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Effects of αs1­casein (CSN1S1) and κ­casein (CSN3) genotypes on milk coagulation properties in Murciano­Granadina goats

Francisco Caravaca, José Luis Ares, Juan Carrizosa, Baltasar Urrutia, Francisca Baena, Jordi Jordana, Bouabid Badaoui, Armand Sànchez, Antonella Angiolillo, Marcel Amills and Juan Manuel Serradilla

Journal of Dairy Research / Volume 78 / Issue 01 / February 2011, pp 32 ­ 37DOI: 10.1017/S002202991000083X, Published online: 10 January 2011

Link to this article: http://journals.cambridge.org/abstract_S002202991000083X

How to cite this article:Francisco Caravaca, José Luis Ares, Juan Carrizosa, Baltasar Urrutia, Francisca Baena, Jordi Jordana, Bouabid Badaoui, Armand Sànchez, Antonella Angiolillo, Marcel Amills and Juan Manuel Serradilla (2011). Effects of αs1­casein (CSN1S1) and κ­casein (CSN3) genotypes on milk coagulation properties in Murciano­Granadina goats. Journal of Dairy Research, 78, pp 32­37 doi:10.1017/S002202991000083X

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Effects of αs1-casein (CSN1S1) and κ-casein (CSN3) genotypes onmilk coagulation properties in Murciano-Granadina goats

Francisco Caravaca1, José Luis Ares2, Juan Carrizosa3, Baltasar Urrutia3, Francisca Baena6,Jordi Jordana4, Bouabid Badaoui4, Armand Sànchez4, Antonella Angiolillo5, Marcel Amills4

and Juan Manuel Serradilla6*1Departamento de Ciencias Agroforestales, E.U.I.T.A., Universidad de Sevilla, 41013 Sevilla, Spain2 Instituto Andaluz de Investigación y Formación Agraria y Pesquera, Alameda del Obispo s/n, 14004 Córdoba, Spain3 Instituto Murciano de Investigación y Desarrollo Agrario y Alimentario (IMIDA). Estación Sericícola. La Alberca, Murcia, Spain4Departament de Ciència Animal i dels Aliments, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain5Dip. Scienze per la Salute, via de Sanctis snc, Università del Molise, Campobasso, Italy6Departamento de Producción Animal, Campus de Rabanales, Universidad de Córdoba, 14071 Córdoba, Spain

Received 15 December 2009; accepted for publication 1 August 2010

The effects of the caprine αs1-casein (CSN1S1) polymorphisms on milk quality and cheese yield havebeenwidely studied in French and Italian goat breeds.Much less is known about the consequences ofκ-casein (CSN3) genotype on the technological and coagulation properties of goat milk. In the currentstudy, we have performed an association analysis between polymorphisms at the goat CSN1S1 andCSN3 genes and milk coagulation (rennet coagulation time, curdling rate and curd firmness) andtechnological (time to cutting of curd and cheese yield) properties. In this analysis, we have included193 records from 74 Murciano-Granadina goats (with genotypes constituted by differentcombinations of alleles B, E and F of the gene CSN1S1 and alleles A and B of the gene CSN3)distributed in three herds, which were collected bimonthly during a whole lactation. Data analysis,using a linear mixed model for repeated observations, revealed significant associations betweenCSN1S1 genotypes and the rate of the curdling process. In this way, milk from EE goats had asignificantly higher curdling rate than milk from BB individuals (P<0·05). Contrary to previousexperiments performed in French breeds, cheese yield was not significantly different in BB, EE and EFgoats. Moreover, we have shown that CSN3 genotype has a significant effect on the rennetcoagulation time (BB>AB, P<0·05) but not on cheese yield. No interaction between theCSN1S1 andCSN3 genotypes was observed.

Keywords: Goat, αs1-casein, κ-casein, milk coagulation parameters.

