FOOD MICROBIOLOGY www.elsevier.nl/locate/jnlabr/yfmic Food Microbiology 21 (2004) 657–666 Bacterial microflora of carp (Cyprinus carpio) and its shelf-life extension by essential oil compounds Barakat S.M. Mahmoud a, *, Koji Yamazaki a , Kazuo Miyashita b , Shin Il-Shik c , Chang Dong-Suk d , Tetsuya Suzuki a a Laboratory of Marine Food Science, Graduate School of Fisheries Science, Hokkaido University, Minato, Hakodate 041-8611, Japan b Laboratory of Bioresources Chemistry, Graduate School of Fisheries Science, Hokkaido University, Minato, Hakodate 041-8611, Japan c Faculty of Marine Bioscience, Kangnung National University, Kangnung 210-702, South Korea d College of Fisheries Science, Pukyong National University, Busan, South Korea Received 18 September 2003; accepted 2 March 2004 Abstract The microflora of common carp (Cyprinus carpio) skin, gill and intestine were analysed and the antimicrobial activities of garlic oil and nine constituents of essential oils (allyl isothiocyanate, carvacrol, cinnamaldehyde, citral, cuminnaldehyde, eugenol, isoeugenol, linalool and thymol) against the carp isolates were studied to identify compounds that might extend the shelf-life of carp fillet. A total of 90 isolated strains were identified to belong to seven genera: Acinetobacter (6), Alcaligenes (2), Bacillus (2), Flavobacterium (20), Micrococcus (2), Moraxella (6) and Pseudomonas (4), and two families Enterobacteriaceae (14) and Vibrionaceae (34). The dominant micro-organisms of carp were found to be Flavobacterium (37%) and Vibrionaceae (33%) in skin, Flavobacterium (33%) in gill and Vibrionaceae (63%) and Flavobacterium (37%) in intestine. Against these isolates, thymol, carvcarol and cinnamaldehyde had the strongest antimicrobial activities, followed by isoeugenol, eugenol, garlic oil, and then citral. The antimicrobial properties of the other constituents tested (cuminnaldehyde, linalool and allyl isothiocyanate) were low. In tests of mixed compounds, a combination of carvacrol and thymol had the highest antimicrobial activity. Moraxella, Flavobacterium and Vibrionaceae were more sensitive to the compounds, whereas Alcaligenes strains were resistant. Dipping carp fillets in a solution of 0.5% carvacrol and 0.5% thymol before storage at 5  C and 10  C reduced both the total microbial load by about 100-fold and the Volatile Bases Nitrogen (VB-N), as compared with controls. In addition, dipping treatment delayed bacterial growth and extended the shelf-life of the fillets from 4 to 12 days at low temperature (5  C). However, the treated and control fillets showed little difference during storage at 10  C. Data from sensory evaluation showed that dipped fillets in 1% (carvacrol+thymol) extended the shelf-life of carp fillets by 8 and 4 days at 5  and 10  C, respectively. Thus, carvacrol and thymol dipping can improve the microbial stability of fish fillets by removing bacteria and by inhibiting bacterial growth. r 2004 Elsevier Ltd. All rights reserved. Keywords: Antimicrobial; Carp fillet; Essential oil; Microflora; Shelf-life 1. Introduction Fresh seafood has a short shelf-life, which causes substantial practical problems for its distribution. Improvements in the shelf-life of a product can have an important economic impact by reducing losses attributed to spoilage and by allowing the products to reach distant and new markets (Rhodehamel, 1992). In addition, food borne illnesses are still a major threat, even in developed countries (Meed and Laurence, 1999). It has been known since ancient times that the essential oils in some spices have preservative properties. The use of essential oils extracted from cinnamon, clove and cassia in mummifying processes by ancient Egyp- tians is well documented (Bullerman et al., 1977). Spices are also used as culinary ingredients and in medicine (Thyagaraja and Hosono, 1996). Essential oils have natural antimicrobial properties with the potential to extend the shelf-life of food when used alone or in combination with other preservation techniques ARTICLE IN PRESS *Corresponding author. Tel/Fax: +81-138-40-5564. E-mail address: barakatsmm@yahoo.com (B.S.M. Mahmoud). 0740-0020/$-see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.fm.2004.03.001