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Food Control 19 (2008) 278–285

Effects of heat treatment and starter culture on the propertiesof traditional Urfa cheeses (a white-brined Turkish cheese)

produced from bovine milk

A. Ferit Atasoy a,*, Atilla Yetis�meyen b, Huseyin Turkoglu c, Barbaros Ozer c

a Sanlıurfa Vocational High School, Department of Food Technology, Harran University, 63010 Sanlıurfa, Turkeyb Faculty of Agriculture, Department of Dairy Technology, Ankara University, Ankara, Turkey

c Faculty of Agriculture, Department of Food Engineering, Harran University, Sanlıurfa, Turkey

Received 5 December 2005; received in revised form 4 April 2007; accepted 10 April 2007

Abstract

The objective of the present research was to determine the effects of heat treatment and starter culture on some properties of Urfacheese produced from bovine milk. Proteolysis developed more rapidly in the cheese made with mesophilic starter culture. Whereasthe cheese inoculated with thermophilic starter culture received higher sensory scores. High heat treatment (at 72 �C for 5 min) affectedthe sensory and chemical properties of Urfa cheese adversely. Therefore, incorporation of low heat treatment (at 65 �C for 20 min) isrecommended for the production of Urfa cheese, with addition of a culture of Lactococcus lactis subsp. lactis + Lactococcus lactis subsp.cremoris.� 2007 Elsevier Ltd. All rights reserved.

Keywords: Urfa cheese; Heat treatment; Starter culture

1. Introduction

Urfa cheese is a traditional semi-hard brined Turkishcheese type produced mainly in the southeast Anatoliaregion of Turkey from raw ovine milk or appropriate mix-tures of ovine and caprine milk, without any starter cul-ture. Since lactation period of ovine and caprine milk inTurkey is very short (approximately 6–7 months), it isnot always possible to extend Urfa cheese production overthe all year without the use of bovine milk. Recently, theindustrial production of Urfa cheese has been made frombovine milk, and therefore, today this cheese variety hasgained nationwide popularity.

The final sensory quality of cheese is affected by thetreatment of milk including heat treatment. Heat treatment

0956-7135/$ - see front matter � 2007 Elsevier Ltd. All rights reserved.

doi:10.1016/j.foodcont.2007.04.004

* Corresponding author. Tel.: +90 414 247 03 91/279; fax: +90 414 24703 92.

E-mail address: afatasoy@hotmail.com (A.F. Atasoy).

to cheese milk is important in order to maintain uniformquality, promote safety and achieve better production con-trol. The safety aspect is the driving force for makingcheese from pasteurized milk (Pandey, Ramaswamy, &St-Gelais, 2003). Despite the safety concern, there is stilla large demand for cheeses made from raw milk becausethey possess strong and unique flavours, and therefore,raw milk cheeses are popularly sold in many parts of theworld including Turkey. Raw milk cheese has often beenassociated with outbreaks of diseases. Especially, cheese-borne salmonellosis, listeriosis and brucellosis are verycommon in southeast of Turkey where Urfa cheese produc-tion is prevailing (Ozer, Uraz, Yılmaz, & Atasoy, 2004).Therefore, raw milk cheeses are suggested to be storedunder appropriate conditions at least 90 days before con-sumption (Kurt, 1996). In order to minimize the risk ofmicrobial contamination, raw milk was replaced with pas-teurized milk in the production of Urfa cheese, withoutimpairing the overall quality of the final product.

Table 1Urfa cheese production in the present work

Cheesetrials

Mesophilicculturea

Thermophiliccultureb

Heat treatedmilkc

Heat treatedmilkd

B0 �e � � �B1 + � + �B2 � + + �B3 + � � +B4 � + � +

a Lc. lactis subsp. lactis and Lc. lactis subsp cremoris.b Lb. delbrueckii subsp. bulgaricus and Str. thermophilus.c At 65 �C for 20 min.d At 72 �C for 5 min.e +, addition �, no addition.