In goats, the polymorphism of the αS1-casein (CSN1S1) locushas been associated with phenotypic variation of milkcoagulation and cheese-making properties (Remeuf 1993;Vassal et al. 1994). The caprine CSN1S1 gene has 18 allelicvariants associated with high (A, B1, B2, B3, B4, B’, C, H, L,and M ), medium (E and I alleles), low (D, F and G alleles)and null (01, 02 andN alleles) milk CSN1S1 content (Martinet al. 2002; Moioli et al. 2007; Caroli et al. 2007). Remeuf(1993) observed a significant influence of CSN1S1 genotypeon milk curdling rate, curd firmness and cheese yield.Similarly, Vassal et al. (1994) detected differences in freshcheese yields amongst AA and EE and AA and FF CSN1S1

genotypes (AA>EE; AA>FF). Moreover, milk containing ahigh level of CSN1S1 has been found to have a greatercurdling rate and firmer curd than milk with a low content ofCSN1S1 (Ambrosoli et al. 1988; Clark & Sherbon 2000),although rennet coagulation time was longer. Another locusthat appears to be very polymorphic in goats is the κ-casein(CSN3) gene, with 16 alleles (A, B, B′, B″, C, C′,D, E, F, G, H,I, J, K, L, and M ) identified to date (Yahyaoui et al. 2003;Jann et al. 2004; Prinzenberg et al. 2005). Recent studieshave shown evidence of an effect of the CSN3 genotype ongoat milk composition (Chiatti et al. 2007, Caravaca et al.2009), but associations with milk coagulation propertieshave not been explored so far.The current work had two different goals. First, wewanted

to assess the effects of goat CSN1S1 genotype on milkcoagulation properties in Spanish goats. This investigation is*For correspondence; e-mail: pa1semaj@uco.es

Journal of Dairy Research (2011) 78 32–37. © Proprietors of Journal of Dairy Research 2010doi:10.1017/S002202991000083X

32

very relevant because in a previous study we found that, instrong contrast with French goat breeds, CSN1S1 genotypewas not associated with protein or total caseins contents inMurciano-Granadina goats. This latter result allows us toanticipate that the effect of the CSN1S1 locus on milkrenneting properties of Murciano-Granadina goats can bequite different from that observed in Alpine or Saanenbreeds. Moreover, we also reported that CSN3 genotype isassociated with milk protein and casein contents, with goatscarrying the B-allele showing higher values than thosecarrying the A-allele (Caravaca et al. 2009). Interestingly, theB variant of the bovine CSN3 gene, which differs from theA-allele at 2 positions (A: Thr136 and Asn148, B: Ile136 andAla148), has been associated with an increased proteincontent and a shorter renneting time (reviewed by Martinet al. 2002). These findings brought us to the second goal:to study the effect of the goat CSN3 genotype on milkcoagulation properties as well as to find out if there is anytype of interaction between CSN1S1 and CSN3 genotypes.

Materials and Methods

Experimental design

Initially 509 goats, distributed in three herds that werereproductively unconnected, were genotyped for theCSN1S1 gene following the protocols reported byCaravaca et al. (2008). Three groups, representing threedifferent levels of CSN1S1 synthesis, high (BB), medium (EE)and medium-low (EF), were chosen. These genotypes can beascertained unambiguously with the genotyping methodsreported above and they were well represented in theMurciano-Granadina population under analysis. Not en-ough FF goats were found to be able to include a “low group”in our study. Other heterozygous genotypes were notincluded in the experiment in order to optimize the use ofexperimental resources (CSN1S1 homozygous genotypesare expected to display more significant differences thatheterozygous ones and their effects have been widelyreported in the scientific literature). Subsequently, thesegoats were typed for the CSN3 gene by using a primerextension analysis protocol (Yahyaoui et al. 2003). Withregard to CSN3, only AA, AB and BB goats were selected

because these three genotypes were the most abundant onesin the Murciano-Granadina breed, while the remainingalleles (G and F ) where found at very low frequencies(Caravaca et al. 2009). The CSN1S2 and CSN2 genes werenot analysed in the current study because previous resultsindicated that alleles associated with a reduced or nullamount of either of these two proteins were not segregatingin the Murciano-Granadina breed (Caravaca et al. 2009).The total volume of milk at one milking was collected

every other month from each of the 74 goats throughout anentire lactation period. Total protein, fat, SNF and lactosecontents were determined for each individual milk sample ata professional laboratory (Milk Interprofessional Laboratory,Cantabria, Spain) using a spectrophotometer (C9 CombiFossFT 6000, Foss Electric, Hillerød, Denmark) for routineanalyses. In addition, a near infrared spectrophotometer(Foss-NIRSystems 6500 SY-II, Foss NIRSystems, SilverSpring, MD), previously calibrated (Agüera et al. 2004),was used to measure total casein, CSN1S1, and CSN1S2contents using the method described by Caravaca et al.(2008).

