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Article

Effects of Dietary Rhodotorula Yeast Culture Supplementation on Physicochemical Properties, Antioxidant Capacity, Shelf Life, and Flavor Substance of the Longissimus dorsi Muscle in Fattening Lambs

by
Guang Yang
†,
Meiru Chen
†,
Xinyu Lu
,
Gaowei Zhang
,
Ke Wang
,
Xiangtan Su
and
Aiqin Gao
*
College of Animal Science, Inner Mongolia Agricultural University, Hohhot 010018, China
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work and should be considered co-first authors.
Agriculture 2025, 15(12), 1265; https://doi.org/10.3390/agriculture15121265
Submission received: 11 May 2025 / Revised: 7 June 2025 / Accepted: 10 June 2025 / Published: 11 June 2025
(This article belongs to the Section Agricultural Product Quality and Safety)
Browse Figures
Versions Notes

Abstract

This study evaluated the effects of dietary Rhodotorula yeast culture (RYC) supplementation on carcass traits, meat quality, antioxidant capacity, shelf life, and flavor substance in fattening lambs. Twenty-four three-month-old male Dorper × Han crossbred sheep (body weight: 36 ± 4 kg) were randomly assigned to four groups: R0 (basal diet), R10 (basal diet + 10 g RYC/day), R20 (basal diet + 20 g RYC/day), and R40 (basal diet + 40 g RYC/day). The experiment lasted 75 days. Compared to the control group, the R10, R20, and R40 groups exhibited significant reductions in shear force (p < 0.01), malondialdehyde levels (p < 0.01), and day-15 total volatile basic nitrogen values (p < 0.05), along with significant increases in glutathione peroxidase activity (p < 0.05) and total umami-taste amino acid content (p < 0.01). The R20 group also demonstrated significant increases in backfat thickness, muscle crude protein content, and total antioxidant capacity (p < 0.05). These results indicate that dietary supplementation with 20 g RYC improves physicochemical properties, antioxidant capacity, shelf life, and flavor compounds in fattening lambs.

1. Introduction

Lamb, renowned for its high protein content and low-fat profile, holds significant commercial value in the global meat market. However, modern sheep production faces numerous challenges, such as high concentrate inclusion rates [1], suboptimal feed quality, and inadequate housing conditions [2,3], all of which negatively impact sheep health and production performance. To address these issues, antibiotics are commonly used in livestock production. However, the indiscriminate use of antibiotic use can lead to the development of bacterial resistance, jeopardizing animal welfare and meat safety. Consequently, there is an urgent need for sustainable alternatives to antibiotics that can maintain animal health while enhancing product quality.
Yeast culture (YC), a microecological preparation produced through strict anaerobic fermentation of live yeast strains using specialized media under controlled conditions [4,5], contains bioactive components such as fermentation substrates, bacterial proteins, yeast metabolites, and yeast cell walls [6]. Known for its functional properties—including enhanced nutrient absorption in animals, non-toxicity, residue-free composition, and high efficacy with environmental sustainability [7,8]—YC is widely used as a protein-supplemented feed for ruminants in production systems [9]. Studies have shown that dietary YC supplementation significantly increases carcass weight [10], reduces cooking loss, drip loss, and shear force in muscle tissue [11], and elevates intramuscular crude fat content and chroma values [12]. Additionally, YC supplementation has been found to significantly boost the content of essential amino acids (EAAs) in meat, particularly lysine, leucine, and threonine [11]. It also substantially increases total umami amino acids, with notable rises in glutamic acid and alanine concentrations [13]. Studies in mutton sheep further demonstrate that YC enhances systemic antioxidant enzyme activity [14], reduces serum malondialdehyde (MDA) levels, and improves overall antioxidant capacity [15].
Rhodotorula mucilaginosa, a stress-tolerant yeast species within the genus Rhodotorula, is ubiquitously distributed in natural environments [16] and exhibits chemoorganoheterotrophic, thermotolerant, acidotolerant, and facultatively anaerobic characteristics [17,18,19]. This species synthesizes bioactive metabolites—including carotenoids, saccharides, digestive enzymes, and vitamins [20,21]—that demonstrate significant antioxidant capacity by regulating antioxidant enzyme expression and scavenging oxygen free radicals [18,19,22]. Among these metabolites, carotenoids effectively neutralize free radical activity and prevent cellular oxidative damage through their conjugated double-bond system, which scavenges superoxide anions and hydroxyl radicals [23,24]. This mechanism explains how carotenoids in R. mucilaginosa enhance the physicochemical attributes of meat. For instance, Wen et al. demonstrated that dietary lycopene (a carotenoid) supplementation in finishing pigs significantly improved the physicochemical properties of the Longissimus dorsi muscle by reducing MDA levels [25]. In a recent experiment with mice, R. mucilaginosa was found to appreciably increase antioxidant capacity [17]. Similarly, Wu et al. discovered that R. mucilaginosa can significantly improve the growth performance of Leizhou black duck by enhancing their immune function and antioxidant capacity [26]. Sun et al. found that the solid-state fermentation product of carotenoid-rich R. mucilaginosa improved yolk color and carotenoid content, thereby enhancing the intestinal health of laying hens [27]. Additionally, Hu et al. demonstrated that R. mucilaginosa enhanced the growth performance of piglets, boosted their antioxidant capacity, improved gastrointestinal digestion, and maintained intestinal microecological balance [20].
With economic development and growing public health awareness, consumers are increasingly favoring nutrient-rich meat products [28]. Mutton, a globally consumed meat, is particularly popular in Asian and African regions [29,30]. Driven by distinctive dietary traditions and its unique nutritional profile, mutton imports have shown a steady increase in developed nations [31,32]. Mutton quality, nutritional value, and shelf life are critical factors for consumers and serve as primary determinants for meat grading and quality traceability systems [33].
Current studies indicate that yeast culture (YC) demonstrates beneficial effects on the physicochemical properties, antioxidant capacity, and flavor profile of fattening lambs. Notably, R. mucilaginosa possesses the distinctive ability to produce carotenoids. Therefore, it is hypothesized that YC derived from R. mucilaginosa (RYC) may not only retain the advantages of conventional YC but also incorporate the unique properties of carotenoids. However, no comprehensive research has yet elucidated the specific impacts of RYC on fattening lambs. Consequently, this study aims to conduct a preliminary assessment of RYC’s potential as an antibiotic feed alternative by evaluating its effects on meat physicochemical properties, antioxidant capacity, shelf life, and flavor profile in fattening lambs.

