Composite milk protein phenotypes in relation to composition and cheesemaking properties of milk

IiIl. D0ir.v Journal 7 (1997) 305-310 112 1997 Elsevier Science Ltd PII:

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SO958-6946(97)00019-S

ELSEVIER

Composite Milk Protein Phenotypes in Relation to Composition and Cheesemaking Properties of Milk H. K. Mayer”“, Martina Ortner b, E. Tschager ’ and W. Ginzinger’ UDepartment of Dairy Research and Bacteriology, University of Agriculture, Gregor Mendel-Str. 33, A-1180 Vienna, Austria bDepartment of Animal Breeding, University of Agriculture, Gregor Mendel-Str. 33, A-1180 Vienna, Austria “Federal Research Station of Dairy Science, Rotholz, A-6200 Jenbach, Austria (Received

7 February

1997; accepted

14 April 1997)

ABSTRACT The effects of composite milk protein phenotypes on the composition and cheesemaking properties of milk were studied. Pooled milks from 12 selected groups of Brown cattle with particular phenotype combinations of /?-casein (A*A*, A*B), k-casein (AA, AB, BB) and /I-lactoglobulin (AA, BB) were investigated. cr,,-Cn BB was common to all animals. Milk collection and cheesemaking trials on a pilot scale were repeated four times during winter 1993. The interaction between all three gene loci (/I-Cn, k-Cn, /I-Lg) was found to be highly significant (P < 0.001) for the contents of total protein, casein, whey protein and fat. The casein number was 04% (absolute) higher for /I-Lg BB milk than for /I-Lg AA milk. The relative amount of rc-casein consistently increased from rc-Cn AA to k-Cn BB. The losses of fat and curd tines in the whey and moisture-adjusted cheese yield were also affected by the genotype combinations. Recovery of milk solids was 3% higher for b-Cn A*B milk than for ,GCn A*A* milk (P= 0.010). 0 1997 Elsevier Science Ltd. All rights reserved

Keywords:

milk proteins;

polymorphism;

composite

phenotypes;

milk composition;

properties

shown for k--Cn, some authors found differences in cheese yield between rc-Cn AA and BB milks to be up to about 10% (Mariani et al., 1976) while others found no effect (Schaar et al., 1985). This indicates that the findings are highly dependent on the type of cheese produced as well as on cheesemaking procedure, especially cooking temperature (Jakob and Puhan, 1992). In most studies, attention was focused on the effect of a single milk protein locus, rather than on the effect of composite phenotypes on the composition and cheesemaking properties of milk. Because of the close linkage between the casein loci (Ferretti et al., 1990; Threadgill and Womack, 1990), attention should be paid to the effect of composite phenotypes or haplotypes on the technological properties of milk (Jakob, 1994a). The objective of the present study was to evaluate the effect of composite milk protein phenotypes (/I-Cn, KCn, /)-Lg) on the composition and cheesemaking properties of milk.

INTRODUCTION Milk protein polymorphism has been the object of great interest within the dairy industry because of a possible relationship with milk production traits, milk composition and technological properties of milk (Buchberger, 1990; Jakob and Puhan, 1992; Jakob, 1994a). In many studies, genetic variants of milk proteins are related to the amount and relative proportion of each of the milk constituents. However, contradictory results have been published and some of the findings on milk composition are still controversial (Jakob and Puhan, 1992). In some cases, the statistical model used determined whether or not the effect of a gene locus was significant (Bovenhuis et al., 1992) and in some breeds the effect of a gene locus was opposite to that in other breeds (Ortner et al., 1995), or the effect of an allele was not significant because of its rarity (Delacroix-Buchet et al., 1993). Of the numerous possible relationships between genetic polymorphism of proteins and the composition and technological properties of milk, only a few have been well confirmed, for example the effect of p-Lg variants on casein number, or the association between K-Cn alleles and the renneting properties of milk (Jakob, 1994a). Although the studies dealing with the effects of genetic variants of milk proteins on cheesemaking revealed some striking results, these must be viewed with caution. As *Corresponding

cheesemaking

MATERIALS AND METHODS Experimental

design and sampling

During the autumn of 1992, individual milk samples from 1742 Brown cattle cows were collected and phenotyped for genetic variants of milk proteins using isoelectric focusing (Braun et al., 1990; Mayer et af.,

author.

