Yun, Jeong Hyun
(Department of Food Biotechnology, Korea University of Science and Technology)
,
Kim, Jae Ho
(Research Group of Traditional Food, Korea Food Research Institute)
,
Lee, Jang-Eun
(Department of Food Biotechnology, Korea University of Science and Technology)
In the present study, we aimed to determine the cause of surface film formation in three rice vinegars fermented using the traditional static fermentation method. The pH and total acidity of vinegar were 3.0-3.3 and 3.0-8.7%, respectively, and acetic acid was the predominant organic acid present. Co...
In the present study, we aimed to determine the cause of surface film formation in three rice vinegars fermented using the traditional static fermentation method. The pH and total acidity of vinegar were 3.0-3.3 and 3.0-8.7%, respectively, and acetic acid was the predominant organic acid present. Colonies showing a clear halo on GYC medium were isolated from the surface film of all vinegars. Via 16S rDNA sequencing, all of the isolates were identified as Acetobacter pasteurianus. Furthermore, field-emission scanning electron microscopy analysis showed that the bacterial cells had a rough surface, were rod-shaped, and were ${\sim}1{\times}2{\mu}m$ in size. Interestingly, cells of the isolate from one of the vinegars were surrounded with an extremely fine threadlike structure. Thus, our results suggest that formation of the surface film in rice vinegar was attributable not to external contamination, to the production of bacterial cellulose by A. pasteurianus to withstand the high concentrations of acetic acid generated during fermentation. However, because of the formation of a surface film in vinegar is undesirable from an industrial perspective, further studies should focus on devising a modified fermentation process to prevent surface film formation and consequent quality degradation.
In the present study, we aimed to determine the cause of surface film formation in three rice vinegars fermented using the traditional static fermentation method. The pH and total acidity of vinegar were 3.0-3.3 and 3.0-8.7%, respectively, and acetic acid was the predominant organic acid present. Colonies showing a clear halo on GYC medium were isolated from the surface film of all vinegars. Via 16S rDNA sequencing, all of the isolates were identified as Acetobacter pasteurianus. Furthermore, field-emission scanning electron microscopy analysis showed that the bacterial cells had a rough surface, were rod-shaped, and were ${\sim}1{\times}2{\mu}m$ in size. Interestingly, cells of the isolate from one of the vinegars were surrounded with an extremely fine threadlike structure. Thus, our results suggest that formation of the surface film in rice vinegar was attributable not to external contamination, to the production of bacterial cellulose by A. pasteurianus to withstand the high concentrations of acetic acid generated during fermentation. However, because of the formation of a surface film in vinegar is undesirable from an industrial perspective, further studies should focus on devising a modified fermentation process to prevent surface film formation and consequent quality degradation.
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가설 설정
pasteurianus, AB3, has been isolated from rice vinegar with an acetic acid content of ]9% (v/v) [15]. Based on these findings, we proposed that the vinegar sample contained the inoculated pure strain, A. pasteurianus, that the surface film formation in vinegar was not attributable to contamination by external factors.
제안 방법
The selected strain was isolated from farmhouse vinegar in Chungbuk province, Korea, because it has high acid-producing ability. The collected vinegars were categorized as vinegar 1 (V1), vinegar 2 (V2), and vinegar 3 (V3) on the basis of the morphological characteristics of their surface films. Glucose, yeast extract, and calcium carbonate (GYC) culture medium was used to culture causative species of surface film formation isolated from the vinegar samples.
Nonetheless, only a few studies have examined the contamination of, and cellulose film formation in, vinegar in Korea[12]. Therefore, the present study aimed to determine the cause of the occurrence of surface in static-fermented rice vinegar by analyzing the characteristics of the vinegar and the responsible strains.
대상 데이터
Culture conditions were maintained at 27℃ for 5 days. The PCR primers used for identification were 27 F 50- (AGA GTT TGA TCM TGG CTC AG)-30 and 1492 R 50-(TAC GGY TAC CTT GTT ACG ACT T)-30 . PCR was carried out using EF-Taq (SolGent, Daejeon, Korea) with 20 ng of genomic DNA as the template in a 30 mL reaction mixture.
이론/모형
Table 2. 16S rDNA gene analysis of the microorganism isolated from three rice vinegar produced by static fermentation method.
An ABI Prism 3730XLDNA analyzer (Applied Biosystems) was used for analysis. The phylogenetic analysis was conducted in MEGA7 using Maximum Likelihood method.
Table 1. pH, total acidity and organic acid of rice vinegar produced by static fermentation method.
성능/효과
All isolates were identified as A. pasteurianus with >99.9% sequence similarity.
In contrast, the cell surface becomes rough in a medium with 4% ethanol and it becomes smooth in the medium with 4% acetic acid and 0% ethanol at the end of fermentation. In addition, the results of their study suggested that formation of a rough cell surface in A. pasteurianus was associated with a decrease in the content of capsular polysaccharides (CPSs) which are a type of polysaccharide observed on the surface of gram-negative bacteria along with exopolysaccharides, and are strongly resistant to acetic acid. It has been found that dTDP-rhamnose, a constituent of CPSs, is not synthesized when dTDP-4-dehydrorhamnose reductase is downregulated.
In conclusion, the findings of the present study indicate that A. pasteurianus cells in rice vinegar produced biofilm to withstand the high acetic acid concentration (above 8%), and that the surface film in the vinegar samples was formed by the aggregation of the bacteria and polysaccharides. However, it is speculated that some other factors might have been responsible for the formation of the pink floating matter found in V1, because of its unique morphological characteristics and the physicochemical properties of V1.
후속연구
However, its presence is undesirable if high-quality vinegar needs to be produced, because it causes turbidity and overoxidation. Thus, further studies should focus on devising a modified fermentation process to prevent surface film formation and consequent quality degradation, and determine the cause of pellicle formation through further analyses.
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