Undergraduate laboratory exercises specific to food spoilage microbiology

Food spoilage has an enormous economic impact, and microbial food spoilage plays a significant role in food waste and loss; subsequently, an equally significant portion of undergraduate food microbiology instruction should be dedicated to spoilage microbiology. Here, we describe a set of undergraduate microbiology laboratory exercises that focus specifically on food spoilage which were taught in 2 lab periods as part of the undergraduate food microbiology lab curriculum at Cornell University. The lab was broken down into 3 exercises. Two exercises lead students to determine the likely source of contamination in a canned salsa through (exercise 1a) plating and observation of colony morphology and (exercise 1b) determination of the thermal resistance for those isolates. The final exercise (2) involved detection of the spoilage bacterium Alicyclobacillus in apple juice. Spoiled juice demonstrations were also prepared in this exercise for students to observe sensorial changes resulting from spoilage, emphasizing that spoilage is not always visually detectable. Students were able to successfully determine the source of contamination based on the results of their laboratory findings, which they used to make recommendations for production to reduce microbial food spoilage in the canned salsa product. Based on student answers to discussion questions provided following lab exercises, participants were able to (a) identify the significance of microbial spoilage and how spoilage is principally different from food safety, (b) describe varying sensorial changes associated with microbial spoilage, and (c) employ methods and analysis to evaluate sources and type of contamination. Downloadable handouts and stepwise instructions are available as supporting information.