Microbiological, biochemical and technological properties of Turkish White cheese ‘Beyaz Peynir’

International Dairy Journal 12 (2002) 635–648

Review

Microbiological, biochemical and technological properties of Turkish White cheese ‘Beyaz Peynir’ A.A. Hayaloglua,*, M. Guvena, P.F. Foxb b

a Department of Food Engineering, Agricultural Faculty, University of Cukurova, TR-01330 Adana, Turkey Food Chemistry, Department of Food Science, Food Technology and Nutrition, University College, Cork, Ireland

Received 7 August 2001; accepted 27 February 2002

Abstract Turkish White cheese is a brined (or a pickled) cheese variety with a soft or semi-hard texture and a salty, acid taste. Some aspects of this cheese are reviewed: e.g., milk supply, use of starters and enzymes, manufacturing technology, chemical composition and microflora, chemical and biochemical changes during ripening in brine. Several characteristics of Turkish White cheese are compared to other White brined cheese varieties such as Feta and Domiati. The findings of this review suggest that future research on Turkish White cheese should characterise the changes in microflora, biochemistry and texture during ripening. Previous studies tended to focus on the chemical composition of Turkish White cheese, and little attention was directed towards the detailed characterisation of nitrogen fractions, flavour compounds, rheological and microbiological properties and their effects on the quality of the end-product. r 2002 Published by Elsevier Science Ltd. Keywords: Turkish White cheese; Beyaz peynir; Brine; Ripening

Contents 1.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

636

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Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

636

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Cheese manufacture . . . . . . . . . . . . . . . . . . . 3.1. Treatment of milk . . . . . . . . . . . . . . . . . 3.1.1. Characteristics of milk . . . . . . . . . . . 3.1.2. Roles of H2O2, heat treatment and CaCl2 . 3.2. Manufacturing steps . . . . . . . . . . . . . . . . 3.3. Composition and yield of cheese . . . . . . . . . .

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Quality of Turkish White cheese . . . . . . . . . . . . . . 4.1. Effects of starter culture . . . . . . . . . . . . . . . 4.2. Effects of rennet and other coagulants . . . . . . . . 4.3. Effects of salting . . . . . . . . . . . . . . . . . . . 4.3.1. Salt absorption and diffusion during brining 4.3.2. Salting methods . . . . . . . . . . . . . . .

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Microbiology of Turkish White cheese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.1. Natural flora of the cheese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2. Pathogens and other microflora of the cheese . . . . . . . . . . . . . . . . . . . . . . . . . . . .

641 641 642

*Corresponding author. Fax: +90-322-338-6173. E-mail address: [email protected] (A.A. Hayaloglu). 0958-6946/02/$ - see front matter r 2002 Published by Elsevier Science Ltd. PII: S 0 9 5 8 - 6 9 4 6 ( 0 2 ) 0 0 0 5 5 - 9

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6.

Ripening of Turkish White cheese . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1. Proteolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.2. Lipolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

643 643 644

7.

Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

645

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References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

645

1. Introduction Cheese evolved in the ‘‘Fertile Crescent’’ between the Tigris and Euphrates rivers, about 8000–9000 years ago (Fox, O’Connor, McSweeney, Guinee, & O’Brien, 1996; Kosikowski & Mistry, 1997). This area now forms part of Turkey, Iraq and Iran. More than 1000 varieties of cheese are produced around the world. In Turkey, 40–50 cheese varieties are known, but only three of them have national and economic value: Turkish White (its original name is Beyaz peynir), Kasar and Tulum cheeses. In Turkey, milk is generally produced on village farms as a supplementary source of income for villagers. Dairy plants with a large capacity have been established during the past 10 years. Kocak and Gursel (1992) stated that a large proportion of the milk produced is retained for home consumption. The cheese produced may be consumed while fresh but it is mostly eaten after being ripened in brine (Erkmen, 2000). Therefore, it is difficult to estimate the production quantities of milk and cheese. According to Anonymous (2001) data, milk production in Turkey is about 10.1 million tonnes per annum and 243,000 tonnes of White cheese are produced annually; Turkish White cheese represents 60–80% of total cheese production. Other cheeses important in Turkey are Kasar (like Kashkaval or Kasseri cheeses), Tulum (ripened in skin bags or plastic material), Lor, Dil, Cokelek, Otlu (with herbs) and Mihalic. White cheese is known by different names and similar varieties are produced in the Mediterranean region and in other countries, such as Greece (Feta), Yugoslavia (Beli Sir U Kriskama), Bulgaria (Bjalo Salamureno Sirene), Egypt (Domiati), Israel (Brinza), Romania (Teleme), Denmark (Feta) and the United States of America (Queso Blanco). The objective of this review is to describe technological, microbiological and biochemical aspects of Turkish White cheese during manufacture and ripening, and to consider future work on certain specific topics. For this purpose, the cheese was compared with other brined cheeses, e.g., Feta, Domiati.

2. Definition Turkish White Cheese is brine-salted and ripened in brine (B12–14 g/100 g NaCl solution). Generally, the cheeses are cubical or rectangular, typically 7  7  7 or

7  7  10 cm3 and weigh about 350 or 500 g. The cheese is a rindless, white-coloured, close textured (no evidence of holes) variety with a salty acid taste; it may have a slight piquant flavour (Dinkci & Gonc, 2000), especially when made from sheeps’ milk. It is matured for a period of 1–3 months. Turkish White cheese is a semi-hard variety according to some authors (Uraz, Kocak, & Alpar, 1983; Anonymous, 1986; Turantas, Unluturk, & Goktan, 1989; Turhan & Kaletunc, 1992; Tekinsen, 1997); however, according to others it is a soft (Tekinsen, 1983; Yildiz, Kocak, Karacabey, & Gursel, 1989) or semi-soft (Erkmen, 2000; Erkmen, 2001) variety. Based on its moisture content (55–65 g/100 g), Turkish White cheese is a soft variety (Abd El-Salam, 1987). Although Turkish White cheese has a soft texture when fresh, after ripening for 3 months in brine, it can be classified as a semi-hard or semi-soft variety. There is no definition of Turkish White cheese based on texture in the Turkish Standards Institute (Anonymous, 1995). In the present standards, there are 4 categories of the cheese based on the % fat-in-dry matter (FDM): * * * *

full-fat cheese, containing at least 45% FDM, semi-fat cheese containing 30–44% FDM, low-fat cheese, containing 20–29% FDM, non-fat cheese containing o20% FDM (Anonymous, 1995).

