Abstract: Cheese slurries,made from fresh Swiss cheese curd, were treated at 345 or 550 MPa for 10 or 30 minutes in an isostatic press at 25 °C. The slurries were ripened at 30 °C for 0, 3 and 5 days. The growths of coliforms, yeasts and molds, starter bacteria (Lactococci and Streptococci), non-starter lactic acid bacteria (Lactobacilli), and presumptive coagulase-positive Staphylococcus were determined. An electronic nose was used to evaluate aroma development of the cheese slurries. Commercial Swiss cheeses with different ages were used as aroma references.The degree of inactivation of organisms was found to be a function of pressure intensity, exposure time, type of organism, and cheese slurry pH. In general, slurries treated at a higher pressure and with a longer exposure time showed a greater reduction in numbers and had less out-growth of organisms during ripening. Coliforms, yeasts and molds were completely inactivated at the pressures and time used. Starter bacteria appeared to be more resistant to being inactivated by high pressure treatment and had a greater out-growth rate than Lactobacilli and Staphylococci.Based on canonical analysis, nineteen samples for each batch were assigned to three groups. In general, higher intensity of pressure or longer exposure time caused less aroma development in the cheese slurries. When the cheese curd was incubated overnight prior to making the cheese slurries, stronger slurries with stronger aroma were observed. This study provided an explanation of the relative importance of relationships among high pressure treatment, starter bacteria, and aroma development during accelerated ripening.

Key words: high pressure, microorganisms, cheese slurry, aroma, electronic nose

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