Biogenic amines in cheese are mainly generated from the decarboxylation of free amino acids by adventitious microorganisms rather than by starter bacteria (46). The sheep's and goat's milk used for Feta cheesemaking sometimes receives a thermal treatment below pasteurization conditions. Also, the manipulation of the curd during dry salting facilitates a contamination by various bacterial species, eventually possessing decarboxylating properties. This could, therefore, cause the production of high amounts of biogenic amines. However, investigations have shown that the average total amine content of Feta (390 mg/ kg) is much lower than that reported for cheeses suspected in outbreaks of food poisoning. It seems, therefore, that the characteristic features of Feta (low pH, high salt content, ripening and storage in brine, not extended proteolysis) create an environment unfavorable for amine accumulation (20). Tyramine is the main biogenic amine in mature samples (about 42% of the total).
Lipolysis is important for the development of the characteristic flavor of Feta cheese. Free fatty acid (FFA) content in mature cheese ranges from 1000 to 6000 mg/kg (16,18,47). The extent of lipolysis varies with the kind of rennet (homemade rennets are rich in lipases), the kinds of starter bacteria and NSLAB, the temperature in draining and dry salting, and so forth. High temperatures during draining enhance the lipolytic activity (13). Short-chain volatile acids (C2-C8) constitute 30-50% of the total FFA in mature cheese; among them, acetic acid is dominant at 29-47% of the total FFA (13,16,18,47-49).
Due to the lack of pressing, the curd of Feta cheese retains a high moisture level and provides to the starter microorganisms and NSLAB enough lactose for fermentation. Quick lactose metabolism to lactate and a subsequent drop of the pH to about 4.6 is vital for the quality of the cheese (50). Later, the high acidity and salt content of the cheese create an environment unfavorable for the growth and metabolism of starter bacteria. However, NSLAB survive and may continue to metabolize lactose, citrate, and other cheese constituents to flavor compounds (2).
The main volatile compound of Feta is ethanol, followed by acetic acid, acetalde-hyde, acetoin, and other short-chain alcohols, aldehydes, and ketones (22,49,51). High concentrations of ethanol (over 1000 mg/kg) in mature cheese were determined by dynamic headspace analysis. Ranges for acetaldehyde are 4-15 mg/kg; higher values are found in cheeses for which yogurt microorganisms were used as starter culture (18,22,25). Diacetyl is not found in mature Feta (18,22).
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