1. Introduction
2. Materials and Methods
2.1. Sample collection
2.2. Fatty acid analysis
2.3. Calculation of lipid health indices
2.4. Statistical analysis
3. Results and Discussion
4. Conclusion
1. Introduction
Mutton is an important source of high-quality animal protein and dietary lipids [1], and its nutritional value largely depends on its fatty acid composition. In recent years, with increasing concern for cardiovascular health, the balance between saturated and unsaturated fatty acids in meat lipids has attracted growing attention [2]. Lipid health indices calculated based on fatty acid compositions such as the ratio of polyunsaturated to saturated fatty acids (PUFA/SFA), the n-6/n-3 ratio, have been widely applied to comprehensively evaluate the nutritional quality of meat lipids [3, 4]. Seasonal variation is an important factor influencing lipid metabolism and fatty acid composition in grazing livestock. Seasonal changes in forage availability, plant species composition, and climatic conditions can affect rumen fermentation processes and lipid deposition mechanisms, thereby altering the composition of muscle lipids. Previous studies have shown that, compared with intensive grain-feeding systems, pasture-based feeding systems generally increase the proportion of unsaturated fatty acids and result in a more favorable n-6/n-3 ratio. However, under natural production conditions, systematic investigations into the effects of seasonal variation on fatty acid composition and lipid health indices of mutton remain limited [5].
Dundgovi Province, located in the central Gobi region of Mongolia, is characterized by a typical continental arid climate, with low annual precipitation (95–150 mm) and large seasonal temperature variation [6]. Sheep in this region are mainly raised under natural grazing conditions, which may influence meat quality and lipid composition. Against this background, the present study focused on mutton from Erdenedalai soum in Dundgovi Province to investigate seasonal differences in fatty acid composition and lipid health indices, aiming to provide a scientific basis for evaluating the nutritional characteristics of Mongolian mutton.
2. Materials and Methods
2.1. Sample collection
Mutton samples were collected in winter and spring from sheep raised under local production conditions. After slaughter, representative muscle samples were excised, visible connective tissues were removed, and the samples were stored at –20°C until analysis. All samples were subjected to identical storage and pretreatment procedures to minimize the influence of non-experimental factors on the results.
2.2. Fatty acid analysis
Total lipids were extracted from mutton samples using standard methods, and fatty acid methyl esters (FAMEs) were subsequently prepared. Fatty acids were analyzed using gas chromatography (GC) in accordance with AOAC Official Method 963.22 and CA318:2016. Individual fatty acids were identified by comparing their retention times with those of authentic FAME standards. The results were expressed as the relative percentage of each fatty acid with respect to total fatty acids.
2.3. Calculation of lipid health indices
Lipid health indices were calculated based on fatty acid composition data, including the ratio of polyunsaturated to saturated fatty acids (p, PUFA/SFA), the n-6/n-3 ratio, the saturation index (S/P), the AI, and the TI. The calculation formulas for AI and TI were adopted from the method proposed by Ulbricht and Southgate [7].
2.4. Statistical analysis
Given the descriptive nature of the data in this study, the results were presented as relative fatty acid contents and calculated lipid health indices, and descriptive comparisons were performed to evaluate variation trends between samples collected in different seasons.
3. Results and Discussion
The fatty acid composition of Mongolian mutton is presented in Table 1. A total of 19 fatty acids were identified, with oleic acid (C18:1 n-9) being the predominant component (34.66%–43.57%). Compared with winter, higher levels of palmitic acid (C16:0) and oleic acid were observed in spring, whereas butyric acid (C4:0) was higher in winter. These results indicate clear seasonal variation in fatty acid composition.
Table 1.
Fatty acid composition of mutton in different seasons (% of total fatty acids)
Lipid health indices calculated from fatty acid composition are summarized in Table 2.
Table 2.
