Surface Film Formation in Static-Fermented Rice Vinegar: A Case Study

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 ∼1 × 2 µm 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.

Screening of Thermotolerant Acetic Acid Bacteria Involved in Cocoa Fermentation in Six Major Cocoa Producing Regions in Côte d’Ivoire

Aims: This work intends to screen and to identify thermotolerant acetic acid bacteria with acetic acid production capacity at high temperature in cocoa beans fermentation from six cocoa producing regions of Côte d’Ivoire. Study Design: Thermotolerant acetic acid bacteria were isolated from cocoa fermentation. These thermotolerant strains were biochemically characterized and tested for the production of acetic acid in culture medium. Place and Duration of Study: This study was performed in Biotechnology Laboratory, University Félix Houphouët-Boigny (Côte d’Ivoire) from January to November 2017. Methodology: Several strains of acetic acid bacteria were isolated from the traditional cocoa beans heap fermentation process occurred in six major cocoa producing regions of Côte d’Ivoire. These isolates were screened to select thermotolerant strains that were able to produce a good amount of acetic acid. Biochemical identification of thermotolerant acetic acid bacteria was carried out on the basis of biochemical characteristics analysis as acid production from ethanol, oxidation of acetate and lactate, ketogenesis from glycerol or mannitol, formation of water-soluble brown pigment, growth on different carbon sources and acid production from sugars and sugar alcohols. Results: A total of 821 acetic acid bacteria strains were isolated from the cocoa beans heap fermentation of these six regions. Among them, 26 (31.15%) showed growth capacity at 45°C and six (6) grown at 50°C. These 26 strains displayed also acid production capacity at 35°C and at 45°C with acid amount ranged from 1.2 to 24.63 and 0.80 to 1.70 respectively. Biochemical analyses of these thermotolerant strains revealed that the isolates belong to three genera notably Acetobacter, Gluconacetobacter or Gluconobacter. Moreover, all strains were able to grow in medium containing 10% ethanol and to produce acid from various carbohydrates sources. In addition, strain T6HS14 displayed acetoin production capacity while 8 strains were able to produce brown pigment on Yeast extract-Ethanol-Peptone-Glucose medium. Conclusion: This study highlighted the presence of thermotolerant acetic acid bacteria strains involved in Ivorian cocoa fermentation. Furthermore, some isolates displayed a diversity of technological properties which could be used for the improvement of cocoa fermentation process. These predictors, however, need further work to validate reliability.

Bacteria isolated from Korean black raspberry vinegar with low biogenic amine production in wine

Abstract A high concentration of histamine, one of the biogenic amines (BAs) usually found in fermented foods, can cause undesirable physiological side effects in sensitive humans. The objective of this study is to isolate indigenous Acetobacter strains from naturally fermented Bokbunja vinegar in Korea with reduced histamine production during starter fermentation. Further, we examined its physiological and biochemical properties, including BA synthesis. The obtained strain MBA-77, identified as Acetobacter aceti by 16S rDNA homology and biochemical analysis and named A. aceti MBA-77. A. aceti MBA-77 showed optimal acidity % production at pH 5; the optimal temperature was 25 °C. When we prepared and examined the BAs synthesis spectrum during the fermentation process, Bokbunja wine fermented with Saccharomyces cerevisiae showed that the histamine concentration increased from 2.72 of Bokbunja extract to 5.29 mg/L and cadaverine and dopamine was decreased to 2.6 and 10.12 mg/L, respectively. Bokbunja vinegar prepared by A. aceti MBA-77 as the starter, the histamine concentration of the vinegar preparation step was decreased up to 3.66 mg/L from 5.29 mg/L in the wine preparation step. To our knowledge, this is the first report to demonstrate acetic acid bacteria isolated from Bokbunja seed vinegar with low spectrum BA and would be useful for wellbeing vinegar preparation.

Blackberry Vinegar Produced By Successive Acetification Cycles: Production, Characterization And Bioactivity Parameters

ABSTRACT: Blackberry vinegar was produced in successive acetification cycles and content of total phenolics, anthocyanins and antioxidant activity were evaluated along the production. Firstly, blackberry wine was obtained in bench-scale bioreactor, being verified 0.39 g/g ethanol yield, 1.78 g/L.h volumetric productivity and 76% efficiency. After, three successive acetification cycles were conducted efficiently in grapia barrel with average acetic acid production of 51.6 g/L, 72.2 % acetic acid yield and 0.4 g/L.h volumetric productivity. Appreciable contents of polyphenolic compounds, anthocyanins and high antioxidant activity were observed in the raw material, wine and vinegar obtained in each cycle of acetic acid transformation. Acetic acid transformation led the small reduction of antioxidant activity compared to alcoholic fermentation, but the antioxidant potential was maintained along the cycles. The content of total phenolics and anthocyanins also suffered a reduction in step of acetification.

Research Progress on the Polyphasic Taxonomy of Acetic Acid Bacteria / 微生物学通报

Acetic acid bacteria are Gram-negative,obligate aerobic bacteria that have the ability to incompletely oxidize alcohols or sugars to organic acids as end products. The taxonomy of acetic acid bacteria has undergone many changes in the last 30 years. The early classification systems for these bacteria were based on morphological and biochemical characteristics. Today,the acetic acid bacteria are classified as the consensus result of a polyphasic analysis,combining phenotypic,chemotaxonomic and genotypic data. This paper reviewed the polyphasic taxonomy of acetic acid bacteria,mainly introduced the current classification of acetic acid bacteria,then discussed the application of phenotypic,chemotaxonomic and genotypic method in the taxonomy of acetic acid bacteria.