A.F. Atasoy et al. / Food Control 19 (2008) 278–285 279

Heat treatment of milk prior to cheese-making is notonly an effective way of preventing the detrimental effectof microorganisms, but also causes changes in physico-chemical properties of milk compounds leading, eventually,to variations in the quality parameters of cheese. In order toemploy appropriate heat treatment norm for cheese milk, acontrol method for the upper limit of heat load is needed.Hardly any routine method exist to measure the upper limitfor heat load to cheese milk that could assure preservationof the important properties of milk for production of differ-ent cheese varieties (Ardo, Lindblad, & Qvist, 1999).

Cheese flavour is the result of the breakdown of milkcomponents by indogeneous or exogeneous enzymesderived from milk, rennet or microorganisms, which pro-duce a series of volatile and non volatile compounds. Theenzymes from cheese-related microorganisms, particularlylactic acid bacteria, are the chief factors responsible forthe formation of many such compounds that are essentialfor cheese flavour (Martinez-Cuesta, Fernandez de Palen-cia, Requena, & Pelaez, 2001). Therefore, starter bacteriaare of critical importance for production of flavour com-pounds in cheeses made from heat treated milk.

The amount of information available about the charac-teristics of industrial Urfa cheese is limited (Atasoy, Ozer,& Turkoglu, 2003; Ozer, Atasoy, & Akın, 2000, 2002; Ozer,Atasoy, Yetis�meyen, & Deveci, 2004; Ozer, Robinson, &Grandison, 2003). Since Urfa cheese is technologically pro-duced from raw milk, to the best of our knowledge, no studyhas, so far, been carried out on the effect of different heattreatments and starter cultures on this cheese variety. There-fore, the objectives of this study were to investigate theeffects of heat treatment (at 65 �C for 20 min or at 72 �Cfor 5 min) and starter culture combinations (Lactococcus

lactis subsp. lactis + Lactococcus lactis subsp. cremoris orLactobacillus delbrueckii subsp. bulgaricus + Streptococcus

thermophilus) on the basic compositions, proteolysis, lipoly-sis and sensory characteristics of the Urfa Cheese.

2. Materials and methods

2.1. Materials

Raw bovine milk supplied from Koc-Ata Dairy(Sanlıurfa, Turkey) was used in the manufacture of cheesesamples. Rennet of animal origin was used to coagulatemilk. The starter cultures were obtained in a freeze driedfrom Peyma-Chr. Hansen (Istanbul, Turkey). Mesophilicstarter was a blend of Lc. lactis subsp. lactis and Lc. lactis

subsp. cremoris and thermophilic starter was a blend of Lb.

delbrueckii subsp. bulgaricus and Str. thermophilus in equalproportions.

2.2. Methods

2.2.1. Cheese-makingFive Urfa cheese-making trials denoted B0, B1, B2, B3

and B4. Urfa cheeses were made from either raw or heat

treated milk using starter culture with three experimentseach repeated three times at different days. Use of culturesand heat treatment norms are detailed in Table 1. In thefirst experiment, milk (80 kg) (control cheese) was warmedup to 32 �C. Then raw milk was coagulated with animalrennet for 90 min and after curdling, the curd was cut intosmall cubes, approximately 1 cm3, and left to rest (15 min).The curd was drained in ‘‘parzins’’, special moulds of trian-gular shape, for about 18 h at room temperature. Afterwhey separation was complete, the cheese blocks werescalded in their own whey at 90 �C for 3 min. The cheeseblocks were cooled down to room temperature and thenplaced into plastic containers aseptically. Cheeses werebrine-salted at 4 �C for 90 days. The brine concentrationwas 14% (w/v) and amount of brine added was 0.75-foldof the cheese weight.

In the second and third experiments, milk (each part160 kg) was heated 65 �C for 20 min and 72 �C for 5 minin the vat, respectively, and cooled to 32 �C. After cooling,CaCl2 was added at rate of 0.02%. Each part was dividedinto two separate batches. The first batch of each experi-ment was inoculated with mesophilic culture at a rate of1.0% (w/w) and second batch of each experiment was inoc-ulated with thermophilic culture at a rate of 0.5% (w/w).Milk was rested at 32 �C for 30 min to allow growth ofstarter bacteria before renneting. The rest of the manufac-turing procedure was identical to the control cheese.

2.2.2. Milk analysesThe pH was determined by means of a combined elec-

trode pH-meter (Orion 420). Total solids, fat, titratableacidity were determined according to TS (1981). Totalnitrogen (TN), was measured by the Kjeldahl methodaccording to IDF (1993). All analyses were performed induplicate.

