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Outline
This study aimed to develop yak milk Emmental cheese enriched with conjugated linoleic acid (CLA) by incorporating high-CLA-converting lactic acid bacteria and to evaluate the resulting changes in cheese quality and lipid oxidation characteristics. The ripening environment of Emmental cheese was simulated to screen optimal bacterial strains for preparing a direct-to-vat set adjunct culture. Cheese with the adjunct culture served as the experimental group, while cheese without it served as the control group. At 1, 25, 50, 75, and 100 days of ripening, the microstructure, volatile compounds, lipolysis, and fatty acid composition of the cheeses were compared using sensory evaluation, scanning electron microscopy, headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (HS-SPME-GC-MS), Soxhlet extraction, and gas chromatography–mass spectrometry (GC-MS). Results showed that Lactobacillus fermentum S57 and Lactobacillus delbrueckii S60, with CLA conversion rates of 15.27% and 15.82%, respectively, were selected as the optimal strains. 2-Nonanone and ethyl lactate were identified as characteristic flavor compounds produced by the high-CLA-converting LAB in the experimental cheese. The casein micelles in the experimental group were finer and had larger gaps compared to those in the control group. As ripening progressed, the fat content in all cheese groups first increased and then decreased, remaining higher at 100 days than at the initial stage. Acid degree value (ADV) and thiobarbituric acid (TBA) value gradually increased with ripening time, and the TBA value of the experimental group remained below 0.5 mg/kg, without producing any off-flavor. The CLA conversion rates in cheeses made with L. fermentum S57 and L. delbrueckii S60 reached up to 6.09% and 7.06%, respectively, both higher than that of the control group. At 25, 50, and 100 days of ripening, significant differences (P<0.05) in the health promotion index were observed between the experimental and control groups, with the experimental group showing a higher level of health promotion. Therefore, the application of high-CLA-converting lactic acid bacteria in yak milk Emmental cheese improves cheese quality and enhances lipid oxidation profiles, indicating promising potential for development and application.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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