Abstract: Exopolysaccharides (EPS) from Lactiplantibacillus plantarum have been found to possess a variety of biological activities such as antitumor and antioxidant, but few studies on the synthesis of EPS by L. plantarum in skim milk have been reported. The aim of the present study was to screen L. plantarum with high EPS production capability in skim milk, which will be great significance to the application of L. plantarum in dairy products. L. plantarum RT-6 (CGMCC No. 26778), with a high capability of producing EPS, was isolated from homemade yogurt collected in Guilin, Guangxi, China by the colony thread-drawing method. Its EPS producing capability was compared with that of other L. plantarum strains. The culture conditions for EPS production by L. plantarum RT-6 were optimized using one-factor-at-a-time (OFAT) method and response surface methodology (RSM). It was found that among all tested L. plantarum strains, RT-6 exhibited the highest EPS yield when cultured in reconstituted skim milk, whereas most other strains grew slowly or even could not grow. The optimal culture conditions were determined as 39 h, 32 ℃, 101 mg/mL and 1.488 mmol/L for fermentation time, fermentation temperature, skim milk concentration and concentration of mixed essential amino acids, respectively. Under the optimized conditions, the yield of EPS was 241.1 mg/L, 2.6 times higher than that before optimization.

Key words: Lactiplantibacillus plantarum; screening; identification; exopolysaccharide; culture conditions optimization

摘要： 植物乳植杆菌（Lactiplantibacillus plantarum）胞外多糖（exopolysaccharide，EPS）具有抗肿瘤、抗氧化等生物活性，但是关于其在脱脂乳中合成EPS的研究报道较少。筛选在乳中高产EPS的L. plantarum，对拓展L. plantarum在乳制品中的应用具有重要意义。采用拉丝法，从广西桂林采集的家庭手工发酵乳中分离到一株高产EPS的L. plantarum RT-6（CGMCC No. 26778），比较该菌株与部分L. plantarum其他菌株在脱脂乳中的产糖能力，最后运用单因素试验和响应面法确定L. plantarum RT-6在脱脂乳中产糖的最佳培养条件。在经过测试的L. plantarum 菌株中，菌株RT-6在脱脂乳中表现出高产EPS的特性，这与大部分L. plantarum在牛乳中生长缓慢或不生长的情况不同。该菌株在脱脂乳中最优产糖条件为：发酵时间39 h，发酵温度32 ℃，脱脂乳质量浓度101 mg/mL，混合必需氨基酸浓度1.488 mmol/L。经过培养条件优化后，L. plantarum RT-6在发酵乳中EPS产量可达241.1 mg/L，比优化前提高2.6 倍。

关键词: 植物乳植杆菌；筛选；鉴定；胞外多糖；条件优化