Preliminary observations on bacteriological quality of fresh N.C. blue crab meat

[From the U.S. Government Printing Office, www.gpo.gov]

PRELIMINARY OBSERVATIONS ON BACTERIOLOGICAL QUALITY

OF FRESH N. C. BLUE CRAB MEAT

Special Scientific Report No. 6

North. Carolina Department of Conservation & Developm.ent
Division of Commercial Fisheries
Raleigh, North Carolina

October, 1965

QR
118
P7
1965

PRELIMINARY OBSERVATIONS ON BACTERIOLOGICAL QUALITY

OF FRESH N. C. BLUE CRAB MEAT"

F. F. Busta, Joyce B. Moore, F. B. Thomas, and W. A. B. Thomson*
Department of Food Science, North Carolina State University, Raleigh,
North Carolina

Relatively little information is available on the bacteriology
of fresh crab meat from the Atlantic blue crab (Callinectes sapidus)
as it is delivered to the consumer, and none is available on crab
meat processed in North Carolina. Furthermor-e, information on pro,-
cedures and methods for the evaluation of the bacteriological qu,ality
is exceptionally limited. In order to propose standards for quality
control or regulation, data had to be obtained on the present
bacteriological condition of the North Carolina product. In addition,
projected studies on pasteurization of crab meat necessitated the
selection of adequate procedures and the evaluation of the raw
material. Therefore, a project was initiated to select suitable
methods for the bacteriological analyses of crab meat products and
to determine the levels of bacterial populations in the fresh pro-
duct immediately after processing and during refrigerated storage.

Table 1. Influence of sampling on apparent bacteriological quality
of fresh crab meat. Crabs processed on same day, cans selected at
random, total colony count obtained with Plate Count Agar at 250C.

Position of Crab Meat 4
in Container Counts x 10 /q
Can I Can 2 Can 3-

Top 3.9 2.9 17
Center 3.6 2.3 13
Bottom 3.7 2.7 12

*Presented by F. B. Thomas at 10th Annual Atlantic Fisheries
Technological Conference, Charlottetown, Prince Edward Island,
Canada, October 3 - 6, 1965.

**Distribution of this report does not constitute publication. The
data contained herein are preliminary and are subject to correction
and/or revision.

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Table I presents data indica-ting the influence of sampling
on the apparent bacteriological quality of fresh crab meat. Three
one pound containers were selected at random at one processing
plant three areas within the container Were sampled. These counts
were obtained by blending 50 grams of fresh crab meat with 3%
NaCl diluent and making serial dilutions with the same dilue-nt.
Previous studies in our laboratory had indicated that blending
of the sample resulted in higher counts than those obtained when
the crab meat was dispersed in the diluent by shaking with glass
beads. Also, previous studies suggested that when NaCl solution,
phosphate buffer, and distilled water were compared, diluent had
little or no effect on subsequent counts. Bacto-Plate Count Agar
(Difco) was used as the plating medium and the plates were in-
cubated at 250C for 7 days after which time additional incubation
did not increase counts. Incubation at 320C consistently re-
sulted in counts that were lower than those obtained,at 250C.
These data presented in this table indicate that total colony
counts obtained from selected areas within a given container were
essentially equal; however, considerable variation was observed
among counts obtained from each container.

Table 2. Apparent bacteriological quality of several grades of
crab meat. Crab processed on same day, cans selected at random,
total colony count obtained with Plate Count Agar at 250C.

GRAD�
Count x 10 /g

Sampling Backfin (lump) S@ecial (Flake) Claw

1 7.3 24 4.3
2 5.0 27 10
3 4.0 15 7.5
4 5.0 14 25
5 3.5 19
6 3.6 6.0

Table 2 shows the variation in total colony counts among
types or grades of crab meat. Each sampling was made on products
from a selected plant on a specific day in an attempt to obtain
samples of all three types of crab meat from one batch of crabs
processed under similar conditions. Backfin or lump grade con-
sistenily had the lowest total count and special grade (white,
regular, or flake) generally had the highest total count. Back-
fin meat can be removed from the crab in one piece, but special
meat is removed in many pieces, and we feel that the additional
handling contributes to the higher bacterial counts. Variation
in claw meat count can be attributed to the variation in manual
dexterity among pickers.

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Table 3. Influence of source and season on total colony count
on fresh N. C. Blue Crab Meat (special grade) obtained with
Plate Count Agar at 250C.

Plant Month Total colony count x 10
fresh crab meat

A Jan. 0.92
May 1. 1
June 0.57
June 3.9. 2.6, 14.
Aug. 3.8

B Feb. 2.4
Mar. 1.4
Apr. 2.0

C Mar. 1.6
Apr. 1 . 1

D May 4.7
June 13

Table 3 indicates the influence of source and season on
the total bacterial count observed in samples of fresh crab
meat obtained from several plants during several months of 1965.
No count from a given plant was unusually high or low; however,
the counts from samples of Plant A generally were lower than
the average. Subjective evaluation of the sanitation program
at this plant suggested little room for improvement. The counts
from samples of Plant D generally were higher and in turn,
evaluation of sanitation at Plant D indicated considerable room
for improvement.

