Microbiological quality and safety of pizza held out of temperature control in university dining halls
Creators: name: Xu, Yanzhe
Publisher: name: No Publisher Supplied
Year: 2023

description: Pizza has become a very popular food and USDA estimates that about 13% of the US population will consume pizza on any particular day. While any food may occasionally be out of temperature control, the fraction of the time that this is true for pizza at Rutgers University is greater than for other foods. Hot food temperatures obtained from 19,754 non pizza samples and 1,336 pizza temperatures taken from dining facilities operated by Rutgers University between and 2001 and 2020. A more focused project was designed to further study the microbiology, pH and water activity of pizza, and a total of 57 pizza samples were collected for this phase of the project. Pizza was tested for total aerobic plate count, Staphylococcus aureus, Bacillus cereus, Lactic acid bacteria, coliforms and E. coli. Pizza water activity was measured using a digital aw meter Surface pH of each individual pizza component (topping, cheese, bread) was measured by using a bench-top pH meter. Predictions for the growth of four relevant pathogens, both with and without lag phase were made for select pH and water activity values identified at 20, 25 and 30 °C using ComBase. Rutgers University dining hall data show that most (approximately 90%) of foods that are not pizza are held at the appropriate temperature. It’s also true that only about 60% of all foods that are pizza are held at the appropriate temperature. At least 70% or more of all pizza sample tested contain some detectable level of microorganisms. When pizza contained detectable microorganisms, the average total aerobic plate count ranged from 2.72 log CFU/g for cheese pizza to 3.34 log CFU/g for pizza topped with vegetables. Only two pizza samples (one pepperoni, one cheese) collected contained detectable S. aureus and contained ~50 CFU/g. Two other samples contained hemolytic Gram-positive rods (B. cereus) with ~50 and 100 CFY/g and these were found on pizza with mushrooms and pizza with red onions, and bell peppers. Five pizza samples (2 cheese, 2 vegetable and 1 meat) contained coliforms with a range from 4 to 9 MPN/g and no E. coli were detected. While samples picked up at higher temperatures, tended to have a slightly lower concentration of bacteria, the correlation coefficients (R2 values) are quite low (Cheese 0.0544, Vegetarian 0.0097, Meat 0.026). Based on the pH and water activity measurements most (but not all) of the pizza samples would be considered to potentially require time temperature control for safety. When high counts occur on pizza, this is generally due to the presence of lactic acid bacteria most likely from the cheese. The modeling analysis shows that the organism most likely to pose a risk would be S. aureus, and the largest magnitude increase predicted is 0.89 log CFU at 30 °C, pH 5.52 and water activity 0.963. The overall conclusion from this analysis is that while pizza represents a theoretical risk, the actual risk would likely only manifest for pizza samples that are held out of temperature control for time periods in excess of eight hours.