Banca de DEFESA: MAYARA DOS SANTOS TAVARES

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
STUDENT : MAYARA DOS SANTOS TAVARES
DATE: 19/12/2022
TIME: 14:00
LOCAL: on line
TITLE:

Incidence of Listeria sp. and Listeria monocytogenes in ready-toeat
fish products: Correlation with the background microbiota

KEY WORDS:

Seafood, kanikama, ready-to-eat, lactic acid bacteria (LAB), Listeria.

PAGES: 79
BIG AREA: Ciências Agrárias
AREA: Ciência e Tecnologia de Alimentos
SUBÁREA: Ciência de Alimentos
SPECIALTY: Microbiologia de Alimentos
SUMMARY:

The consumption of ready-to-eat fish has grown significantly in recent years in Brazil, due to its high
nutritional value and practicality for consumption. However, a health problem becomes evident, since
ready-made products do not require heating before consumption, providing cases of listeriosis, a
disease caused by Listeria monocytogenes bacteria capable of growing under refrigeration. . This
research aimed to evaluate the incidence of Listeria sp. and L. monocytogenes in ready-to-eat fish
products with pH ≥5.0 and Aa ≥ 0.94, as established by the microbiological standards for food, as
well as to correlate with the presence of the background microbiota. Seventy-two samples of kanikama
were evaluated, with 3 subunits from the same lot analysed at 3 different times and 48 samples
of smoked and sliced salmon, with 2 subunits and two different times, collected in the city of Rio de
Janeiro and metropolitan region. The samples were examined immediately after purchasing the frozen
products, which was considered the time zero, and after 7 and 15 days of storage at 5°C for kanikama,
and after 30 days for smoked and sliced salmon, simulating the possibility of storing the
products under refrigeration in its original packaging. From the 72 kani-kama samples, 23.6% and
45.8% tested positive for Listeria sp. by the culture and PCR methods, respectively. Of the samples
that showed presumptive turquoise colonies characteristic of Listeria on ALOA agar, 12.5%
corresponded to Gram positive bacteria of interfering genera. Regarding the presence of L.
monocytogenes, 4.2% of the kani-kama samples were confirmed positive by phenotypic tests, and
29.2% by qPCR. The highest count of Listeria sp. in kani kama was observed with the brand kani 1
after 7 days of storage at 5°C with an average of 2 ± 1.1 Log CFU/g. No sample showed contamination
with L. monocytogenes above the maximum limit of 2 Log CFU/g. From 48 smoked and sliced
salmon samples, 33.3% and 56.2% tested positive for Listeria sp by culture and PCR methods,
respectively. For L. monocytogenes 10.4% were confirmed positive by phenotypic tests and 47.9%
by qPCR. Listeria sp. in salmon were significantly higher after 30 days of storage (P<0.001), and in
two of the commercial brands, the number exceeded 2 Log CFU/g. Nevertheless, for L.
monocytogenes, no sample exceeded the count of 2 Log CFU/g, which is in accordance with Brazilian
health standards. As expected, a larger population of aerobic mesophiles, psychrotrophs and lactic
acid bacteria was detected in smoked salmon compared to kani-kama. Although none of these
populations exceeded 6 Log CFU/g, the salmon was already sensory compromised. Lactic acid
bacteria population was higher in smoked salmon than in kani-kama, reaching ca 2 Log CFU/g, but
yet too low to exert any kind of interaction with L. monocytogenes. It was concluded that the PCR
technique showed greater sensitivity for the detection of Listeria sp and L. monocytogenes compared
to the traditional culture method. Although no sample of kani-kama or smoked salmon showed
numbers of L. monocytogenes greater than 2 Log CFU/g, a higher number of positive samples was
observed during refrigerated storage compared to time zero, indicating that

COMMITTEE MEMBERS:
Presidente - 359403 - ROSA HELENA LUCHESE
Interna - 3333721 - GESILENE MENDONCA DE OLIVEIRA
Externa à Instituição - KAREN SIGNORI PEREIRA - UFRJ