Molecular diagnostics for the prediction and improvement of mixed starter culture performance in cheese production

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In 2007, dairy products sales were evaluated at $11.6 billion, accounting for 15% of the Canadian food and beverage sector. Cheddar production continues to increase, hitting 67,127,000 kg in 2008 for Quebec alone, which is 46.5% of Canada's production of Cheddar cheese. Cheeses represent 24.6% of Canadian dairy product exports, but these exports make up only 1% of dairy products on the international market. The large quantity of lactic starter cultures required for making this amount of cheese represents an important investment and any problems with quality control can lead to considerable losses due to fermentation or ripening failures. For Cheddar cheese, starters are composed of mixed strains of Lactococcus lactis subsp. cremoris and there is a strong relationship between cheese quality and flavour and the technological aptitudes of the lactococcal strains used. However, not all strains are compatible in mixed culture and may produce undesired effects such as bitter or off-flavours in the cheese that are only detected after the costly ripening period, resulting in cheese downgrading and loss of consumer confidence. Many strains become sensitive to phage attack, and must be replaced. Thus, considerable effort in time and money is put into characterization and evaluation of the performance of lactococcal strains by conventional methods in terms of their metabolic activities. A rational choice of industrial strains must be founded on objective criteria of technological aptitude and performance, which could be facilitated using innovative predictive modelling issuing from a deeper understanding of strain stability and compatibility that will be revealed through gene and protein expression. The aim of this project is to predict milk fermentation performance by classifying gene and protein expression profiles as indicators of