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LWT - Food Science and Technology xxx (2013) 1e8

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Characterization of Siahmazgi cheese, an Iranian ewe’s milk variety:Assessment of physico-chemical, textural and rheologicalspecifications during ripening

Ghazaleh Farahani a, Hamid Ezzatpanah a,*, Soleiman Abbasi b

aDepartment of Food Science and Technology, Science and Research Branch, Islamic Azad University, P.O. Box 14515.775, Tehran, IranbDepartment of Food Science and Technology, Faculty of Agriculture, Tarbiat Modares University, P.O. Box 14115-336, Tehran, Iran

a r t i c l e i n f o

Article history:Received 8 June 2012Received in revised form6 May 2013Accepted 3 June 2013

Keywords:Siahmazgi cheeseRipeningTextureRheology

* Corresponding author. Tel.: þ98 21 44865137; faxE-mail addresses: [email protected], h

(H. Ezzatpanah).

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a b s t r a c t

Siahmazgi cheese is an Iranian locally-made cheese produced from ewe’s milk or a mixture of ewe andgoat’s milks in the suburbs of Rasht in the north of Iran. This kind of cheese is kept in sheepskin for sixmonths under special condition which cause distinct physicochemical and textural characteristics.Therefore, in the present study the effect of ripening time (6 months) on the chemical, physicochemical,rheological and textural characteristics of Siahmazgi cheese (18 samples) was investigated. The rheo-logical and textural properties were determined using rheometer (frequency sweep) and textureanalyzer (uniaxial compression). Based on our findings, the measured values including pH, titratableacidity (TA), dry matter, fat, protein, ash, salt content, water soluble nitrogen in total nitrogen, and non-protein-nitrogen in total nitrogen significantly increased during ripening (P < 0.05). Furthermore, theresults showed that the six-month ripened Siahmazgi cheese contained high values of dry matter(59.95 � 0.08 g/100 g), salt (5.65 � 0.05 g/100 g), and ash (7.24 � 0.02 g/100 g). Regarding rheologicaland textural properties, storage modulus (G0), loss modulus (G00), fracture stress (sf) and firmnessincreased while loss tangent and fracture strain decreased.

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1. Introduction

One of the traditional Iranian cheeses is Siahmazgi cheese pro-ducing from ewe’s milk or a mixture of ewe and goat’s milks. It iskept in special circumstances in sheepskin during ripening in theSiahmazgi village, suburbs of Rasht, Gilan province-Iran. This kindof cheese has an extremely firm texture with some pea-sized holes,yellowish appearance and fermented taste. All these characteristicsdepend on productionmethod and special storage condition duringripening. As the ripening proceeds, the physical and chemicalchanges affect the body of the unripened cheese (Tunick, 2000).

Cheese ripening is a complex process due to many physico-chemical changes which include mainly pH variation, progressivebreakdown of the proteins to smaller polypeptides, and the gradualaccumulation of amino acids where all these changes can leadto some unique characteristics in cheese varieties (Fox, Law,McSweeney and Wallace, 1993).

: þ98 21 [email protected]

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Rheological properties of cheese have a significant role to playin determining body and texture characteristics. It is believed thatcheese has viscoelastic nature which shows both elastic andviscous behaviors (Konstance and Holsinger, 1992). Therefore,instrumental measurements (mechanical and rheological tests)may be performed to obtain different information (Del Nobile,Chillo, Mentana & Baiano, 2007). In general, the most commonmethods employed to investigate the mechanical properties tocharacterize cheese varieties and also to distinguish them fromeach other by specifying their elastic and viscous natures, are non-destructive (such as oscillation, stress relaxation and creep tests)and destructive (stress-strain tests and texture profile analysis)deformations (Tunick, 2000). The former is useful to obtain datarelating to structure down to the molecular level (Shoemaker,Natz, Bonnans & Noble, 1992) while the latter determines frac-ture properties (Messens, Van de Walle, Arevalo, Dewettinck &Huyghebaert, 2000).

