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Effects of somatic cell counts on the physicochemical and rheological properties of yoghurt made from sheep’s milk: Physicochemical and rheological properties of yoghurt

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Effects of somatic cell counts on the physicochemical and rheological properties of yoghurt made from sheep’s milk: Physicochemical and rheological properties of yoghurt
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  Original article Effects of somatic cell counts on the physicochemical andrheological properties of yoghurt made from sheep’s milk Masoud Najaf Najafi, 1 * Arash Koocheki, 2 & Saeedeh Valibaigy 1 1 Institute of Scientific, Applied Higher Education Jihad-e- Agriculture, Tehran, Iran2 Department of Food Science and Technology, Ferdowsi University of Mashhad (FUM), Mashhad, Iran (Received 15 September 2009; Accepted in revised form 7 January 2010) Summary  In the present work, yoghurts were made from sheep’s milk with two different somatic cell count (SCC), atlow (200 000 cells mL ) 1 ) and high (750 000 cells mL ) 1 ) levels. The characteristics of the final product wereanalysed for pH, acidity, protein, total solids, fat, syneresis, water holding capacity (WHC) and apparentviscosity. Samples were analysed on days 1, 7 and 14 after production of yoghurts. The SCC had nosignificant effect either on the acidity or pH of the yoghurt at 24 h ( P  > 0.05) but a significant effect( P  < 0.05) was observed at 168 h. No effects of SCC were observed on total solids and fat content of theyoghurt after 24 and 168 h. High SCC (HSCC) yoghurt had higher protein content ( P  < 0.05). The yoghurtwith the highest SCC had the highest level of syneresis. Viscosity of HSCC yoghurt was higher than that of the low SCC yoghurt on days 1, 7 and 14 of storage. The flow properties also showed that the low SCCyoghurt was softer than that from milk with high content in somatic cells. Keywords  Apparent viscosity, flow properties, sheep’s milk, somatic cell count, yoghurt. Introduction The availability of sheep’s milk in Iran is highlyseasonable, since the lactation period of sheep lasts afew months. In addition, the majority of sheep’s milk isproduced during the spring months (April–June), so thepossibility of producing sheep’s milk products all yearround relies on the ability to change to other products,e.g. yoghurt, fermented milk and cheese while main-taining the quality of fresh milk (Rauschenberger  et al  .,2000). Sheep milk is especially suitable for yoghurtproduction because of its high content in proteins andsolids (Haenlein, 1998). In general, the overall propertiesof yoghurt such as its level of acidity, pH, nutritionalvalue and the production of aromatic compounds, aswell as its sensory profile are important characteristics of the product. These aspects are affected by the chemicalcomposition of the milk base, processing conditions andthe activity of the starter culture during the incubationperiod (Bonczar  et al  ., 2002). All milk from differentspecies contains some level of somatic cell counts (SCC).Neutrophils comprise the major cell type in milk fromuninfected sheep (Paape  et al  ., 2001). Bacterial infection,tissue damage and other inflammation processes affect-ing the mammary tissue increase the number of SCC inmilk dramatically (Jaeggi  et al.,  2003; Najaf Najafi &Nakhchian, 2003). This increase in SCC count resultsfrom a transfer of white blood cells from the blood intomilk (Pirisi  et al  ., 2000). In addition, the relativeproportions of different types of SCC present in milkchange significantly. Mastitis induces changes in milkthat influence dairy product quality (Barbano  et al  .,1987). Somatic cell count has some effects on yoghurtcompositions (Vivar-Quintana  et al  ., 2006). Fernandesa et al.  (2007) reported that SCC did not affect pH,acidity, fat content and proteolysis of the yoghurt. Theeffect of SCC in Baluchi sheep’s milk on the propertiesof yoghurt has not yet been studied. Thus the aim of thepresent work was to investigate the effect of SCC on thephysicochemical and rheological properties of yoghurtmade from sheeps’ milk. Materials and methods Raw material Milk (from Baluchi breed sheep) with two SCC wascollected: <200 000 and >750 000 cells mL ) 1 . In thisexperiment, ten to fifteen sheep were used for bulkingthe milk within each SCC category. Milk was fromherds with identical husbandry practices and feedingregimes. The SCC was measured according to ourprevious study (Najaf Najafi  et al. , 2009). In brief, milk *Correspondent: Fax: +98 511 6074147;e-mail: masoudnajafi@yahoo.comInternational Journal of Food Science and Technology 2010,  45 , 713–718  713 doi:10.1111/j.1365-2621.2010.02185.x   2010 The Authors. Journal compilation    2010 Institute of Food Science and Technology  samples were collected aseptically in sterile bottles of 100 mL and kept in ice before transportation to thelaboratory. During milk collection and preparation,efforts were made to avoid microbial contamination.The raw unpreserved samples were stored over night at+4   C until utilisation. Duplicate samples of bulkedraw milk of each SCC category were analysed for SCCby Cell Fossomatic 250 (Hillerød, Denmark). Chemical analyses of the milk Milk samples were analysed for fat (Gerber method,British Standards Institution (BSI) 1995, pH (pH-meter,Metrohm, AG, Switzerland), titratable acidity (Dornicmethod, Tamime & Robinson, 1999), lactose (IDF,1974), protein (IDF, 1986) and total solids (IDF, 1987).On the same day as they were collected, milk sampleswere submitted for Somatos SCC analyses at thecertified laboratory of the Jihade-Agriculture organiza-tion of Khorasan Razavi (Iran). Manufacture of yoghurts Yoghurts were prepared according to the methoddescribed by Vivar-Quintanaa  et al.  (2006). In brief,milks were standardised (20% total solids) by theaddition of skim milk powder. The standardised milkwas pasteurised at 65   C for 30 min and cooled to 37   C.The pasteurised milk was inoculated with a commercialyoghurt culture comprised of   Lactobacillus delbrueckii  subsp  bulgaricus  and  Streptococcus thermophilus  (Chr.Hansen_s Laboratory, Horsholm, Denmark). Inocu-lated milk (150 mL) was poured into plastic containers,which were covered with lids and incubated at 45   Cuntil the pH had decreased to about 4.5. The containerswere then transferred to refrigerator at 4   C to cool theproduct and to terminate acid development. Some of thesamples were analysed after 24 h, while the remainingsamples were stored cool (4   C) for 14 days. Chemical analyses of yoghurt Analyses were performed after mechanical stirring(magnetic stirrer, 10 min) of the yoghurts at 20   C.The yoghurts were analysed for pH (pH-meter, Metr-ohm, AG, Switzerland), titratable acidity using theDornic method (after mixing 10 g of yoghurt with anequal mass of distilled water (Katsiari  et al  ., 2002), fat(Gerber method; British Standards Institution, 1995),lactose IDF, 1974 and total solids (IDF, 1991). Syneresis of yoghurt Twenty-five grams of yogurt samples were weighed on afilter paper No. 615 (Macherey-Nagel, Du ¨ren, Ger-many) placed on top of a funnel. Syneresis of whey wascarried out by gravity and the quantity (grams) of wheycollected in a flask of known weight was used as asyneresis value. The drainage time and temperature were120 min and 4   