2.2.3. Cheese analyses

2.2.3.1. Cheese yield. Cheese yield was calculated by usingthe formula: Amount of total cheese · 100/Amount oftotal milk (Lucey & Kelly, 1994).

2.2.3.2. Chemical analyses. In the cheese, total solids, titrat-able acidity and salt were determined according to TS

280 A.F. Atasoy et al. / Food Control 19 (2008) 278–285

(1989). The pH was determined by using a pH-meter(Orion 420). The fat content was determined by the Gerbermethod (TS, 1978). The total nitrogen (TN), water solublenitrogen (WSN) and non-protein nitrogen (NPN) weremeasured by Kjeldahl method according to Gripon, Des-mazeaud, Bars, and Bergere (1975). Proteose-peptonenitrogen (PPN) was calculated by difference of WSN fromNPN. The ripening index was calculated using the formula:WSN · 100/TN.

2.2.3.3. Electrophoretic analyses. Mini alkaline urea gelelectrophoresis technique was employed in the determina-tion of proteolysis (Creamer, 1991). The gel concentrationwas 30% (w/w) and the ratio of acrylamide/bisacrylamidewas 37.5/1. All the chemicals used were electrophoreticgrade (SIGMA ALDRICH Co. D 82039 Deisenhofen,Germany).

2.2.3.4. Lipolysis analyses. Acid degree value was deter-mined according to Renner (1986). Total volatile fattyacids were determined according to Kosikowski (1978).

2.2.3.5. Sensory analyses. The sensory evaluations of the90 day-old cheeses were carried out with three replicationsby 12 trained panellist who were members of Dairy Tech-nology Department of Food Engineering staff. The attri-butes were organised into color, taste (saltiness, bitternessand characteristic after taste), aroma (characteristicaroma), texture (texture and firmness) categories. Colorattribute was scored between 0 (white) and 7 (yellowish).Characteristic after taste, characteristic aroma and textureattributes were assessed on a 0–7 scale (0 = lowest quality,7 = best quality). Panellists were asked to evaluate the salt-iness (0 = no salty, 7 = too salty) and bitterness of cheeses(0 = no bitter, 7 = too bitter). Firmness was assessed on a0–7 scale (0 = soft, 7 = hard). Panellists were wanted toexpress the cheese similar sensory characteristic with thecontrol cheese.

2.2.3.6. Statistical analyses. The experiment was conductedaccording to completely randomized blocks arranged in afactorial design with 2 (heat treatment) · 2 (starter cul-ture) · 2 (storage period) · 3 (replications). Data were sub-jected to analysis of variance. The significant means were

Table 2Chemical compositions of raw and pasteurized milka

BR

pH 6.68 ± 0.081Titratable acidity (g 100 g�1 l) 0.20 ± 0.007Total solids (g 100 g�1) 12.8 ± 0.060Fat (g 100 g�1) 4.14 ± 0.023Total nitrogen (TN) (g 100 g�1) 0.55 ± 0.005

BR = Raw bovine milk; BP1 = Pasteurized bovine milk at 65 �C for 20 min; Ba Arithmetic mean of three replicates.

separated using Duncan’s multiple range test using SPSSsoftware program.

3. Results and discussion

3.1. Milk compositions

Chemical compositions of raw and pasteurized milk areillustrated in Table 2. In general, the heat treated milk hadlower titratable acidity, fat than raw milk. On contrary,raw milk had lower pH, total solids, total nitrogen (TN).However, effects of heat treatments on the properties ofbovine milk were found to be insignificant (P > 0.05).

3.2. Cheese yield

The yield of the cheeses B0, B1, B2, B3 and B4 were 14.1,14.1, 14.6, 14.8 and 15.5 g cheese 100 g�1 milk, respectively.In general, heat treatment at different temperatures led to aslight increase in yield (P < 0.05). This minor increase wasthought to be due to the denaturation of whey protein andtheir subsequent association with caseins. Similar resultswere reported by Lucey and Kelly (1994) and Kosikowskiand Mistry (1997). The type of starter culture used in theproduction of Urfa cheese had a slight influence on thecheese yield. Cheeses made with thermophilic starter bacte-ria had slightly higher yield than that of made with meso-philic starter bacteria. This difference could be due to fasterand more extensive development of acidity by mesophilicstarter (see Table 3) during cheese-making which resultsin an increase mineral losses (Lucey & Fox, 1993). On con-trary to the heat treatment, effect of starter culture on theyield was insignificant (P > 0.05).