To date,many studies have investigated the physicochemical andrheological properties of different kinds of cheeses during ripening(Cichoscki, Valduga, Valduga, Tornadijo & Fresno, 2002; Hort & LeGrys, 2001; Juan, Trujillo, Guamis, Buffa & Ferragut, 2007;Kahyaoglu & Kaya, 2003; Karami, Ehsani, Mousavi, Rezaei & Safari,

hmazgi cheese, an Iranian ewe’s milk variety: Assessment of physico-T - Food Science and Technology (2013), http://dx.doi.org/10.1016/

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G. Farahani et al. / LWT - Food Science and Technology xxx (2013) 1e82

2009; Lucey, Johnson & Horne, 2003; Madsen & Ardö, 2001; Milci,Goncu, Alpkent & Yaygin, 2005; Pappa, Kandarakis & Mallatou,2007; Raphaelides, Antoniou, Vasilliadou, Georgaki & Gravanis,2006; Sadowska, Bialobrzewski, Jeli�nski & Markowski, 2009; SanMartín-González et al., 2007; Tarakci & Kucukoner, 2006). More-over, there have been several researches on various kinds of Iraniancheese including microbiological and chemical quality of Lighvancheese (Mirzaei, Ghiasi Khosrowshahi & Karim, 2008), Tavalesh andAsalem cheeses and their production methods (Kashkuli, 1975), aswell as the physical and chemical properties of Lighvan and Gol-payegan White-brined cheese during ripening (Mahdavi Adeli,Mirhadi & Yusefi, 2010). Despite the fact that Siahmazgi cheesehas a long tradition of production in Iran, there is no published dataon characterization of this kind of traditional Iranian cheese. Its highquality, special taste and firm texture have made it hugely popularamong the regional consumers. Therefore, the major aims of thisstudy were to evaluate the physicochemical properties of cheesemilk, the characterization of the traditional process for the manu-facture of Siahmazgi cheese, and to determine the chemical andphysicochemical characteristics as well as textural and rheologicalproperties of it during six months ripening.

2. Materials and methods

2.1. Cheese-making procedure

Siahmazgi cheese was manufactured using traditional methodon farms as fresh raw ewe and goat milks (33% goat milk and 67%ewe milk from the morning and evening milking) were obtainedfrom a local native herd in region of Rasht, north of Iran. Thecollected raw milk was filtered through a filter cloth fastenedtightly around a copper container in order to eliminate non milksubstances. Temperature of cheese milk was adjusted at 28 � 2 �Cand 30 mL of natural stomach juice, from milking young lambs(came from the same flock of sheep), was added directly to the 10 Lmilk as the main coagulant and mixed well. Coagulation processwas carried out at 20 � 2 �C for 110e120 min. Afterwards, the co-agulumwas heated (48 �C for 30 min) under continued agitation tofacilitate and accelerate whey removal. The curd was then trans-ferred in cloth bag for curd draining, and then it was manuallypressed into spherical molds. In order to complete the drainage ofthe whey, the curd left at rest in 16e18 �C for 15 h. After draining,the curd was taken out from the mold and crystallized fine-grainedsalt was sprinkled on the surface of the cheese blocks to make thecurd firm.

In the meantime, the whey was heated (88 �C, 30 min), undercontinued agitation, in order to allow the whey proteins toaggregate. Subsequently, the agitation was stopped to enable thewhey protein aggregates on the surface. Then, the aggregatescooked and separated from the residual serum phase by cloth bag.Then, crystallized fine-grained salt was added to the serum phasewhich used as brine to fill the sheepskins containers. The amountof crystallized fine-grained salt was 25 g/kg cheese blocks on thebasis of the volume of whey. Later, the cheese blocks were placedin sheepskin containers where salted serum phase (18e20% w/v)was added and then the sheepskin containers were packed tightly.Finally, the cheeses were ripened in a cottage (Siahmazgi village,suburbs of Rasht, Gilan province-Iran) for six months at anaverage temperature of 10e18 �C (depending on the cheesemanufacture season, 10 �C in spring and 18 �C in summer) and at arelative humidity of 80e90%. The experiments were replicatedthree times and changes in chemical, physicochemical, texturaland rheological characteristics were measured at time points of 3days and 1, 2, 3, 4, 5, and 6 months (at the end of each month)after production.

Please cite this article in press as: Farahani, G., et al., Characterization of Siachemical, textural and rheological specifications during ripening, LWj.lwt.2013.06.002

2.2. Stomach juice preparation

In order to extract stomach juice, the forth compartment of adead suckling lamb stomach belonging to the same flock was dried(20 � 2 �C for 3e4 days) and wrapped with filter cloth. Then, it wasplaced in a small bowl containing 20e25 mL of hot water (90e100 �C). To extract the juice, it was gently pressed by hand.

