Biomedical Engineering Reference
In-Depth Information
eaten without further cooking. The risks of bacterial contamination during process-
ing and the zero tolerance level imposed by administrations for
L. monocytogenes
in ready-to-eat seafood products strengthen the needs to apply additional preser-
vation methods. In one study, the combined effect of nisin and moderate heat on
L. monocytogenes
in cans of cold-pack lobster was investigated (Budu-Amoako
et al.
1999
). Heat processing lobster meat in the presence of nisin (25 mg/kg of can
content) at 60 °C internal temperature for 5 min achieved 3- to 5-log reductions in
L. monocytogenes
viable cell counts, whereas nisin or heat alone achieved 1- to
3-log reductions. The effect of the combined treatment was considered to be satis-
factory, since reported
L. monocytogenes
levels in the commercial product never
exceeded 10
2
CFU/g. An additional advantage was that a reduced heat process in
combination with nisin allowed a considerable reduction in drained weight loss
compared to the standard heating process used by industry.
In brined shrimp, addition of carnocin UI49 (from
C. piscicola
UI49) did not
extend the shelf life, while crude bavaricin A (a cell-free supernatant of
Lactobacillus
bavaricus
MI 401) resulted in a shelf life of 16 days, while a nisin Z preparation
extended the shelf life for 31 days (Einarsson and Lauzon
1995
). The addition of
nisin Z and bavaricin A preparations extended the product shelf-life, although the
effi cacy of bacteriocin treatments was much more limited compared to brined
shrimp stored in a benzoate-sorbate solution (Einarsson and Lauzon
1995
). It was
observed that the dominant microbiota towards the end of treatments was domi-
nated by Gram-positive bacteria in samples treated with carnocin UI49 and bavari-
cin A as well as in the untreated controls, while in the nisin Z treatment a
Gram-negative microbiota was more pronounced. In another study, it was shown
that dipping in organic acids solutions followed by vacuum packaging and chilled
storage can help reduce
L. monocytogenes
and native microbiota, but not
Salmonella
,
on fresh shrimps (Wan Norhana et al.
2012
). In that study, beheaded and peeled
fresh shrimps dipped in solutions containing nisin (500 IU/ml), EDTA (0.02 M),
potassium sorbate (PS) (3 %, w/v), sodium benzoate (SB) (3 %, w/v) or sodium
diacetate (SD) (3 %, w/v) alone or in combination were vacuum packaged and
stored at 4 °C for 7 days. Nisin-EDTA-potassium sorbate and nisin-EDTA-sodium
diacetate signifi cantly reduced
L. monocytogenes
numbers, but none of treatments
reduced
Salmonella
counts on shrimps throughout storage. Overall, the applied
treatments improved the microbiological quality of shrimps. For example, on day 7
for storage, numbers of aerobic bacteria, psychrotrophic bacteria and
Pseudomonas
on combined nisin-EDTA-salt of organic acids treated shrimps were signifi cantly
lower by 4.40-4.60, 3.50-4.01, and 3.84-3.99 log CFU/g respectively, as compared
to the control (Wan Norhana et al.
2012
).
Caviar is heat labile, and conventional pasteurization processes affect its texture,
color, and fl avor negatively. Refrigerated storage is currently the only available
means to preserve and extend the shelf life of caviar as a ready-to-eat product.
Chum salmon caviar (ikura) and sturgeon caviar were treated by immersion in
500 IU/ml nisin solution and heat processed (an 8-D process without nisin or a 4-D
process with 500 IU/ml nisin) in a radio frequency (RF; 27 MHz) heating method at
60, 63, and 65 °C (Al-Holy et al.
2004
). The combination of RF heating and nisin
