Contamination of an Unpreserved Semisoft Baked Cookie with a Xerophilic Aspergillus species

Abstract

An Aspergillus mold was isolated that had contaminated an unpreserved semisoft baked cookie with visible mycelial growth. Due to the xerophilic nature of the contaminating mold, the Aspergillus isolate went undetected using conventional plating media and incubation times. Spread plating onto rose bengal osmophilic potato dextrose (rose-osmo) agar, a reduced water activity (aw) medium, was used for isolation and enumeration of the isolate from contaminated cookies and in microbiological assessments of the production facility. Rose-osmo plates were sealed in plastic and incubated at 25°C for up to 6 weeks to allow the isolate to sporulate. The minimum aw that permitted growth was determined by inoculating both MY70GF agar plates and production cookies with fresh spores of the Aspergillus isolate. Inoculated samples were incubated for up to 6 weeks in humidity chambers adjusted to various moisture levels. The minimum aw required for growth of the Aspergillus isolate was found to be between 0.60 and 0.65 on MY70GF agar and approximately 0.65 on the cookie. To evaluate the potential delayed growth of the isolate on reformulated cookies of a lowered aw, long-term growth studies were conducted on cookies adjusted to various aw levels and monitored for up to 280 days. In these studies, the minimum aw test range found to support visible mycelial growth of the Aspergillus isolate was 0.67. Microbiological assessment of the production facility identified potential sources of xerophilic molds and the Aspergillus isolate (teleomorph Eurotium chevalieri) and identified the manner in which the cookies became contaminated. These methods and results proved helpful in both production and process risk assessments and in successful reformulation of the cookie at an aw low enough to prevent spoilage and provide an organoleptically acceptable product.