2.3. Sheepskin container production

In order to prepare sheepskin containers, the sheep’s skin wascarefully removed without any hacks. Then, it was washed, salted,and dried under direct sun exposure for 20e25 days. Afterwards,the skins were washed again and fleeced partially. The stomachsectionwas completely sewed and the parts of feet and hands werefastened tightly by plastic strings. The internal section of thesheepskin container, where the cheese blocks are placed in, was thewoolen side and the external section of the container was the fleshyside. A flow chart of the preparing process of sheepskin container ispresented in Fig. 1.

2.4. Chemical analysis

In order to assess the physicochemical properties of milk, someliters of morning and evening milkings were collected and their fat,protein, lactose, and dry matter were measured using Milkoscan(model 134 A/B N, Foss Electric, Denmark). The pH was determinedusing a pH-meter (model 632 Metrohm, Switzerland) and the ashcontent was measured by AOAC method (AOAC, 1945).

Regarding the cheese samples, their water contents wereanalyzed in triplicate by heating to a constant weight using amoisture analyzer (Sartorius Ltd., Epsom, UK) and fat according tothe Gerber method (AOAC 2000). For pH measurement, the gratedcheese samples (10 g)mixedwith equal quantities of distilled water(10 mL) and the pH of dispersion was measured using pH-meter(Ardö & Polychroniadou, 1999). Titratable acidity of milk andcheese samples was determined by Dornic method (Robinson &Wilbey, 1998, p. 457). Cheese samples were analyzed for salt con-tent by Volhard (AOAC, 2000) and ash content by dry ashmethod at550 �C (AOAC, 2000). The nitrogen content of cheese and milksamples was determined using Kjeldahl method (AOAC, 2001). Thewater-soluble nitrogen fraction (WSN) was measured by using themethod described by Polychroniadou, Michaelidou & Paschaloudis(1999) as 20 g of grated cheese samples was homogenized in100 mL of distilled water using a stomacher for 5 min and the sus-pension was incubated (40 �C for 1 h). Then, the insoluble solidswere separated by centrifugation (3000 g � 30 min, 4 �C). The su-pernatant was then filtered and the nitrogen content in the filtratewas measured using Kjeldahl method. The non-protein nitrogen(NPN)was also assigned by Kjeldahlmethod as follows: 4mL of TCA(60%) was added to 16 mL of WSN filtrate and then filtrated(Whatman No. 42) after 1 h (Alizadeh, Hamedi & Khosrowshahi,2006). In this study the ripening factors (WSN/TN% and NPN/TN%)were estimated according to [(WSN/Total Nitrogen) � 100] (Alais,1984, p. 814) and [(NPN/Total Nitrogen) � 100] (Alizadeh et al.,2006). All physical and chemical measurements were carried outin triplicate.

2.5. Mechanical and rheological properties

2.5.1. Uniaxial compressionThis test was carried out on cheese samples during ripening (on

the third day and at the end of each month for 6 month) using aHTE Universal Testing Machine (S-Series Bench U.T.MModel H5K-S,Hounsfield Test Equipment Ltd., UK). The cubic samples (2*2*2 cm)


Fig. 1. A flow chart of illustrating the preparation stages of sheepskin containers.

G. Farahani et al. / LWT - Food Science and Technology xxx (2013) 1e8 3

were taken from the depth (2 mm) of cheese blocks with parallelblades (Romeih, Michaelidou, Biliaderis & Zerfiridis, 2002) andequilibrated at room temperature (23 � 1 �C) at least for 4 h(Madadlou, Khosrowshahi, Mousavi & Farmani, 2007). Then, theywere compressed (70% of their original height) at a constant tem-perature (20 �C) using a 500 N load cell and a crosshead speed of

Table 1The chemical compositiona of milks for manufacturing of Siahmazgi cheese (Means � SD

pH Titratable acidity (Dornic degrees) Dry matter (%w/w)

6.63 � 0.1 21.33 � 1.03 15.74 � 0.02

a Average values from two batches of the cheese milk, three replicates per analysis.


30 mm/min (Pappa et al., 2007). The stress-strain curves wereconstructed and the true stress (s) (N/m2) and the true strain (ε) (�)were calculated following the Eq. (1) and Eq. (2) of Calzada & Peleg(1978):

sðtÞ ¼ FðtÞ=AðtÞ (1)

ε ¼ lnðH0Þ=ðH0 � DHÞ (2)

Where s(t) (N/m2) is the true stress at time (t); F(t) (N) the force attime (t); A (t) (m2) the area at time (t); ε (�) is the true strain; H0 (m)the original height; and DH the change in height.

