inoculated, bread products by themselves rarely support R. stolonifer growth, while fatty baked products (e.g., biscuits, desserts), animal products, and products with sauces, glazes, or gravy are more
likely to support growth. Our results indicate that moisture and
preservatives are likely the most important factors regulating mold
We used standard worksheets and electronic spreadsheets for both
exercises. Worksheets prompted students to list the ingredients of
their food items to the best of their ability, using online lists of
ingredients or food labels. Students would then write a hypothesis
explaining why the item would or would not allow visible mold
growth, based on the ingredients and condition of the food item
(Table 2). To help our students, we explained to them that fat,
carbohydrates, and proteins were beneficial nutrients for the
growth of all heterotrophs. Antimicrobial and preservative ingredients were also identified. Students were also able to recognize
that cooking could sterilize food items or make them too dry to
support growth (Table 2). In the screening exercise, students were
only prompted to predict the presence or absence of mycelial
growth; however, in the experiment exercise, students were
prompted to predict which item the class investigated would have
the greatest diameter of mycelial growth. This prompt allowed us
to correct vague or innacurate wording (e.g., “The [restaurant
name] burger . . . will not grow a lot of mold” or “We believe. . .”).
Each measurement was entered into a shared electronic spreadsheet, and our students used the shared data to compare items, calculate means, and draw conclusions. Students completed the
exercises by concluding whether the item was a suitable substrate
for fungal growth or not.
Student Survey & Results
In spring 2018, we assessed the exercises using a survey to determine attitudes about online information and student attitudes
related to the nutritional value of fast food. Half of our students
(10/21) reported that they ate fast food at least twice a week, and
only two students claimed to eat fast food less than once a week.
The majority of our students (14/21, 66%) were familiar with the
online stories about fast-food hamburgers, and students from both
groups were equally likely to have read them. Students who inoculated hamburgers (Group 1) were more likely to say that hamburgers decomposed after the exercises than students who inoculated
other food items (Group 2). The most common reasons students
gave for hamburgers not decomposing were “fake meat” and preservatives, and these responses were given after seeing R. stolonifer
growth. The “fake meat” response indicated that students did not
necessarily connect “fake meat” with inhibition of fungal growth,
even if the idea of “fake meat” deterred them from eating fast food.
Clearly, the “fake ingredient” claims the students had seen online
for years influenced their views. In the future, we recommend further examination of the actual content of hamburgers (Prayson
et al., 2008).
Two items on the survey prompted students to rate the nutritional values of fast food overall and of hamburgers in particular,
using a 1–10 scale. The exercises did not significantly change
how students rated the nutritional value of fast food overall or of
hamburgers (Figure 4). Group 1 assigned them lower values of
nutrition both before and after the exercises than Group 2, which
is an artifact of our sample group. Students did not associate suit-ability for R. stolonifer growth with a food’s being healthy for
humans, given that fungal growth is a far simpler variable to measure than human health. Human nutrition is associated with interactions among several complex systems.
Table 2. Examples of student hypotheses, predictions, and results. For some items, students generated
hypotheses for both presence and absence of mold growth.
Item Example Hypotheses Prediction Result
Uncooked pepperoni slice
Protein and fat facilitate
Salt, spices, and bacterial
cultures inhibit mold
Mold will grow. No mold growth.
Beef patty with cheese
Proteins and fats in both
items facilitate mold
Moisture in cheese makes
up for dry patty.
Mold will grow. Mold growth over entire patty.
French fry, no ketchup
Dry, cooked, salty exterior
inhibits mold growth.
Mold will not grow. Mold visible only at location of
fry (multiple chain
Sugar and moisture in
ketchup facilitate mold
Ketchup’s acidity inhibits
Mold will grow. No mold growth on some; mold
growth covering <50% of
surface on others.