Measurement of milk coagulation properties andcheese manufacture

Milk coagulation properties were measured with anOptigraph® coagulometer (Ysebaert, Frepillon, France).This equipment calculates (i) Rennet coagulation time (R)in mins (time elapsed from rennet addition to milk tocurdling starting); (ii) Curdling rate (S2, S4) in mins (time toachieve a level of curd firmness causing an attenuation of thesignal, measured through the voltage variation of 1000 and2000 V of the electric energy generated in the receptors ofthe NIR bean transmitted through the sample); and (iii) Curdfirmness (AR, A2R, A20 and A30), by measuring in real timethe voltage of the electric energy at specific time points of thecoagulation process. Equivalences between these param-eters and those measured with the Formagraph device(Guyonnet 1999; Panari et al. 2002; Kübarsepp et al. 2005)are shown in Table 1. Two replicates of each individualmilk sample were measured and the corresponding meanvalue was used for statistical analyses. The rennet added(3 μl/sample) was powder rennet CHR-Hansen, strength

Table 1. Equivalences among coagulation variables measured with Formagraph and Optigraph equipments (elaborated with informationfrom Guyonnet 1999; Panari et al. 2002; Kübarsepp et al. 2005)

Coagulation Variable DescriptionFormagraphmeasurement

Optigraphmeasurement

Rennet coagulation time Time (in min) elapsed from rennet addition tocoagulation onset

r (min) R (min)

Curdling rate (rate of curd formation) Time elapsed from coagulation onset until a width of 20mmis reached on the diagram (fork) of coagulation

k20 (min) S2 and S4 (min)

Curd firmness Span on the diagram (fork) of coagulation at R min,twice R and 30 minutes after rennet addition

ar ARa2r A2Ra30 (millimetres) A30 (Volts)

Goat CSN1S1 and CSN3 genotypes and milk coagulation properties 33

1300 IMCU/g, IDF standard 157, diluted 1:100 weight/volume.

The whole volume of milk collected from each goat at onemilking was used to elaborate a single cheese at anexperimental cheese manufacture laboratory (Centro deInvestigación y Formación Agraria de Hinojosa del Duque,Cordoba, Spain). A total of 193 cheeses were elaboratedfollowing a traditional recipe adapted by Ares (1995).Dornic acidity and pH of milk, cutting time (in mins) sincerennet is added to cutting of curd and cheese yield (in kgmilk/kg cheese) were recorded during each individualelaboration.

Statistical analysis

Only records having complete information for genotype,milk composition analysis, coagulation parameters andcheese manufacture data were used for the statisticalanalyses (193 milk samples collected from 74 goats).Numbers of goats and observations for each CSN1S1 andCSN3 genotypes are shown in Table 2. The MIXEDprocedure from SAS (SAS V8e 2007) was employed toestimate differences between genotypes for repeated obser-vations analysis, following Littell et al. (1998). The mixedmodel used was:

Y ¼ Xbþ Zuþ e

where βwas the vector of fixed parameters or values of levelsof fixed factors:CSN1S1 andCSN3 genotypes (3 levels each)and their interaction (9 levels); herd-year-season (5 levels);parity number (5 levels); number of kids born (3 levels), andnumber of months elapsed from kidding to sampling day(10 levels) and covariates (milk pH and Dornic acidity); Xwas the incidencematrix for these effects; uwas the vector ofrandom animal effects; Z was the incidence matrix forrandom effects, and e was a vector of the residual randomerrors, assumed to be normally distributed with meanE (e)=0 and variance V (e)=R. Linear combinations ofparameters values L′β (L being a vector of coefficients) andtheir corresponding variances V (L′β), estimated with thismodel, allowed for testing differences between genotypemeans using a t distribution. The Bonferroni correction formultiple comparisons was applied.