The hardness was also measured and it was defined as themaximum force during the first compression cycle (Konstance &Holsinger, 1992). The test was performed six times for eachreplicate.

2.5.2. Dynamic oscillatory testingUsing a rheometer (Anton Paar Physica, MCR 300, LR 101,

Austria), the viscoelastic parameters including storage modulus(G0), loss modulus (G00) and the ratio between the viscous andelastic properties of the material, phase angle tangent (tan d) weredetermined under various frequency range (0.1e100 Hz) in a linearviscoelastic region (Dimitreli & Thomareis, 2008; Steffe, 1996, pp.294e349). The cheese samples were prepared from depth (2 cm) ofthe cheese blocks at 8 � 1 �C. These samples were stored in airtightplastic bags (to prevent dehydration) and equilibrated at roomtemperature (25 � 1 �C) for at least 3 h. A small piece of sampleswas put on the geometry (25 mm parallel plates) and then theupper plate was slowly pushed down (gap size 3 mm). Excessivecheese pieces were trimmed off carefully with a razor blade. Thisstage was followed by relaxing the sample for 10 min in therheometer to reduce the stresses during sample handling (Juanet al., 2007). All rheological measurements were done in triplicate.

2.6. Statistical analysis

All experimental data (pH, titratable acidity, dry matters, fat,protein, salt, total nitrogen/dry matters (TN/TS), water soluble ni-trogen/total nitrogen (WSN/TN) and ash) were statisticallyanalyzed using a general linear model (GLM) procedure of SPSS forWindows Release 8.0 (SPSS Inc., Chicago, USA) by analysis of vari-ance (ANOVA) followed by Duncan’s multiple range test duringripening (at the third day and at the end of each month until 6month). Values P < 0. 05% were considered to be significant.

3. Results and discussion

3.1. Composition of milk

Table 1 shows the main physicochemical parameters of the milkused for the manufacture of Siahmazgi cheese. In general, thechemical composition of the milk had a significant influence oncoagulation, which in return had an important role in the quality ofthe cheese. Many factors can affect the variation of the chemicalcomposition of the milk, such as the type of breed, kind of feeding,lactation stage, etc (Auldist, Walsh & Thomson, 1998). The results

).

Fat (%w/w) Protein (%w/w) Lactose (%w/w) Ash (%w/w)

5.55 � 0.01 4.57 � 0.01 5.02 � 0.01 0.60 � 0.01



showed that the average values of the pH and titratable acidityof the milk were similar to those described by other authorsfor ewe’s milk in natural state (Haenlein & Wendorff 2006; Klinger& Rosenthal, 1997; Kurkdjian & Gabrielian, 1962; Mahmood &Usman, 2010) while the average values of dry matter, fat, proteinand ash were lower (Jandal, 1996; Mahmood & Usman, 2010; Pavic,Antunac, Mioc, Ivankovic & Havranek, 2002; Sahan, Say & Kaçar,2005) which can be attributed to the combination of ewe andgoat’s milks in which it is normally used for producing this kind ofcheese. Lactose content of the milk was similar to that reportedby Mahmood and Usman (2010); Pavic et al. (2002), and Bylund(1995, p. 436).

3.2. Effect of ripening on physicochemical parameters

Average values of the main composition of Siahmazgi cheesethroughout ripening are shown in Table 2. In all cases significantincrease of dry matter can be seen during ripening except the sixthmonth which has decreased (P < 0.05). In general, dry mattercontent of brined cheeses can be affected and increased by somefactors such as initial moisture, pH, and brine concentration duringripening (Rotaru, Mocanu, Uliescu & Andronoiu, 2008). Whencheese is placed in brine, a dynamic diffusion process took place. Inthis case, NaCl molecules transmit from the brine into the cheesetexture as water diffuses out through the cheese matrix (Guinee &Fox, 1987). This trend can decrease the moisture content of cheeseand therefore increase the values of dry matter and salt duringripening (Kaya, 2002; Khosrowshahi, Madadlou, Musavi & Emam-Djome, 2006; Melilli et al., 2005). On the other hand, proteolysisincreases the polarity groups therefore it brings about an increasein water holding capacity and decrease in dry matter of cheese(Brunner, 1981). The values of dry matter were lower than thosedescribed for Prato (Cichoscki et al., 2002) but higher than thosereported for Halloumi cheese (Raphaelides et al., 2006). The cheesemanufacturing process and ripening conditions can also affect thedry matter content of cheese (Cichoscki et al., 2002) which isapplicable in case of Siahmazgi cheese because of its specificmaintenance condition during ripening (in sheepskin). As cheese isripened, the inner moisture evaporates through sheepskin surfaceand therefore it can lead to higher level of dry matter as well as saltin the body of cheese.

