Contamination from Alicyclobacillus species is a major concern for processors of acidic juices and concentrates such as apple, orange and cranberry. What makes spoilage by Alicyclobacillus a headache is its resistance to normal thermal processing and the fact that an off-flavour is virtually the only way to detect it.

Scientists at Cornell University said that although the bacterium is recognised as a widespread problem, its contamination has yet to be thoroughly investigated.

Writing in the International Journal of Food Microbiology the researchers therefore collected 141 Alicyclobacillus isolates from different drinks for study.

Spoilage patterns

Author Randy Worobo told BeverageDaily.com that the new research indicates that the propensity for specific Alicyclobacillus species depends on the type of juice and whether it is from fresh or concentrate sources.

The most frequently isolated species was found to be Alicyclobacillus acidoterrestris at 45 per cent. This was most frequently associated with citrus and citrus concentrates and accounted for the majority of thermotolerant sporeformers isolated from apple juices and concentrates.

But the researchers also found other strains including A. acidocaldarius subsp. acidocaldarius and A. acidocaldarius can be responsible for contamination.

Worobo said: “Some juice and beverage manufacturers have been concerned with only A. acidoterrestris detection in finished product or starting ingredients but our results suggest that depending on the juice concentrate or ingredient used, the pertinent Alicyclobacillus may not be A. acidoterrestris but may be other Alicyclobacillus strains that are also capable of producing guaiacol and other off odors.”

Additional research is in the final stages of completion that is investigating the correlation between Alicyclobacillus strains and their heat resistance and guaiacol (off-flavour) production levels. Worobo and his colleagues hope that their work will help processors chose spoilage control techniques tailored to the relevant Alicyclobacillus species and avoid unnecessary over-processing.

Elimination and prevention

For the most part, the techniques available for eliminating the bacterium are limited. Filtration and some preservative combinations have been shown to be effective and thermal processing can work but at the levels needed it usually has negative effects on the sensory properties of drinks.

As for prevention, Worobo made the following recommendations. “One of the first ways to protect from Alicyclobacillus spoilage is prevention at the ingredient source by having COA’s (Certificate of Analysis) for the concentrate or ingredients (sugar) they are buying.

“The amount of concentrate analyzed for Alicyclobacillus should also be increased by filtration or enrichment rather than direct plating of concentrate to increase the sensitivity of their analysis.”