Turkish White cheese was manufactured originally from sheeps’ or goats’ milk, but cows’ milk or a combination of milks is now generally used for its production. Since the lactation period of sheep or goats is short (about 3–5 months), the cheese is usually produced from cows’ milk during most of the year (Yildiz et al., 1989). It is produced in small dairy plants or on farms (‘‘mandira’’, a regional name for farm) and private houses. Therefore, it is difficult to find a standard product with respect to composition and other qualities. Nowadays, there are several modern mechanised plants where standardised production methods are used. In the traditional or artisanal manufacture of Turkish White cheese, starter culture is not added to the cheesemilk. The milk may or may not be pasteurised and the curd is handled extensively by the cheese maker (Turantas et al., 1989; Erkmen, 1995).

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3. Cheese manufacture 3.1. Treatment of milk 3.1.1. Characteristics of milk A milk supply of exceptionally high bacteriological and chemical quality is essential for the production of cheese of consistently good quality. Desirable characteristics of the milk used for the manufacture of Turkish White cheese were summarised by Ucuncu (1999) and include sheeps’ milk with a high level of casein, good rennet coagulability, absence of antibiotics, detergents, disinfectants or other chemical residues, and absence of coliform, Clostridium and Bacillus microorganisms, which produce gas, swelling and crumbly defects. The chemical composition of the milk affects the quality of the final cheese. To obtain a good quality Turkish White cheese, high-quality milk must be used in its production. Aksoydan (1996), who standardised the casein-to-fat ratio in experimental cheeses to 0.6, 0.9, 1.2 or 1.5, reported that the best quality cheese was obtained from milk adjusted to a casein-to-fat ratio of 0.6 or 0.9. Differences in the casein-to-fat ratio had a statistically significant effect on cheese yield. Gollu and Kocak (1989) reported that adjusting the casein-to-fat ratio to 0.8 positively influenced the total solids, fat, total volatile fatty acids, taste and aroma of Turkish White cheese. However, Tekinsen (1997) reported that a casein-to-fat ratio of 0.7 was optimal for cheese quality. 3.1.2. Roles of H2O2, heat treatment and CaCl2 Yildirim (1991) studied the effects of treating milk with H2O2 on some properties of Turkish White cheese. H2O2 was added to cows’ milk at levels of 0 (control), 0.02, 0.10 or 0.30 g per 100 mL, held at 301C for 4 h, and then manufactured into White cheese. The addition of H2O2 had little effect on the rate of acidification but resulted in an increase in the level of rennet required to coagulate the milk. The cheese made from H2O2-treated milk was found to have a softer consistency and received higher organoleptic scores than the control cheese. Yildirim (1991) concluded that the addition of H2O2 at a level of 0.02 g/100 mL was more suitable than carbonate, antibiotics, formaldehyde or other substances used for the same purpose, i.e., improvement of the microbiological status of milk and cheese. The effects of adding H2O2, heat treating the cheesemilk or their combination (H2O2 and pasteurisation) on cheese quality were investigated by Sahan (1993) who found that the cheese made from raw or H2O2-treated milk showed early swelling in summer; moreover, all chemical quality attributes of the cheese during storage were influenced by adding H2O2. Cheese produced from milk to which H2O2 was added and

637

then heat treated at 551C for 10 min was preferable to cheese made from pasteurised (651C for 20 min) milk (Sahan, 1993). It was observed that heat treatment of cows’ milk at 801C for 5 min and addition of CaCl2 to a level of 0.04 g/ 100 g reduced the loss of milk components in the whey and thus increased the yield of cheese (Hazir, 1995). Furthermore, the results of Hazir (1995) indicated no significant effects of added CaCl2 (0.02, 0.04 or 0.06 g per 100 g) on the composition and quality of the cheese during ripening; however, the addition of an increasing level of CaCl2 reduced the draining time. Alpar et al. (1985) reported that the levels of total solids and nitrogenous matter in whey obtained from raw milk were higher than in whey from pasteurised milk. Gursel, Ergullu, Gursoy, and Erdogdu (1987) reported that the highest levels of total solids, fat and protein were found in cheese made from cows’ milk to which 0.03 g/100 g CaCl2 had been added. 3.2. Manufacturing steps The stages in the production of commercial Turkish White cheese are summarised in Fig. 1. Raw milk (preferably from sheep) is clarified and standardised with respect to the casein:fat ratio and pasteurised at 80–851C for 2–3 s or 631C  30 min or 651C  5 min. After the milk has been cooled to 321C, it is transferred to cheese vats, and starter culture is added at a level of 1–2 g/100 g and CaCl2 at a level of 0.2 g/L cheesemilk. The inoculated milk is held for 30 min, and liquid rennet is added at a level (B10 g/100 kg cheesemilk) sufficient to coagulate the milk in 90 min. The milk starts to form a gel after 30–45 min, and the gel is sufficiently firm after 75–90 min. The coagulum is cut into cubes (B2 cm) and the curds are allowed to rest in the whey for 5–10 min. The curds are then transferred to stainless steel moulds, which vary in sizes and are lined with cheese cloth. The surface of the cheese is covered with cheese cloth, followed by a plate on which weights are placed to compact the curd. Pressure is applied at room temperature (211C) for 3–6 h or until whey drainage has stopped or decreased to a low level. The pressure is 20–40 kg weights for each 100 kg of cheesemilk (Eralp, 1974; Yetismeyen, 1995). The weights are removed, the cheese cloth opened and the cheese mass divided with a knife into blocks of about 7  7  7 or 7  7  10 cm3, weighing 350–500 g. The blocks are placed in brine (14–16 g/100 g NaCl) for 6–12 h at 15–161C. The brined blocks are then arranged on the bottom of a tinned can (18 L), the can is filled with brine (14 g/100 g NaCl) and the container is closed. The salt concentration in the brine is checked and adjusted periodically during ripening. The cheese is ripened in the cans for 30–60 days at 12–151C and is then ready for consumption.

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Raw milk
Clarification
Standardisation of fat ratio
o

Pasteurisation (15-20 sec at 72-74 C, but not pasteurised on farms)
o

Cool (to 30-32 C)
Addition of starter culture (1-2 g 100 g-1 mesophilic culture)
Addition of CaCl2 (20 g 100 L-1 cheesemilk)
Renneting (at 28-32 oC, coagulation complete in 75-90 min)
Cutting (the coagulum is cut into 1-3 cm cubes and the curds rested for 5-10 min)
Draining (25-30 min, no pressing in cheese cloth)
Pressing and moulding
o

Salting (pieces of curd salted in 14-16g 100 g-1 NaCl at 15-16 C for 6-12 h)
Packaging (cheese blocks placed in tinned cans filled with brine, 14-16 g 100 g-1 NaCl)
o

Ripening (at 12-15 C for 30-60 days)
o

Storage (at 5 C) Fig. 1. Flow-sheet for manufacture of Turkish White cheese (adapted from Ucuncu, 1999).