2. Materials and Methods

This study was conducted in compliance with animal ethics guidelines (NND2022110). RYC, provided by the Institute of Animal Science of CAAS, was prepared through solid-state fermentation using soybean meal as the substrate and inoculated with a liquid culture of R. mucilaginosa.

2.1. Experimental Design

Twenty-four three-month-old male Dorper × Han crossbred sheep, with an average weight of 36 ± 4 kg, were randomly assigned to four groups. The groups were as follows: the R0 group, which was fed a basal diet; the R10 group, which was fed the basal diet supplemented with 10 g of RYC per day; the R20 group, which was fed the basal diet supplemented with 20 g of RYC per day; and the R40 group, which was fed the basal diet supplemented with 40 g of RYC per day. The experiment lasted 90 days, comprising a 15-day adaptation phase and a 75-day trial phase. Throughout the experiment, all fattening lambs were housed in individual pens. Scheduled feeding was conducted twice daily at 08:00 and 18:00, and water was provided ad libitum via in-pen drinking devices. Every day before 8:00 a.m., a precise amount of RYC was administered to each sheep, followed by the provision of the basal diet.

2.2. Diet Composition

The basal diet was formulated by Inner Mongolia Fuchuan Feed Co., Bayannur, China, according to China’s Nutrient Requirements of Mutton Sheep (NY/T 816-2021). The nutritional components of the diet are detailed in Table 1. Metabolic energy was calculated using the standard equations:
DE = 17.211 − 0.135 × NDF; ME = 0.046 + 0.820 × DE (MJ/kg DM)

2.3. Physicochemical Properties

The slaughter and carcass dissection procedures were conducted in accordance with the Chinese sheep slaughter and inspection operation specification (GB/T 43562-2023) [34]. At the end of the experimental period, all animals were weighed, and after fasting overnight, and six fattening lambs from each group were selected for Islamic slaughter and sampling [35]. The left Longissimus dorsi muscle was removed from each carcass for physicochemical property.
The pH of the Longissimus dorsi muscle was measured using a calibrated portable pH meter (Matthaus, Pöttmes, Germany) at 45 min and 24 h postmortem, with an ambient temperature maintained at 4 °C. The instrument was calibrated using pH 4.0 and 7.0 standard buffers prior to analysis.
Colorimetric parameters (L* = lightness, a* = redness, b* = yellowness) were determined using a portable colorimeter (SMY-2000sf, SMY Technology Co., Ltd., Beijing, China).
Drip loss was assessed as follows: (1) fresh meat samples (5 cm × 3 cm × 2 cm) were excising at 45 min postmortem; (2) initial weight (W1) was recorded; (3) samples were suspended in a drip-loss container at 4 °C for 24 h; (4) samples were blot-dried and reweighed (W2). Drip loss (%) was calculated as:
Drip loss (%) = [(W1 − W2)/W1] × 100%
The water loss rate was determined using standardized filter paper absorption. Fresh Longissimus dorsi samples were weighed 45 min post slaughter (W3), then subjected to 135 kPa compression for 5 min using a computer-controlled meat pressure tester (RH-1000, Guangzhou Runhu Instrument Co., Ltd., Guangzhou, China) with an 18-layer filter paper stack containing a medical gauze interlayer. Post-compression weights (W4) were recorded for calculation. Water loss rate (%) was calculated as:
Water loss rate (%) = [(W3 − W4)/W3] × 100%
To ensure data validity, all measurements were performed in triplicate with results averaged. Approximately 30 g muscle samples were individually vacuum-packed. After fascial removal, samples were weighed (W5), uniformly heated to a core temperature of 70 °C in an 80 °C water bath, then cooled to room temperature and reweighed (W6). Cooking loss (%) was calculated as:
Cooking loss (%) = [(W5 − W6)/W5] × 100%
Shear force (N) was measured using a texture analyzer (C-LM3B, Northeast University, Shenyang, China). Values represent the mean of three replicate measurements per sample [36].
The Longissimus dorsi muscle was further analyzed for proximate composition. Moisture content was determined using a freeze-drying machine. Crude fat content was determined by the Soxhlet extraction method. Crude protein content was determined by the Kjeldahl method. Crude ash content was determined by the dry-ashing method [37].

