IAFP 2009 Program Book and Abstract Book - AB149

Significance: According to this study, the MPN method is better for enumerating Bacillus cereus in milk than plating on MYP. Even though the inoculum level of 3.6 was achieved, better methods of Bacillus spp. spore production should be studied further. P3-03 Thermal Resistance of Listeria monocytogenes Scott A in Concentrated Ultrafiltered Milks and Reconstituted Milk Powder Related to the Effect of Different Milk Components KINGA SZLACHTA, Susanne Keller, A. Shazer and Stuart Chirtel NCFST, IIT, Summit-Argo, IL, USA Introduction: Pasteurization parameters for standard milk are well established and set by regulation (PMO). However, as solids levels increase, an increased amount of heat is required to destroy any pathogens present. This effect is not well characterized. Despite this shortcoming, innovations in food processing have led to a desire to create liquid products with higher levels of solids. Purpose: To determine the effect of increased dairy solids levels on the thermal resistance of L. monocytogenes in milks through the use of ultrafiltered milk, reconstituted milk powder, milk and the milk components fat, lactose, and caseinate. Methods: L. monocytogenes was cultured, harvested, and resuspended in ultrafiltered milk, reconstituted milk powder, and the milk components of differing concentrations. Samples were sealed into capillary tubes, heated at different temperatures for varying times and enumerated to evaluate survival. Results: Increased lactose and caseinate concentrations did not result in increased thermal resistance. In addition, the level of milk fat, up to 10 % of the total solids in ultrafiltered whole milk, did not increase thermal resistance when compared to ultrafiltered skim milk. Reconstituted skim milk powder at higher concentration (27% total solids D62 = 1.26 +/- 0.19 min, z = 5.70) did result in increased thermal resistance (P < 0.05), as compared to reconstituted skim milk powder at 17.5 % (D62 = 0.82 +/- 0.08 min, z = 5.57) and ultrafiltered whole milk at 27% total solids (D62 = 0.68 +/- 0.08 min, z = 5.04). Significance: It was demonstrated that total solids could not be used as the sole predictor of increased thermal resistance through the range tested. Increases in thermal resistance measured were most likely due to the presence of salts or the combination of salts with other milk components. Other components of milk, such as fat, did not increase thermal resistance. P3-04 Use of Nisin and Caprylic Acid to Control Listeria monocytogenes in Queso Fresco FRANCISCO DIEZ-GONZALEZ, Mary B. Kamnetz and Zata M. Vickers University of Minnesota, Food Science and Nutrition, St. Paul, MN, USA Introduction: Listeria monocytogenes is a foodborne pathogen responsible for outbreaks due to consumption of contaminated fresh Hispanic cheeses. “Queso fresco” is the most popular fresh Hispanic cheese, but it may be susceptible to contamination and growth of Listeria since it is preserved only by refrigeration. Purpose: The objective of this research was to determine the inhibitory effect of caprylic acid (CA) and nisin additions on the population of L. monocytogenes in queso fresco and the impact of those additions on the microbial quality and sensory characteristics. Methods: Batches of queso fresco curds were inoculated with mixtures of six L. monocytogenes strains, mixed with nisin (0.5 g/kg as Nisaplin®) and CA (0.8 to 3.2 g/kg), molded, packed and stored at 4°C for 3 weeks. Counts of L. monocytogenes were obtained on PALCAM agar plates. Aerobic plate count (APC), lactic acid bacteria (LAB) and psychrotrophic bacteria (PB) counts were determined by standard methods. A 3-alternative forced choice test (3-AFC) protocol with 31 volunteers was used to detect sensory differences between samples, and 67 Hispanic consumers rated their liking of the cheeses. Results: Combinations of nisin and caprylic acid rapidly reduced the initial count (3.5 log CFU/g) of L. monocytogenes in cheese samples to almost undetectable levels (< 2 log CFU/g) and its count rarely reached 2 log CFU/g or greater during storage. Cheese with nisin and CA had significantly less APC and LAB counts than control samples. Panelists distinguished differences between treated and control samples, but those differences did not appear to have a marked impact on acceptance by queso fresco consumers. Significance: These results indicated that combinations of nisin and CA can be effective treatments to control L. monocytogenes in queso fresco, with little impact on product quality. This treatment may contribute to prevention of future listeriosis cases. P3-05 Evaluation of 3M™ Petrifilm™ Aerobic Count Plate for Enumerating Psychrotrophic Microorganisms in Dairy Products ADRIANA R. TASSINARI, Katia Leani O. Souza, Maria Teresa Destro, Bernadette G. Franco and Mariza Landgraf 3M do Brasil Ltda, Microbiology, Sumare, Brazil Introduction: Traditional methodologies used for enumeration of psychrotrophic microorganisms in food are time consuming, usually taking up to 10 days. There are very few studies suggesting the reduction of this time by increasing incubation temperatures; however, one of these suggestions, found at American Public Health Association [APHA], uses the combination of 25 h at 21°C for milk and cream. 3M™ Petrifilm™ Aerobic Count [AC] Plates have been designed to be used in the enumeration of mesophilic microorganisms, but to date, there has been little published data for enumeration of psychrotrophs. Purpose: This study was initiated to evaluate the efficacy of incubation for 25 h at 21°C for the enumeration of psychrotrophs in naturally contaminated dairy product samples, and to verify the usefulness of the AC plate under these conditions. Abstract Book — 149 Poster

IAFP 2009 Program Book and Abstract Book

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