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Title: Microbial growth and the effects of mild acidification and preservatives in refrigerated sweetpotato puree

Author
item Perez Diaz, Ilenys
item Truong, Van Den
item Webber, Ashlee
item McFeeters, Roger

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2007
Publication Date: 3/1/2008
Citation: Perez Diaz, I.M., Truong, V., Webber, A.M., McFeeters, R.F. 2008. Microbial growth and the effects of mild acidification and preservatives in refrigerated sweetpotato puree. Journal of Food Protection. 71(3):639-642.

Interpretive Summary: Currently, canning and freezing are well-established methods for the processing and distribution of sweetpotato purees. While canned purees lose nutrients due to the excessive thermal treatment, frozen purees require considerable investment in distribution and storage. With these constraints, there is interest in production of refrigerated sweetpotato purees. Although, most microorganisms present on the raw root will be killed during production of the puree to be refrigerated, there is the potential for post production contamination by both pathogenic and non-pathogenic bacteria. Therefore, the capability of sweetpotato puree to sustain growth of pathogenic bacteria was studied. Bacteria that can cause human illness were capable of growing in the refrigerated sweetpotato puree. However, addition of preservatives commonly used in foods, like sorbic acid, benzoic acid and citric acid prevented growth of these bacteria in the refrigerated sweet potato puree.

Technical Abstract: Refrigerated sweetpotato puree is a convenient form of this vegetable to be used as an ingredient in formulated foods. The microbiology of refrigerated sweetpotato puree during storage for up to 5 weeks, was evaluated. Since puree is made by comminuting steam cooked sweetpotatoes prior to refrigeration, microbial counts during the storage period were below the detection limit. However, if post processing microbial contamination of the puree were to happen, growth could proceed. Inoculation of sweetpotato puree stored at 4°C with 10^6 CFU/ml of common infectious pathogens resulted in a 3-log increase in Listeria monocytogenes and a 1-log increase in E. coli O157:H7 and Salmonella spp., after 3 weeks storage. Supplementation of the sweetpotato puree with 0.06% (w/v) sorbic acid or benzoic acid prevented growth of L. monocytogenes during storage at 4°C. Mild acidification of the sweetpotato puree to pH 4.2 with citric acid also prevented growth of L. monocytogenes during storage at 4°C