3.3. Composition and yield of cheese The reported chemical composition of Turkish White cheese differs considerably (Table 1). This difference can be attributed to lack of standardisation of the raw milk and to the lack of standardised procedures for the manufacture and ripening of the cheese (Turantas et al., 1989). Each dairy plant or cheese maker has an individualised method for all steps in the manufacture of Turkish White cheese, e.g., pasteurising, clotting, pressing, salting, etc. (Tekinsen, 1983; Yildiz et al., 1989). Hence, the composition of cheeses manufactured in the same dairy plant can vary significantly (Uraz et al., 1983; Turantas et al., 1989). The mineral composition of Turkish White cheese was determined in some studies, but as far as we are aware, changes of the mineral composition of the cheese and pickle during ripening have not been determined.

Diraman and Demirci (1998) studied Turkish White cheeses collected from 12 dairy factories; the concentrations of Ca and P ranged from 960–1420 to 358–519 mg/ 100 g, respectively. Demirci (1989) had reported values of 8407165.6, 430.6762.87, 289.5732.27, 114.6713.41 and 39.673.48 mg per 100 g for Ca, P, Na, K and Mg, respectively, in unripened Turkish White cheese. The average yield of fresh Turkish White cheese from sheeps’ milk is 26–28 kg/100 kg while that from goats’ or cows’ milk is 15–16 kg/100 kg (Ucuncu, 1999).

4. Quality of Turkish White cheese 4.1. Effects of starter culture Cheese starters are used primarily to convert lactose to lactic acid, which in turn affects several aspects of

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Table 1 Mean composition of commercial and experimental (fresh and mature) Turkish White cheese as reported by different studies Cheese age

Parameters (g/100 g)

References a

b

c

d

e

f

g

Total solids

Fat

Salt

Acidity

TN

WSN

NPN RI

PP-N

PTA-SN

Ash

Commercial Commercial Commercial Fresh

41.52 47.68 41.12 35.84

19.25 21.30 17.83 14.55

3.94 3.88 3.72 3.26

2.77 3.80 1.95 NA

2.47 2.75 2.56 2.10

0.462 0.630 0.480 0.310

NAh NA NA NA

18.70 22.30 18.75 14.76

NA NA NA NA

NA NA NA NA

4.96 NA 4.78 NA

Mature

36.34

15.36

4.49

NA

2.10

0.536

NA

25.52

NA

NA

NA

Fresh Mature Fresh Mature Fresh Mature Fresh Mature Fresh

41.18 37.51 43.63 45.30 44.40 37.40 41.71 40.89 46.94

17.25 15.75 17.17 17.93 18.38 18.21 20.67 19.10 22.75

6.20 6.89 4.17 5.53 4.64 6.02 4.00 3.34 2.00

0.37 0.76 0.82 1.16 0.55 0.68 1.31 1.21 0.94

2.30 2.02 2.71 2.71 2.57 2.13 2.29 2.41 3.72

0.069 0.388 0.130 0.353 0.199 0.288 0.460 0.520 0.430

NA NA NA NA NA NA 0.281 0.289 0.280

3.00 19.21 4.80 13.03 7.74 13.52 20.08 21.57 11.55

NA NA NA NA NA NA 0.179 0.230 0.150

NA NA NA NA NA NA 0.106 0.116 0.150

7.68 7.64 6.21 8.11 NA NA NA NA NA

Mature

39.05

18.88

4.38

0.88

2.56

0.580

0.360 22.66

0.220

0.140

NA

Eralp (1956) Toral (1969) Gunduz and Daglioglu (1989) Yildiz, Kocak, Karacabey, and Gursel (1989) Yildiz, Kocak, Karacabey, and Gursel (1989) Cakmakci and Kurt (1993) Cakmakci and Kurt (1993) Kurt and Ozdemir (1995) Kurt and Ozdemir (1995) Saldamli and Kaytanli (1998) Saldamli and Kaytanli (1998) Uraz and Simsek (1998) Uraz and Simsek (1998) Gursoy, Gursel, Senel, Deveci, and Karademir (2001) Gursoy, Gursel, Senel, Deveci, and Karademir (2001)

a

Lactic acid. Total nitrogen. c Water-soluble N: d Non-protein N: e Ripening index (WSN percentage of TN). f Proteose–Peptone N: g Phosphotungstic acid-soluble N: h Not available. b

Table 2 Starter bacteria used in Turkish White cheese Microorganisms

References

Lactococcus lactis subsp. cremoris+Lactococcus lactis subsp. lactis+Leuconostoc cremoris Enterococcus durans 41770+Lactobacillus delbrueckii subsp. bulgaricus CH2 Lc. lactis subsp. cremoris+Lactobacillus casei+Lactobacillus plantarum Lc. lactis subsp. cremoris+Lc. lactis subsp. lactis Lc. lactis subsp. lactis+Lb. casei Lc. lactis subsp. lactis+Lc. lactis subsp. cremoris+Lactobacillus sake Lc. lactis subsp. lactis+Lb. casei and/or Lb. plantarum Lc. lactis subsp. lactis+Lc. lactis subsp. cremoris+Lactobacillus helveticus

Ucuncu (1971); Celik (1982) Tunail (1978) Ergullu (1980) Kaymaz (1982); Tekinsen (1983); Kurt (1991) Yildiz, Kocak, Karacabey, and Gursel (1989) Akgun (1995) Ucuncu (1999) Gursoy, Gursel, Senel, Deveci, and Karademir (2001)

cheese manufacture, including coagulant activity, retention of coagulant in the curds, rate of proteolysis during storage, cheese yield, cheese moisture and rate of pH decline in the cheese (Pappas, Kondyli, Voutsinas, & Malatou, 1996a). Different mixed starter cultures, including thermophilic and/or mesophilic bacteria, are used in the production of Turkish White cheese (Table 2). Uysal (1996a) used a lactic culture (1:1 mixture of Lactococcus lactis subsp. lactis and Lc. lactis subsp. cremoris) at two levels in the manufacture of Turkish

