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Objective To isolate lactic acid bacteria (LAB) with the ability to degrade milk fat, providing a theoretical foundation and technical support for dairy fermentation process optimization and probiotic development. Methods Primary screening employed media with butter as the main carbon source, followed by secondary screening using media with butter as the sole carbon source. The target strains were validated via carbon-free media. The selected strains underwent chromogenic assays for lipase characterization. Fermentation properties were assessed through viable count, acidity, acid value, and free fatty acid measurements. Probiotic potential was evaluated via acid/bile salt tolerance and cholesterol reduction assays. Results Through primary screening, secondary screening, and validation, ten strains with the ability to degrade milk fat were selected. Among them, a strain with faster growth than the others was identified as Lactobacillus delbrueckii grx601 through morphological and molecular biological characterization. This strain exhibited high lipase activity during logarithmic and stationary phases, with intracellular and extracellular enzyme activities of 14.14 U/mL and 11.45 U/mL, respectively. Enzymatic characterization showed that the optimal substrate for intracellular and extracellular lipases was p-nitrophenol palmitate, with the optimal reaction conditions of pH 7.0 and 40 ℃. The relative activity remained above 50% at 5% NaCl, which indicated certain salt tolerance. The fermentation characteristic experiment showed that L. delbrueckii grx601 significantly increased the acidity, acidity value, and free fatty acid content during the fermentation process. Moreover, the survival rates of L. delbrueckii grx601 in artificial simulated solutions with pH 3.0 and 0.30% bile salt were 83.87% and 47.70%, respectively, which indicated acid/bile salt tolerance of the strain. In addition, the cholesterol degradation rate of the strain was 7.95%. Conclusion L. delbrueckii grx601 was successfully isolated and characterized as a potent milk fat-degrading strain. Its high intra/extracellular lipase activity, favorable enzymatic properties, robust fermentation performance, and probiotic attributes (acid/bile salt tolerance, cholesterol reduction) indicate significant potential for dairy fermentation and probiotic applications.
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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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