Abstract
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 oC 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 oC, 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 levels of enterococci and enterobacteria than RMC samples, while yeasts grew at similar levels during storage at 4 oC. All cheese samples (25 g) were free of Salmonella and Listeria monocytogenes. Coagulase- -positive staphylococci exceeded the 5-log safety threshold in fresh RMC samples, whereas they were suppressed (<100 CFU/g) in all PMC samples. Consequently, pasteurization of raw goat milk's and utilization of commercially defined or natural mesophilic LAB starters are recommended for standardizing the biochemical, microbial and safety qualities of fresh soft Xinotyri cheese.
Highlights
Traditional raw milk cheese is an authentic dairy product characterized by a rich and diverse microbiota and generally superior sensorial qualities compared to similar types or varieties of pasteurized milk cheese produced industrially with commercial starter cultures [1]
The evolution of the primary and secondary proteolysis and lipolysis of soft Xinotyri cheese was not affected by the use of raw or pasteurized goat’s milk
The cheese samples produced from pasteurized milk contained significantly lower populations of enterobacteria, enterococci and mainly coagulase-positive staphylococci, which were detected at unsafe levels in raw milk cheese curds
Summary
Traditional raw milk cheese is an authentic dairy product characterized by a rich and diverse microbiota and generally superior sensorial qualities compared to similar types or varieties of pasteurized milk cheese produced industrially with commercial starter cultures [1]. Flavour compounds are produced as catabolic products and play a critical role in the quality of the final cheese [6]. Cheese flavour is the result of a complex balance among volatile and non-volatile chemical compounds from milk fat, milk proteins, and carbohydrates during ripening [7,8,9]. Milk pasteurization prior to cheese processing is recommended or demanded by food regulators in many countries, including Greece, because it protects public health and results in the manufacture of a uniform and safe product of constant quality. Pasteurization, alters the biochemistry of cheese ripening by suppressing the indigenous microbiota of the milk, by partial or complete inactivation of certain indigenous enzymes which contribute to ripening, and/or by slight denaturation of whey proteins [13,14,15,16]
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