2.4. Antioxidant Capacity

Muscle homogenates (10% w/v in pre-cooled saline) were centrifuged at 4 °C, and the supernatants were collected for analysis. Antioxidant parameters in Longissimus dorsi muscle, including total antioxidant capacity (T-AOC), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), and catalase (CAT), were quantified using commercial kits (Jiancheng Bioengineering, Nanjing, China) in accordance with the manufacturer’s protocols. Malondialdehyde (MDA) content was determined using the thiobarbituric acid assay, following a 10 min incubation of homogenates at 37 °C (Jiancheng Bioengineering, Nanjing, China).

2.5. Shelf Life for Sale

The determination of total volatile basic nitrogen (TVB-N) in muscle samples was conducted according to the Chinese National Standard (GB 5009.228-2016) (Determination of volatile base nitrogen in foods) with modifications [38]. In accordance with the Chinese National Standard, the acceptable limit for TVB-N in lamb meat is 15 mg/100 g, which serves as a critical reference for evaluating meat freshness and quality. In brief, fat and tendons were removed from lamb meat, and 5 g of lean tissue (weighed to 0.001 g accuracy) was homogenized with 37.5 mL distilled water in a conical flask using a handheld homogenizer. After 30 min immersion, the homogenate was filtered into a volumetric flask. Following the manufacturer’s protocol for the fully automated Kjeldahl nitrogen analyzer, reagent blank values were obtained prior to sample distillation. The distillate was titrated with 0.01 mol/L HCl standard solution to the endpoint for TVB-N calculation.
The total viable count in muscle samples was determined according to the Chinese National Standard (GB 4789.2-2022) (Microbiological examination of food) [39]. Precisely 0.5 g of sample was added to a sterile centrifuge tube containing 4.5 mL of physiological saline and homogenized using a handheld homogenizer to prepare a 1:10 homogenate. Subsequently, 0.5 mL of this homogenate was transferred to a second tube containing 4.5 mL of physiological saline, mixed thoroughly to obtain a 1:100 dilution (10−2, first dilution). Serial decimal dilutions were performed to achieve 10−6 (sixth dilution). At days 0, 5, 10, 15, and 20, appropriate dilutions (10−1 to 10−6) were plated on standard plate count agar, incubated at 36 ± 1 °C for 48 ± 2 h, and plates with 30–300 bacteria were counted.

2.6. Meat Flavor Substances

Amino acid content was determined using an automatic amino acid analyzer (L8900, Hitachi, Chiyoda City, Japan) in accordance with the national standard ‘Determination of amino acids in feed’ (GB/T 18246-2019) [40].
For the analysis of volatile flavor compounds in meat, mutton samples were first thawed at 4 °C in a refrigerator until equilibrated to room temperature. Subsequently, each sample was placed in an injection cup, sealed with preservative film, and analyzed using an electronic nose system (PEN3, AIRSENSE, Schwerin, Germany). Table 2 lists the sensitive compounds corresponding to the 10 metal oxide sensors comprising the PEN3 electronic nose.

2.7. Data Analysis

The normality of the data was assessed using the Shapiro–Wilk test (PROC UNIVARIATE, SAS 9.2). Subsequently, one-way analysis of variance (ANOVA) was performed on the four groups of data. Duncan’s multiple comparison test was used for post hoc analysis. Data are presented as mean ± standard error of the mean (SEM). Significance levels were defined as follows: p < 0.05 (significant), p < 0.01 (highly significant), and p ≥ 0.05 (not significant). Graphical data represent mean ± standard error of the mean (SEM). Figures were generated with GraphPad Prism 9.5 (GraphPad Software, Boston, MA, USA), while electronic nose radar plots from PEN3 detection were visualized using WinMuster v1.6.2.15 (Airsense Analytics, Schwerin, Germany).

3. Results

3.1. Carcass Traits

As shown in Table 3, compared with the R0 group, the GR value of the R40 group significantly increased (p < 0.0), with an increase of 27.91%. Similarly, the GR value of the R40 group was significantly higher than that of the R20 group (p < 0.05), showing an increase of 22.22%. Compared with the R0 group, the backfat thickness of the R20 group significantly increased (p < 0.05), with an increase of 7.14%. Additionally, the backfat thickness of R20 group was significantly higher than that of the R10 group (p < 0.05), with an increase of 5.47% (Table 3).

