Betydning av genetiske varianter av kasein og myseprotein på syre og løpe koagulering av melk.

The overall idea of the project was to increase the understanding of the meaning of the genetic milk protein variants for further processing of milk. The focus has been on milk from Noewegian red cattle (NRF). In the project, milk from cows has been used in the barn at the Center for Livestock Experiments NMBU. All the cows in the NMBU crew were genotype (SNP test). To have a large enough animal material all the time, it has been necessary to still genotype new cows that have entered the crew. All cows are tested for 10 genetic protein variants. Technological properties of genetic protein variants are shown to vary between different cow breeds, and therefore, results obtained with other cow breeds can not be transmitted directly to the NRF cow. It will be a goal to have a NRF cow that has the right protein composition as possible from industry needs to optimize the utilization of raw materials and reduce waste both in the production of cheese and in the production of fresh fermented milk products. This project has revealed that these two types of productions have different requirements for the properties of the proteins. The project has provided knowledge of how genetic variants of protein in milk affect the coagulation of milk by means of acid and rennet koagulation. Genotypes of milk protein associated with better rennet coagulation have impaired acid coagulation properties and vice versa. A favorable rennet coagulation was found for ?s1-CN BC, ?-CN A1A2 and ?-CN BB compared to BB, A2A2 and BE genotypes of the respective caseins. For composite casein variants, BC-A2A2-BB (?s1-?-?-CN) was associated with improved rennet coagulation properties compared to the rest of the composite genotypes. Surprisingly, improved acid coagulation properties were favored by ?-CN AA and the combined casein variant BB-A2A2-AA, which has been associated with poor renneting coagulation properties. Furthermore, it has been shown that two genotype variants (?s1-?-?-CN) are associated with both poor running and acid coagulation properties and new breeding programs should focus on reducing these genotypes in the NFR population. Milk with different genetic protein variants has different coagulation properties. With fractional trials, it was desirable to evaluate whether these differences were amplified or decreased after fractionation and concentration of the milk. The fractionation study required a lot of milk which has been a small challenge for some of the protein variants. It was shown that rennet coagulation of concentrated milk was influenced by various genotypes of the caseins. Composite genotypes of the caseins (?s1-?-?-CN) affected the renneting characteristics of concentrated milk. The BB-A2A2-AA and BC-A2A2-AA protein combinations were associated with shorter time to renneting (RCT) and higher clot firmness (A30) compared to BC-A2A2-BB and BB-A2A2-BB. Culture milk was chosen as a product to test the difference between the different genetic variants. It was shown that acid gel gave better coagulation for the BB variant of ?-LG compared to the AB and AA variants and less syneresis for ?s1-CN BC was found than for the BB variant. For the ?-LG variants, variant AB was better than variant BB with regard to syneresis.

Teknologiske egenskaper til genetiske proteinvarianter er vist å variere mellom ulike ku raser, og man kan derfor ikke overføre resultater oppnådd med andre kuraser til NRF-kua direkte. Men det vil være en målsetning å få en NRF-ku som har så riktig prote insammensetning som mulig ut fra industriens behov om å optimalisere råstoffutnyttelsen og redusere svinn både ved produksjon av ost og ved produksjon av ferske fermenterte melkeprodukter. Dette prosjektet skal bidra til å avklare om disse to typer produk sjoner har ulike krav til proteinenes egenskaper. Genetiske proteinvarianter er i dag ikke en del av avlsmålet til NRF-kua, prosjektet vil bidra til å avklare om det bør være det. Den overordnede ideen i dette prosjektet vil være å øke forståelsen av hvil ken betydning de genetiske melkeproteinvariantene har for videre prosessering av melk. Fokuset vil være på melk fra Norsk Rødt Fe (NRF). Prosjektet skal spesifikt gi kunnskap om hvordan genetiske varianter av protein i melk (spesielt beta-lactoblobulin (b eta-LG) og kappa-kasein) påvirker koagulering av melk vha syre- og løpefelling. I tillegg skal prosjektet gi økt forståelse av hvordan prosessteknikker som varmebehandling og filtrering kan brukes for å øke råstoffutnyttelsen og redusere prosesseringen.