Bacteria that were the most sensitive to propionic acid, benzoic acid, and sorbic
acid were used to determine MIC of preservatives in unprocessed animal products
(eggs, chicken breast, chicken legs, pork ribs, pork sirloin, beef ribs, beef
chunk, and milk) and processed animal products (processed butter, ground meat
product, natural cheese, and smoked eggs). The selected bacteria were
Campylobacter coli ATCC33559, Campylobacter
jejuni ATCC33560, Erwinia carotovora KCCM11319,
Micrococcus luteus KCCM11211, and Moraxella
catarrhalis KCCM42707. A mixture of the bacteria was prepared
according to the procedure described in the section of ‘Inoculum
preparation’. Inoculum 0.1 mL was inoculated to 25 g of food sample in a
sample bag to obtain a concentration of 4 Log CFU/g. A hundred microliters of
the preservatives were then spiked in samples to have 0, 100, 500, 1,000, and
1,500 (1,200 ppm for sorbic acid) ppm. Pork ribs, pork loin, beef ribs, beef
chunks, milk, processed butter, fermented milk, and natural cheese were stored
at 10°C. Poultry and processed meat products were stored at 5°C,
and smoked eggs were stored at 25°C. The sample (25 g) was aseptically
transferred to a sample bag containing 225 mL of buffered peptone water (BPW;
Becton Dickinson, Sparks, MD, USA), and the sample was pummeled for 60 s in a
pummeler (BagMixer® 400, Interscience, Saint Nom la Bretehe,
France). One milliliter of the homogenate was serially diluted with BPW, and the
homogenates were dispensed on an aerobic bacteria count plate (AC Petrifilm;
3MTM Petrifilm aerobic count plate, 3M, St. Paul, MN, USA) to
quantify the total bacteria. The AC Petrifilms were incubated at 35°C for
48 h, and the colonies were then manually counted. The end time of the storage
was determined as the time when the bacterial cell counts in the 0-ppm sample
increased to 6 Log CFU/g. This experiment was repeated three times. The
bacterial cell counts for each concentration of preservatives at the end of the
storage were compared to the cell counts on day 0. This comparison was conducted
by pairwise t-test at α=0.05 with the general linear model
procedure (proc glm) of SAS® (ver.9.4, SAS Institute, Cary,
NC, USA). If the difference was not significant, the concentration was
determined as MIC per each replication. Among the MIC of 3 replications, the
lowest MIC was determined as a final MIC.
acid were used to determine MIC of preservatives in unprocessed animal products
(eggs, chicken breast, chicken legs, pork ribs, pork sirloin, beef ribs, beef
chunk, and milk) and processed animal products (processed butter, ground meat
product, natural cheese, and smoked eggs). The selected bacteria were
Campylobacter coli ATCC33559, Campylobacter
jejuni ATCC33560, Erwinia carotovora KCCM11319,
Micrococcus luteus KCCM11211, and Moraxella
catarrhalis KCCM42707. A mixture of the bacteria was prepared
according to the procedure described in the section of ‘Inoculum
preparation’. Inoculum 0.1 mL was inoculated to 25 g of food sample in a
sample bag to obtain a concentration of 4 Log CFU/g. A hundred microliters of
the preservatives were then spiked in samples to have 0, 100, 500, 1,000, and
1,500 (1,200 ppm for sorbic acid) ppm. Pork ribs, pork loin, beef ribs, beef
chunks, milk, processed butter, fermented milk, and natural cheese were stored
at 10°C. Poultry and processed meat products were stored at 5°C,
and smoked eggs were stored at 25°C. The sample (25 g) was aseptically
transferred to a sample bag containing 225 mL of buffered peptone water (BPW;
Becton Dickinson, Sparks, MD, USA), and the sample was pummeled for 60 s in a
pummeler (BagMixer® 400, Interscience, Saint Nom la Bretehe,
France). One milliliter of the homogenate was serially diluted with BPW, and the
homogenates were dispensed on an aerobic bacteria count plate (AC Petrifilm;
3MTM Petrifilm aerobic count plate, 3M, St. Paul, MN, USA) to
quantify the total bacteria. The AC Petrifilms were incubated at 35°C for
48 h, and the colonies were then manually counted. The end time of the storage
was determined as the time when the bacterial cell counts in the 0-ppm sample
increased to 6 Log CFU/g. This experiment was repeated three times. The
bacterial cell counts for each concentration of preservatives at the end of the
storage were compared to the cell counts on day 0. This comparison was conducted
by pairwise t-test at α=0.05 with the general linear model
procedure (proc glm) of SAS® (ver.9.4, SAS Institute, Cary,
NC, USA). If the difference was not significant, the concentration was
determined as MIC per each replication. Among the MIC of 3 replications, the
lowest MIC was determined as a final MIC.