The average content of protein and fat in dry matter showed asignificant increase during ripening (P < 0.05). In line with ourfindings, Kaya (2002) perceived that the higher the amount of saltin brine, higher the amounts of fat, protein and salt in Gaziantep

Table 2Influence of ripening period on some chemical and physical properties of Siahmazgi che

Characteristics Ripening time (days)

3 30 60

Dry matter (%w/w) 41.53 � 0.18a 50.10 � 0.12b 59.81 � 0.17cFat (%w/w) 18.12 � 0.25a 22.62 � 0.48b 29.12 � 0.50cFat in dry matter (%w/w) 46.64 � 0.49a 45.16 � 0.86b 48.70 � 0.68cTotal nitrogen 3.11 � 0.04a 3.28 � 0.07b 3.60 � 0.05dProtein (%w/w) 19.83 � 0.25a 20.94 � 0.44b 22.96 � 0.29dAsh (%w/w) 2.40 � 0.03a 5.74 � 0.14b 7.50 � 0.05dSalt (%w/w) 0.51 � 0.03a 4.01 � 0.24b 5.44 � 0.10cS/Mb (%w/w) 0.86 � 0.05a 7.44 � 0.39b 11.92 � 0.15cWSN 0.110 � 0.003a 0.143 � 0.004b 0.146 � 0.003bWSN/TN (%w/w) 3.57 � 0.06a 4.39 � 0.09b 4.06 � 0.04bNPN 0.046 � 0.003a 0.068 � 0.002a 0.079 � 0.006bNPN/TN (%w/w) 2.08 � 0.08a 2.08 � 0.03a 2.18 � 0.14apH 7.25 � 0.02e 5.11 � 0.02d 5.07 � 0.01dTitrable acidity (Dornic degree) 77.50 � 1.00a 80.25 � 1.25b 92.00 � 2.31c

a Means within the same rows with different common letters differ significantly (P <b Salt e in-moisture, calculated using the means of moisture and salt.


cheese. The increasing trend in fat in dry matter and protein duringripeningwas similar to those reported by Sadowska et al. (2009) forDutch, Cichoscki et al. (2002) for Prato, Taraksi and Kucukoner(2006) for Kashar and Karami et al. (2009) for UF-Feta cheeses.

Lipolysis and proteolysis play an important role in changing theflavor and aroma of cheese, whereas proteolysis changes thetexture either. As a result of proteolysis, the content of peptides andamino acids increase regularly. Therefore, peptide content is a goodindex of the maturity degree of cheese (Cooker, Crawford, Johnston,Singh & Creamer, 2005). In this study, the increased content ofpeptides measured by WSN and NPN as total nitrogen, observedduring ripening which supports the proper ripening of the cheese(Küçüköner & Haque, 2003). These findings are also in goodagreement with the data reported by Hesari, Ehsani, Khosrowshahi& McSweeney (2006) for Iranian UF white cheese, Karami et al.(2009) for Iranian UF-Feta cheese and Sadowska et al. (2009) forDutch-type cheese.

Moreover, the salt content increased throughout ripeningcontributed to the increase in ash content of Siahmazgi cheese. Theash content at the end of ripening (7.24 � 0.2) was higher thanthose described by Cichoscki et al. (2002) for Prato and Milci et al.(2005) for Holloumi cheeses.

The titratable acidity significantly increased (P< 0.05), while pHvalues significantly (P < 0.05) decreased during ripening (sixmonths). The increase in titratable acidity and therefore thedecrease in pH were due to lactic acid and hydrogen formation bylactic acid bacteria used lactose (Dervisoglu & Yazici, 2001). Thevariation trends of pH and titratable acidity values of Siahmazgicheese during ripening were similar to that described by Tarakciand Kucukoner (2006) for Kashar cheese.

