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107 CFU g−1 the first day of ripening and remained almost constant, while in cheeses made with HP starter strain lactobacilli grew throughout ripening. Soluble nitrogen at pH 4.4 was higher in cheeses made with starter HP. Different values for free amino acids were noted for the three starter strains and between cheeses with and without lactobacilli, while peptide profiles varied from one starter strain to another and showed quantitative differences between cheeses with and without lactobacilli. Casein fraction profile was essentially the same for all cheeses.
doi:10.1016/j.fm.2007.11.006 
Copyright © 2007 Elsevier Ltd All rights reserved.
Tyramine production in Dutch-type semi-hard cheese from two different producers
Received 26 March 2007;
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Abstract
Tyramine content and counts of lactic acid bacteria (LAB) and enterococci were measured (including tyrosine-decarboxylase activity testing, and testing of the presence of the tyrosine-decarboxylase gene sequence, tyrdc, by PCR) during ripening (0, 26, 54, 88, 119, 146, and 176 days) in the core (C)- and edge (E)-samples of Dutch-type semi-hard cheese produced from pasteurized milk by two dairies (R, H) with two levels of fat content (30 and 45%) using two different starter cultures (Y, L), respectively. Tyramine content (y, mg kg−1) increased (P<0.001) with increasing time of ripening (x, days) in the cheeses of both producers (R: y=0.88x−31.4, R2=0.30; H: y=0.50x−6.3, R2=0.18), and its content was higher (P<0.01) in E-samples in comparison with C-samples. Time of ripening, part of the cheese and starter culture accounted for 67%, 28%, and 4% of explained variability of tyramine content in the cheese, respectively. After 26 days of ripening, using decarboxylase screening medium (DCM), tyrosine-decarboxylase positive LAB isolates constituted 7–27% and 6–32% of the square root of total countable colonies of LAB isolates of the producer R and H, respectively; tyrosine-decarboxylase positive enterococci were present only in R-cheeses (4–26% of the square root of total countable colonies). Tyrdc was confirmed only in 13% and 42% of the tyrosine-decarboxylase positive LAB and enterococci isolates, respectively (presumably due to the tendency of DCM to give false-positive results). Lactobacillus curvatus subsp. curvatus and Enterococcus durans, Enterococcus faecalis, and Enterococcus casseliflavus were identified as tyrdc-positive LAB and enterococci in the cheeses, respectively.
Keywords: Tyramine; Tyrosine-decarboxylase; Tyrosine-decarboxylase gene; Lactic acid bacteria; Enterococci; PCR; Ripening cheese
Article Outline
- 1. Introduction
- 2. Materials and methods
- 2.1. Cheese-making
- 2.2. Tyramine determination
- 2.3. Microbiological counts
- 2.4. Screening of microorganisms with tyrosine-decarboxylase activity and confirmation of tyramine formation
- 2.5. Isolation of DNA and PCR screening of the tyrosine-decarboxylase (tyrdc) gene fragment
- 2.6. Specification of tyrdc-positive isolates
- 2.7. Statistical evaluation
- 3. Results and discussion
- 3.1. Tyramine content in cheeses
- 3.2. Microorganisms associated with the cheeses
- 3.3. Screening of tyrosine-decarboxylase activity and tyrosine-decarboxylase gene
- 4. Conclusions
- Acknowledgements
- References
