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Cheese yield is largely determined by the concentrations of protein, particularly casein, and fat in milk (Lawrence, 1993). An important indicator of milk suitable for cheese production would therefore be casein number (weight percentage of casein to total protein). It is, however, possible that rather than regarding caseins as a homogenous group, some of the caseins may play a more significant role for the cheese yield, i.e. there may be room for improvement of the casein composition. Rather than analysing concentration of the various milk proteins, many studies have been looking for associations between polymorphisms in the milk protein coding genes and milk coagulation, thereby addressing the impact of structural variation of allelic milk protein variants. Studies have shown that selection for genetic variants of milk proteins could be an option to change the protein composition of milk (Ikonen et al. 1997; Lodes et al. 1997; Bobe et al. 1999; Hallén et al. 2008), thereby possibly obtaining improved processing properties resulting in a higher dairy product yield and quality (Rahali & Ménard, 1991; Boland & Hill, 2001; Ikonen et al. 1999).
Several of the studies on the detailed protein composition and cheese making potential of milk have focused on rheological properties such as curd firmness (Storry et al. 1983; van den Berg et al. 1992; Ikonen et al. 1997; Jõudu et al. 2008), whereas fewer have also related the protein composition to actual cheese yield (Ikonen et al. 1999; Auldist et al. 2004; Wedholm et al. 2006). Curd firmness at cutting has been positively associated with cheese yield (Bynum & Olson, 1982; Riddell-Lawrence & Hicks, 1989), but in practice gel firmness may have minor consequences for cheese yield as long as the coagulation process is relatively consistent (Lucey & Kelly, 1994). Hurtaud et al. (1995) showed that actual cheese yield (Camembert) was more accurately predicted by laboratory scale cheese yield than through coagulation measures obtained by Formagraph. Being the main constituents of cheese, measures of caseins lost to the whey may be more relevant for actual cheese yield than rheological properties.
The present work studied how the milk protein composition and the genetic polymorphism of milk proteins were associated with the retention of casein in curd at chymosin-induced coagulation...