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Microbial Quality of and Biochemical Changes in Fresh Soft, Acid-Curd Xinotyri Cheese Made from Raw or Pasteurized Goat’s Milk


Eleni C. Pappa1*orcid tiny, Thomas G. Bontinis2orcid tiny, Maria Tasioula-Margari2† and John Samelis1orcid tiny

1Dairy Research Department, Institute of Technology of Agricultural Products, Hellenic Agricultural
Organization, DEMETER, Ethnikis Antistaseos 3, Katsikas, GR-45221 Ioannina, Greece
2Department of Chemistry, University of Ioannina, University Campus of Ioannina, GR-45110 Ioannina, Greece


Article history:
Received: May 8, 2017
Accepted: October 10, 2017


Key words:
microbiological and physicochemical characteristics, goat’s milk, soft Xinotyri cheese,
lipolysis, volatiles, proteolysis


Summary:
The microbiological quality of and changes in the main physicochemical parameters, together with the evolution of proteolysis, lipolysis and volatile profiles of soft Xinotyri, a traditional Greek acid-curd cheese (pH≈4.4, moisture 65 %, salt 1 %) made from raw (RMC) or pasteurized (PMC) goat’s milk without starters, were evaluated during aerobic storage at 4 °C for 60 days. No statistically significant differences between the total nitrogen (TN) and nitrogen fraction (% of TN) contents, the degradation of intact αs- or β-caseins, total free amino acid (FAA) contents, and the ratio of hydrophilic and hydrophobic peptides in the water-soluble fraction of RMC and PMC were found. Threonine, alanine and lysine were the principal FAAs. Oleic, palmitic, capric and caprylic acids, and ethyl hexonate, ethyl octanoate, ethyl decanoate, ethanol, 3-methyl butanol, phenyl ethyl alcohol and acetone were the most abundant free fatty acids and volatile compounds, respectively. Cheese lipolysis evolved slowly at 4 °C, and milk pasteurization had no significant effect on it. Mesophilic lactic acid bacteria (LAB) were predominant in fresh cheese samples. PMC samples had significantly lower  evels of enterococci and enterobacteria than RMC samples, while yeasts grew at similar levels during storage at 4 °C. All cheese samples (25 g)  ere free of Salmonella and Listeria monocytogenes. Coagulase-positive staphylococci exceeded the 5-log safety threshold in fresh RMC samples,  hereas they were suppressed (<100 CFU/g) in all PMC samples. Consequently, pasteurization of raw goat milk’s and utilization of commercially  efined or natural mesophilic LAB starters are recommended for standardizing the biochemical, microbial and safety qualities of fresh soft Xinotyri

cheese.



*Corresponding author:  tel3  +30 26 510 94 785
                                                fax2  +30 26 510 92 523
                                                 email3  pappa.eleni@yahoo.gr


 

In memory of Professor Maria Tasioula-Margari

 



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