3.2. Physicochemical Properties

As shown in Table 4, compared with the R0 group, the shear force of the R10, R20, and R40 groups significantly reduced (p < 0.05), with reductions of 7.51%, 8.77%, and 11.50%, respectively. However, there were no significant differences in shear force among the three experimental groups (Table 4).
As shown in Table 5, compared with the R0 group, the crude protein content of the R10 and R20 groups was significantly increased (p < 0.05), with increases of 2.82% and 5.22%, respectively. Additionally, the crude protein content of the R20 group was significantly higher than that of the R10 group (p < 0.05), showing an increase of 2.34% (Table 5).

3.3. Antioxidant Capacity

As shown in Figure 1, compared with the R0 group, the activity of T-AOC in the R10 and R20 groups increased significantly (p < 0.05). Additionally, the MDA content in the R10, R20, and R40 groups was significantly reduced (p < 0.05), while the GSH-Px activity in these groups significantly increased (p < 0.05). However, there was no significant difference in MDA content among the three experimental groups (Figure 1).

3.4. Shelf Life for Sale

As shown in Figure 2a, compared with the R0 group, the TVB-N values of the R10 and R20 groups were significantly lower on the 15th day (p < 0.05). According to the national standard ‘fresh and frozen carcass mutton’ (GB/T9961-2008) [41], the TVB-N value should be ≤15 mg/100 g. The order of time exceeding this standard was: R0 group > R40 group > R10 group > R20 group (Figure 2a).
As shown in Figure 2b, compared with the R0 group, the total number of total bacterial counts in the R10, R20, and R40 groups showed a downward trend on days 0, 5, 10, 15, and 20; however, these differences were not significant (p > 0.05). Additionally, there were no significant differences in the total number of total bacterial counts among the three experimental groups (Figure 2b).

3.5. Meat Flavor Substances

As shown in Table 6, compared with the R0 group, the content of aspartic acid in the R20 and R40 groups increased significantly (p < 0.05), with increases of 16.24% and 14.73%, respectively. Similarly, the content of glutamic acid in the R20 group was significantly higher (p < 0.05), showing an increase of 8.65%. The isoleucine content in the R10, R20, and R40 groups also increased significantly (p < 0.05), with increases of 6.07%, 9.71%, and 6.37%, respectively; however, there were no significant differences among the three experimental groups.
The leucine content in the R10, R20, and R40 groups increased significantly (p < 0.05), with increases of 13.86%, 14.88%, and 10.49%, respectively. Similarly, the lysine content in these groups increased significantly (p < 0.05), with increases of 14.21%, 18.95%, and 14.08%, respectively.
Compared with the R0 group, the total content of umami amino acids in the R10, R20, and R40 groups increased significantly (p < 0.05), with increases of 4.88%, 11.62%, and 8.57%, respectively; however, there were no significant differences among the three experimental groups (Table 6).
As shown in Figure 3, electronic nose analysis revealed differences in volatile flavor compounds within the Longissimus dorsi muscle of lambs among the four experimental groups (Figure 3). Sensors W2W, W1W, W2S, and W1S exhibited higher response values in the R10, R20, and R40 groups compared to the R0 group, with the R20 group showing the highest values. In contrast, sensors W3S and W6S showed minimal variation in response values across the groups. The elevated W2W/W1W ratio indicated that dietary RYC supplementation (especially R20) increased the content of aromatic compounds and sulfides. The increased W2S/W1S response suggested that R10 and R20 promoted the generation of alcohols, aldehydes, ketones, and methane compounds. Minimal differences in the W3S/W6S ratio implied that RYC supplementation had limited effects on high-concentration hydrocarbons and hydrides.
As shown in Figure 4, principal component analysis (PCA) of the PEN3 electronic nose data for the four lamb groups revealed that the first two principal components (PC1 = 72.6%, PC2 = 15.8%) collectively accounted for 88.4% of the total variance (Figure 4). The groups showed clear separation in the principal component space. The R0 group formed a distinct cluster, with the other three groups located in adjacent regions. Notably, the R20 group exhibited the greatest separation distance from R0 along the PC1 axis.