C, respectively (Tamime  et al  ., 1996;Sahan  et al  ., 2008). Water-holding capacity of yoghurt For measurement of water-holding capacity (WHC) inthe experimental yogurt samples, 5 g of yogurt wascentrifuged at 1800  ·  g  for 30 min at 10   C. Aftercentrifugation, the supernatant was removed and thepellet was collected and weighed. The WHC wascalculated as follows:WHC ¼  1  w t w i    100where  w t  is weight (g) of the pellet and  w i  is initial weight(g) of the sample (Wu  et al  ., 2000). Rheological measurements Rheological measurements were carried out using arotational viscometer (Bohlin Model Visco 88; BohlinInstruments, Malvern, UK) equipped with C30 measur-ingspindlesandaheatingcirculator(Julabo,ModelF12-MC; Julabo Labortechnik, Seelbach, Germany). Foreach test, approximately 15–25 mL sample was trans-ferredtosamplecompartment(bobandcup)followingby3 min pre-shearing at 50 s ) 1 to obtain uniform solution.The instrument was programmed to set temperature of 25   Candequilibratefor10 min.Theshearrateincreasedlinearly from 0 to 300 s ) 1 in 3 min. Herschel–Bulkleyequation was found to be an adequate model to describetheflowbehaviourofthestirredyoghurt.Flowbehaviourwas described by the fitting of the Herschel–Bulkley)model to experimental data (shear stress–shear rate): s ¼ s 0 þ k c n where  s  is the shear stress (Pa); ( c ) is the shear rate (s ) 1 ); k  is the consistency coefficients (Pa s n );  n  is the flowbehaviour index (dimensionless); and  s 0  is the yieldpoint (Pa s). Statistical analysis Data on chemical composition and rheological proper-ties were analysed by one-way analysis of variance( anova ). For chemical analysis and determination of SCC in milk, two replications were used. Means werecompared by the Student’s  t -test at the significance levelof   a  = 0.05. However, for measuring the properties of yoghurt, three replications were used for each SCCcategory. Analyses were performed using Minitab soft-ware (Version 13.1) and Slide write (Version 2.0). Physicochemical and rheological properties of yoghurt  M. N. Najafi   et al. 714 International Journal of Food Science and Technology 2010    2010 The Authors. Journal compilation    2010 Institute of Food Science and Technology  Results and discussion Impact of SCC on milk composition The SCC in milk had a significant effect on acidity( P  < 0.05) of sheep milk (Table 1). Similar trend wasalso observed in our previous study on cow milk (Najaf Najafi  et al  ., 2009). Milk with high SCC (HSCC) hadlower acidity and higher pH. Similar to our results,several authors (Pirisi  et al  ., 1996, 2000; Pellegrini  et al  .,1997; Nudda  et al  ., 2001; Albenzio  et al  ., 2004, 2005;Bianchi  et al  ., 2004) reported the effect of SCC on thepH value of sheep milk. They also have reported thatpH increased with elevated SCC. The fat content of themilk decreased significantly ( P  < 0.05) with the increasein SCC (Table 1), which is in agreement with ourprevious data on fat content in cow’s milk (Najaf Najafi et al  ., 2009). On the contrary, several authors showedthat SCC did not affect the fat content of ewe (Diaz  etal. , 1996; Pirisi  et al  ., 1996) or goat milk (Pasquini  et al  .,1996; Ying  et al  ., 2002). Pisoni  et al  . (2004) found thatthe lower fat content in goat milk was due to theinfection of the mammary gland with  S. aureus  (meanSCC 4.65 million cells mL ) 1 ) compared to non-infectedmilk (mean SCC 1.03 million cells mL ) 1 ). Baudry  et al. (1997) reported a non-significant decrease in fat contentfor HSCC goat milk.The protein content of milk was slightly higher formilk with HSCC, although no significant differenceswere observed between the values for milk with differentSCC (Table 1). Effects of SCC on protein constituents insheep milk are numerous and sometimes conflicting.Diaz  et al.  (1996), El-Saied  et al.  (1999), Nudda  et al. (2003), Albenzio  et al.  (2004) and Bianchi  et al.  (2004)reported that sheep milk with a HSCC contains moretotal protein than milk with low SCC. On the contrary,Jaeggi  et al.  (2003) found that total protein content waslowest in milk with the highest SCC levels. Pirisi  et al. (1996, 2000), Pellegrini  et al.  (1997) and Albenzio  et al. (2005) reported no significant difference between proteincontents of milk with high or low SCC. Increase in theconcentration of proteins from blood during mastitisleads to an increase in the concentration of soluble wheyproteins (Pirisi  et al  ., 1996, 2000; Nudda  et al  ., 2003;Albenzio  et al  ., 2004). The greater whey protein contentin the milk with HSCC may also increase true proteincontent and lower casein number, expressed as apercentage of true protein. However, the casein content(g L ) 1 ) in HSCC milks is usually found to be the same.Contrary to the results with cow milk, for which adecrease in casein concentration during mastitis is wellaccepted, studies with sheep milk are contradictory.Several authors showed no significant decrease in caseinassociated with SCC (Pirisi  et al  ., 1996, 2000; Pellegrini et al  ., 1997; Nudda  et al  ., 2003; Albenzio  et al  ., 2004,2005). HSCC in goat milk was also associated withhigher soluble protein contents (Pasquini  et al  ., 1996),which results in lower casein percentage. Ying  et al. (2002) found higher protein contents for early and latelactation HSCC goat milks.The lactose content of milk decreased significantlywith increased SCC ( P  < 0.05) (Table 1). It is wellaccepted that an increase of SCC causes a decrease inthe concentration of lactose in sheep (Diaz  et al  ., 1996;Pirisi  et al  ., 1996, 2000; Nudda  et al  ., 2003) and goatmilk (Jaubert  et al  ., 1996), while no effect was observedby Pasquini  et al  . (1996) on individual goat milks. Thedecrease in synthesis function of the mammary gland incase of mastitis results in lower lactose concentrations.The SCC also had no significant effect on total solidsin milk (Table 1). The total solids of milk decreased withthe increase in SCC. Jaeggi  et al.  (2003) found that totalsolids in milk was lower in sheep milk with HSCC, whilePirisi  et al  . (1996, 2000) reported no influence of SCC. Impact of SCC on yoghurt composition The properties of yoghurts produced from milk of eachSCC category are shown in Table 2. The SCC did nothave a significant effect on the acidity or pH of theyoghurt after 24 h ( P  < 0.05) but a significant effectwas observed after 168 h of storage ( P  < 0.05). Inyoghurts, the acidification process seems to be relatedmostly to the starter culture activity and to the totalsolids content of the srcinal milk (Spreer, 1991), whichwere standardised in all treatments to 20% (w   ⁄   v) priorto yoghurt production. The yoghurt made from milkwith the highest SCC had the highest content of proteinafter 24 and 168 h (Table 2). No effect of SCC wasobserved on total solids and fat content of the yoghurtafter 24 and 168 h ( P  > 0.05). According to Tamime &Robinson (1999), low lipolysis activity occurs in yoghurtdue to lipolytic enzymes from starter bacteria, as theoriginal lipases in milk are completely inactivated bypasteurisation. In this trial, the same starter culture was Table 1  Effect of somatic cell count on the composition of sheep’s milkused in the manufacture of yoghurt Yoghurt propertiesSomatic cell of milk ( · 1000 mL ) 1 )<200 >750 Acidity 16.2 ± 1.12 a 15.1 ± 1.23 b pH 6.5 ± 0.06 b 6.7 ± 0.02 a Fat (%, w   ⁄   w) 5.28 ± 1.28 