Calculated lipid health indices of mutton in different seasons, %
The PUFA/SFA ratios of all samples ranged from 1.03 to 1.39%, while the S/P ratios were all below 1.0. The n-6/n-3 ratios were consistently lower than 2.0 and differed between winter and spring samples. Overall, the calculated AI and TI values were within low to moderate ranges, with some variation observed between samples from different seasons. Table 3 summarizes the seasonal differences in fatty acid composition and lipid nutritional indices of Mongolian mutton.
Seasonal differences were observed in the fatty acid composition of Mongolian mutton (Table 3). Compared with winter samples, spring mutton exhibited a lower proportion of saturated fatty acids (41.24%) and a higher proportion of polyunsaturated fatty acids (55.78%), whereas winter samples showed relatively higher SFA (45.10%) and lower PUFA (51.53%). The proportion of monounsaturated fatty acids remained relatively low in both seasons, with only minor variation. As a result of these structural changes, the PUFA/SFA ratio increased from 1.14 in winter to 1.35 in spring. The n-6/n-3 ratios remained low and stable across seasons, ranging from 1.55 to 1.61.
Table 3.
The seasonal comparison of fatty acid classes and lipid nutritional indices in Mongolian mutton (mean ± SD)
The seasonal variation in fatty acid composition observed in this study is closely associated with changes in pasture availability and forage quality. The reduction in SFA and the increase in PUFA in spring mutton likely reflect improved intake of fresh green forage, which is richer in unsaturated fatty acids and their precursors. The PUFA/SFA ratios in both seasons were substantially higher than the FAO/WHO-recommended threshold of 0.4, indicating a favorable lipid nutritional profile [8, 9]. Notably, the higher PUFA/SFA ratio in spring suggests an improvement in lipid quality associated with seasonal pasture regeneration. In addition, the consistently low n-6/n-3 ratios (<2.0) observed in both seasons are characteristic of grass-fed ruminant systems and contrast with those typically reported for grain-fed meat products. These findings are consistent with previous studies demonstrating that pasture-based feeding systems significantly influence fatty acid composition in lamb meat.
The results of this study indicate that the fatty acid composition of Mongolian mutton is dominated by oleic acid (C18:1 n-9), which is consistent with the lipid metabolism characteristics of ruminants. In ruminant animals, dietary unsaturated fatty acids undergo partial biohydrogenation in the rumen, resulting in a relatively high proportion of monounsaturated fatty acids, particularly oleic acid, which subsequently becomes the predominant fatty acid in muscle lipids. Similar fatty acid profiles have also been reported in previous studies on pasture-grazed lamb.
The PUFA/SFA ratio and the n-6/n-3 ratio, calculated based on fatty acid composition, are widely used indicators for evaluating the nutritional quality of meat lipids [10]. In the present study, all samples exhibited relatively high PUFA/SFA ratios, while the n-6/n-3 ratios were consistently below 2.0, indicating a well-balanced lipid structure. Moreover, the AI and TI were generally within low to moderate ranges, further reflecting the favorable nutritional characteristics of Mongolian mutton lipids from an index-based perspective [11].
It should be noted that this study compared samples collected only in winter and spring and did not encompass seasonal variations throughout the entire year. In addition, differences in sample size and production conditions may also have influenced the fatty acid composition. Future studies should incorporate samples from additional seasons and diverse production systems to provide a more comprehensive evaluation of the lipid characteristics of Mongolian mutton.
4. Conclusion
This study evaluated the fatty acid composition and lipid nutritional quality of Mongolian mutton in winter and spring. Oleic acid (C18:1 n-9) was the predominant fatty acid, and clear seasonal variations were observed, with spring mutton showing lower saturated fatty acids (SFA) and higher polyunsaturated fatty acids (PUFA), resulting in an increased PUFA/SFA ratio. The n-6/n-3 ratios remained consistently low (<2.0), and AI and TI values were within low to moderate ranges, indicating a favorable lipid nutritional profile. Overall, Mongolian mutton exhibits a relatively balanced fatty acid composition, and seasonal pasture conditions play an important role in shaping its lipid characteristics.