4. Discussion

Carcass traits are critical indicators of meat production capacity, adiposity deposition, and visceral development in livestock [42,43], reflecting both economic returns and animal health status. Our results demonstrated that the R40 group exhibited a significantly elevated GR value in fattening lambs, a phenomenon potentially attributable to the abundant presence of β-glucans and nucleotides in RYC [44,45]. These compounds are known to enhance adipogenesis and growth performance through the activation of the PPARγ signaling pathway and modulation of the AMPK/mTOR axis [46,47]. Notably, backfat thickness peaked in the R20 group but plateaued in the R40 group. We hypothesize that this dose-dependent response may be mediated by sterol regulatory element-binding protein-1c (SREBP-1c)-driven negative feedback regulation [48]. Simultaneously, supplementation with RYC improved carcass weight, preslaughter live weight, dressing percentage, and loin-eye area, although these improvements did not reach statistical significance. This outcome may be attributed to RYC’s ability to modulate the gastrointestinal environment and microbiota structure, thereby enhancing nutrient digestion, absorption, and utilization efficiency in animals. However, the effects of YC on carcass traits remain inconsistent across existing studies. For instance, Liu et al. found that YC supplementation significantly increased backfat thickness [10], while Ren et al. and Hao et al. observed that the addition of 20 g/day and 40 g/day YC had a modest improvement effect on carcass weight and slaughter rate in sheep, though the differences were not statistically significant [49,50]. Conversely, Wang et al. found that YC supplementation significantly reduced the GR value in sheep [51]. These discrepancies may stem from variations in yeast strains, dietary composition, husbandry conditions, dosage regimens, and animal models.
Zhang et al. demonstrated that supplementing broiler diets with 0.1% Rhodotorula yeast (a high-carotenoid-producing strain) significantly increased average daily gain (ADG), slaughter yield, flock uniformity, and enhanced skin and shank pigmentation [52]. In contrast, Paryad et al. reported that dietary inclusion of 1.5% Saccharomyces cerevisiae only improved ADG and feed intake [53]. Notably, the effective dosage of carotenoid-enriched Rhodotorula yeast (0.1%) accounted for merely 1/15 of the Saccharomyces cerevisiae supplementation level (1.5%), yet elicited more comprehensive multidimensional improvements in growth performance, carcass traits, and external product quality. From an economic perspective, Rhodotorula yeast’s lower dosage requirement (0.1% vs. 1.5% for Saccharomyces cerevisiae) reduces feed additive costs per unit of livestock. Its multidimensional benefits, including enhanced growth performance and product quality, may also improve the marketability and profitability of lamb products. However, further evaluation of its production and processing costs is needed to assess its cost-effectiveness relative to other additives. The practical application of Rhodotorula yeast in sheep feeding is promising due to its low inclusion rate and multifunctional benefits. However, challenges such as storage stability and interactions with other feed components must be addressed to ensure widespread adoption.
Our results demonstrated that the addition of RYC significantly reduced the shear force of sheep muscle (up to 11.50%) and improved muscle tenderness. This improvement can be attributed to two primary mechanisms. First, RYC enhanced the antioxidant capacity of muscle, as evidenced by significantly increased activity of T-AOC and GSH-Px and a decreased MDA content in the R20 group. It is speculated that the yeast cell wall polysaccharides in RYC may upregulate the expression of antioxidant genes such as Nrf-2, thereby enhancing the body’s antioxidant capacity [54]. Second, RYC increased the crude protein content of the muscle, with the R20 group showing a significant rise. Studies suggest that YC is rich in proteins and amino acids, which can directly provide raw materials for muscle synthesis, thereby increasing the crude protein content of muscle [55]. The increase in crude protein content may be accompanied by the degradation of myofibrillar proteins [56], leading to a looser muscle fiber structure and further reducing shear force [57].
Collagen, the main component of connective tissue, also plays a critical role in meat tenderness. Its content, thermal solubility, and degree of protein crosslinking significantly influence tenderness [58]. Tenderness is negatively correlated with collagen content and crosslinking degree [59] but positively correlated with collagen thermal solubility [60], consistent with the findings of Lu et al. [61]. Therefore, we speculate that the addition of RYC may enrich mutton with more collagen of high thermal solubility, making it easier to degrade into gelatin during cooking. This process would result in more tender muscle and reduced shear force. Additionally, antioxidant components such as carotenoids and polyphenols in Rhodotorula yeast can scavenge free radicals, reduce oxidative stress, protect cells, delay the oxidative deterioration of meat, and extend its shelf life [62].
In terms of shelf life, we focused on the effect of RYC on TVB-N values and total bacterial counts. The results showed that the TVB-N values of the R10 group and R20 group were significantly lower than those of the R0 group on the 15th day, indicating that RYC could delay the decomposition of meat proteins, reduce the formation of alkaline nitrogenous substances, and slow spoilage. Additionally, the total bacterial counts in the R10, R20, and R40 groups showed a downward trend. Although this reduction is not statistically significant, it suggested that RYC has an antibacterial effect, potentially inhibiting microbial growth and prolonging shelf life. The antibacterial properties of RYC may be attributed to the β-glucan of the yeast cell wall, which can block the adhesion of pathogenic bacteria [63,64]. Furthermore, RYC may inhibit the oxidation of fat and myoglobin, and delay the deterioration of meat color by increasing the content of umami amino acids and enhancing the activity of GSH-Px [12,65]. While the TVB-N values of the R10, R20, and R40 groups increased over time, the time required for these groups to reach the national standard limit (15 mg/100 g) was significantly delayed, indicating that RYC could extend the shelf life of mutton. This finding aligns with the results of Zhang et al. [66]. Similarly, the total bacteria count in the R10, R20, and R40 groups decreased over time, suggesting that RYC may reduce the proliferation of spoilage bacteria by regulating the intestinal microbiota, which is consistent with the findings of Georgescu et al. [67].
In terms of flavor, our results showed that the total contents of aspartic acid, glutamic acid, isoleucine, leucine, lysine, and umami amino acids in the R20 and R40 groups were significantly increased. This not only improved the nutritional value of the meat but also enhanced its flavor. The yeast protein in RYC is broken down into amino acids [68], which directly increases the amino acid content in the muscle. Additionally, RYC may improve the absorption and utilization efficiency of amino acids by regulating the intestinal microbiota. As a sensory detection technology based on biological inspiration principles, the electronic nose can rapidly respond to and recognize patterns of volatile compounds through its multi-sensor array, enabling sensitive discrimination of subtle differences between samples [69]. Electronic nose analysis revealed that the effect of RYC on the volatile flavor compounds of Longissimus dorsi muscle was primarily reflected in sulfides and organic sulfides. The underlying mechanisms may include: (1) the increase in sulfur-containing amino acid metabolic intermediates (such as glutathione), whose decomposition products generate meat characteristic meat flavor substances through the Maillard reaction [70,71]; and (2) the thiamine (vitamin B1) in RYC, which promotes the synthesis of aromatic compounds [72]. Furthermore, the increase in fat content was positively correlated with the increase in amino acid content, further enhancing the flavor of the meat [73]. Fat acts as a solvent for flavor compounds, providing a medium for the accumulation of flavor substances [74]. Studies have shown that the addition of yeast culture can increase the content of essential amino acids and flavor amino acids in animal muscle, improving both taste and nutritional value [11], which aligns with the findings of this study.