a 4.76 ± 1.14 b Protein (%, w   ⁄   w) 5.21 ± 0.34 a 5.73 ± 0.47 a Lactose (%, w   ⁄   w) 5.13 ± 0.18 a 4.65 ± 0.22 b Total solids (%, w   ⁄   w) 16.79 ± 0.93 a 16.29 ± 1.03 a Results are reported as means ± SE, for two replicates of each SCCcategory. Means within a row with different letters differ statistically( P   < 0.05). Physicochemical and rheological properties of yoghurt  M. N. Najafi   et al.  715   2010 The Authors. Journal compilation    2010 Institute of Food Science and Technology  International Journal of Food Science and Technology 2010  used in equal proportions for all treatments, the higherfat observed in yoghurts produced with HSCC milk maybe a consequence of the SCC in the srcinal milk. Theyoghurt with the highest SCC had the highest level of syneresis, pointing to the poor consistency of thecoagulum of this milk and its inability to retain serum(Table 2). The milk from animals with mastitis had ahigh level of serum proteins, and low level of casein(Pirisi  et al  ., 1996). For this reason, milk with HSCCwould give rise to soft coagula with a reduced ability toretain serum (Tamime & Robinson 1999). The amountof whey separated was significantly higher after 24 h of storage compared to that after 168 h (Table 2). Theseparation decreased significantly in all samples duringstorage ( P  < 0.05), agreeing with the observations byTamime  et al.  (1996), Guzel-Seydim  et al  . (2005), Guven et al  . (2005) and Isleten & Karagul-Yuceer (2006). TheWHC values in the samples were not significantlydifferent ( P  < 0.05) (Table 2). A slight decrease wasobserved in WHC values during storage, but thisdecrease was not significant. The milk with HSCC didnot change the WHC of yoghurts. Flow behaviour Rheological parameters of the yoghurt from sheep‘smilk containing different SCC are given in Table 3.From the industrial point of view, all of the rheologicalmodels were considered suitable to represent the rheo-logical data on yoghurts from sheep milk due to the highvalues of the determination coefficient. However theHerschel–Bulkley model was chosen to fit the experi-mental data in this work due to its characteristics of being a full model that could describe all the rheologicalparameters (yield stress, consistency coefficient and flowbehaviour index) compared to other models. For theHerschel–Bulkley model, the determination coefficient( R 2 ) values were 0.99 thus these results showed a good fitfor the Herschel–Bulkley model.Yield stress is an important quality control parameterin industrial processes, particularly for comparing theoverall characteristics of products made on differentproduction lines (Haminiuk  et al  ., 2006). Stirred yoghurtcontaining SCC behaved as pseudoplastic fluids exhib-iting yield stress. For HSCC yoghurt, the yield stressvaried between 50.34 and 52.23 Pa while the magnitudewas much higher for low SCC yoghurt (51.73–54.50 Pa).The yield point ( s 0 ) was also positively related to thestorage day; however, this trend was not apparent foryoghurt with low SCC (Table 3).The consistency coefficient ( k ) of the manufacturedyogurts ranged from 11.90 to 14.10 Pa s n for HSCC andfrom 11.50 to 13.52 for low SCC. Yogurts made withHSCC had the highest shear consistency. The consis-tency coefficient increased during storage of yoghurt.This increase was more pronounced for yoghurt con-taining HSCC, however for the fresh yoghurt andyoghurt stored for 7 days there were no significantdifferences between yoghurts with high and low SCC.Similar results were reported by Fernandesa  et al.  (2007)for yoghurt from cow’s milk. These results are differentfrom those reported by Rogers & Mitchell (1994), whoobtained a negative correlation between yoghurt viscos-ity and SCC in milk, and by Oliveira  et al  . (2002), whoobserved lower grades attributed to loss of consistencyin a sensory evaluation of HSCC yoghurt after10–30 days storage.Since somatic cells are related to conversion of plasminogen to plasmin in milk (Verdi & Barbano,1991), the occurrence of age-thickening gelation pro-cesses associated with the plasmin content in milk couldalso be a possible explanation for the higher viscosityobserved in yoghurt produced from milk with HSCC.The flow behavior index ( n ) of yogurts ranged from0.14 to 0.23 for HSCC and 0.17 to 0.27 for low SCC.These indices increased during storage for both low andHSCC yoghurt meaning that the pseudoplastisitydecreased during storage.The apparent viscosity of yoghurts decreased with theincrease in shear rate until the Newtonian platform was Table 2  Effect of somatic cell counts on yoghurt after 24 and 168 h of storage Yoghurt propertiesSomatic cell of milk ( · 1000 mL   1 )<200 >75024 h 168 h 24 h 168 h pH 4.3 ± 0.02 3.8 ± 0.08 4.45 ± 0.04 4.1 ± 0.05Acidity 150 ± 1.15 173 ± 2.15 147 ± 1.50 178 ± 2.56Protein (%, w   ⁄   w) 4.9 ± 0.15 3.3 ± 0.22 5.3 ± 0.27 4.1 ± 0.21Fat (%, w   ⁄   w) 5.1 ± 0.12 4.2 ± 1.8 5.3 ± 0.10 4.6 ± 1.9Synersis (mL) 4.62 ± 0.03 1.08 ± 0.16 6.4 ± 0.12 2.7 ± 0.08WHC 40.2 ± 0.21 38.7 ± 0.09 40.7 ± 0.76 39.1 ± 0.05Total solids (%, w   ⁄   w) 21.4 ± 0.40 21.1 ± 0.05Results are reported as means ± SE, for three replicates of each SCCcategory. Table 3  Effect of somatic cell counts on yield stress ( s 0 ), consistencycoefficient ( k ) and flow behavior index ( n ) of yoghurt made fromsheep‘s milk Somatic cell Time  s 0  k n R  2 High 1 50.34 ± 1.5 11.90 ± 0.52 0.14 ± 0.03 0.997 52.00 ± 1.1 12.47 ± 0.75 0.18 ± 0.01 0.9914 52.23 ± 1.2 14.10 ± 0.48 0.23 ± 0.04 0.99Low 1 51.73 ± 0.9 11.50 ± 0.72 0.17 ± 0.03 0.997 52.77 ± 0.7 12.10 ± 0.42 0.20 ± 0.02 0.9914 54.50 ± 0.6 13.52 ± 0.21 0.27 ± 0.01 0.99 Physicochemical and rheological properties of yoghurt  M. N. Najafi   et al. 716 International Journal of Food Science and Technology 2010    2010 The Authors. Journal compilation    2010 Institute of Food Science and Technology  reached (Fig. 1). After a sharp reduction, the apparentviscosity changed slightly and became steady at highershear rates. This could be related to the reduction in sizeof the colloidal aggregates as the shear rate increased(Ibanoglu, 2002).From an industrial point of view, the decrease inviscosity facilitates the flow and heat exchange duringprocessing. It is known that fluids with lower viscosityhave lower head loss during flow, resulting in adecreased energy demand for the process. Yoghurt fromlow milk SCC was softer than yoghurt from milk withhigher SCC. Conclusions This study confirms that SCC in sheep milk is associatedwith changes in milk composition and effects onproperties of yoghurt. The SCC had no significant effecton acidity and pH of the yoghurt after 24 h. However,this effect was significant after 168 h of storage. SCChad no significant effect on total solids and fat contentof the yoghurt after 24 and 168 h. High SCC yoghurthad higher protein content. The yoghurt with thehighest SCC had the highest level of syneresis. Theresults showed that the low SCC yoghurt was softerthan yoghurt from milk with higher SCC. There is agreat need for further research to determine carefully thethreshold at which SCC affects sheep milk characteris-tics, and the quality of related dairy products. References Albenzio, M., Caroprese, M., Santillo, A., Marino, R., Muscio, A. &Sevi, A. (2005). Proteolytic patterns and plasmin activity in ewe’smilk as affected by somatic cell count and stage of lactation.  