Variation in size of goat milk casein micelles related to casein genotype

Abstract

Summary -Casein (CN) micelle size was determined in 2 goat milks from animais with different genotype for OEs1CN.One milk lacked OEs1CN,the other had an OEs1CNcontent of 4.7 9 kg-l, ln comparison, the goat bulk milk has 3.3 9 kg-1 OEs1CN.The mean diameter of micelles in milk without OEs1CNwas found to be 280 nm, while the diameter was 199 nm in milk with a high content of OEs1CN, ie a decrease by 29%. Micellar sizes were estimated by photon correlation spectroscopy (PCS) and by transmission electron microscopy (TEM) associated with negative staining. Miceilar volume distribution according to slze showed that milk without OE s lCN had the typical distribution of goat milk, ie a large spread of diameters from 20 to 270 nm without any clear maximum in frequency and a high proportion of case in forming the large micelles. In contrast, milk with a high level of OEs1CNshowed a narrow unimodal distribution of frequency. The chemical analysis of milks, total casein, individual caseins, total and soluble minerais showed that the only difference is the OEs1CN level. The results might imply a role of OEslCN in miceile size regulation.goat milk 1 casein 1 micelle 1 OEslcasein 1 size 1 TEM microscopy 1 photon correlation spectroscopy Résumé -Taille des micelles de caséine du lait de chèvre en relation avec la variation géné-tique de la composition du lait.

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

“…These differences were statistically significant and in good agreement with previous studies (Pierre et al 1995(Pierre et al , 1998a(Pierre et al , 1999Tziboula and Horne 1999), all of which concluded that the mean size of casein micelles increased as the level of α s1 -casein decreased. Caseinmicelles in caprine milks with a low content of α s1 -casein have been described as more highly hydrated than those from milks having a high content of this protein (Mora-Gutierrez et al 1997).…”

“…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.…”

Characterization of aroma compounds in the volatile fraction of soft goat cheese during ripening

“…Individual caseins in the cheese were separated by HPLC, using a procedure described elsewhere [15]. The cheese sample (l g) was dispersed in 4 mL ofbuffer (6 mollL urea; trisodium citrate 1.3%; 0.1 mol/L tris-hydroxymethylamino methane, pH 7.0; 10 mmol/L dithiotreitol).…”

Influence de la teneur en caséine $\beta$ sur les caractéristiques physico-chimiques et l'aptitude à la coagulation enzymatique du lait de chèvre

“…Cette hypothèse est étayée par les observations récentes de Tziboula et Horne [35], selon lesquelles le variant F de la caséine α s1 , dé-pourvu d'une partie des sites de phosphorylation du variant d'origine, est associé à une répartition plus périphérique de la caséine au sein de la micelle. Dans les laits correspondants, les micelles sont plus grosses [23,26,29], ce qui pourrait indiquer une structure moins compacte, plus relâchée, dans laquelle le variant F de la caséine α s1 , moins phosphorylé, n'aurait pas le même effet de pontage entre les molécules caséiques. Les observations réalisées dans le présent travail, à partir des laits de chèvres pyré-néennes, vont dans le même sens, puisque les micelles dépourvues de caséine β sont proportionnellement plus riches en caséines α s (α s1 et α s2 ), et présentent une taille ré-duite par rapport aux micelles des laits A/A.…”