The organisation’s senior research officer, Andres Rodriguez told FoodNavigator.com: “The problem does not happen very often then but when it does, it can have huge economic impact for the food industry. Product quality is severely affected but this is not a food safety issue.”
Soup thinning affects particularly starchy soups or white soups such as cream of chicken.
Insufficient heating
Scientists are working to understand what causes the problem. So far, insufficient heating and acidity are thought to be critical factors.
Thinning is believed to result from starch breakdown, caused by heat resistant amylases from Bacillus species that are not inactivated by the heat process. Another important factor is thought to be the growth of Bacillus species that have survived the heating process and subsequently go on to produce amylase enzymes.
Most of the soups that suffer thinning have a pH between 6 and 7.
Further research will focus on revealing the source of the Bacillus species implicated in the thinning and the critical conditions for enzyme production together with reaching a clearer understanding of the enzyme's thermal resistance.
“One potential solution is to establish a maximum limit on bacterial spores in the raw ingredients,” said Rodriquez. “Additional steps may need to be used to establish a critical heat treatment that could reduce or eliminate the spore load in the soups during processing.”
Last week, Campden BRI scientists presented a poster on their soup thinning research at the International Association for Food Protection annual meeting held in Anaheim, California.
Alpha-amylase
Researchers studied three soups with different pH values including cream of tomato, potato and leek, and cream of chicken. Each was incubated with spores of B. subtilis, B. licheniformis, and B. megaterium, or B. licheniformis alpha–amylase at three different concentrations.
The three bacilli were able to grow to a high level in the potato and leek and cream of chicken soups within 48 hours causing rapid thinning.
The addition of alpha–amylase had a similar effect.
But in the more acidic tomato soup, only B. licheniformis grew and growth was relatively small and slow. No thinning was observed in this soup following incubation with Bacillus, and only the highest enzyme level had a thinning effect.
A summary of the research appeared in Campden BRI’s August 2010 newsletter.