3.3. Effect of ripening on mechanical properties

To investigate the mechanical properties of cheese, the mostcommon method is the uniaxial compression test. In this test, aconstant rate of compression is applied to the material and thevalues of stress are continuously recorded (Pappa et al., 2007). Theresults of the test are suitable for the assessment of the rheologicalbehavior of cheese samples on ripening. This test was frequentlyapplied at large deformation to determine fracture properties.Fracture stress is a point of maximum stress, where the materialshows macroscopic failure (Watkinson et al., 1997) and fracturestrain is the point which describes the deformability of cheese. Ahigh numerical value in the fracture stress point indicates tough-ness of material while in the fracture strain point, refers to greater

ese (Means � SD)a

90 120 150 180

61.08 � 0.61d 62.76 � 0.47e 62.65 � 0.13e 59.95 � 0.08c31.75 � 0.64f 30.12 � 0.25d 31.87 � 0.47f 31.00 � 0.41e51.98 � 0.58e 48.00 � 0.21c 50.88 � 0.68d 51.71 � 0.61de3.33 � 0.04bc 3.82 � 0.11f 3.71 � 0.03e 3.40 � 0.01c

21.30 � 024bc 24.37 � 0.74f 23.73 � 0.21e 21.71 � 0.09c8.03 � 0.1e 8.26 � 0.39e 7.04 � 0.33c 7.24 � 0.02cd5.71 � 0.10d 6.49 � 0.14e 5.46 � 0.27c 5.65 � 0.05cd

12.79 � 0.12e 14.83 � 0.14f 12.75 � 0.52de 12.36 � 0.07d0.149 � 0.002b 0.179 � 0.008cd 0.181 � 0.009d 0.170 � 0.010c4.46 � 0.01c 4.68 � 0.12d 4.88 � 0.19de 4.99 � 0.27e

0.090 � 0.015c 0.131 � 0.004d 0.146 � 0.002e 0.145 � 0.008e2.69 � 0.42b 3.44 � 0.03c 3.93 � 0.02d 4.26 � 0.21e4.78 � 0.03c 4.57 � 0.03b 4.46 � 0.05a 4.46 � 0.03a

122.50 � 1.00d 125.00 � 0.81e 134.50 � 0.58f 135.25 � 0.50f

0.05).


1.0E+00

1.0E+01

1.0E+02

1.0E+03

1.0E+04

0.01 0.1 1 10 100 1000

G'/

G"

(Pa)

Strain, (%)

Fig. 2. Elastic and loss moduli of Siahmazgi cheese as a function of shear strain(oscillating frequency 0.1 Hz, temperature 25 �C): (B) storage modulus (G0); (6) lossmodulus (G00).

1.0E+07


deformability (Juan et al., 2007). On the basis of previous studies, allmain components of a cheese such as water, fat, protein, and salt(brine) can affect the rheological and consequently the texturalbehavior of the cheese (Prentice, 1987).

According to Table 3, as the ripening advanced the fracturestress increased (P < 0.05) while the fracture strain decreased(P < 0.05) which were similar to what were reported for semi-hardewe’s milk cheese (Juan et al., 2007), Manchego type (Pavia,Guamis, Trujillo, Capellas & Ferragut, 1999) and Cheddar cheese(Wick, Nienaber, Anggraeni, Shellhammer & Courtney, 2004).Furthermore, the hardness, the required force to compress thesample up to 70% of its initial height, increased during ripening. Theincrease in fracture stress and hardness and the decrease in fracturestrain values can be described by losing of water content throughripening since water could cause inhomogeneous areas promotingthe ease of fracture (Prentice, 1987). Similar results were reportedfor semi-hard ewe’s milk cheese (Juan et al., 2007), Manchego type(Pavia et al., 1999), Gouda (Visser, 1991), and Swiss-type (Rohm,Lederer & Ginzinger, 1992) cheeses. In addition, lower fractur-ability and higher hardness can be attributed to the brine concen-trationwhich led to the increased salt uptake by cheese body (Kaya,2002). It is also reported that decrease of the water available forsolvation of the protein chains and the loss of elastic structuralelements during ripening can result to a harder, less easilydeformed cheese (Creamer & Olson, 1982).

3.4. Effect of ripening on rheological properties

Frequency sweep tests were performed to determine theviscoelastic characteristics of the cheeses. In order to point out thelinear viscoelastic region, preliminary experiments were used. Anamplitude strain sweep test was conducted (frequency 0.1 Hz) andresulting strains recorded (0.01e200%). Then, a proper strain, inlinear viscoelastic region, was determined (0.1%) and a frequencysweep test (0.1e100 Hz) was carried out. Parameters describing theviscoelastic properties of the cheeses include G0 (the storage orelastic modulus) related to the molecular events of elastic nature ofmaterial; G00 (the loss or viscous modulus) related to the viscousbehavior of material, and loss tangent (tan d ¼ G00/G0) related to therelative effects of viscous and elastic components (Gunesakaran &Ak, 2000). The lower the tan d value (closer to 0), the less thecheese flows. The linear viscoelastic properties of Siahmazgi cheeseduring the ripening are presented in Figs. 2e5. Fig. 2 shows thelinear region for one of the samples. For all the other samples,similar behavior was observed.