Results and Discussion

The statistical analysis revealed that there was no interactionbetween CSN1S1 and CSN3 genotypes for any of thevariables. Results will therefore be presented separately foreach of them.Analysis of the effects of casein loci on goat milk

composition and coagulation properties is a critical step

Table 2. Least squares means and standard errors of milk composition traits and coagulation and cheese elaboration variables (measured withan Optigraph device) in Murciano-Granadina goats with different αs1-casein (CSN1S1) and κ-casein (CSN3) genotypes

Genotype (N;n) 1,2

CSN1S1 CSN3

BB(32;80) EE(35;96) EF(7;17) AA(15;36) AB(30;81) BB(29;76)

Milk compositiontraits

Fat,% 4·93±0·28 4·87±0·30 4·92±0·43 4·62±0·35 4·86±0·31 5·23±0·35Protein,% 3·46±0·16 3·57±0·17 3·45±0·23 3·43±0·17 3·57±0·14 3·61±0·16Casein,% 2·77±0·12 2·87±0·13 2·67±0·18 2·71±0·14 2·88±0·11 2·91±0·12CSN1S1, g/l 8·18±0·56a 6·48±0·60b 6·39±0·84 b 7·25±0·69 6·96±0·62 6·84±0·67CSN1S2, g/l 3·23±0·15 3·22±0·17 3·16±0·25 3·11±0·19 3·24±0·17 3·27±0·21Lactose,% 4·50±0·06 4·41±0·07 4·25±0·09 4·45±0·08 4·40±0·07 4·30±0·08Solid-not-fat,% 8·79±0·17 8·73±0·18 8·42± 0·25 8·62±0·21 8·70±0·19 8·63±0·20

Coagulometervariables3

R(minutes) 12·39±1·36 11·61±1·47 12·06±2·12 12·09±1·48ab 11·22±1·19b 13·43±1·35a

S2(minutes) 6·40±2·10a 3·18±2·11b 4·66±3·23ab 6·35±2·69 4·88±2·45 4·42±2·90S4(minutes) 15·37±5·50a 7·76±5·53 b 11·23±8·38ab 15·60±7·42 12·00±6·54 11·09±7·54AR(volts) 4·29±1·08 4·22±1·15 3·38±1·61 2·94±1·33 4·40±1·18 4·55±1·32A2R(volts) 6·81±1·54 5·35±1·63 3·08±2·28 4·02±1·88 5·59±1·71 5·64±1·83A20(volts) 2·71±1·01 2·51±1·08 1·67±1·48 1·69±1·23 2·59±1·10 1·61±1·21A30(volts) 5·02±1·44 4·36±1·53 2·46±2·13 3·23±1·76 4·29±1·60 4·33±1·71

Cheese elaborationvariables4

Tcut (minutes) 48·56±3·63 45·34±3·86 45·83±5·40 47·85±4·43 46·00±3·96 45·88±4·42Cheese yield (Kgmilk/kg cheese)

6·03±0·42 6·14±0·44 7·14±0·63 6·66±0·51 6·34±0·45 6·3±0·52

1N: Number of goats; n: number of complete records (for milk chemical analysis, coagulation properties and cheese making evaluation) for each CSN1S1 andCSN3 genotype2Means significantly different at P40·05, with Bonferroni correction are shown with different superscript letters within the same row for each locus3R: rennet coagulation time; S2: coagulation rate at S=1000 volt; S4: coagulation rate at S=2000 volts (less time means grater coagulation rate); AR: curdfirmness obtained at R minutes after curdling started; A2R: curd firmness obtained at 2R minutes after curdling started; A20: curd firmness at 20 minutes afteradding rennet; A30: curd firmness at 30 minutes after adding rennet4Tcut: total coagulation timemeasured during cheese elaboration since rennet is added to cutting of curd. Cheese yield in litres of milk per kg of cheese obtained