5. Conclusions

In conclusion, dietary supplementation with RYC enhances GR value and backfat thickness in fattening lambs while increasing intramuscular crude protein content and reducing shear force, thereby improving meat tenderness. RYC also increases T-AOC and GSH-Px activities while decreasing MDA concentration, extending meat shelf life. Additionally, RYC enriches umami-enhancing amino acids (e.g., aspartic acid, glutamic acid) and boosts volatile flavor substances in lamb muscle. Supplementing 20 g of RYC improves the physicochemical properties, antioxidant capacity, shelf life, and flavor profile of fattening lambs, demonstrating its potential as a feed additive to enhance meat quality.

Author Contributions

Conceptualization, G.Y., M.C. and A.G.; methodology, G.Y., M.C. and A.G.; validation, G.Y. and M.C.; formal analysis, G.Y. and M.C.; investigation, G.Y., M.C., X.L., G.Z., K.W. and X.S.; resources, G.Y., M.C., X.L., G.Z., K.W. and X.S.; data curation, G.Y. and M.C.; writing—original draft preparation, G.Y. and M.C.; writing—review and editing, X.L., G.Z., K.W., X.S. and A.G.; visualization, G.Y. and M.C.; supervision, A.G.; project administration, A.G.; funding acquisition, A.G. All authors have read and agreed to the published version of the manuscript.

Funding

This research was financially supported by the Natural Science Foundation of the Inner Mongolia Autonomous Region under grant number 2023LHMS03064, and by the High-level Achievement Cultivation Project of the Animal Science College at the Inner Mongolia Agricultural University under grant number BZX202212.

Institutional Review Board Statement

The animal study protocol was approved by the Animal Welfare and Ethics Committee of Inner Mongolia Agricultural University (NND2022110).

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed at the corresponding author.

Acknowledgments

The authors express their gratitude for the support provided by Inner Mongolia Fuchuan Farming Polytron Technologies, Inc. (Bayannur, China) for the care of the animals.

Conflicts of Interest

The authors declare no conflicts of interest.