3.4.1. Storage and loss moduliFigs. 3 and 4 show the changes in the storage and loss moduli of

Siahmazgi cheese as a function of oscillation frequency duringripening (six months). Cheeses in the present study showed a

Table 3Mechanical parameters (compression test) of Siahmazgi cheese at different stages ofripening (Means � SD)a

Ripeningtime (days)

Fracture stress (kPa) Fracture strain (e) Hardness (N)

3 83.84 � 4.89b 0.515 � 0.02c 57.25 � 1.48a30 110.71 � 0.30a 0.145 � 0.02a 157.25 � 7.42b60 330.88 � 11.31bcd 0.285 � 0.01ab 286.00 � 55.15cd90 383.88 � 10.42cd 0.370 � 0.13bc 385.40 � 3.11e120 440.25 � 56.57d 0.230 � 0.14ab 496.00 � 6.08f150 240.80 � 10.71abc 0.125 � 0.02a 308.70 � 25.60d180 186.04 � 9.89ab 0.115 � 0.05a 246.80 � 12.73c

a Values within the same column not sharing a common letter differ significantly(P < 0.05).


significant increase in storage and loss moduli through ripeningperiod. In the case of storage and loss moduli, the elastic behaviordominates over the viscous behavior when G0>G00 and on thecontrary, the viscous behavior dominates over the elastic behaviorwhen G00>G0 (Steffe, 1996, pp. 294e349). As in the current study, allcheeses showed greater G0 than G00 at any given point, the elasticcomponent dominates to the viscoelasticity (Subramanian &Gunasekaran, 1997) which indicates a viscoelastic solid behavior(Rao & Steffe, 1992). The results were similar to those described byJuan et al. (2007) for a kind of ewe’s milk cheese and by Kahyaogluand Kaya (2003) for Gaziantep cheese. In addition, both G0 and G00 ofthe cheeses were dependent on frequency exhibiting the visco-elastic nature of the material (Drake, Gerard, Truong & Daubert,1999). Three-day-old cheeses showed the lowest storage and lossmoduli throughout the frequency range. G0 modulus of three-day-old cheese increased from 43.05 � 103 to 130.50 � 103 Pa at thestated frequency range (0.1e100 Hz). The changes of G0 modulustrend for 180-day-old samples were within 1290 � 103e2480 � 103 Pa at the same frequency range. The changes of G00

modulus at the mentioned frequency range were 12.85 � 103e35.20� 103 for three-day-old and 311�103e558� 103 for 180-day-old cheese samples.

3.4.2. Loss tangentAccording to Fig. 5, cheese samples in the present study showed

a decrease of tan d during ripening. At the applied frequency range(0.1e100 Hz), the tan d decreased from 0.39 to 0.27 for the three-day-old cheese to 0.24e0.20 for the 180-day-old cheese. The tand of all Siahmazgi cheese samples were between 0.20 and 0.40. This

1.0E+04

1.0E+05

1.0E+06

0.1 1 10 100

G' (

Pa)

Frequency (Hz)

Fig. 3. Storage modulus (G0) of cheese samples during ripening: (A) 3 days; (-) 30days; (:) 60 days; ( � ) 90 days; (6) 120 days; (C) 150 days; (þ) 180 days.


1.0E+04

1.0E+05

1.0E+06

0.10 1.00 10.00 100.00

G''(

Pa)

Frequency (Hz)

Fig. 4. Loss modulus (G00) of cheese samples during ripening:(A) 3 days; (-) 30 days;(:) 60 days; ( � ) 90 days; (6) 120 days; (C) 150 days; (þ) 180 days.

0.000

0.050

0.100

0.150

0.200

0.250

0.300

0.350

0.400

0.450

Los

s ta

ngen

t (-)

Frequency (Hz)

Fig. 5. Loss tangent (tan d) of cheese samples during ripening: (A) 3 days; (-) 30days; (:) 60 days; ( � ) 90 days; (6) 120 days; (C) 150 days; (þ) 180 days.


range was similar to the values for Gaziantep cheese (Kahyaoglu &Kaya, 2003), Mozzarella cheese (Yun, Hsieh, Barbano & Rohn,1994)and UF-Feta cheese (Karami et al.,2009).

