Casein micelle size in relation with casein composition and α_s1, α_s2, β and Κ casein contents in goat milk

Abstract

The relationship between micelle size and casein micelle composition was studied on 21 individual goat milks from animais homozygous for as1casein variants A, B 2 , C, E, F and O. A large variation in milk composition was obtained, as a sl secretion levels varied from 7.2 g-kg"! in A milks to none in 0 milks. Mean micelle size (MMS), determined by photon correlation spectroscopy, varied between samples from 192 nm to 287 nm. This was explained by the different aspects of the histograms of casein distribution according to the size, determined from transmission electron microscopy data, which showed a maximum either in the low diameter range (20-130 nm) or in the large diameter region (130-260 nm), or even intermediary figures with a bimodal distribution. The caseins, as1CN, a s2 CN,~CN and KCN were determined in milks from nitrogen malter determinations (N x 6.38) and RP-HPLC analysis of casein. Polynomial relations were calculated between micelle size and milk composition al parameters. MMS was correlated on one side to the as1CN and KCN levels in milks (g-kg'") and, on the other side, to the proportions of as1CN %, a s2 CN % and~CN % in total casein. These polynomial relations allowed the prediction of the mean micelle size in milks from the casein levels, with aiS % accuracy. Monofactorial correlations also showed a significant effect of as1CN (r = -0.77), but not any of KCN. Mineral composition of milks was determined, calcium by atomic absorption spectrophotometry and phosphorus, by a colorimetrie method. Goat milks were characterized by a constant colloidal inorganic P level (12.4 (SO = 1.7) mmol-kg "). In contrast, colloidal Ca (Cac), SerineP and total colloidal P (Pc) were correlated to the total casein content. The ratio CaclPc was the most constant parameter in goat milks, amounting 1.22 (SO = 0.05), presumably characterizing an unique mode of association of caseins in milk. No significant correlation was obtained between the colloidal Ca and P levels in milks and the size of micelles. © InralElsevier, Paris.goat milk 1 casein 1 micelle size 1 a sJ caseinl colloidal calcium and phosphorus Résumé -Taille des micelles du lait de chèvre en relation avec la composition de la caséine et les teneurs en caséines a sJ ' a s2 '~et K dans le lait. La relation entre la taille des micelles de caséine et la composition de la fraction caséine des laits a été étudiée sur 21 laits individuels provenant de * Correspondence and reprints.

Extreme frequencies of the αs1-casein “null” variant in milk from Norwegian dairy goats – Implications for milk composition, micellar size and renneting properties

“…Previously reported differences in mean size between α s1 -casein "null" and "strong" micelles were much more pronounced than those reported in the current study (216±26 vs. 207±35 nm); 280 vs. 200 nm (Pierre et al 1995) and 260 vs. 220 nm (Pierre et al 1998c). These previous studies included only three α s1 -casein "null" goats, compared to the present study including 150 homozygous α s1 -casein "null" goats.…”

“…The studies by Pierre et al (1995Pierre et al ( , 1998c concluded that the content of α s1 -casein was negatively correlated to the mean size of casein micelles in caprine milks.…”

Composition, Structure, and Digestive Dynamics of Milk From Different Species—A Review

“… # Source: Adapted and modified from Claeys et al ( 19 ) . Values derived from other references are represented by uppercase case letters: A, Roy et al ( 29 ); B, Nguyen et al ( 42 ), Pierre et al ( 43 ), and Pierre et al ( 44 ); C, Roy et al ( 29 ); D, Dalgleish ( 45 ), Wang et al ( 46 ), and Dewan et al ( 47 ); E, Pellegrini et al ( 48 ); F, Remeuf et al ( 49 ); G, Ahmad et al ( 50 ); H, Luo et al ( 51 ); I, Beaucher et al ( 52 ) . …”

Casein polymorphism in goat's milk

“…In the last two decades research has continued to reveal the extensive casein polymorphism occurring in goat, but in spite of a large number of papers dealing with the wide heterogeneity of the casein fraction, the studies on the related impact are not so numerous. Several studies investigated Casensitive caseins (α s1 , α s2 and β), located within the micelles, establishing that they affect the technological properties of milk: strong alleles improve cheese-making and fat percentage: on the contrary, defective and null alleles make these features worse [15,40,60,66,67,75,76,85,89,91]. According to these findings genotypes at α s1 and β casein loci have been used for selection in breeding programs in some French and Spanish breeds [4,55,74,91,97,99].…”