White cheese and analysed the cheeses during 90 days of storage. The results showed that while the acidity, salt, water-soluble nitrogen content and ripening index values of the White cheese increased during storage, the pH and the level of total nitrogen in the cheese decreased. The level of proteolysis in the cheese increased as the level of starter culture used was increased. Recently, Gursoy, Gursel, Senel, Deveci, and Karademir (2001) assessed the use of a heat-treated (651C for 20 min) culture of Lactobacillus helveticus or

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Lb. delbrueckii subsp. bulgaricus (at a level of 0.5 g/ 100 g) in the manufacture of low-fat Turkish White cheese as an adjunct culture to accelerate ripening. The authors demonstrated that the heat-treated cultures can be used successfully for low-fat White cheese to shorten the ripening time, i.e., the adjunct culture-treated cheese developed the desirable levels of proteolysis and overall quality after 30 days of ripening and Lb. helveticus gave the best results. Tunail (1983) and Ucuncu (1999) stated that the lactic cultures used in the manufacture of Turkish White cheese should be resist to the phages, the salt and the high concentration of acid and must be competitive with undesirable microorganisms (e.g., staphylococci, clostridia, some Gram-negative bacteria) to ensure a product of standard quality. 4.2. Effects of rennet and other coagulants Coagulation of milk is a fundamental part of cheesemaking and this is usually accomplished by rennet under suitable conditions. In the production of Turkish White cheese, commercial calf rennet has usually been used in a liquid form. Also, home-prepared rennet extracts (called ‘‘sirden’’ locally) from young calves’, lambs’ or kids’ stomachs are still used as a milk coagulant. For this purpose, stomachs are air dried while shaded from the sun, cut into slices, and then placed in 10 g/100 g NaCl solution containing 5 g/100 g boric acid. After 1 or 2 weeks, the rennet extract—prepared by blending macerated stomach slices in the NaCl solution—is clarified by filtration and the liquid is used as a coagulant (Eralp, 1974; Kurt, 1987). A shortage of calf rennet and the consequent increase in price has led to the use of rennet substitutes, including proteinases from other animals and from microorganisms. Despite the availability of numerous milk coagulants, only six rennet substitutes have been found to be acceptable for cheese production: bovine pepsin, porcine pepsin and chicken pepsin and acid proteinases from Rhizomucor miehei, R. pusillus and Cryphonectria parasitica (Fox & McSweeney, 1997). Microbial, or fermentation-produced, chymosin produced by genetically engineered microorganisms, is now available and widely used for cheese in many countries. Some microbial coagulants (R. miehei, R. pusillus and C. parasitica) and calf rennet were used for the production of Feta cheese by Alichanidis, Anifantakis, Polychroniadou, and Nanou (1984). It was observed that calf rennet substitutes are suitable for the manufacture of Feta cheese, but the highest level of proteolysis was found in the cheese made using calf rennet. Yesilyurt (1992) found no significant differences in cheese yield, titratable acidity, dry matter, fat and NaCl contents between experimental Turkish White

cheese made with calf rennet or with two microbial rennets (Fromase or Rennilase from R. miehei). But significant differences were found between the calf rennet and microbial rennet cheeses with regard to water-soluble nitrogen and total free fatty acid content (Yesilyurt, 1992). Yetismeyen, Cimer, Ozer, Odabasi, and Deveci (1998) used a microbial rennet (from R. miehei) or calf rennet to manufacture Turkish White cheese from ultrafiltered milk. The ripening index, water-soluble nitrogen, nonprotein nitrogen and free tyrosine content increased slightly during the 60-day storage period and the increase was greater in cheese made with microbial rennet. However, the sensory quality of cheese made with calf rennet was better than that of the other samples (Yetismeyen et al., 1998). The use of chicken pepsin, or a mixture of chicken pepsin and added calf rennet (at a ratio of 50:50 or 70:30) for the manufacture of Turkish White cheese did not significantly affect the water-soluble nitrogen content, acidity, pH or sensorial scores of the cheeses (Uysal, 1996b). In a comparative study, Saldamli and Kaytanli (1998) assessed microbial rennet enzymes, such as Fromase 46T (from R. miehei), Rennilase 150L (from R. miehei) or Maxiren 50 (from Kluyveromyces marxianus var. lactis) as alternative coagulants to commercial calf rennet in the manufacture of Turkish White cheese. They showed that Maxiren 50 and calf rennet had identical activities in the cheese, and suggested that these coagulants may be used in the manufacture of Turkish White cheese. 4.3. Effects of salting Salting is a major operation in the manufacture of Turkish White cheese and ensures its characteristic properties. The concentration of salt and its distribution in the cheese mass are important parameters affecting its quality and acceptability (Turhan & Kaletunc, 1992). Salt acts as a flavour enhancer and as a preservative which permits the cheese to be held in the warm prevailing climate. Salt plays a multi-faceted role in cheese ripening and influences the physical, chemical and biological properties of cheese (Lampert, 1970; Guinee & Fox, 1987; Tzanetakis & LitopoulouTzanetaki, 1992). These effects can be summarised as follows (Pappas, Kondyli, Voutsinas, & Malatou, 1996b): control of microbial growth and activity; control of various enzyme activities in cheese; reduction of cheese moisture content; physical changes in cheese proteins which influence cheese texture, protein solubility and protein conformation, and flavour development. 4.3.1. Salt absorption and diffusion during brining When cheese is placed in brine, NaCl molecules move from the brine into the cheese as a consequence of the osmotic pressure difference between the cheese moisture

