Effects of the detailed protein composition of milk on curd yield and composition measured by model micro-cheese curd making of individual milk samples

摘要

The effect of the contents of casein (CN) and wheyprotein fractions on curd yield (CY) and compositionwas estimated using 964 individual milk samples.Contents of αS1-CN, αS2-CN, β-CN, γ-CN, glycosylatedκ-CN (Gκ-CN), unglycosylated κ-CN, β-LG, andα-LA of individual milk samples were measured usingreversed-phase HPLC. Curd yield and curd compositionwere measured by model micro-cheese curd makingusing 25 mL of milk. Dry matter CY (DMCY) waspositively associated with all casein fractions but especiallywith αS1-CN and β-CN. Curd moisture decreasedat increasing β-CN content and increased at increasingγ-CN and Gκ-CN content. Due to their associationswith moisture, Gκ-CN and β-CN were the fractionswith the greatest effect on raw CY, which decreasedby 0.66% per 1-standard deviation (SD) increase inthe content of β-CN and increased by 0.62% per 1-SDincrease in the content of Gκ-CN. The effects due tovariation in percentages of the casein fractions in totalcasein were less marked than those exerted by contents.A 1-SD increase in β-CN percentage in casein (+3.8%in casein) exerted a slightly negative effect on DMCY(β = −0.05%). Conversely, increasing amounts of αS1-CN percentage were associated with a small increasein DMCY. Hence, results suggest that, at constantcasein and whey protein contents in milk, the DMCYdepends to a limited extent on the variation in theαS1-CN:β-CN ratio. κ-Casein percentage did not affectDMCY, indicating that the positive relationship detectedbetween the content of κ-CN and DMCY can beattributed to the increase in total casein resulting fromthe increased amount of κ-CN and not to variation inκ-CN relative content. However, milk with increasedGκ-CN percentage in κ-CN also shows increased rawCY and produces curds with increased moisture content.Curd yield increased at increasing content andrelative proportion of β-LG in whey protein, but thisis attributable to an improved capacity of the curd toretain water. Results obtained in this study support thehypothesis that, besides variation in total casein andwhey protein contents, variation in protein compositionmight affect the cheese-making ability of milk, but thisrequires further studies.