3.3. Cheese compositions

The basic compositions of the cheese samples are shownin Table 3. In general, the total solids content of the cheesesdeclined during 90 days of storage with more remarkable inthe samples B1 and B3. This decrease may be due mainly tobreaking of peptide bonds and releasing new ionic groups(Creamer & Olson, 1982). Atasoy et al. (2003), Ozeret al. (2000, 2002) and Ozer, Atasoy, et al. (2004) reportedthat the total solids content of Urfa cheese decreasedthroughout storage as a result of extended proteolysis. At

BP1 BP2

6.77 ± 0.049 6.71 ± 0.0400.19 ± 0.005 0.19 ± 0.00513.0 ± 0.020 13.0 ± 0.0944.03 ± 0.037 4.01 ± 0.0210.56 ± 0.017 0.57 ± 0.004

P2 = Pasteurized bovine milk at 72 �C for 5 min.

Table 3The basic compositions of the cheese samplesxa

Cheese samples Level of significance

SDb B0 B1 B2 B3 B4 HT SC

pH 1 6.11 ± 0.10b 4.89 ± 0.09a 5.93 ± 0.17b 5.06 ± 0.11a 6.10 ± 0.11b *** ***

90 5.75 ± 0.05c 4.91 ± 0.01a 5.57 ± 0.09bc 4.99 ± 0.08a 5.48 ± 0.10b *** ***

T.Ac (g 100 g�1 la) 1 0.35 ± 0.08a 0.74 ± 0.15b 0.28 ± 0.03a 0.76 ± 0.05b 0.30 ± 0.05a NS **

90 0.66 ± 0.09a 0.99 ± 0.06bc 0.71 ± 0.15ab 0.99 ± 0.14c 0.75 ± 0.01abc NS *

Total solids (g 100 g�1) 1 44.3 ± 0.46ab 45.9 ± 0.86ab 44.9 ± 0.61ab 46.3 ± 0.97 b 43.5 ± 0.71a NS *

90 43.1 ± 1.32 44.0 ± 0.97 43.7 ± 0.35 42.0 ± 1.04 43.0 ± 0.79 NS NSFat-in-dry matter (g 100 g�1) 1 46.9 ± 0.08 48.9 ± 1.03 47.1 ± 0.82 49.2 ± 1.56 46.7 ± 0.19 NS NS

90 48.1 ± 0.10 47.0 ± 1.84 46.4 ± 0.15 46.7 ± 0.88 46.8 ± 0.76 NS NSSalt-in-dry matter (g 100 g�1) 1 8.7 ± 0.20 8.1 ± 0.48 9.5 ± 0.15 8.8 ± 0.71 9.3 ± 0.73 NS NS

90 11.4 ± 0.34a 13.7 ± 0.97b 12.7 ± 0.23ab 13.9 ± 0.63b 12.2 ± 0.36a * *

Total nitrogen (g 100 g�1) 1 2.67 ± 0.06 2.79 ± 0.17 2.69 ± 0.12 2.72 ± 0.11 2.56 ± 0.11 NS NS90 2.49 ± 0.09 2.48 ± 0.08 2.57 ± 0.13 2.33 ± 0.15 2.41 ± 0.08 NS NS

HT = Heat treatment; SC = Starter culture; NS = Non-significant.a Arithmetic mean of three replicates.b Storage days.c Titratable acidity.x Different letters indicate statistical differences within the samples at the same storage day.* Significant at P < 0.05.