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and the brine. Consequently, water in the cheese diffuses out through the cheese matrix so as to restore osmotic pressure equilibrium (Guinee & Fox, 1987). After the cheese blocks have been removed from the brine, salt and moisture diffusion continues within the cheese (Payne & Morison, 1999). The rate of salt transportation from the brine into the cheese mass depends on the characteristics of the cheese (i.e., moisture and fat content, acidity, surface area) and brining conditions (i.e., salt concentration, temperature, brining time, acidity of the brine) (Ucuncu, 1983). Turhan and Kaletunc (1992) reported that the diffusion coefficient of salt in Turkish White cheese curd is 0.21  10 9 m2/s at 41C and 0.31  10 9 m2/s at 12.51C for brine concentrations of 15 and 20 g per 100 g NaCl; the corresponding values for the diffusion coefficient at 201C were 0.39  10 9 m2/s (15 g/100 g NaCl brine) and 0.34  10 9 m2/s (20 g/100 g NaCl brine). The authors found that the effective diffusivity of salt in Turkish White cheese changed with temperature and with brining time for 3–54 days of storage. Ucuncu (1983) found that the salting time depends on the characteristics of the brine, the desired salt content and the fat content of the cheese, and suggested optima for the different brining conditions: temperature, 13–141C; concentration, 1.116–1.161 g/mL NaCl; acidity, 0.35–0.40 g/100 mL lactic acid. Cakmakci and Kurt (1993) determined the physical and chemical properties of Turkish White cheese brined in 14 or 17 g per 100 g NaCl brine and ripened for 90 days. Increasing the salt concentration from 14 to 17 g per 100 g NaCl influenced the cheese pH, titratable acidity and water-soluble nitrogen content during ripening. 4.3.2. Salting methods Akbulut et al. (1996a, b) studied the effects of two different salting methods, i.e., salting of cheesemilk (before renneting) or salting of curd (before pressing) at the levels of 2, 3, 4 or 6 g NaCl per 100 g of milk or per 100 g curd on the quality of Turkish White cheese. They used the method of immersion in brine as a control cheese for comparing these experimental cheeses. Cheese produced from salted milk or from curd salted at a level of 6 g/100 g NaCl was unacceptable. The numbers of total bacteria and coliform bacteria in cheeses produced from both salted milk and from curd salted were higher than those in cheese salted by brine immersion. The authors found that cheese samples produced from salted milk or from curd salted at a level of 2 or 3 g per 100 g NaCl were not significantly different from brine immersed cheese in terms of all chemical quality parameters. Pappas, Kondyli, Voutsinas, and Malatou (1996b) investigated the effect of numerous salting methods (dry salting for 1 day followed by addition of 6 g/100 g NaCl brine to the cans, dry salting for 1, 2 or 3 days followed

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by addition of 7 g/100 g NaCl brine to the cans, or dry salting for 3 days followed by addition of 8 g/100 g NaCl brine to the cans) on the composition and quality of Feta cheese. The authors emphasised that dry salting of cheese for 1 day and storage in 7 g/100 g NaCl brine was the most appropriate salting method for practical application. Additionally, the salting method influenced proteolysis, lipolysis, organoleptic and rheological properties of the cheeses. The effect of cheese size (7  7  7 or 7  7  11 cm3) on salt absorption by Turkish White cheese during 30 days was investigated by Uraz and Gencer (2000). Salt absorption varied according to the size of the pieces of cheese and was very rapid during the first 15 days of ripening but then slowed down. The size of the cheese had a significant effect on the salt content at the centre (po0:01) and at the corners (po0:05) of the cheese samples. A new approach in the production of brined cheeses is the replacement of the NaCl by KCl, as a high intake of Na may cause hypertension, osteoporosis and increase the incidence of kidney stones and other ailments. However, the taste of KCl is distinctly different from that of NaCl and has a bitter flavour (Guinee & Fox, 1987; Katsiari, Alichanidis, Voutsinas, & Roussis, 2000a). Aly (1995) reported that Feta-type cheese of acceptable quality could be manufactured using a blend of NaCl and KCl (at a ratio of 1:1) at a level of 2 g/100 g. In addition, Katsiari, Voutsinas, Alichanidis, and Roussis (2000a, b) reported that the partial substitution of NaCl by KCl in the manufacture of Feta cheese using mixtures of NaCl/KCl (3:1 or 1:1, w/w basis) did not influence the extent and depth of proteolysis and lipolysis during ripening. These results are in accordance with those of Guven and Karaca (2001) who reported that proteolysis in Turkish White cheese salted with brine (14 g/100 g) prepared from NaCl (control) or from mixtures of NaCl with CaCl2, KCl or MgCl2 at a ratio of 1:1 (molar basis) were similar in control and all experimental cheeses.

5. Microbiology of Turkish White cheese 5.1. Natural flora of the cheese The composition of the lactic bacterial flora of Turkish White cheese was investigated by Karakus, Borcakli, and Alperden (1992). At the beginning of ripening, Lc. lactis subsp. lactis was the predominant species and enterococci (E. faecalis and E faecium) were the second most numerous group. Other species of lactic acid bacteria, e.g., Lb. casei, Lb. plantarum, Lb. fermentum, Lb. brevis, Leuconostoc lactis and Leu. mesenteroides subsp. dextranicum were also present. Lactococci declined during ripening, while Lactobacillus

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species increased, the predominant species being Lb. casei and Lb. plantarum. Tzanetakis and LitopoulouTzanetaki (1992) reported that lactobacilli (especially Lb. plantarum) predominated over enterococci and pediococci in Feta cheese during ripening. The acidifying and proteolytic activities (as determined by soluble tyrosine formation) of some lactic acid bacteria isolated from Turkish White cheese were investigated by Karakus (1994). The acidifying activity of strains of Lc. lactis subsp. lactis and Lc. lactis biovar. diacetylactis was very strong, while that of Lb. casei and Lb. plantarum was considerably weaker. Proteolytic activity in Lactococcus species was found to vary extensively and the proteolytic activities of Lactobacillus species were generally lower than that of lactococci. Karakus (1995) isolated some strains of Lc. lactis subsp. lactis, Lc. lactis biovar. diacetylactis, Lactobacillus casei and Lb. plantarum species isolated from Turkish White cheese at the different stages of manufacturing and ripening and characterised their enzymatic activities by the API-ZYM method; he suggested that the starter strains should be selected based on their enzymatic activities. Karakus and Alperden (1992) reported that Turkish White cheeses obtained from three different plants contained species of enterococci, staphylococci, micrococci and coliform bacteria at various levels. Throughout ripening, the number of enterococci remained relatively constant while counts of coliform, staphylococci and micrococci decreased. The microflora of Turkish White cheese produced at the same factory can vary depending on various factors. Uraz and Gundogan (1998), who studied 132 samples of commercial Turkish White cheese during a ripening period of 10 weeks, found Bacillus, Lactobacillus, Leuconostoc, Pediococcus, Staphylococcus aureus and coliform bacteria in all samples. Generally, Lactobacillus, Leuconostoc, Pediococcus and Streptococcus were the dominant microorganisms present during storage and grew to higher numbers than other groups of microorganisms. El-Zayat et al. (1995) isolated Lactobacillus farciminis, Lb. alimentarius, Lb. casei, Enterococcus faecalis, E. faecium, Propionibacterium jensenii, Microbacterium lacticum and Brevibacterium linens from 10 commercial samples of Domiati cheese and emphasised that these microorganisms affect cheese flavour. 5.2. Pathogens and other microflora of the cheese Turkish White cheese is usually produced under unmechanised or artisanal conditions and is handled at various stages of manufacture. Thus, various types of microorganisms may enter the cheese during manufacture and subsequent handling (Turantas et al., 1989). These authors reported the presence of high numbers of