1991a). 305

Based

on

these

results

(Mayer

and

FoiBy,

306

H. K. Mayer

1992), a selection was made to make up 12 groups of animals with particular phenotype combinations of /Icasein (A*A*, A*B), rc-casein (AA, AB, BB) and plactoglobulin (AA, BB). a,i-Casein BB was common to all animals. Each group consisted of 8 cows, spread over different farms in the Tyrol, Austria. Milk protein phenotypes of the selected second lactation cows were checked again prior to experiments. In February and March 1993, milk collection and cheesemaking trials on a pilot scale were repeated four times on consecutive days for each group. Morning milk from each group with a particular phenotype combination (fi-Cn, Ic-Cn, /I-Lg) was collected and transported in cooled insulated containers to the Federal Research Station of Dairy Science, Rotholz. Milks were pooled and sampled for the investigation of composition and renneting properties of the milk. Approximately 50 kg of the pooled milk were used for cheesemaking on a pilot scale. Edam cheese was produced from raw milk without addition of CaC12, according to the standard manufacturing schedule. Whey was sampled for chemical analysis. Cheese samples for chemical analysis were taken before salting. After 8 weeks of ripening, cheese samples were analysed for water-soluble nitrogen.

et al. Chemical analyses of whey and cheese samples

Whey was analysed for curd tines (Tschager, 1988) fat (VDLUFA, 1985) an d casein content (IDF, 1964b, 1993). Cheese samples taken before salting were analysed for total solids (IDF, 1982), total protein (IDF, 1964a) and fat (VDLUFA, 1985). Eight-week-old cheese samples were analysed for water-soluble nitrogen (Tschager, 1994). Statistical

To study the relationship between genetic variants of /I-Cn, rc-Cn and /I-Lg and the composition and cheesemaking properties of milk, an analysis of variance was carried out using the General Linear Model (GLM) Procedure of the Statistical Analysis System (SAS, 1988). The model included the fixed effects of b-Cn, ic-Cn and /I-Lg loci as well as the interactions between two and three of these gene loci. The following model was used to estimate the effects of milk protein genotypes on the composition and cheesemaking properties of milk: Y+ =

/l +

/I-Cni + iC-Cllj+ /?-Lg,

+ (/I-Cni * JC-Cnj)+ (B-Cni * B-LgJ

Chemical analyses of milk samples

Pooled milks from the 12 selected groups of Brown cattle with particular phenotype combinations of /I-Cn, ic-Cn and b-Lg were analysed for total solids, nitrogen fractions, fat content and renneting properties as described below. All measurements were performed in duplicate. Total solids were determined by the oven method (IDF, 1982). Total nitrogen (TN), non-casein nitrogen (NCN) and non-protein nitrogen (NPN) were determined by the Kjeldahl method (IDF, 1964b, 1993). Whey protein N was calculated from the difference between NCN and NPN, and casein N from TN and NCN, respectively. Protein equivalents were calculated from nitrogen data using a factor of 6.38. The casein number was calculated as IOOxCasein N/TN (“A). Fat content was determined gravimetically (VDLUFA, 1985). The relative amounts of the individual caseins (QCn, cr,2-Cn, fl-Cn, Ic-Cn) were estimated by highperformance liquid chromatography (HPLC) using a 600E Waters system incorporating a model multisolvent deliyery system, a U6K injector and a wide-pore (1000A) Waters Protein Pak DEAE-5PW (7.5cmx7.5mm) column (Waters Corporation, Milford, MA, USA). Preparation of whole casein and chromatographic conditions were according to the method of Visser et al. (1986). Column eluates were monitored at 280nm using a Waters 484 UVjVIS spectrophotometric detector interfaced with a PC using Waters Maxima 820 software for automatic quantitation and documentation (Mayer et al., 1991b). The values were calculated by expressing the individual peak areas as a percentage of the sum of all casein peak areas (van den Berg et al., 1992). Clotting time (r), firming time (&J and firmness of the coagulum (A2e) were measured using a Formagraph (Foss Electric) according to the method of Tschager (1987).

