Flavour precursor development in Cheddar cheese due to lactococcal starters and the presence and lysis of Lactobacillus helveticus.

The rapid release of intracellular enzymes due to autolysis of lactic acid bacteria in the cheese matrix has been shown to accelerate cheese ripening. The objective of this work was to investigate the evolution of the flavour precursors, individual free amino acids (FAAs), free fatty acids (FFAs) and volatile compounds that contribute to the sensory profiles of cheeses at 2, 6 and 8 months of ripening in Cheddar cheese manufactured using starter systems which varied with respect to their autolytic properties. Starter system A contained a blend of two commercial Lactococcus lactis strains (223 and 227) which had a low level of autolysis. System B was identical to A but also included a highly autolytic strain of Lactobacillus helveticus (DPC4571). System C contained only strain DPC4571. Levels of all individual FAAs were elevated in cheeses B and C relative to A after 2 months of ripening. By 8 months of ripening the main FAA were glutamate, leucine, lysine, serine, proline and valine. Levels of C6:0, C8:0, C12:0 and C18:0 fatty acids did not vary greatly over ripening, while levels of C4:0, C10:0, C14:0, C16:0 and C18:1 were elevated in cheeses B and C. Principal component analysis of the headspace volatiles separated cheese A from cheeses B and C. Cheeses B and C had highest levels of dimethyl disulphide, carbon sulphide, heptanal, dimethyl sulphide, ethyl butanoate, 2-butanone, and 2-methyl butanal and were described as having a ‘caramel’ odour and ‘sweet’, ‘acidic’ and ‘musty’ flavour. Cheese A had highest levels of 2-butanol, 2-pentanone, 2-heptanone, 1-hexanol and heptanal and was described as having a ‘sweaty/ sour’ odour and ‘soapy’, ‘bitter’ and ‘mouldy’ flavour. The results highlight the impact of starter lactococci on flavour precursor development and the positive effect of Lb. helveticus and the lysis of this strain on enhancing levels of substrate and flavour precursors early during ripening resulting in early flavour development.