Influence of milk pre-treatment, and changes in cheese structure and carbon dioxide solubility on the development of split defects in cheese

Abstract

The objective of this research was to understand the underlying issues leading to the development of undesirable split or crack defects within continental semi-hard cheeses made from a seasonally produced milk supply. Such defects result in poor aesthetic quality (a key retail requirement) and poor performance under high speed slicing for global food service markets, with consequential economic loss. Centrifugation (at centrifugal force of 9,000 × g) and incorporation of high heat-treated (HHT) centrifugate are common milk pre-treatment methods/practices prior to continental cheese manufacture. Centrifugation had little effect on the composition, texture, volatile profile and ripening characteristics of Maasdam cheese, except for significantly lower butyric acid levels. However, incorporating HHT centrifugate into the cheese milk significantly increased the levels of moisture in non-fat substance and decreased the hardness of the resultant cheeses. This may have the potential to influence subsequent eye formation characteristics, and possibly influence split or crack development. Primary proteolysis and levels of insoluble calcium content are considered to influence the fracture properties of cheese, including fracture stress and fracture strain. The present research found that (1) inhibition of rennet activity during ripening; (2) reduction of rennet activity during ripening; and (3) reduction of ripening temperature decreased the hydrolysis of αS1-casein by ~95%, ~45%, or ~30%, respectively, after 90 d of ripening. During the same ripening period, ~35% of β-casein was hydrolysed for all cheeses, except for those ripened at a lower temperature (~17%). The proportion of insoluble calcium as a percentage of total calcium decreased significantly from ~75% to ~60% between 1 and 90 d of ripening. Further results showed that although modulation of αS1-casein hydrolysis is an effective means to maintain the strength of the cheese matrix during ripening, maintaining higher levels of intact β-casein or insoluble calcium content (or both) within the cheese matrix results in reduced levels of shortness or brittleness of cheese texture. For the first time, dynamic microscopy was applied to understand the microstructural changes occurring in semi-hard eye-type cheeses during large-strain tensile deformation. It was observed that pre-existing micro-defects within cheese matrices led to the formation of undesirable slits or cracks. Gas behaviour, including solubility, is considered one of the critical factors for development of eyes, and also slits or cracks within cheese matrices. Therefore, CO2 solubility behaviour was studied in casein matrices, representing the protein-water phase of cheese matrices. It was observed that the CO2 solubility of casein matrices largely depends on the moisture-to-protein ratio, salt-in-moisture content, pH and temperature. Overall, this research provides a knowledge base to minimize or avoid development of splits or cracks defects and thus improves the quality and consistency of continental-type cheeses.