Journal
INTERNATIONAL JOURNAL OF FOOD MICROBIOLOGY
Volume 145, Issue 1, Pages 365-369Publisher
ELSEVIER SCIENCE BV
DOI: 10.1016/j.ijfoodmicro.2011.01.012
Keywords
Fungal contamination; Microbiological monitoring; Tea based drinks; Rapid enumeration; Automated system; Microcolony method
Categories
Funding
- JSPS [21256002]
- Grants-in-Aid for Scientific Research [21256002] Funding Source: KAKEN
Ask authors/readers for more resources
Aseptically prepared cold drinks based on tea have become popular worldwide. Contamination of these drinks with harmful microbes is a potential health problem because such drinks are kept free from preservatives to maximize aroma and flavour. Heat-tolerant conidia and ascospores of fungi can survive pasteurization, and need to be detected as quickly as possible. We were able to rapidly and accurately detect low numbers of conidia and ascospores in tea-based drinks using fluorescent staining followed by an automated counting system. Conidia or ascospores were inoculated into green tea and oolong tea, and samples were immediately filtered through nitrocellulose membranes (pore size: 0.8 mu m) to concentrate fungal propagules. These were transferred onto potato dextrose agar and incubated for 23 h at 28 degrees C. Fungi germinating on the membranes were fluorescently stained for 30 min. The stained mycelia were counted selectively within 90 s using an automated counting system (MCS-10LD; Chuo Electric Works, Osaka, Japan). Very low numbers (1 CFU/100 ml) of conidia or ascospores could be rapidly counted, in contrast to traditional labour intensive techniques. All tested mould strains were detected within 24 h while conventional plate counting required 72 h for colony enumeration. Counts of slow-growing fungi (Cladosporium cladosporioides) obtained by automated counting and by conventional plate counting were close (r(2) = 0.986). Our combination of methods enables counting of both fast- and slow-growing fungi, and should be useful for microbiological quality control of tea-based and also other drinks. (C) 2011 Elsevier B.V. All rights reserved.
Authors
I am an author on this paper
Click your name to claim this paper and add it to your profile.
Reviews
Recommended
No Data Available