Journal of Dairy Research ,  72 , 86–92.Albenzio, M., Caroprese, M., Santillo, A., Marino, R., Taili, L. & Sevi,A. (2004). Effects of somatic cell count and stage of lactation on theplasmin activity and cheese making properties of ewe milk.  Journal of Dairy Science ,  87 , 533–542.Barbano, D.M., Verdi, R.J. & Rasmussen, R. (1987). Influence of milksomatic cell count on cheese manufacturing and cheese yield.  24thAnnual Marschall Invitational Italian Cheese Seminar, Wisconsin,USA . Pp. 12–16.Baudry, C., De Cremoux, R., Chartier, C. & Perrin, G. (1997). Impactof mammary gland inflammation on milk yield and composition ingoats.  Veterinary Research ,  28 , 277–286.Bianchi, L., Bolla, A., Budelli, E., et al. (2004). Effect of udder healthstatus and lactation phase on the characteristics of Sardinian ewemilk.  Journal of Dairy Science ,  87 , 2401–2408.Bonczar, G., Wszolek, M. & Siuta, A. (2002). The effects of certainfactors on the properties of yoghurt made from ewe’s milk.  Food Chemistry ,  79 , 85–91.British Standards Institution (BSI) (1995).  Gerber Method for theDetermination of Fat in Milk and Milk Products . British Standard696. London: British Standards Institution.Diaz, J.R., Muelas, R., Segura, C., Peris, C. & Molina, P. (1996).Effect of mastitis on milk composition in Manchega ewes:preliminary results.  Somatic Cells and Milk of Small Ruminants .Pp. 305–309. EAAP Publication No 77. Wageningen, The Nether-lands: Wageningen Pers.El-Saied, U.M., Carriedo, J.A., De la Fuente, L.F. & San Primitivo, F.(1999). Genetic parameters of lactation cell counts and milk andprotein yield in dairy ewes.  Journal of Dairy Science ,  82 , 639–644.Fernandesa, A.M., Oliveiraa, C.A.F. & Lima, C.G. (2007). Effects of somatic cell counts in milk on physical and chemical characteristicsof yoghurt.  International Dairy Journal  ,  17 , 111–115.Guven, M., Yasar, K., Karaca, O.B. & Hayaloglu, A.A. (2005). Theeffect of inulin as a fat replacer on the quality of set-type low-fatyogurt manufacture.  International Journal of Dairy Technology ,  58 ,180–184.Guzel-Seydim, Z.B., Sezgin, E. & Seydim, A.C. (2005). Influences of exopolysaccharide producing cultures on the quality of plain set typeyogurt.  Food Control  ,  16 , 205–209.Haenlein, G.F.W. (1998). The value of goats and sheep to sustainmountain farmers.  International Journal of Animal Science ,  13 , 187– 194.Haminiuk, C.W.I., Sierakowski, M.R., Vidal, J.R.M.B. & Masson,M.L. (2006). Influence of temperature on the rheological behavior of whole araca pulp ( Psidium cattleianum sabine ).  LWT  ,  39 , 426–430.Ibanoglu, E. (2002). Rheological behavior of whey protein stabilizedemulsions in the presence of gum Arabic.  Journal of Food Engineering ,  52 , 273–277.International Dairy Federation (IDF). (1974).  Determination of theLactose Content of Milk . IDF Standard 28 A. Brussels, Belgium:IDF.International Dairy Federation (IDF). (1986).  Milk. Determination of Nitrogen Content (Kjeldahl method) and Calculation of CrudeProtein Content . IDF Standard 20 A. Brussels, Belgium: IDF. Low somatic cell High somatic cell 00.511.522.533.544.55050100150200250300 Shear rate (1/s)    A  p  p  a  r  e  n   t  v   i  s  c  o  s   i   t  y   (   P  a .  s   ) Day 1Day 7Day 14 0123456050100150200250300 Shear rate (1/s)    A  p  p  a  r  e  n   t  v   i  s  c  o  s   i   t  y   (   P  a .  s   ) Day 1Day 7Day 14 Figure 1  The apparent viscosity of the yoghurts containing differentSCC during storage. Physicochemical and rheological properties of yoghurt  M. N. Najafi   et al.  717   2010 The Authors. Journal compilation    2010 Institute of Food Science and Technology  International Journal of Food Science and Technology 2010
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