Generally speaking, some factors including water content, pro-teolysis and pH can affect the viscoelastic behavior of cheese (Juanet al., 2007). For instance, a decrease in water content causes areduction in tan d while proteolysis can increase this parameter(Luyten,1988) onwhich the loss of tan dof Siahmazgi cheese samplesduring ripening can be described.Moreover, Vesser (1991) explainedthat any increase in pH of Gouda cheese resulted in a decrease intan d. Dimitreli & Thomareis (2008) also found that the moduli (G0

and G00) increased with decreasing moisture content whichwere similar to the present study. On the other hand, the fatcontent also can reduce storage and loss moduli and increases losstangent. Due to the role of fat as a lubricant and filler in the caseinmatrix, the cheese texture shows a more liquid-like behaviormore likely (Dimitreli & Thomareis, 2008; Kahyaoglu & Kaya, 2003;Madadlou, Khosrowshahi & Mousavi, 2005). Similar results havebeen explained by Subramanian,Muthukumarappan&Gunasekaran(2006) who concluded that fat reduction causes an increase inviscoelastic characteristics of processed cheese. The role of protein inviscoelastic behavior of samples is different. With higher proteincontent, all the viscoelastic properties (except loss tangent) areincreased which contrasts with moisture and fat roles in cheesetexture. Joshi, Muthukumarappan & Dave (2004) also found thesame results in processed cheese. This matter described by Fox,Guinee, Cogan & McSweeney (2000), as increasing concentrationof caseins in the cheese matrix puts up the intra- and inter-strandlinkages which provide the elastic character to cheese texture. Asmentioned earlier, during ripening, the fat, protein and salt contentsof Siahmazgi cheese samples were significantly increased (P < 0.05)while the water content was significantly decreased (P < 0.05).Therefore, during ripening, despite the increase of fat content, thestorage modulus was increased either. It can be described byDimitreli and Thomareis (2008) as the unfolded protein moleculesget closer to each other by attractive forces, thus the role of proteinsin the cheesematrix becomedominant over that ofwater and fat andultimately the viscoelastic properties of the sample increase and amore solid-like behavior is resulted. In other words, as Madadlouet al. (2007) reported, when the moisture content of the samplesdecreased and their protein content increased, fat did not replace themoisture on an equal basis, so the total filler volume decreased andthe firmness of texture increased. Moreover, based on Karami et al.(2009) justifications, the disruption of fat globules during theripening can lead to a decrease in the weak point and an increase inthe cross-links among the non-linear strands of caseinwhich resultsin the greater elasticity of cheese and consequently a decrease in the


tan d (Fig.5). Thismatterwas the case of some studies (Wium&Qvist,1998; Wium, Kristiansen & Qvist, 1998) and it was in agreement tothe results obtained at the present study.

Another factor which had a major role on viscoelastic propertiesof cheese was pH (Tunick, 2000). In a sample of soft cheese, regionswith the lower pH values had higher storage and loss moduli(Karoui & Dufour, 2003). On the basis of these studies, as much asthe pH of Siahmazgi cheese samples was reduced during six monthripening, the higher values of G0 and G00 were anticipated.

Gunasekaran and Ak (2002, p. 437) also reported that the valuesof two textural parameters, sf and G0 which correlate with firmnessof cheese in sensory evaluation, increased with increasing of brineconcentration and the values of salt in the cheese texture.

4. Conclusions

According to our findings, all the measured values containingpH, acidity, dry matter, fat, protein, ash, salt, water soluble nitrogenin total nitrogen, and non-protein-nitrogen in total nitrogen havebeen significantly increased during ripening (P < 0.05). In addition,storage modulus (G0), loss modulus (G00), fracture stress (sf) andfirmness of the cheese samples increased while the amount of losstangent and fracture strain reduced. Moreover, the elasticity naturewas greater than the viscous nature of samples in terms of thedomination of storage modulus over loss modulus during ripening.This kind of cheese is characterized by its respectively high valuesof dry matter (59.95 � 0.08 g/100 g), salt (5.65 � 0.05 g/100 g), andash (7.24 � 0.02 g/100 g) where on the basis of Codex categories,the traditional Siahmazgi cheese can be categorized as a kind offull-fat semi-hard cheese.

Acknowledgments

The authors would like to thank the residents of Siahmazgivillage for their patience, kindness and supporting this research.

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