34 F Caravaca and others

before using this information in selection schemes devotedto improve these traits. Moreover, the existence of breed-specific allelic effects of the casein loci reinforces the need toevaluate their impact on a population basis. Our data(Table 2) showed that, as demonstrated in previous studiesperformed in the same breed (Caravaca et al. 2008, 2009),CSN1S1 genotype affects the average milk CSN1S1 con-centration, with BB goats (8·18±0·56 g/l) displaying higherlevels than their EE (6·48±0·60 g/l) and EF counterparts(6·39±0·84 g/l). In close agreement with Caravaca et al.(2009), CSN1S1 genotype did not significantly affect proteinor casein concentrations. However, and contrary to resultspublished for French breeds (Martin et al. 2002), EE goatshad the highest levels of caseins (although these differenceswere not significant). This is an interesting point becausecasein concentration is the main determinant of milkrenneting properties and cheese yield. Consistent with this,we found that EE goats display a greater curdling rate(lesser time to get different degrees of curd firmness) thantheir BB counterparts (S2: EE<BB, P<0·05; S4: EE<BB,P<0·05). Similarly, studies performed in cows (Marziali &Ng-Kwai-Hang 1986; Pagnacco & Caroli 1987; Politis & Ng-Kwai-Hang 1988) and to a lesser extent in goats (Storry et al.1983; Remeuf & Lenoir 1986; Ambrosoli et al. 1988) havegenerally shown that the higher the protein and caseinscontents, the greater the rate of curdling and the firmer thecurd. Furthermore, Colin et al. (1992) found that the curdlingrate explains 74% of the variation of the fresh cheeseyield. In our study, however, we did not detect significantdifferences in curd firmness or cheese yield amongstCSN1S1 genotypes.

It should be mentioned that our results do not matchresults provided by Remeuf (1993) for French breeds,showing that milk from AA goats (genotype associatedwith “high” CSN1S1 content in the same way as BB) displaya significantly higher curdling rate than milk from EE and FFgoats. Moreover, Remeuf (1993) and Pirisi et al. (1994) founda significant effect of CSN1S1 genotype on rennet coagu-lation time, curd firmness and cheese yield. However, it isdifficult to get a clear picture of the effects of CSN1S1genotype on rheological parameters in goats because studiesperformed so far suffer from a lack of consistency. Just to givean example, Ambrosoli et al. (1988) did not find a significantrelationship between milk CSN1S1 content and curdlingrate. In contrast, Zullo et al. (2005), using a Formagraph,reported significant associations in Cilentana goats betweenCSN1S1 genotype and curdling rate, with milk from BB goatsshowing a lower curdling rate than that of EE, AA and ABgoats, in agreement with our results. Discrepancies amongststudies might be the consequence of technical andbiological factors. Amongst the technical factors, cheese-making conditions, such as culture and type and concen-tration of curdling enzyme and incubation temperature, arewell known to strongly influence the coagulation processand cheese yield (Clark & Sherbon 2000). Sample size andmethods of measurement might be also important factorsinfluencing the nature and significance of the associations

found. The stringency of the statistical analysis (with orwithout correcting for multiple testing) might also influencethe significance of the data. Differences in the geneticbackground and the management of the analysed breedsmight also explain the existence of contradictory resultsamongst studies. At a biological level, the proportion of totalcaseins, the main parameter determining the rheologicalproperties of milk, seems to be associated with CSN1S1genotypes in French (Martin et al. 2002) but not in Spanishgoat breeds (Caravaca et al. 2009). This lack of association isquite intriguing because milk CSN1S1 levels are influencedby CSN1S1 genotype in the Murciano-Granadina andMalagueña breeds (Caravaca et al. 2008). Paradoxically, inour study BB goats have more CSN1S1 than their EEcounterparts (as expected from previous studies), but lesstotal casein. This findingmight be explained by the existenceof a compensatory mechanism that regulates the imbalanceproduced by a decreased rate of CSN1S1 synthesis. Theexistence of such effect has been demonstrated in β-caseindeficient mice that display an increased secretion rate ofother milk proteins (Kumar et al. 1994). Moreover, measure-ment of genetic correlations between casein levels in cattlehas shown that CSN1S1 content is negatively correlated withCSN1S2 (rg=�0·49) and CSN3 (rg=�0·56) contents(Schopen et al. 2009), showing that increasing CSN1S1content in milk does not necessarily imply that total caseinconcentrations will augment concomitantly. In summary,while the CSN1S1 genotype has a clear effect on thesynthesis rate of this protein in all caprine populationsanalysed so far, we hypothesize that the magnitude of theconsequent compensatory effect on total casein levels mightvary from breed to breed due to genetic and environmentalfactors. This would translate into differences between breedswith regard to the effect of the CSN1S1 genotype on milkcomposition as well as on its rheological properties.With regard to the effects of CSN3 genotype on milk