** Significant at P < 0.01.*** Significant at P < 0.001.

A.F. Atasoy et al. / Food Control 19 (2008) 278–285 281

the early stages of storage, the effect of starter culture onthe total solids was significant (P < 0.05). The pHs ofcheeses decreased during storage except the sample B1.The effect of heat treatment and starter culture on pH weresignificant (P < 0.001). In parallel to the variation in pHvalues, the titratable acidity values of the samples increaseduntil 30-day of ripening, then fluctuated during the rest ofstorage (data not shown). The increase in titratable acidityduring the first month of cheese in brine is due mainly toalmost completion of the lactose fermentation and the lib-eration of amino and free fatty acids following proteolysisand lipolysis. The decreases in titratable acidities after the60th day of storage could be due to catabolism of lacticacid and passing into brine and the production of ammoniaby deamination of free amino acids (FAA) (Azarnia,Ehsani, & Mirhadi, 1997; Grappin & Beuvier, 1997; Poly-chroniadou, 1994; Prieto, Urdiales, Franco, Fresno, &Carballo, 2000). While the effect of heat treatment ontitratable acidity was insignificant (P > 0.05), the type ofstarter culture had significantly affected the developmentof acidity (P < 0.05). At the beginning of the storage, thefat-in-dry matter contents of the samples were between46.7 g 100 g�1 and 49.2 g 100 g�1 and these figures didnot change significantly at the end of storage (P > 0.05).

Salt-in-dry matter contents of the cheeses increased upto 30-day of ripening, then remained almost unchanged.Regardless of the treatments, the salt (NaCl) penetrationinto the cheese was much faster during early stage of stor-age. Salt is driven into cheese by concentration gradientbetween cheese blocks and brine, and this gradient is muchlarger at the beginning of ripening (Azarnia et al., 1997).The salt contents of the cheeses were lower than the valuesreported in previous studies (Atasoy et al., 2003; Ozeret al., 2000, 2002; Ozer, Atasoy, et al., 2004). The control

cheese (raw milk cheese) had lower salt-in-dry matter leveland at the same heat treatment, cheese made with meso-philic culture had higher salt content then its thermophiliccounterpart. The share effect of heating norm and starterculture on salt-in-dry matter were significant (P < 0.05).

3.4. Proteolysis of cheeses

As seen in Table 3, the total nitrogen (TN) levels of Urfacheeses decreased during storage irrespective of treatments.Due to the proteolysis, the amount of nitrogen decreasesduring ripening, releasing amino acids that are transformedinto volatile compounds. The continuous decrease in TNcontent of Urfa cheese throughout cold storage wasreported earlier (Atasoy et al., 2003; Ozer et al., 2000,2002; Ozer, Atasoy, et al., 2004). The effect of heat treat-ment and starter culture on total nitrogen content wereinsignificant (P > 0.05).

In order to better understand development of proteoly-sis in cheese, it is necessary to investigate the nitrogen frac-tions formed during storage (Law, 1987). Variations in thenitrogen fractions and ripening indices of Urfa cheese sam-ples are illustrated in Table 4. Cheeses manufactured withmesophilic culture (B1 and B3) contained more watersoluble nitrogen (WSN) than cheeses manufactured withthermophilic culture (B2 and B4). The effect of starter cul-ture on WSN level of the cheeses was significant, with moreremarkable at the later stages of ripening (P < 0.001). Thecheeses inoculated with mesophilic culture and heated at65 �C had higher WSN values than the sample producedwith the same culture but heated at higher temperature(72 �C). Similar trend was noted for the cheeses manufac-tured with thermophilic culture as well. Similar findingswere reported by Benfeldt and Sorensen (2001). Effect of

Table 4Variations of nitrogen fractions and ripening indices of cheese samplesxa

Cheese samples Level of significance

SDb B0 B1 B2 B3 B4 HT SC

WSN (g 100 g�1) 1 0.29 ± 0.05ab 0.38 ± 0.01c 0.26 ± 0.02ab 0.34 ± 0.03bc 0.22 ± 0.01a NS **

90 0.46 ± 0.05a 0.63 ± 0.03b 0.44 ± 0.01a 0.57 ± 0.01b 0.40 ± 0.02a NS ***

NPN (g 100 g�1) 1 0.05 ± 0.01a 0.19 ± 0.05b 0.05 ± 0.01a 0.14 ± 0.00b 0.04 ± 0.01a * **

90 0.20 ± 0.02a 0.39 ± 0.02b 0.21 ± 0.03a 0.37 ± 0.01b 0.19 ± 0.03a ** ***

PPN (g 100 g�1) 1 0.25 ± 0.05 0.18 ± 0.04 0.20 ± 0.02 0.19 ± 0.02 0.17 ± 0.01 NS NS90 0.26 ± 0.03 0.24 ± 0.04 0.22 ± 0.04 0.20 ± 0.01 0.20 ± 0.03 NS NS

