Sang Yue, Wang Jian, Zhang Yongxiang, Gao Haina, Ge Shaoyang, Feng Haihong, Zhang Yan, Ren Fazheng, Wen Pengcheng, Wang Ran
College of Food Science and Engineering, Gansu Agricultural University, Lanzhou 730070, China.
Key Laboratory of Functional Dairy, Co-Constructed by Ministry of Education and Beijing Government, Department of Nutrition and Health, China Agricultural University, Beijing 100083, China.
Microorganisms. 2023 Jan 11;11(1):181. doi: 10.3390/microorganisms11010181.
Maintaining optimum temperature during freeze-drying is crucial to ensuring the viability of strains. In this study, we evaluated the effect of pre-freezing, sublimation and desorption temperatures on the viability of BB68S (BB68S). Moreover, we examined the water content, water activity, enzyme activities, and scanning electron microscope of BB68S to explore mechanisms underpinning the effect of temperature on viability. Our analyses revealed the highest survival rates of BB68S collected after pre-freezing and sublimation drying at -40 °C (94.9 ± 2.2%) and -10 °C (65.4 ± 3.8%), respectively. Additionally, response surface methodology demonstrated that the optimum conditions for freeze-drying of BB68S were pre-freezing temperature at -45.52 °C and sublimation temperature at -6.58 °C, and the verification test showed that survival rates of BB68S could reach 69.2 ± 3.8%. Most of the vitality loss occurred during the sublimation drying phase. Further studies showed that different sublimation temperatures affected water content and activity, β-galactosidase, lactate dehydrogenase, Na-K-ATP and Ca-Mg-ATP activities. In conclusion, the temperature during freeze-drying, especially sublimation temperature, is a key factor affecting the survival rate of BB68S, and the vitality loss during freeze-drying process might be due to compromised cell membrane integrity and permeability.
在冷冻干燥过程中维持最佳温度对于确保菌株的活力至关重要。在本研究中，我们评估了预冻、升华和解吸温度对BB68S活力的影响。此外，我们检测了BB68S的含水量、水分活度、酶活性以及扫描电子显微镜观察结果，以探究温度对活力产生影响的潜在机制。我们的分析显示，分别在-40°C（94.9±2.2%）预冻和-10°C（65.4±3.8%）升华干燥后收集的BB68S存活率最高。此外，响应面法表明，BB68S冷冻干燥的最佳条件是预冻温度为-45.52°C，升华温度为-6.58°C，验证试验表明BB68S的存活率可达69.2±3.8%。大部分活力损失发生在升华干燥阶段。进一步研究表明，不同的升华温度会影响含水量和活性、β-半乳糖苷酶、乳酸脱氢酶、钠钾ATP酶和钙镁ATP酶的活性。总之，冷冻干燥过程中的温度，尤其是升华温度，是影响BB68S存活率的关键因素，冷冻干燥过程中的活力损失可能是由于细胞膜完整性和通透性受损所致。