coliforms (log10 values ranged from 0.60 to 5.15 cfu/g) and Escherichia coli (log10 ranged from 0.60 to 5.15 cfu/ g), extremely high numbers (log10 ranged from 2.81 to 7.14 cfu/g) of faecal streptococci and low numbers (log10 ranged from 1.30 to 1.70 cfu/g) of Staphylococcus aureus. Salmonella spp. and Clostridium perfringens were not present from the cheese samples. Akbulut, Kinik, and Kavas (1993) investigated the survival of some pathogens in Turkish White cheese made with or without a starter culture. Results showed the presence of high numbers (the log10 values ranged from 3.04 to 3.38 cfu/g) of Salmonella typhimurium, Staphylococcus aureus (log10 ranged from 2.90 to 3.23 cfu/g) and extremely high numbers (log10 ranged from 5.28 to 5.45 cfu/g) of E. coli in cheese made with or without a starter culture at the end of the 90-day ripening period. Moreover, Akbulut et al. (1993) reported that Yersinia enterocolitica and Campylobacter jejuni were not present in the samples at the end of ripening. However, it has been observed that the numbers of Y. enterocolitica and S. aureus increase during cheese manufacture but decrease during the later stages of ripening at a rate dependent on the salt concentration, starter activity and storage time (Erkmen, 1995; Erkmen, 1996). Listeria monocytogenes was isolated from 13.4% of commercial Turkish White cheeses analysed by Gonc and Kilic (2000). Erkmen (2000) and Erkmen (2001) reported that L. monocytogenes survived during Turkish White cheese manufacture and ripening and may persist for at least 3 months in cheese stored at +41C. Arici, Demirci, and Gunduz (1999) stated that L. monocytogenes originating from Turkish White cheese may be a potential hazard for public health at the end of 18 weeks of ripening and it may survive in cheese more than 20 weeks at +41C. The need to maintain proper sanitary procedures during production, handling and cheese processing was emphasised by Erkmen (1995), as was the need to pasteurise the cheesemilk and to use a starter culture capable of producing nisin (Arici et al., 1999). The results obtained above indicate that the survival of L. monocytogenes in White brined cheese depends on ecological conditions, such as temperature, sanitary conditions and NaCl concentration (Katic, 1995), and starter activity and the initial microbial load in the cheesemilk (Gonc & Kilic, 2000; Erkmen, 2001). Papadopoulou et al. (1993) reported that the growth of Salmonella could not be suppressed in Feta cheese during ripening at 17–181C, but could be inhibited partially by ripening at 41C. Some yeast species capable of causing a bitter taste, putrefaction and gas formation in Turkish White cheese were identified by Ozturk and Sahin (2000); the yeast were identified as Candida spp., Kluyveromyces lactis, Pichia amethionina var. amethionina and Debaryomyces hansenii. These yeasts were capable of growth in the

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presence of 12.5 g/100 g NaCl; it was suggested (Ozturk & Sahin, 2000) that pasteurisation of the cheesemilk and good hygiene during manufacture could prevent yeast growth. The occurrence of D. hansenii, Saccharomyces cerevisiae, Yarrowia lipolitica, Kluyveromyces marxianus and other yeast species has also been reported in Gouda cheese by Welthagen and Viljoen (1998). Considering that D. hansenii was the most resistant to low temperature and high salt concentrations, it could be recommended as part of the starter for this type of cheese (Welthagen & Viljoen, 1998).

6. Ripening of Turkish White cheese Ripening of cheese involves a complex series of biochemical and chemical events which lead to the characteristic taste, aroma and texture of each cheese variety. Five agents are responsible in the ripening of cheese: the coagulant (rennet or rennet substitute), indigenous milk enzymes, starter bacteria and their enzymes, secondary or adjunct starter bacteria, and nonstarter bacteria (Fox, 1989; Fox et al., 1996). Ripening involves three primary biochemical events: glycolysis of residual lactose and its constituent monosaccharides, glucose and galactose, lipolysis and proteolysis (Fox & McSweeney, 1996). Most of the characteristic changes in Turkish White cheese occur in brine during ripening which varies from a few weeks to 2 months. Some limited information is available on proteolysis during the ripening of Turkish White cheese; it is compared below with that in Feta and Domiati cheeses, which are brine-salted varieties similar to Turkish White cheese. 6.1. Proteolysis Proteolysis is a major process in cheese ripening; it has an obvious role in determining the texture, background flavour and the availability of flavour precursors in all matured cheese varieties (Law, 1987; Fox et al., 1996). Proteolysis in Turkish White cheese continues during storage in brine. Increasing the salt content of the cheese brine slightly reduces the rate and extent proteolysis at all stages of ripening (Gahun, 1983; Cakmakci & Kurt, 1993). The milk clotting enzyme contributes to proteolysis in Turkish White cheese. This is due to the high level of retention of the coagulant in cheese curd with a high moisture content, and to storage of cheese in salted whey which contains residual coagulant. Alichanidis et al. (1984) reported that the rate of proteolysis in Feta varies because of the use of calf rennet and other microbial milk clotting enzymes which vary their proteolytic activities. Similar work on Turkish White cheese was reported by Saldamli and Kaytanli (1998),

