THE INFLUENCE OF GENETIC-VARIANTS OF MILK-PROTEINS ON THE COMPOSITIONAL AND TECHNOLOGICAL PROPERTIES OF MILK .2. RENNET COAGULATION TIME AND FIRMNESS OF THE RENNET CURD
A. Lodes et al., THE INFLUENCE OF GENETIC-VARIANTS OF MILK-PROTEINS ON THE COMPOSITIONAL AND TECHNOLOGICAL PROPERTIES OF MILK .2. RENNET COAGULATION TIME AND FIRMNESS OF THE RENNET CURD, Milchwissenschaft, 51(10), 1996, pp. 543-548
Milk samples (total = 870) of different genetic Variants of the milk p
roteins were analysed for the rennet coagulation time (RGT) and the cu
rd firmness (A(R)-value) using a gelograph. Natural variations in the
milk composition and differences in the pH-value and protein content o
f the milk were considered. Special interest was given to the rare gen
etic variants (alpha(s1)-casein (Cn) C, beta-Cn B or C, kappa-Cn C or
E, and beta-lactoglobulin (Lg) C, D or W). There were significant rela
tionships between the genotypes of the alpha(s1)-Cn (p<0.01), beta-Cn
(p<0.001) and kappa-Cn (p<0.001) locus and the RCT of milk. Milk with
the genotype alpha(s1)-Gn CC clotted significantly faster than milk wi
th the genotype alpha(s1)-Cn BB. The beta-Cn locus had the greatest in
fluence on the RCT, with the RCT increasing from 9.5 min to 12.5 min i
n the following order: beta-cn BB<A(1)B<A(1)C<A(2)B<A(1)A(1)<A(1)A(2)/
A(2)A(2). Milk with the kappa-Cn genotype AC clotted significantly slo
wer than milk of any other kappa-Cn genotype. The RCT for the kappa-Cn
genotypes increased in the following order: kappa-Cn BE<BB<AB<AE/AA<B
C<AC. A significant relationship was also observed between the genotyp
es of the beta-Cn, kappa-Cn and beta-Lg locus and the curd firmness. F
or the beta-Cn genotypes only the differences between the curd firmnes
s of milk with the beta-Cn BB-type and all other beta-Cn genotypes wer
e significant. The kappa-Cn locus had the greatest effect on curd firm
ness. Milk with the rare type kappa-Cn AE and BE was characterized by
a very weak curd as was the curd made from kappa-Cn AA-milk, whereas k
appa-Cn BB and BC-milk formed a very strong curd. The curd firmness of
kappa-Cn AB- and AC-milk took an intermediate position. The beta-Lg g
enotype also had a significant influence on the curd firmness. Milk fr
om cows with the beta-Lg genotype BB showed a significantly higher A(R
)-value than the genotypes beta-Lg AA, AB, AD and ED, whereas the A(R)
-values for the other genotypes were very similar.