Acetic acid bacteria detection

Table 8.3 Conventional and rapid detection and characterisation methods for heer spoilage acetic acid bacteria, Zymomonas, and Enterobacteriaceae species...

Acetic acid produced by LAB is often sensorially different from that resulting from growth of acetic acid bacteria (AAB). In the latter case, VA is often perceived as a mixture of acetic acid and ethyl acetate, whereas with LAB, the ethyl acetate component is either missing or present at very low levels (Henick-Kling, 1993). Sensorially, acetic acid, in the absence of the acetate ester, is less easily detected even at levels well in excess of legal limits. 

In traditional fermented foods in Asia such as soy sauce (shoyu), fermented soybean-barley miso) in Japan, and pickles such as kimchi in Korea and tsukemono in Japan, various organic acids, such as acetic acid, lactic acid, and citric acid, are detected by chemical and liquid chromatographic analyses. The largest amount of lactic acid is contained in Japanese pickles, tsukemono, followed by acetic, citric, formic, mahc, and glutamic acids (Tomomatsu et al. 1972). More than 13 species of lactic acid bacteria and 10 species of yeast isolated from six kinds of tsukemono were identified by 16S rRNA sequence analysis (Asada and Ueno 2009). However, no acetic acid bacteria were detected. By cultivatiOTi of isolated yeast strains, acetic acid, citric acid, and succinic acid were detected in the fermentation broth. However, more careful experiments would be required to conclude that the special yeast can form acetic acid. 

G. oxydans N44-1 expressing SNDHai gene also converts o-sorbitol and L-sorbose to vitamin C, via L-sorbosone as the intermediate. SNDHai enzymes were also detected enzymatically and genetically in other acetic acid bacteria strains such as Gluconobacter strains NBRC 3292, 3244, 3287, and ATCC 15164 (Berry et al. 2003). 

Short-chain and low molecular weight organic acids, such as acetic acid and formic acid, can be formed by certain bacteria. The resulting organic acid salts are not easily detected without specialized analytical equipment in a laboratory. 

These exceptions may be linked to cases of difficnlt alcoholic fermentation, leading to abnormally high concentrations of acetic acid produced by yeast. It is, however, possible to detect by analysis whether the acetic acid in a wine was produced exclusively during fermentation, without the involvement of bacteria (Volume 1, Section 14.2.3). Lactic bacterial activity leads to concentrations higher than 200 mg/1 of isomers of lactic acid and acetic bacteria produce ethyl acetate levels above 160 mg/1. 

A recent research project targeted the brewery-specific identification of microorganisms found in local biofihn stracmres. As the main inhabitants of the fully grown biofihns that were analyzed, various wild yeasts were detected. In single cases, also lactic acid- or acetic acid-producing bacteria were detected. 

The separation by TLC of the 2,4-dinitrophenylhydrazone (DNP) of dehydroascorbic acid is extremely specific and has been employed for detection and determination of vitamin C in food and feeding stuffs, fats, fruit juices, wines and bacteria etc. In the method of Stroheckeb et al. [129, 130] the ascorbic acid in the extracts is oxidised with 2,6-dichlorophenol-indophenol (Vuilleumieb and Nobile [139] use bromine for this) the dehydroascorbic acid formed is then reacted for 3 hours at 70 C with 2,4-dinitrophenylhydrazine in the presence of a little trichloroacetic acid and thiourea [131]. After cooling 10 min in ice, the red or red-brown precipitate is collected on a sintered glass filter, washed with water and dissolved in ethyl acetate or acetone the solution is evaporated and the residue taken up in acetone. 0.1—1.0 ml (20 to 50 [xg vitamin C) of this solution is applied as a band to air dried silica gel H layers and chromatographed with chloroform-ethyl acetate (50 + 50) or, better, with chloroform-ethyl acetate-acetic acid (60 + 35 -f 5). The red DNP of the dehydroascorbic acid is thus clearly separated... 

Additional yeast spoilage is induced by species of the genera Candida Mycoderma), Pischia and Hansenula (Willia). Other microorganisms are involved in the formation of viscous, moldy and ropy wine flavor defects. Bacterial spoilage may involve acetic acid and lactic acid bacteria. In this case vinegar or lactic acid souring is detectable. It has usually been associated with mannitol fermentation which may result in considerable amounts of mannitol. 

The anaerobic metabolism of acrylate and 3-mercaptopropionate (3-MPA) was studied in slurries of coastal marine sediments. The rate of these compounds is important because they are derived from the algal osmolyte dimethylsulfoniopropionate (DMSP), which is a major organic sulfur compound in marine environments. Micromolar levels of acrylate were fermented rapidly in the slurries to a mixture of acetate and propionate (1 2 molar ratio). Sulfate-reducing bacteria subsequently removed the acetate and propionate. 3-MPA has only recently been detected in natural environments. In our experiments 3-MPA was formed by chemical addition of sulfide to aciylate and was then consumed by biological processes. 3-MPA is a known inhibitor of fatty acid oxidation in mammalian systems. In accord with this fact, high concentrations of 3-MPA caused acetate to accumulate in sediment slurries. At lower concentrations, however, 3-MPA was metabolized by anaerobic bacteria. We conclude that the degradation of DMSP may ultimately lead to the production of substrates which are readily metabolized by microbes in the sediments. 

---