RI (%) 1 10.8 ± 1.47abc 13.5 ± 0.43c 9.6 ± 1.09ab 12.3 ± 0.72bc 8.4 ± 0.46a NS *

90 18.5 ± 1.37b 25.2 ± 0.72c 17.1 ± 0.37ab 24.6 ± 1.06c 15.1 ± 0.37a NS ***

WSN = Water soluble nitrogen; NPN = Non-protein nitrogen, PPN = Proteose-peptone nitrogen; RI = Ripening index; HT = Heat treatment;SC = Starter culture; NS = Non-significant.

a Arithmetic mean of three replicates.b Storage days.x Different letters indicate statistical differences within the samples at the same storage day.* Significant at P < 0.05.

** Significant at P < 0.01.*** Significant at P < 0.001.

282 A.F. Atasoy et al. / Food Control 19 (2008) 278–285

heat treatment on water soluble nitrogen content of Urfacheeses was insignificant (P > 0.05). The non-protein nitro-gen (NPN) levels of the Urfa cheeses increased with ripen-ing. Increasing NPN level in bovine milk Urfa cheeseduring ripening were reported (Atasoy et al., 2003; Ozeret al., 2000, 2002; Ozer, Atasoy, et al., 2004). As withWSN, NPN levels of the cheeses were significantly affectedby the starter cultures (P < 0.001). The effect of heat treat-ment on NPN content of Urfa cheeses was found to be sig-nificant (P < 0.01). The joint effect of starter culture andheat treatment on NPN content was more pronounced dur-ing ripening.

The proteose-peptone nitrogen (PPN) fraction is madeup of large peptides. The initial and final PPN fractionsare higher than NPN for B0, B2 and B4 cheese. This allowsus to conclude that rennet is the main agent of the proteol-ysis in the cheeses in question and that the microbialenzymes have a secondary role in the extended degradationof peptides into small molecular weight peptides and aminoacids these cheeses. This finding is line with Prieto et al.(2000) and Franco et al. (2001). The effect of heat treatmentand starter culture on PPN content of Urfa cheeses wereinsignificant (P > 0.05).

The process of proteolysis is affected by various factors,including natural flora of raw milk, starter culture, milkcoagulating enzyme and production parameters. In thisstudy, the raw milk of the same origin was used for thecheese manufacturing and the production parameters wereconstant for each individual cheese batches, except type ofstarter culture and heat treatment norms. The effect ofheating norm on ripening index (RI) of cheeses was insig-nificant (P > 0.05), on contrary, the starter culture affectedRI values of cheeses significantly (P < 0.001). At the begin-ning of storage RI of the samples B0, B1, B2, B3, B4 were10.8%, 13.5%, 9.6%, 12.3%, 8.4%, respectively. After 90days of ripening period, these values increased to 18.5%,25.2%, 17.1%, 24.6% and 15.1%, in the same order.

According to a classification of white cheeses on the basisof RI values, as proposed by Kurt (1972), B0, B2 and B4

cheeses are classified as unripened (RI < 20%), B1 and B3

cheese are semi-ripened (RI between 20% and 30%).

3.5. Electrophoresis of cheese

The alkaline urea gel electrophoretograms of 1 day and90 day-old cheeses are illustrated in Fig. 1. The density ofbands representing as1-casein (as1-CN) and b-casein (b-CN) decreased throughout ripening and as1-CN degrada-tion products became more evident, except the samplesB0. A more extensive hydrolysis of b-CN was noted inB0. No band representing as1-casein degradation productswas observed. In general, degradation of casein fractionsin Urfa cheeses was limited throughout storage, indicatinglower degree of proteolysis in the cheeses. This could bedue mainly to high salt/moisture ratio (between 8.6 g100 g�1 and 10.7 g 100 g�1 in 90 day-old cheeses). Thomasand Pearce (1981) found that at 4% salt/moisture ratio,as1-CN was degraded almost completely in Cheddarcheese, however, increasing the ratio of salt/moisture to8% in the same cheeses led to a sharp decrease in degrada-tion of this casein fraction. Mulvihill and Fox (1978) andThomas and Pearce (1981), showed that the rennet actionon b-CN was also influenced by the NaCl concentration.Effects of mesophilic and thermophilic lactic acid bacteriaon the caseins were very limited. These findings are in goodagreement with previous studies (Farkye, Fox, Fitzgerald,& Daly, 1990; Law, Fitzgerald, Uniacke-Lowe, Daly, &Fox, 1993; Oberg, Davis, Richardson, & Ernstrom, 1986).

