Abstract #185

# 185
Differentiating between the effects of chymosin-mediated proteolysis, coagulant type, ripening temperature and calcium solubilization on fracture behavior of Maasdam-style cheese.
P. Lamichhane1,2, P. Sharma1, D. Kennedy1, A. L. Kelly2, J. J. Sheehan*1, 1Teagasc Food Research Centre Moorepark, Fermoy, Cork, Ireland, 2University College Cork, Cork, Ireland.

Ripening-related changes within the cheese matrix influence cheese properties, such as texture perception and development of undesirable slits and cracks. However, the individual contribution of various factors on cheese properties remains unclear; therefore, the aim of this study was to decouple and explore the individual roles of chymosin-mediated proteolysis, coagulant-type, ripening temperature and calcium solubilisation on the fracture behavior of Maasdam-style cheese. Addition of a chymosin inhibitor, i.e., pepstatin A, to the curd/whey mixture during cheese manufacture completely inhibited the breakdown of αS1-casein over 90 d of ripening, while substitution of fermentation-produced bovine chymosin with fermentation-produced camel chymosin decreased breakdown of αS1-casein by ~40%. However, neither treatment influenced the hydrolysis of β-casein or the solubilisation of colloidal calcium. Ripening of cheese at a consistent low temperature (8°C) decreased the rate of breakdown of αS1-casein and β-casein and solubilisation of colloidal calcium as compared with cheeses ripened for a period at higher temperature (warm-room stage at 23°C between 20 and 48 d ripening). A significant positive correlation was found between intact αS1-casein content and fracture stress, suggesting that the hydrolysis of αS1-casein has an important role in the softening of cheese texture. However, no significant association between levels of intact αS1-casein and strain at fracture was observed, suggesting that breakdown of αS1-casein had no pronounced influence on the brittleness of Maasdam-style cheese. In contrast, the strain at fracture was significantly positively correlated with the level of intact β-casein and insoluble calcium content. Results from this study provide a new perspective on potential opportunities for cheese-makers to reduce the incidence of slits and cracks in cheese.

Key Words: proteolysis, insoluble calcium, fracture properties