提高冷冻酸面团中乳酸菌抗冻性的研究

Study on Improvement of Cryopreservation of Lactic Acid Bacteria in Frozen Sourdough Starters during Freezing and Frozen-Storage

本文用植物乳杆菌和短乳杆菌混合发酵酸面团,将酸面团置于-80℃下速冻,随后置于-20℃下冻藏,冻藏时间30d,来研究不同添加剂对酸面团中乳酸菌抗冻性的影响。通过选用添加剂还原型谷胱甘肽(GSH)、果糖、谷氨酸钠、VC,同时做空白样(未加添加剂)实验,随后测量经过冻藏酸面团中菌体总的存活率和产酸能力,每隔10d测定一次。采用平板菌落计数法测定经过冻藏酸面团中菌体总的存活率,产酸能力采用pH计测定。经冻藏后菌体总的存活率降低,产酸能力降低。结果表明GSH、果糖、谷氨酸钠、VC对低温下的菌体都有保护作用,但GSH和谷氨酸钠比其它添加剂更能有效地在低温下保护植物乳杆菌和短乳杆菌,提高菌体总的存活率和产酸能力。冷冻10、20、30d后添加GSH的样品中菌体总存活率分别为92.69%、86.62%、84.98%,添加谷氨酸钠的样品中菌体总存活率分别为86.65%、68.35%、64.34%。使用这两种添加剂后菌体生长的迟滞期短,产酸快。并且冷冻时间越长,保护效果越明显。本研究为冷冻酸面团的生产打下了理论基础。

Sourdough was prepared with wheat flour and water with lactobacillus （Lactobacillusplantruam and Lactobacillus brevis） at the same portion （10^9 CFU/ml）, incubated at 30℃ with the mixture of suspensions of L plantruam and L brevis. Before that, Lactobacillus was suspended in the water at 30℃. In order to measure the influence of different additives on the Lactobacillus at freezing temperature, four additives （glutanthione, fructose, sodium glutamate, and ascorbic acid） were added during freezing （-80℃） and frozen-storage （-20℃）. The control sample was made without additive. The viability was measured every 10 days throughout 30 days of the frozen-storage period. The pH of the two strains before and after freezing and frozen-storage were measured by a pH meter. The viability was valued by the enumeration of CFU （colony-forming units） and the acidification activity. All additives showed a protective effect on cell viability as compared to saline solution, especially after freeze-drying procedures. Glutanthione was the most effective additives in preserving bacterial viability. After freezing and frozen-storage the viability of the strains was respectively 92.69%（10 days）, 86.62%（20 days） and 84.98%（30 days）. And the viability of the strains protected by sodium glutamate was respectively 86.65%（10 days）, 68.35%（20 days） and 64.34%（30 days）. The lag phase of the strains after using glutanthione and sodium glutamate was shorter, and the acidification activity was stronger. Moreover, the effect was better as the frozen-storage was prolonged. The research built a foundation for the development of frozen sourdough production.