3.6. Lipolysis of cheeses

Acid degree value and total volatile fatty acids contentsof the experimental cheeses are shown in Table 5. At thebeginning of ripening, the acid degree values of the cheeses

Cheese samples

B0 B1 B2 B3 B4

1 90 1 90 1 90 1 90 1 90

γ-casein

β-casein

αs1-casein αs1-casein

degradation product

Fig. 1. Alkaline urea gel electrophoretograms for the caseins after 1 and 90-days of ripening in the Urfa cheese samples.

A.F. Atasoy et al. / Food Control 19 (2008) 278–285 283

B0, B1, B2, B3 and B4 were 2.32, 1.23, 1.07, 1.25, 1.08 mgKOH 100 g�1 fat, respectively, and these figures increasedto 6.39, 1.81, 1.58, 1.64, 1.60 mg KOH 100 g�1 fat after90 days of storage, in the same order. The total volatilefatty acids values of the cheeses were 8.25 (B0), 5.53 (B1),3.84 (B2), 4.59 (B3), 3.36 (B4) mL NaOH 100 g�1 cheesein 1 day-old cheeses, and these figures rose to 14.7, 6.84,5.92, 6.37, 6.12 mL NaOH 100 g�1 cheese in the 90 day-old cheeses, respectively.

B0 (raw milk cheese) had higher acid degree value andtotal volatile fatty acids degree levels than B1, B2, B3 andB4. Similar results were found by McSweeney, Fox, Lucey,Jordan, and Cogan (1993) and Rehman et al. (2000). Thisindicated that native milk lipase was principally responsiblefor the hydrolysis of the lipids in bovine Urfa cheese. Thehydrolyzation of lipids in cheese during ripening is cata-lyzed by indigeneous lipase of the milk and by microbiallipases (Fox, Guinee, Cogan, & McSweeney, 2000; Franco,

Table 5Variations of acid degree value and total volatile fatty acids of cheese sample

Cheese samples

SDb B0 B1 B2

Acid degree valuec 1 2.32 ± 0.64b 1.23 ± 0.02a 1.07 ±90 6.39 ± 2.78b 1.81 ± 0.11a 1.58 ±

TVFAd 1 8.25 ± 0.64d 5.53 ± 0.35c 3.84 ±90 14.7 ± 2.45b 6.84 ± 0.65a 5.92 ±

HT = Heat treatment; SC = Starter culture; NS = Non-significant.a Arithmetic mean of three replicates.b Storage days.c mg KOH 100 g�1 fat.d Total volatile fatty acids (mL NaOH 100 g�1 cheese).x Different letters indicate statistical differences within the samples at the sam* Significant at P < 0.05.

*** Significant at P < 0.001.

Prieto, Urdiales, Fresno, & Carballo, 2001). The heat treat-ment of milk completely inactivate the native milk lipase.Moreover, native milk lipase is optimally active at pHvalue of 8.0–9.0, and is inhibited by NaCl to great extent(Franco et al., 2001; Vlaemynck, 1992). The figures of saltcontent and pH in the experimental cheeses were far fromthe the values indicated for optimum activity of milk lip-ases (pH 5.75–4.91, salt content 4.91–6.01%). Effect ofheating norm was significant on acid degree values andtotal volatile fatty acid values (P < 0.05 and P < 0.001,respectively).

Acid degree value and total volatile fatty acid contentsof the cheeses made with mesophilic (B1 and B3) and ther-mophilic (B2 and B4) lactic cultures were close to eachother. The lipolytic capacities of Lactobacillus spp. andLactococcus spp. are very limited (Fox et al., 2000). Effectof starter culture on acid degree value and total volatilefatty acids was insignificant (P > 0.05).

sxa

Level of significance

B3 B4 HT SC

0.05a 1.25 ± 0.05a 1.08 ± 0.07a * NS0.13a 1.64 ± 0.05a 1.60 ± 0.19a * NS0.22ab 4.59 ± 0.08bc 3.36 ± 0.31a *** *

0.22a 6.37 ± 0.36a 6.12 ± 0.18a *** NS

e storage day.