analysis

(1)

+ (iC-Cnj* B-Lg,) + (/I-C& * K-Cnj * /3-Lgk) +

C&k

where zz

y,,

i-Cni

= =

lC-Cnj

=

fl-Lgk

=

(B-Cni*K-Cnj)

=

(P-Cni*B-Lgk)

=

(K-Cnj*/?-Lgk)

=

(P-Cni*K-Cnj*/?-Lgk)

=

cijk

=

observation ijk overall mean the fixed effect of the B-Cn genotypes i (i= A*A*, A*B) the fixed effect of the ic-Cn genotypes j (j=AA,

RESULTS

AB, BB)

the fixed effect of the /I-Lg genotypes k (k = AA, BB) the interaction of b-Cn and ic-Cn genotypes the interaction of /?-Cn and /I-Lg genotypes the interaction of rc-Cn and fl-Lg genotypes the interaction of B-Cn, K-Cn and /I-Lg genotypes, and the random residual effect.

AND DISCUSSION

Milk composition

The interaction between all three gene loci (P-Cn, KCn, fl-Lg) was found to be highly significant for the contents of total protein, casein and whey protein (P < 0.001). Consequently, an epistatic effect exists between these three gene loci. /I-Lg BB in combination

307

Efl2ct.s of composite milk protein phenotypes 35

Total protein content (%)

I

o 7 Whey protein content (36)

I

I

391 299 2,7 393~~-C11J 295 AA

IlLLgAA AB r-carein

halrein

Fig. 1. Relationship total protein content

B%

A2A2

OB-LgBB -1

AA

I

between phenotype of milk (P < 0.001).

A% rcasein lcasein

BB

“‘”

P?B

combinations

AA

A% lc-casein

AA

8%

Bcasein AW

and

Casein content (X) 23 /~-p

%%

Ecasein AZ%

Fig. 3. Relationship between phenotype whey protein content of milk (PC 0.001). 8.

A% rcasein

combinations

and

combinations

and

Casein number (%)

236 2,4

76

292

74

2

72

196 w-casein Bcasein A2A2

r-casein I

Fig. 2. Relationship between phenotype casein content of milk (P < 0.001).

lkasein

AZ%

combinations

and

/I-Cn A’A’ resulted in decreasing total protein (Fig. I) and casein (Fig. 2) contents from K-Cn AA to ti-Cn BB, whereas in combination with fl-Cn A2B this trend was not as obvious. In the /I-Lg AA groups, the total protein and the casein content was always higher in genotype combinations with rc-Cn BB in comparison to K-Cn AA, whereas the opposite could be observed in p-Lg BB groups. The genotype combinations (/I-Cn, KCn, /GLg) A’A2/AA/BB and A2B/BB/AA showed the highest contents of total protein (Fig. 1) and casein (Fig. 2), whereas the lowest values were found for A2A’/AA/AA. van den Berg et al. (1992) demonstrated the positive effect of K-Cn B on the total protein content of milk, but found no interaction between the effect of K-Cn variants and the effect of p-Lg. Distinct opposite trends with respect to the whey protein content of milk were observed for fi-Cn A2A2 milks (Fig. 3). When combined with ,&Lg AA, the whey protein content increased from rc-Cn AA to K-Cn BB, whereas the opposite was true for B-L! BB groups. In genotype combinations with fl-Cn A B, no clear trends could be observed. The highest whey protein content was found in A’B/AA/AA, the lowest in A2A2/ BB/BB ({GCn, k--Cn, /GLg). The casein number was also significantly influenced by the three-fold interaction between the gene loci (PC 0.001). In the groups , where p-Lg BB was combined with /j-Cn A A-, the casein number increased from ti-Cn AA to K--Cn BB, whereas when combined with ,&Cn A2B it remained almost constant at a high level (Fig. 4). p-Lg AA in combination with p-Cn A2B resulted in a very sharply increasing casein number from ti-Cn AA to rc-Cn BB, while in combination with p-Cn A2A2, no obvious trends were found. The highest casein number was found in A’A’/ BBjBB, and the lowest value in A2B/AA/AA (P-Cn, Kwith

Fig. 4. Relationship between phenotype casein number of milk (P=O.O17).