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Agriculture 15 01265 g001
Figure 1. Effects of different doses of RYC on the antioxidant capacity of mutton sheep muscle. Groups: R0 (basal diet), R10 (basal diet + 10 g RYC/day), R20 (basal diet + 20 g RYC/day), and R40 (basal diet + 40 g RYC/day). Bars with different letters differ significantly (p < 0.06). Data are presented as means ± SEM (standard error of the mean), with n = 6 for each group.
Figure 1. Effects of different doses of RYC on the antioxidant capacity of mutton sheep muscle. Groups: R0 (basal diet), R10 (basal diet + 10 g RYC/day), R20 (basal diet + 20 g RYC/day), and R40 (basal diet + 40 g RYC/day). Bars with different letters differ significantly (p < 0.06). Data are presented as means ± SEM (standard error of the mean), with n = 6 for each group.
Agriculture 15 01265 g001
Agriculture 15 01265 g002
Figure 2. Effects of RYC supplementation on shelf life indicators of mutton sheep muscle during storage. (a) Changes in TVB-N values in each group under different doses of additives; (b) Changes in total bacterial counts across groups at different storage times. Groups: R0 (basal diet), R10 (basal diet + 10 g RYC/day), R20 (basal diet + 20 g RYC/day), and R40 (basal diet + 40 g RYC/day). Lines with different letters at specific time points differ significantly (p < 0.06). Data are presented as means ± SEM (standard error of the mean), with n = 6 for each group.
Figure 2. Effects of RYC supplementation on shelf life indicators of mutton sheep muscle during storage. (a) Changes in TVB-N values in each group under different doses of additives; (b) Changes in total bacterial counts across groups at different storage times. Groups: R0 (basal diet), R10 (basal diet + 10 g RYC/day), R20 (basal diet + 20 g RYC/day), and R40 (basal diet + 40 g RYC/day). Lines with different letters at specific time points differ significantly (p < 0.06). Data are presented as means ± SEM (standard error of the mean), with n = 6 for each group.
Agriculture 15 01265 g002
Agriculture 15 01265 g003
Figure 3. Radar plots of volatile flavor compounds detected by electronic nose at varying RYC addition levels. Groups: R0 (basal diet), R10 (basal diet + 10 g RYC/day), R20 (basal diet + 20 g RYC/day), and R40 (basal diet + 40 g RYC/day). Sensors and their corresponding sensitive materials: W1C (aromatic hydrocarbons), W5S (nitoxides), W3C (ammonia), W6S (hydride), W5C (olefins, aromatics, polar molecules), W1S (ethers), W1W (sulfide), W2S (alcohols, some aromatic compounds), W2W (aromatic components, organic sulfides), and W3S (ethers, aliphatic). n = 6 for each group.
Figure 3. Radar plots of volatile flavor compounds detected by electronic nose at varying RYC addition levels. Groups: R0 (basal diet), R10 (basal diet + 10 g RYC/day), R20 (basal diet + 20 g RYC/day), and R40 (basal diet + 40 g RYC/day). Sensors and their corresponding sensitive materials: W1C (aromatic hydrocarbons), W5S (nitoxides), W3C (ammonia), W6S (hydride), W5C (olefins, aromatics, polar molecules), W1S (ethers), W1W (sulfide), W2S (alcohols, some aromatic compounds), W2W (aromatic components, organic sulfides), and W3S (ethers, aliphatic). n = 6 for each group.
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Agriculture 15 01265 g004
Figure 4. PCA model based on volatile flavor substances at varying RYC addition levels. Groups: R0 (basal diet), R10 (basal diet + 10 g RYC/day), R20 (basal diet + 20 g RYC/day), and R40 (basal diet + 40 g RYC/day). Confidence ellipses (95%) are shown for each group to illustrate statistical separation. Principal component 1 (PC1) and principal component 2 (PC2) represent the orthogonal axes that capture the maximum variance in the dataset. n = 6 for each group.
Figure 4. PCA model based on volatile flavor substances at varying RYC addition levels. Groups: R0 (basal diet), R10 (basal diet + 10 g RYC/day), R20 (basal diet + 20 g RYC/day), and R40 (basal diet + 40 g RYC/day). Confidence ellipses (95%) are shown for each group to illustrate statistical separation. Principal component 1 (PC1) and principal component 2 (PC2) represent the orthogonal axes that capture the maximum variance in the dataset. n = 6 for each group.
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Table 1. Composition and nutrient levels of the basal diet (dry matter basis).
Table 1. Composition and nutrient levels of the basal diet (dry matter basis).
ItemsContent (%)
Ingredients
   Leymus chinensis10.76
   Corn stalks30.79
   Concentrate supplements 152.33
   Corn silage6.12
   Total100.00
Nutrient levels
   Metabolic energy 2 (MJ/kg)8.91
   Crude protein14.31
   Crude fat2.22
   Neutral detergent fibers50.88
   Acid detergent fibers19.85
   Calcium0.96
   Phosphorus0.35
1 Concentrate supplement composition: corn, rapeseed meal, extruded soybean, molasses, cottonseed meal, apple pomace, stone powder, sodium chloride, baking soda, and vitamins. 2 Metabolic energy was determined through calculation, whereas the levels of the remaining nutrients were obtained through direct measurement.
Table 2. Sensitive substances corresponding to electronic nose sensors.
Table 2. Sensitive substances corresponding to electronic nose sensors.
SensorSensitive Materials
W1CAromatic hydrocarbon
W5SNitoxides
W3CAmmonia
W6SHydride
W5COlefins, aromatics, polar molecules
W1SEthers
W1WSulfide
W2SAlcohols, some aromatic compounds
W2WAromatic components, organic sulfides
W3SEthers, aliphatic
Table 3. Effects of dietary RYC supplementation on carcass traits of fattening lambs.
Table 3. Effects of dietary RYC supplementation on carcass traits of fattening lambs.
ItemsTreatmentSEMp-Value
R0R10R20R40
Carcass weight (kg)27.1328.3128.4527.810.850.70
Pre-slaughter live weight (kg)53.6755.8254.8754.791.390.76
Slaughter rate (%)50.5650.7351.7850.800.830.73
GR value (cm)0.86 b1.02 ab0.90 b1.10 a0.060.04
Backfat thickness (cm)2.52 b2.56 b2.70 a2.62 ab0.040.05
Eye muscle area (cm2)17.8018.0119.1917.811.600.91
Different letter superscripts within the same row denote significant differences (p < 0.06). SEM: standard error of the mean, n = 6 for each group.
Table 4. Effects of dietary RYC supplementation on meat quality of fattening lambs.
Table 4. Effects of dietary RYC supplementation on meat quality of fattening lambs.
ItemsTreatmentSEMp-Value
R0R10R20R40
Shear force (N)37.02 a34.24 b33.77 b32.76 b0.76<0.01
Cooking loss (%)34.4033.9432.8733.350.950.69
Water loss rate (%)15.9215.8515.3115.780.620.90
Drip loss (%)3.873.563.223.350.190.13
45 min pH6.506.776.636.540.110.32
24 h pH5.455.465.535.460.150.98
Lightness (L*)37.1436.4836.4535.650.660.48
Redness (a*)13.1814.1613.7614.150.570.59
Yellowness (b*)8.958.848.618.420.490.88
Different letter superscripts within the same row denote significant differences (p < 0.06). SEM: standard error of the mean, n = 6 for each group.
Table 5. Effects of dietary RYC supplementation on routine nutrient content in the muscle of fattening lambs.
Table 5. Effects of dietary RYC supplementation on routine nutrient content in the muscle of fattening lambs.
ItemsTreatmentSEMp-Value
R0R10R20R40
Moisture (%)74.1375.0974.7574.220.610.65
Crude protein (%)16.37 c16.83 b17.22 a16.96 ab0.11<0.01
Crude fat (%)1.731.741.751.730.030.95
Crude ash (%)5.925.956.075.930.310.98
Different letter superscripts within the same row denote significant differences (p < 0.06). SEM: standard error of the mean, n = 6 for each group.
Table 6. Effects of dietary RYC supplementation on amino acids content in fattening lambs.
Table 6. Effects of dietary RYC supplementation on amino acids content in fattening lambs.
ItemsTreatmentSEMp-Value
R0R10R20R40
Asp (%) *8.82 b9.78 ab10.25 a10.12 a0.350.04
Thr (%) #4.234.684.824.650.160.09
Ser (%)3.243.513.653.530.100.07
Glu (%) *13.76 b13.91 b14.95 a14.40 ab0.24<0.01
Gly (%)5.074.734.815.080.230.62
Ala (%)5.565.975.905.870.130.19
Cys (%)2.092.121.621.530.250.24
Val (%) #4.164.434.474.350.090.11
Met (%) #3.213.122.872.780.240.57
Ile (%) #4.34 b4.60 a4.76 a4.62 a0.080.01
Leu (%) #7.35 b8.37 a8.44 a8.12 a0.240.02
Tyr (%)3.624.013.613.430.240.43
Phe (%) #4.435.125.004.910.210.13
Lys (%) #7.90 b9.02 a9.39 a9.01 a0.300.02
His (%) #3.663.603.723.710.230.98
Arg (%)6.567.126.406.990.640.83
Pro (%)10.494.163.724.942.040.11
EAA (%)39.2742.9543.4742.151.040.05
DAA (%)22.58 b23.68 ab25.21 a24.52 a0.49<0.01
TAA (%)13.809.7314.5112.312.620.31
Note: # essential amino acids (EAA); * delicious amino acids (DAA). Different letter superscripts within the same row denote significant differences (p < 0.06). SEM: standard error of the mean, n = 6 for each group.
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Yang, G.; Chen, M.; Lu, X.; Zhang, G.; Wang, K.; Su, X.; Gao, A. Effects of Dietary Rhodotorula Yeast Culture Supplementation on Physicochemical Properties, Antioxidant Capacity, Shelf Life, and Flavor Substance of the Longissimus dorsi Muscle in Fattening Lambs. Agriculture 2025, 15, 1265. https://doi.org/10.3390/agriculture15121265

