Food Protection Trends - September/October 2021 - 477

rice flour, and soybean flour (14, 30, 32, 34), as has suspected
contamination of flour with pathogenic E. coli (8, 33). Thus,
the lethality of cooking methods used to prepare dry pasta
products for consumption warrants assessment.
One product parameter that may substantially impact
the lethality of a cooking method is the water activity of the
product. In general, a decrease in the heat resistance of
S. enterica and pathogenic E. coli is observed as water activity
increases (1, 9, 15, 24, 25, 28). At low water activities,
S. enterica is extremely resistant to heat in general (13, 23)
and when compared with the heat resistance of pathogenic
E. coli (11, 16, 24). Conversely, S. enterica and pathogenic
E. coli are typically readily destroyed by heat in high-wateractivity
matrices (26). During cooking, dry pasta products
become hydrated as they are exposed to heat, transitioning
the water activity of the product from low (<0.70) to high
(>0.97). The dynamic nature of the water activity of dry
pasta as it cooks makes the level of lethality delivered of the
cooking process difficult to predict. Therefore, in this study,
the fate of S. enterica and pathogenic E. coli was determined in
representative dry pasta products when exposed to common
cooking methods: microwave cooking of elbow noodles,
stovetop cooking of flat noodles, and baking of no-boil
lasagna noodles as part of lasagna.
MATERIALS AND METHODS
Pasta ingredients and pasta-making equipment
Enriched durum flour and whole egg powder were provided
by the manufacturer (Zerega's Sons, Inc., Fair Lawn, NJ).
Food coloring, low-moisture shredded mozzarella, shredded
Parmesan cheese, eggs, and spaghetti sauce were purchased
from a local grocery store, and municipal water was used as an
ingredient and in the microwave cooking and stovetop cooking
methods. The National Pasta Association (NPA; Washington,
D.C.) provided elbow noodles, flat noodles, and no-boil lasagna
noodles (both noodles that were commercially available and
noodles produced exclusively for the study), microwave cups
(cup dimensions: 7.62 cm, tall; 7.62 cm, bottom diameter; 10.16
cm, top diameter), and a powdered antifoaming agent.
A stand mixer (KitchenAid®, Benton Harbor, MI) was
used to combine the pasta ingredients into dough. The NPA
provided equipment custom made for the bench-top extrusion
and drying of three pasta products: elbow noodles, flat
noodles, and no-boil lasagna noodles. The equipment included
a pasta press (hand crank), three pasta dies, and a pasta dryer.
Pasta-cooking equipment
Two 1,100-W microwave ovens were purchased from
a local store to deliver the microwave cooking treatment.
The actual power output (in Watts) of the microwaves
was determined using the International Electrotechnical
Commission method IEC 60705 ed. 3.2, 2006. The first
microwave (1.1 cu ft, model FFCM1134LS; Frigidaire;
Charlotte, NC) was used to treat the S. enterica-inoculated
elbow noodles and had an average power output of 720 ± 25
W (n = 6; data not shown). The second microwave (1.1 cu ft,
model OGZJ1104; Oster, Boca Raton, FL) was used to treat
the pathogenic E. coli-inoculated elbow noodles and had an
average power output of 736 ± 3 W (n = 3; data not shown).
An electric four-burner GE® range (model JB700SJ2SS;
General Electric, Louisville, KY) was used to deliver the
stovetop cooking treatment and the baking treatment to the
flat noodles and no-boil lasagna noodles, respectively.
Pathogenic organisms and preparation of inoculum
cocktails
In total, four strains of S. enterica and five strains of
pathogenic E. coli were included in the study. S. enterica
serotypes Agona (ATCC BAA 707; isolation: plant, 1996),
Typhimurium (ATCC 13311; isolation: food poisoning, feces,
human, 1911), Senftenberg (ATCC 43845; 775W; isolation:
no information provided), and Tennessee (ATCC 10722;
isolation: no information provided); and E. coli O104:H4
(ATCC BAA 2309; isolation: human stool, Republic of
Georgia, patient exhibited hemolytic uremic syndrome, May
2011) and E. coli O111:H8 (ATCC BAA 184; isolation:
diarrheal human stool, South Dakota, 2000) were obtained
from the American Type Culture Collection (Manassas,
VA). E. coli O121 (NFPA 4226; isolation: flour/flour-based
outbreak, 2016) and two strains of E. coli O157:H7 (NFPA
4200 isolation: hamburger isolate/Jack-in-the-Box outbreak
and NFPA 4217, USDA RM1913; isolation: patient isolate,
lettuce outbreak) were obtained from the Eurofins Culture
Collection (Fresno, CA). All strains were maintained as frozen
stock at −70°C for long-term storage.
Multistrain cocktails of S. enterica and pathogenic E. coli
were prepared according to a method adapted from Danyluk
et al. (10) and Blessington et al. (3). In brief, each strain
was streaked from frozen stock onto tryptic soy agar (TSA;
Accumedia, Lansing, MI) and incubated at 35°C for 24 to 48
h. An isolated colony of each strain was individually cultured
into tryptic soy broth (Accumedia) and incubated at 35°C
for 18 to 24 h. Aliquots of each culture were then spread onto
large prepoured TSA plates and incubated at 35°C for 24
± 2 h. After incubation, the cell lawns were harvested using
a sterile spreader and 0.1% peptone water (PW; Difco, BD,
Franklin Lakes, NJ). Harvested cells were then combined
in equal volumes by organism to produce two multistrain
inoculum cocktails-one of S. enterica and one of pathogenic
E. coli. Each inoculum cocktail was then combined with an
equivalent volume of sterile water and an aliquot of food
coloring (added to facilitate the differentiation between
inoculated and uninoculated noodles).
Preparation of inoculated dry pasta
Three types of inoculated dry pasta-elbow noodles, flat
noodles, and no-boil lasagna noodles-were produced for
the study. The methods for the preparation of each type of
September/October Food Protection Trends 477
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