Cn, fl-Lg). Thus, fi-Lg B seems to be associated with a higher casein content and a lower amount of whey protein, which resulted in a casein number that was O4% (absolute) higher for /GLg BB milk than for fi-Lg AA milk. This is in agreement with the results reported in many other studies (McLean et al., 1984; Schaar et al., 1985; Ng-Kwai-Hang et al., 1986; Aaltonen and Antila, 1987; van den Berg et al., 1992; Jakob, 1994a). A very clear trend was observed concerning the relative amount of rc-casein (Fig. 5) which consistently increased from rc-Cn AA to Ic-Cn BB (with one exception). As reported in the literature, rc-Cn BB milk could be shown to be correlated with higher relative amounts of K--casein (McLean et al., 1984; Jakob and Puhan, 1986; Aaltonen and Antila, 1987; Ng-Kwai-Hang et al., 1987; van den Berg et al., 1992). However, also with this parameter, an epistatic effect existed between the three gene loci (P < 0.001). The highest relative amount of K--casein was found in A2A2/BB/AA, the lowest amount in A’A’/AA/ BB (b-Cn, ti-Cn, fi-Lg). With respect to the fat content, the effect of the Relative amount of rcasein

I8

(as % of total casein)

t

rase4n 04asein AW

rcasein

I

Bcasein 2%

Fig. 5. Relationship between phenotype combinations relative amount of m-Cn in milk (P
and

308

H. K. Mayer et

genotype combinations of the gene loci was also found to be highly significant (PC 0.001). b-Lg BB in combination with /?-Cn A2A2 resulted in a decreasing fat content from Ic-Cn AA to BB, while in combination with /?-Cn A2B, the opposite was true (Fig. 6). Genotype combinations with fi-Lg AA demonstrated the opposite effect, although this was not as evident. The highest fat content was in A2B/AA/AA, the lowest in A2A2/AA/AA (P-en, Ic-Cn, /?-Lg) milk. Some studies indicated that there might be differences between the breeds in the effect of rc-Cn on the fat content of milk (Aleandri et al., 1990; Bovenhuis et al., 1992; Oloffs et al., 1992). Conflicting results obtained in different studies arose from the fact that p-Cn exhibits a different effect depending on whether it is in combination with /3-Cn A2 or A’ (Jakob, 1994a), which is possibly an indication of the existence of the interactions that were found in the present study.

al. Fat content (%)

4

385 3 35 -,-

AA

AB

BB

AA

KGe5ein

AB

BB

K4mdI

Bcaaein A+?

Bcaaein #lB

Fig. 6. Relationship between phenotype combinations and fat content of milk (P < 0.001).

Fat content of whey (%)

Cheesemaking properties The cheesemaking trials included an investigation of the effects of composite milk protein phenotypes on the renneting properties of milk, the losses of fat and curd fines in the whey, protein and fat recovery and cheese yield. K--Cn BB milk exhibited better rennetability (shorter curd firming time and better curd firmness) than K-Cn AA milk, but again, the three-fold interactions between the gene loci were found to be highly significant for these parameters (results not shown). The favourable effect of rc-Cn B on the renneting properties of milk has also been confirmed in several recent studies (Jakob and Puhan, 1992; Mayer, 1992; Oloffs et al., 1992; van den Berg et al., 1992). The losses of fat (P < 0.001) and curd fines (P= 0.002) in the whey were also affected by the genotype combinations. In the groups where fi-Lg BB was combined with /?-Cn A2A2, the fat content of the whey decreased from u-Cn AA to K-Cn BB, whereas when combined with /?-Cn A2B the opposite was true (Fig. 7). The opposite trends were found in genotype combinations with 8-4 AA. The lowest fat content of the whey was found in A B/AA/BB and A2A2/ AA/BB, the highest in A2B/AA/AA (fl-Cn, k--Cn, p-Lg). The lowest amounts of curd fines in the whey were found in A2B/AA/BB and A2B/BB/BB, the highest in A2A2/AB/ AA (Fig. 8). In the whey obtained from Ic-Cn AA milk, van den Berg et al. (1992) observed significantly higher amounts of fat and about 30% more cheese fines than with K-Cn AB milk. Moisture-adjusted cheese yield was significantly affected by the interaction betweeen the three gene loci and the genotypes of the B-casein locus, respectively (PC 0.001). p-Lg BB in combination with p-Cn A2A2 resulted in a decreasing cheese yield from rc-Cn AA to BB, while in combination with /?-Cn A2B the opposite was true (Fig. 9). Genotype combinations with fl-Lg AA showed the opposite trend, although this was not as evident. As a consequence of these facts, the highest cheese yield was found from A2B/AA/AA, the lowest from A2A2/AA/AA @Cn, Ic-Cn, /SLg) milk. Neither the effect of genotypes nor of genotype combinations was found to be significant for fat and protein recovery from milk. However, the conversion of milk solids into cheese was significantly affected by the genotypes of the p-casein locus (P=O.OlO), as recovery of milk