0

7CHARACTERISTIC AROMA

7 CHARACTERISTIC AFTER-TASTE

7 COLOR

7 TEXTUREFIRMNESS 7

SALTINESS 7

BITTERNESS 7

—×— 0, — — B B B B B1, — — 2, — — 3, — — 4

Fig. 2. Sensory profile of 90 day-old Urfa cheese samples.

284 A.F. Atasoy et al. / Food Control 19 (2008) 278–285

As the control cheese had higher level of lipolysis thanthe cheeses made from milk inoculated with mesophilicor thermophilic lactic starters, it can be concluded thatnative lipases and/or non starter lactic acid bacteria(NSLAB) were primarily responsible for the devolopmentof lipolysis in Urfa cheese.

3.7. Sensory evaluation of cheese

Sensory characteristics of 90 day-old Urfa cheeses aregiven in Fig. 2. All experimental cheeses were whitish incolor. Cheeses manufactured from milk heated at lowertemperature (65 �C) had higher textural characteristicsthan the cheeses made from high heat treated (72 �C) milk.Moreover, cheeses manufactured with mesophilic culturehad lower sensory scores for textural characteristic thanthat made with thermophilic culture. This result was in har-mony with higher protein degradation in the cheese madewith mesophilic culture. According to Tunick et al.(1993), Tunick, Malin, Smith, and Holsinger (1995),Tunick, Cooke, Malin, Smith, and Holsinger (1997), thereis a negative correlation between proteolysis and develop-ment of texture in cheese. Raw milk cheese (B0) receivedhigher overall aroma and pungency and flavour scoresfrom the panel group.

Bitterness is one of the most common defects associatedwith an excessive casein breakdown, leading, eventually, toan accumulation of high-molecular weight bitter peptides.This defect was not detected in the 90 day-old Urfa cheeseand experimental cheeses had almost similar bitternessscores. High saltiness was the main point that was criticizedby the panellists; although, the fact that traditional Urfacheese is a too salty cheese variety (Atasoy, 1999;Yetis�meyen & Yıldız, 2001). While 40% of the panellistsfound the samples B2 and B4 to be hard and well texturedbut poor in acidity. On the other hand, 55% of the panel-

lists pointed out that B1 and B3 cheeses were soft and adhe-sive but the acidity in these samples was well-balanced.Majority of the panel group expressed that B2 cheese hadmore or less similar sensory characteristic with the controlcheese (B0).

4. Conclusions

This work clearly demonstrated the role of heat treat-ment to cheese milk and starter culture on some character-istics of Urfa cheese. Traditional raw milk cheese hadhigher sensory scores, but since traditional applicationsof scalding and brining were insufficient to elimination allpathogens from industrial Urfa cheese (Ozer, Uraz, et al.,2004), incorporation of heat treatment into Urfa cheese-making is inevitable. In the present work, heat treatmentat higher temperature (72 �C) adversely affected the chem-ical and sensory properties of Urfa cheeses. The adverseeffects of heat treatment at lower temperature (65 �C) onproperties of the cheeses were less pronounced. Therefore,it can be concluded that milk used in the production ofUrfa cheese should be heat treated at lower temperature.

While cheeses made by the addition mixed culture con-sisting of Lc. lactis subsp. lactis + Lc. lactis subsp. cremoris

had higher levels of proteolysis, these samples receivedlower preference by the panellists. On contrary, the cheesesproduced with addition of starter culture containing Lacto-

bacillus delbrueckii subsp. bulgaricus + Streptococcus ther-

mophilus had lower levels of proteolysis but highersensory preferences.

Future studies should be intensified on the selection ofsuitable starter combination(s) to manufacture Urfa cheesehaving close physical, chemical and sensory characteristicsto the traditional ones. Also, further studies should be ded-icated to lower the salt level of Urfa cheese without impar-ing the nature of the end products.

A.F. Atasoy et al. / Food Control 19 (2008) 278–285 285

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