1. Determine the range of pHs and levels of NaCl, lactate, and acetate in the moisture phase of traditional, low-fat, light sodium, and low-sodium Cheddar cheeses </P>
2. Examine the most permissive Cheddar cheese compositions determined in Objective 1 for the ability to support the growth of Salmonella, Listeria monocytogenes, Staphylococcus aureus, and Shiga-toxin producing E.coli using a Cheddar cheese model system. </P>
3. Examine the range of Cheddar cheese compositions determined in Objective 1 for the ability to support growth of the pathogen identified in Objective 2 using a Cheddar cheese model system.
This project developed a model cheese system to help determine the safety of low-fat or low-sodium natural cheese under different sets of conditions, particularly when salt, pH, organic acids, and acidity change due to low moisture or low temperatures during ripening. The model was made with liquid extracts from Cheddar cheese aged for 2, 6, and 8 months, and was used to monitor the growth and metabolism of Lactobacillus paracasei ATCC 334. </P> Results show that this organism metabolizes nearly all the major nutrients derived from milk (such as lactose, galactose, and citrate) at 4 months, and continued to survive and produce by-products like ethanol and acetate throughout 8 months. This discovery may indicate that Lb. paracasei is living off components released from other bacteria in the cheese matrix.