AMA Style

Yang G, Chen M, Lu X, Zhang G, Wang K, Su X, Gao A. Effects of Dietary Rhodotorula Yeast Culture Supplementation on Physicochemical Properties, Antioxidant Capacity, Shelf Life, and Flavor Substance of the Longissimus dorsi Muscle in Fattening Lambs. Agriculture. 2025; 15(12):1265. https://doi.org/10.3390/agriculture15121265

Chicago/Turabian Style

Yang, Guang, Meiru Chen, Xinyu Lu, Gaowei Zhang, Ke Wang, Xiangtan Su, and Aiqin Gao. 2025. "Effects of Dietary Rhodotorula Yeast Culture Supplementation on Physicochemical Properties, Antioxidant Capacity, Shelf Life, and Flavor Substance of the Longissimus dorsi Muscle in Fattening Lambs" Agriculture 15, no. 12: 1265. https://doi.org/10.3390/agriculture15121265

APA Style

Yang, G., Chen, M., Lu, X., Zhang, G., Wang, K., Su, X., & Gao, A. (2025). Effects of Dietary Rhodotorula Yeast Culture Supplementation on Physicochemical Properties, Antioxidant Capacity, Shelf Life, and Flavor Substance of the Longissimus dorsi Muscle in Fattening Lambs. Agriculture, 15(12), 1265. https://doi.org/10.3390/agriculture15121265

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