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who found that the highest level of proteolysis during the 90 days of ripening was exhibited by Fromase 46T (proteinase from Rhizomucor miehei), followed by Rennilase 150L (fermentation produced chymosin from R. miehei), calf rennet and Maxiren 50 (recombinant DNA technology from Kluyveromyces marxianus var. lactis). Urea-Polyacrylamide gel (PAGE) of the cheese showed different patterns for all samples, but the most extensive proteolysis was found in the cheese manufactured with Fromase 46T. Only five amino acids (leucine, phenylalanine, arginine, isoleucine and methionine) were found in Turkish White cheese during ripening by Kaymaz (1982), who suggested that the formation of amino acids can be considered as a criterion of ripening and of the suitability of starter cultures for Turkish White cheese. Ucuncu (1981) studied the amino acid profiles of Turkish White cheese made from pasteurised or unpasteurised cows’ or sheeps’ milk, with or without starter culture. The concentration of individual free amino acid (FAA) in some experimental cheeses during ripening are given in Table 3. The total concentration of FAA increased during ripening and leucine, glutamic acid and valine were the principal FAA in the cheeses at all stages of ripening. Serine, phenylalanine, isoleucine and alanine were the second dominant group of FAA in these cheeses. In Feta cheese, lysine, leucine, valine and phenylalanine were among the major FAA in control samples of the experimental cheeses (Alichanidis et al. (1984); Katsiari et al., 2000a, b). However, while the same FAAs were present in Iranian Brine cheese after ripening for 50 days; this situation did not continue to the end of ripening as in Feta, i.e., the amino acid lysine, arginine and glutamic acid were predominant at the end of ripening in the cheese (Azarnia, Ehsani, & Mirhadi, 1997). According to these authors, the decrease in FAA could be due to amino acid catabolism, or as has explained by Caric (1987) the amino acids diffused into the brine. Biogenic amines, tryptamine (0–4.54 mg/100 g), phenylethylamine (0–2.0 mg/100 g), putrescine (0–24.09 mg/ 100 g), cadaverine (0–53.3 mg/100 g), histamine (0– 6.35 mg/100 g) and tyramine (0.78–25.9 mg/100 g) were identified in commercial Turkish White cheese by DurluOzkaya, Alichanidis, Litopoulou-Tzanetaki, and Tunail (1999). The total biogenic amine content of Turkish White cheese samples produced without a starter culture was higher than in the cheeses produced with a starter culture (Durlu-Ozkaya, Alichanidis, LitopoulouTzenetaki, & Tunail, 1999). They reported that tyramine, cadaverine and putrescine were the main biogenic amines in commercial Turkish White cheese. These amines, except for cadaverine, were also the most abundant amines in experimental Feta cheese over a 120-day ripening period (Valsamaki, Michaelidou, & Polychroniadou, 2000).

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Table 3 Free amino acid content of some brined cheeses Amino acid

Alanine Arginine Aspartic acid Cysteine Glutamic acid Glycine Histidine Isoleucine Lysine Leucine Methionine Phenylalanine Proline Serine Threonine Tyrosine Valine Total

Turkish White Cheese (mg/100 g cheese)a Age of cows’ milk cheese (day)d

Age of sheeps’ milk cheese (day)d

Greek Feta Cheese (mg/100 g dry matter)b Age of sheeps’ milk cheese (day)

Iranian Brine Cheese (mg/ 100 g cheese)c Age of cows’ milk cheese (day)

1

60

120

1

60

120

1

60

120

1

50

80

1.25 1.50 0.90 0.92 5.68 0.43 1.03 1.11 2.55 3.36 0.75 1.49 2.13 3.26f 0.59 3.63 1.23 31.81

20.05 4.95 4.05 10.55 58.40 6.10 5.85 20.50 20.75 96.20 16.45 40.10 12.00 49.40f 9.15 12.75 24.30 411.55

38.55 4.65 12.40 18.40 107.60 10.95 19.60 37.35 48.00 120.95 28.55 54.00 20.55 78.85f 14.85 16.05 66.85 698.15

1.44 0.95 0.16 0.90 8.80 0.18 2.20 1.16 0.56 1.17 1.40 2.26 1.70 1.48f 1.42 2.00 2.26 30.04

16.21 5.60 9.00 9.20 68.75 2.98 7.70 14.22 6.72 108.40 14.65 29.66 12.30 21.20f 12.20 7.82 39.26 385.87

47.66 5.81 18.20 10.62 141.60 10.18 11.62 40.30 58.72 192.60 28.22 67.00 29.45 87.48f 17.47 9.88 76.27 853.08

3.1 7.2 2.7 NDe 2.6 8.9 1.4 1.7 5.1 5.8 4.8 2.8 6.1 7.0 1.5 3.0 5.1 68.8

31.0 12.7 18.7 1.7 10.5 9.4 6.9 24.4 131.3 167.5 15.9 82.3 38.2 36.3 13.1 16.9 61.6 678.4

106.5 2.3 23.5 15.5 8.0 24.8 9.7 61.4 107.7 289.8 34.3 127.4 83.7 77.4 64.9 15.4 125.8 1178.1

0.53 0.63 0.27 0.25 1.40 0.20 0.72 1.70 2.97 0 0.31 0.89 2.42 0.56 0.72 0.30 0.87 14.74

13.23 40.05 9.20 0 57.38 6.69 10.58 0 33.97 66.57 6.30 50.44 46.36 8.04 0 5.98 29.71 384.5

61.13 144.07 19.02 5.44 72.40 16.62 14.85 14.80 80.78 54.75 5.73 38.63 57.25 9.56 53.90 5.49 28.15 682.57

a

From Ucuncu (1981). From Alichanidis, Anifantakis, Polychroniadou, and Nanou (1984); in the control cheese made using calf rennet. c From Azarnia, Ehsani, and Mirhadi (1997). d Cheeses made from pasteurised milk and used a starter bacteria. e Not determined. f The sum of serine+asparagine+glutamine. b

The total nitrogen content of Turkish White cheese decreases slightly during ripening, because some nitrogenous compounds diffuse into the brine (Yoney, 1974), as reflected by the concomitant increase in the level of water-soluble nitrogen in the brine during ripening (Yaygin, 1979; Karakus & Alperden, 1992). Proteolysis in pickled cheese, such as Feta, Domiati and White cheese, continues during storage and soluble proteins diffuse into the brine which is in equilibrium with the cheese serum. Abd El-Salam (1987) summarised the changes in the nitrogen fractions of the brined cheese during ripening as follows: *

* *

the total nitrogen content of cheese decreases gradually, while soluble nitrogen fractions increase continuously during storage, indicating continuous proteolysis. The transfer of degradation products to the brine by diffusion explains the decrease in total nitrogen during storage. the cheese microflora contribute to proteolysis. the use of different milk-clotting enzymes in cheese manufacture affects the type and level of proteolysis in brined cheese, indicating that they contribute to proteolysis.

