基于膜滤法处理的预发酵椰子水促进细菌纤维素合成机理

Elucidation of the Mechanism by Which the Filtrate of Naturally Fermented Coconut Water Promotes Bacterial Cellulose Synthesis

研究预发酵椰子水(fermented coconut water,FCW)促进细菌纤维素(bacterial cellulose,BC)合成的原因,采用膜过滤法处理FCW得到膜滤上清液和菌体,分别配制培养基并接种椰冻驹形杆菌(Komagataeibacternataicola)Y19至培养基中30 ℃静置培养7 d。结果显示,上清液组的BC产量达到5.65 g/L,是对照组新鲜椰子水(natural coconut water,NCW)的10 倍,而菌体沉淀组仅为其2.8 倍,促进作用弱于上清液组和FCW组,说明膜滤上清液对BC合成的促进作用显著。通过对膜滤上清液进行气相色谱-质谱分析以及利用高效液相色谱法对预发酵过程中有机酸的变化分析,发现上清液中能检出的挥发性成分总量约为NCW的5 倍,醇类相对含量最高,约占62%,其中乙醇和乙酸含量分别是NCW的4.5 倍和48 倍。预发酵过程中,乙酸和乳酸的含量逐渐增加,经过1~2 d预发酵后葡萄糖酸含量显著降低,其他有机酸在预发酵过程中变化不显著。因此推测椰子水预发酵过程中微生物代谢产物对后期BC合成起到重要作用,且预发酵后变化较大的醇类和酸类物质有可能是通过参与驹形杆菌Y19的代谢调节作用而影响BC的合成。

Komagataeibacter nataicola Y19 was statically cultured at 30 ℃ for 7 days in media with either cell-free filtrate or cell residue of naturally fermented coconut water (FCW). As a result, the production of bacterial cellulose (BC) in the medium with the filtrate was 5.65 g/L, which was 10 times as high as that in natural coconut water (NCW) compared to 2.8 times for the medium with the cell residue, suggesting that the filtrate of FCW significantly promotes BC synthesis. Changes in organic acid contents in the filtrate during the fermentation of coconut water were analyzed by gas chromatography-mass spectrometry (GC-MS) and high performance liquid chromatography (HPLC). The total amount of volatile compounds in the filtrate was about 5 times as high as that in NCW. Alcohols were the major volatile components in the filtrate, accounting for approximately 62% of the total amount, and the contents of ethanol and acetic acid were 4.5 and 48 times as high as those in NCW, respectively. The contents of acetic and lactic acid gradually increased during the fermentation process, while the contents of all other organic acids except gluconic acid, signi ficantly decreasing from day 1 to 3, did not signi ficantly change. Hence, it was deduced that microbial metabolites generated during the fermentation of coconut water make an important contribution to BC synthesis, and that the alcohols and acids greatly changing after the fermentation may affect BC synthesis by participating in regulating the metabolism of K. nataicola Y19.