteristic may enhance the heat stress tolerance. Regarding trace elements, the Tacheng region’s camel milk exhibited highly significant increases in 11 trace mineral elements (including Zn, Be, and V) compared to camel milk from the other two regions. The Sr content in Ili region camel milk was very significantly lower than in the other two regions. These differences may generally be related to climate, soil, and feed. Concerning trace metal elements like Pb, Cd, and Zn, concentrations in Tacheng were generally 1 to 3 times higher than in Ili and Altay. Liu, Y. et al. [29] found that the enrichment of trace elements such as Cu, Cd, Zn, and Pb in the northern Xinjiang region is dominated by human activities. Backward trajectory cluster analysis indicated that trace elements in the Tacheng region are more influenced by air mass transport from Kazakhstan. The high content of Ni, Mn, Cr, Co, and Ti in the Tacheng region may be related to the weathering of mafic rocks in this area, as these rocks are typically rich in iron-group elements [30]. The Altay region has a temperate continental cold climate, strongly influenced by Siberian cold air, with relatively high soil organic matter content but lower soil development due to the cold climate [31]. The Ili region has a temperate semi-humid climate, significantly influenced by the westerlies and topographic uplift, with soils mainly consisting of sierozem soils, and locally, chestnut soil and meadow soil [32]. The Tacheng region has a temperate semi-arid climate, combining continental and mountainous characteristics, also dominated by sierozem.

5. Conclusions

This study quantified 22 mineral elements in Bactrian camel milk collected from Tacheng, Altay, and Ili, as well as in cow, goat, and horse milk from the Tacheng region. The results demonstrate that camel milk exhibits significantly elevated concentrations of macro elements (Ca, P, K, Na) and certain trace elements (Se, Sr, Ni) compared to other milk types. Multivariate statistical analyses confirmed the discriminative capacity of mineral compositions for milk species identification and revealed a distinct mineral profile in camel milk. Notably, camel milk from Tacheng displayed higher levels of Sr, Ni, and Cr, indicating influences from geo-environmental factors. Linear discriminant analysis (LDA) models were developed for both milk species classification and geographic origin traceability, demonstrating high accuracy for authentication purposes.

These findings provide a scientific basis for the dairy industry to differentiate and valorize specialty milk products, offer guidance for consumer nutritional education, and support the authentication of geographical origin. However, this study did not consider potential changes in mineral levels during the lactation period. Thus, future research should extend the sampling to cover broader geographical regions and longer timeframes to enhance the generalizability and commercial applicability of the model.