The nitrogen fractions are affected by the type of milk-clotting enzyme (microbial, vegetable or calf rennet) used, the salt concentration, storage temperature, storage period and other conditions. Studies to date have focussed mainly on the chemical composition (see Table 1) and microbiological properties of White cheese. Proteolysis in Turkish White cheese was assessed by fractionation of nitrogenous substances with various solvents, such as water, trichloroacetic acid (non-protein nitrogen), or phosphotungstic acid. These data are not sufficient to provide objective and comprehensive information related to the cheese biochemistry. We are aware of only one study (Saldamli & Kaytanli, 1998) in which proteolysis in Turkish White cheese during ripening has been studied using urea-PAGE; HPLC does not appear to have been used to study proteolysis (medium or small molecular weight peptides) in the cheese. 6.2. Lipolysis A low level of lipolysis occurs in Turkish White cheese during brining; lipolysis in brine cheeses is less extensive than in some Italian or blue-veined cheeses. Abd ElSalam (1987) reported that lipolysis in brined cheeses is

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affected by the type of milk used, milk lipase, bacterial or added lipases, homogenisation and pasteurisation of the cheesemilk, brine concentration and ripening temperature. Akalin, Kinik, and Gonc (1998), who studied the free fatty acids composition in commercial Turkish White cheese by gas chromatography, reported the following values (expressed as % of free fatty acids and fatty acids in glyceride form): C4: 2.48; C6: 2.48; C8: 2.77; C10: 6.04; C12: 4.13; C14: 11.48; C16: 27.88; C18: 9.12; C18:1: 20.77; C18:2: 1.69 and C18:3: 2.10. According to relative proportions of free fatty acids, palmitic (C16) and stearic (C18:1) acid were the dominant free fatty acids in Turkish White cheese. In Feta cheese, the principal free fatty acids are acetic and palmitic acids in control experimental cheeses (Alichanidis et al., 1984) and all experimental cheeses (Katsiari et al., 2000b). However, Akalin et al. (1998) detected no acetic acid (C2) in commercial Turkish White cheese. The effect of pregastric lipase on the ripening of Turkish White cheese was investigated by Aydemir, Akin, and Kocak (2001). Addition of lipase significantly enhanced the level total free fatty acids and volatile free fatty acids during the 90 days of ripening. These findings agree with the results of Dinkci and Gonc (2000), who reported that the total free fatty acid content of Turkish White cheese increased when lipase (Piccantase A; 0, 2, 3, and 4 g per 100 L cheesemilk) was added to the milk. However, the addition of pregastric lipase did not give a typical flavour in the cheese. Therefore, Dinkci and Gonc (2000) suggested that lipase (Piccantase A) should be added together with a proteinase to the milk to obtain the desired piquant flavour in Turkish White cheese. Kocak, Gursel, Ergul, and Gursoy (1987) reported that pasteurisation (10 min at 681C) of cows’ milk influenced the level of volatile fatty acids in Turkish White cheese due to inactivation of the milk lipase by pasteurisation; the level of volatile fatty acids in cheese prepared from raw milk was significantly higher than that in cheese from pasteurised milk throughout the 90 days of ripening.

7. Conclusions Turkish White cheese is produced on a large scale, but it is not been well understood with respect to: (1) starter type and the ratio of microorganisms; (2) salting, including the changes in cheese and brine during ripening, effects of brining temperature, pH and salt concentration in the brine; and the kinetics of salt absorption and diffusion (migration of some low molecular weight cheese constituents such as peptides and amino acids into the brine) in the cheese; (3) the microbial flora of the cheese, including the usefulness of non-starter lactic acid bacteria and some yeast isolated

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from the cheese or its brine for flavour improvement; (4) proteolysis, including the isolation and identification of peptides, and amino acid sequencing in the cheese during ripening. The common analytical techniques such as, PAGE or capillary electrophoresis (CE) and HPLC could be used to elucidate the type and depth of proteolysis in Turkish White cheese. Catabolism of amino acids and fatty acids in the cheese occur during ripening and contribute to cheese flavour and are very important for the quality of Turkish White cheese. The individual volatile flavour compounds should be assessed by gas chromatography–mass spectrometry. Acidification of the milk by lactic acid bacteria occurs rapidly but their action is limited after a certain salt concentration is attained, except for salt-tolerant strains. It may be useful to develop new starter combinations based on microorganism isolated from raw or pasteurised milk cheese, e.g., lactobacilli, lactococci, micrococci, pediococci and enterococci, which have been identified and their salt tolerance during brining established. Improved hygiene on the farm and at dairy plants, pasteurisation of the cheesemilk, precautions to prevent post-pasteurisation contamination, the use of automated cheesemaking equipment and the use of a starter culture capable of producing nisin would reduce the number of non-starter bacteria in the cheese. This review may help cheese makers to improve the quality of Turkish White cheese, and should encourage further research to evaluate overall characteristics of the cheese at all stages of ripening.

References Abd El-Salam, M. H. (1987). Domiati and Feta type cheeses. In P. F. Fox (Ed.), Cheese: Chemistry, physics and microbiology, Vol. 2. (pp. 277–309). London: Elsevier Applied Science. Akalin, A. S., Kinik, O., & Gonc, S. (1998). Izmir piyasasinda satilan bazi peynir cesitlerinde yag asitleri kompozisyonunun belirlenmesi uzerine arastirmalar. Gida, 23(5), 357–363. Akbulut, N., Kinik, O., & Kavas, G. (1993). A study on the survival fate of some pathogens in White pickled cheese. Ege Universitesi Ziraat Fakultesi Dergisi, 30(1–2), 111–118. Akbulut, N., Gonc, S., Kinik, O., Uysal, H. R., Akalin, S., & Kavas, G. (1996a). Bazi tuzlama yontemlerinin Beyaz peynir uretiminde uygulanabilirligi ve peynir kalitesi uzerinde arastirmalar, I. Duyusal ve mikrobiyolojik ozellikler uzerine etkileri. Ege Universitesi Ziraat Fakultesi Dergisi, 33(1), 9–15. Akbulut, N., Gonc, S., Kinik, O., Uysal, H. R., Akalin, S., & Kavas, G. (1996b). Bazi tuzlama yontemlerinin beyaz peynir uretiminde uygulanabilirligi ve peynir kalitesi uzerinde arastirmalar, II. Kimyasal ozellikler uzerine etkileri. Ege Universitesi Ziraat Fakultesi Dergisi, 33(1), 17–24. Akgun, S. (1995). Beyaz peynir uretiminde Lactobacillus sake’nin starter kultur olarak kullanilmasi. Ankara Universitesi Veteriner Fakultesi Dergisi, 42(3), 271–279. Aksoydan, M. (1996). Beyaz peynire islenen sutlerde protein yag oranlarinin ve olgunlasmanin peynirde kalite ve randimana etkileri. M.Sc. Thesis, The University of Cukurova, Adana, Turkey.

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