Abstract:
The objectives of this research were to determine the appropriate acid types and pH values of making Fetta cheese by direct acidification from raw milk, ultrafiltration milk (UF-milk), and combination of raw milk and ultrafiltration whey (UF-whey). These were acidified to pH 5.6, 5.4, and 5.2 with lactic, phosphoric, and acetic acid. In the first part, it was found that curd made from combination of raw milk and UF-whey acidified to pH 5.4 and 5.2 were too soft and with inadequate yield for making a piece of cheese. Fetta cheese obtained by acidification with acetic acid resulted in highest %protein content, followed by those acidified with phosphoric and lactic acid, respectively. When converted to %yield, cheeses made from both acetic and phosphoric were not significantly different. Lowering pH of milks to 5.6 resulted in the highest cheese weight, %salt, hardness and %yield of the cheeses, followed by pH 5.4 and 5.2, respectively. Thus, the suitable condition for Fetta cheese production by direct acidification was to use acetic acid at pH 5.6. In the second part, storage test (by immersion in 5% brine) of the Fetta cheeses made from raw milk, UF-milk, and combination of raw milk and UF-whey using the above conditions were carried out at 4 ํC during the periods of 3, 30, 60, 120, 180 days. It was found that cheese weight, moisture content, %protein, protein (%dry basis), pH, %yield and L* values of Fetta cheese decreased, but %fat, fat (%dry basis), calcium content, hardness and a* values of Fetta cheese increased with the extended storage time. The total plate count of cheeses increased in the first 2 months and gradually declined thereafter. The mean scores for appearance, body and texture of Fetta cheese that made from UF-milk was steady during 180 days but those from raw milk and combination of raw milk and UF-whey gradually declined. The flavour scores of cheeses made from raw milk and combination of raw milk and UF-whey increased in the first month and gradually declined while that of combination of raw milk and UF-whey cheese has the highest score for this attribute.