“‘I

AA

A0

00

AA

Klein

AB

BB

K-Cash

Llaaein #?P?

Bcaaein P?B

Relationship between phenotype combinations and fat content of whey (P< 0.001).

Fig. 7.

o 3 Curd fines content of whey (g/kg) 9

rcasein l&as&n A2A2

I

Kaawin I

bcaaein 2B

Relationship between phenotype combinations and curd fines content of whey (P = 0.002).

Fig. 8.

37

,

Cheese yield (kg cheese solids/M) kg milk)

395 3,3 391 2,s z7 z5

Fig. 9. Relationship between phenotype combinations and cheese yield (P < 0.001).

solids was 3% higher A2A2 milk. The experiments generally relating rc-Cn B to Puhan, 1992). Pabst

for /I-Cn A2B milk than for p-Cn results of the cheesemaking confirmed earlier investigations higher cheese yield (Jakob and (1995) reported a 2.7% higher

Effects qf composite milk protein phenotypes WSN (as % of TN)

‘”

A% mzasein

AA

Bcasein A2

309

REFERENCES

00

AA

A% xcasein

%%

Bcasein Ph

Fig. 10. Relationship between phenotype combinations water-soluble nitrogen in 8-week-old cheese (P = 0.042).

and

recovery of milk protein in Edam cheese manufactured from ~c-Cn BB milk when compared with rc-Cn AA. van den Berg et al. (1992) found that the amount of glycomacropeptide released into the whey is higher for the K-Cn BB phenotype than for the AA type. Thus, the positive effect of K-Cn B on protein recovery was smaller than was expected from the casein number, and Schaar et al. (1985) who used pasteurised milk, were unable to reveal any effect of K-Cn polymorphism on cheese yield, recovery of milk constituents and cheese composition, except for the fat content of the ripened cheese. As regards the genetic variants of /3-Lg, Schaar et al. (1985) Ng-Kwai-Hang et al. (1986) and van den Berg et al. (1992) found protein recovery from /i’-Lg BB milk to be significantly higher than from p-Lg AA type milk (BB > AB > AA). This was attributed to the higher relative casein content of the /?-Lg BB phenotype. After 8 weeks of ripening, water-soluble nitrogen in cheese (as % of TN) was significantly (P= 0.042) affected by the three-fold interaction between the gene loci (/I-Cn, ti-Cn, ,&Lg). The highest value was found for A2B/AA/AA, the lowest for A2A’/BB/BB (Fig. 10). In Gouda cheese, van den Berg et uf. (1992) found the genetic variants of K-Cn and fi-Lg to have no effect on the degree of proteolysis during the ripening period of 6 months.

CONCLUSION

This study demonstrated the highly significant effect of the genotype combinations of the three gene loci BCn, Ic-Cn and fl-Lg on the composition and cheesemaking properties of milk. The results so far are in accordance with those reported in the literature. However, it was clearly shown that it is insufficient to consider the effect of a single milk protein locus. Because of the close linkage between the casein loci, more attention should be paid to the effect of composite milk protein phenotypes or haplotypes.

ACKNOWLEDGEMENTS

The authors thank the staff of the Federal Research Station of Dairy Science, Rotholz, for their assistance in the collection of milk samples. Thanks are due to Peter Beutel for his technical assistance and also to Prof. EI31 and Dr Solkner for their help with the statistical analysis.

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