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Microbiological Analysis

Alicyclobacillus Acidoterrestris: A New Spoilage Organism in Fruit Juices

Alicyclobacillus acidoterrestris is a spore-forming soil microorganism that has been a cause of spoilage problems for the fruit juice industry. Spoilage has been observed in apple juice, pear juice, orange, peach and white grape juices. It has also caused problems with juice blends, fruit juice containing drinks, tomato juice and canned tomatoes. In apple juice, the spoilage manifests itself as an off-flavor and off-odor in shelf stable products. This spoilage problem has proved to be expensive in the United States and Europe, resulting in consumer complaints and product withdrawals.

Alicyclobacillus acidoterrestris are sometimes called acidophilic thermophilic bacteria (ATB). As the name implies, ATB grow well in acidic environments (such as fruit juice), surviving at pH levels as low as 2.5. They also grows well at elevated temperatures. The spores can survive the pasteurization treatment given to most shelf stable, glass pack fruit juices. The heat treatment activates the spores to begin growth. Most contamination problems show up several days after bottling.

KFL has been researching the problem of A. acidoterrestris spoilage since 1990, when commercial apple juice samples were submitted to us for off-odor evaluation. Our research showed that the off-odor defect in pasteurized apple juice is due to guaiacol, produced by ATB contamination from vanillin in the juice (see Figures 1 and 2).

click to enlarge Figure 1.
Normal Apple Juice

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click to enlarge Figure 2.
Apple Juice Spoiled by ATB

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The odor of guaiacol is quite distinctive and a clear sign that there is a spoilage problem due to ATB. Guaiacol detection in finished juice products is accomplished by methylene chloride extraction, concentration and analysis by GC-MS.

ATB can be detected in spoiled products by pour plating or membrane filtration, with growth on K Agar medium. Concentrates are analyzed for A. acidoterrestris spores by treating the sample to a preliminary heat shock, followed by plating on K Agar medium.

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