composition, we found higher protein and casein concen-trations in BB than in AA goats, although differences werenot significant (Table 2). With regard to milk coagulationproperties and cheese yield,CSN3 genotypewas exclusivelyassociated with rennet coagulation time (Table 2). In thisway, milk from BB goats had a greater R value(13·43±1·35mins) than milk from AB goats (11·22±1·19min) (P<0·05). The lack of a significant difference betweenthe two homozygous genotypes makes difficult the interpret-ation of these findings. In general, minimizing rennetcoagulation time is desirable because it reduces theprocessing time required for cheese production. In cowmilks with high levels of proteins or caseins, rennetcoagulation time tends to be shorter and displays associ-ations with a faster coagulation rate and a higher curdfirmness (cited by Clark & Sherbon 2000). No significantassociation between CSN3 polymorphism and curdling rate(S2 and S4) was detected. However, the ranking ofgenotypes (BB>AB>AA) was the anticipated one, becauseBB milk tended to have more protein and casein contentsthan AA milk (Table 2) and, therefore, it was expected to

Goat CSN1S1 and CSN3 genotypes and milk coagulation properties 35

have a higher curdling rate. Finally, curd firmness andcheese yield were not significantly associated with CSN3genotype (Table 2). These results are in strong contrast withthe ones obtained in cattle showing that the B-allele of thebovine CSN3 gene is associated with a shorter coagulationtime and better curd and cheese yield than the A-allele(Schaar et al. 1985, Marziali & Ng-Kwai-Hang 1986). Theselatter data are consistent with the fundamental role of CSN3in the first stage of rennet coagulation of milk, whereenzymatic proteolysis occurs and about 87–90% of CSN3must be enzymatically degraded before aggregation takesplace (Walstra et al. 1984; Lucey 2002). However, it shouldbe noticed that the set of mutations that characterize B and Avariants in goats and cattle are completely different so weshould not expect identical outcomes in both species.Finally, interaction effects between CSN1S1 and CSN3genotypes were not significant, which rules out the existenceof haplotype effects.

In summary, in the current study, we have observed thatgoats with an EE genotype for the CSN1S1 locus show asignificantly higher curdling rate than their BB or EFcounterparts. This finding is surprising because in Frenchbreeds, milk from goats with “high” genotypes (AA and BBgoats) has better rheological properties than that from“medium” (EE) or “low” (FF) genotypes. We attribute thisdiscrepancy to physiological and genetic differences be-tween French and Spanish caprine breeds as well as totechnical aspects associated with each particular experi-ment. Our data also suggest that the CSN3 genotype mightaffect the rennet coagulation time, although the molecularbasis of this association is unclear and additional experi-ments should be performed to confirm it. At a practical level,we have not observed any association between eitherCSN1S1 or CSN3 genotypes and cheese yield, the mainparameter determining the economic benefits of goatfarming systems in Spain. This finding suggests that, at leastin the case of Murciano-Granadina goat breeders, selectionbased on the genotypic information of these two loci is notexpected to generate increased incomes due to an improve-ment of the cheese transformation process.

This work was funded by a grant from the Spanish Ministry ofEducation and Science (AGL2002-04304-C03-02- GAN).

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