Aside from cleanliness, in-plant handling practices were
noted to vary widely. Often when large amounts of cooked and
cooled crabs were placed on the picking tables some individual
crabs could be left at elevated temperatures for extended
periods of time. This condition would lead to higher bacterial
counts than normal. With a rapid turn-over of cooked crabs
bacterial counts could be lowered appreciably.

Figure 1. (Place count per gram versus Storage time). As
expected, increases in total counts were observed during re-
frigerated storage of fresh samples. When total colony counts
approached 109 per gram, after 13 days storage, the crab meat
was completely unacceptable for consumption. These data indicate
that the crab meat is sufficiently contaminated with psychrophilic
organisms to limit refrigerated storage to not more than two
w e e k s .

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When plating media were evaluated during the study, Plate
Count Agar was found to be inadequate for the enumeration of
psychrophilic organisms which had proliferated on the crab meat,
and '.Tryoticase Soy Agar (BBL) was. found to be the most pro-
ductive of several which were investigated. Other media that
were studied included nutrient agar fortified with glucose and
minerals, glucose minimal salts medium, and crab infusion agar
formulated in our laboratory. (Table 4.)

Figure 2. (Plate count per gram on Two Media versus Storage
time.) This figure presents data on samples stored at 30C up to
10 days. The total population was determined by colony count
with either Plate Count Agar or Trypticase Soy Agar. Each point
represents an average of counts from the number of samples in-
dicated at the top of the figure. Initially, counts at 250C on
either medium were essentially the same. However, as the period
of storage progressed and the psychrophilic organisms increased
in number, the Trypticase Soy Agar enumerated two to four times
as many organisms as were observed with the other medium. Although
Plate Count Agar initially appeared to be adequate, evaluations
of stored samples of crab meat indicated that Trypticase Soy
Agar was the medium of choice.

Figure 3. (Effect of Incubation temperature with Two Media.)
Counts of organisms that had grown at 30C and that were enumerated
at 250C with Trypticase Soy Agar exceeded counts at 250C with
Plate Count Agar. As can be seen in this figure, differences in
counts obtained at 60C with the two,media were even greater than
the differences observed with 250C incubation. Again, on fresh
samples both media were equally productive at 60 or 250C. The
reasons for the enhanced colony formation on Trypticase Soy Agar
are not readily evident, but additional study may illucidate the
specific nature of the psychrophiles which allows them to grow
more readily on the medium without glucose.

Regardless of the reason for the differential in count on
the two media, this differential may prove to be an excellent
tool for the evaluation of the freshness of blue crab meat and
other seafoods since this difference in counts appears after
storage and increases with storage time.

Admittedly methods employing counts at 25 C requiring in-
cubations for at least three days do not lend themselves to
routine production evaluations. Nevertheless, these methods not
only could be used in evaluation samples on a long term basis,
but also should prove valuable as a research tool in studies
on pasteurization of crab meat.

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1010

PLATE 107
COUNT

PER
GRAM 106

104

10 3.
0 12 18

STORAGE TIME (DAYS) AT 30C

FIGURE I

Plate Count per gram versus storage time

NUMBER OF SAMPLES

10 5 4 7 2

X TRYPTICASE SOY AGAR

10 0 PLATE COUNT AGAR

7
10
PLATE

,COUNT

PER 6
10
GRAM

5,
10

104 0

3
10
6@4 2@ 4 6 8 .10

STORAGE TIME (DAYS) AT 3C

FIGURE 2

Plate count per gram on Two Media ve rsus
storage time.
0

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9
10

THYPTICASE SOY AGAR

PLATE COUNT AGAR

107

PLATE 10
COUNT 25@C

PER

GRAM 10

4
10

2 5-@*

ONE SEVEN

STORAGE TIME (DAYS) AT 3 C

FIGURE 3.
1@x

Effect of Incubation temperature with Two Media

Table 4.
MEDIA USED FOR CRAB MEAT STUDIES

Plate Count Agar

(1) Bacto-Beef Extract -------------- 3g.
(2) Bacto-Peptone ------------------- 5g.
(3) Bacto Agar ---------------------- 159.

Trypticase Soy Agar

(1) Trypticase (B-B-L Pancreatic-
Digest of Casein) --------------- 15g.
(2) Phytone (B-B-L Soy Peptone) ----- 5g.
(3) Sodium Chloride ----------------- 5g.
(4) Agar ---------------------------- 15g.

Fortified Nutrient Agar
g./l.

(1) Nutrient Agar ------------- ----- 23g.
(2) Agar ----------------------------- 5g.
(3) NaCl ---------------------------- 8g.
(4) Glucose ------------------------- 0.1g.
(5) CaC12 ---------------------------- 0.08g.
(6) Gb1 minerals -------------------- 100 ml.
(7) H20 ------------------------------ 800 Mi.

Minimal Salts
g. /1.
(1) K HPO 4------- --- 7.0g.
(2) K92PO4 --------------------------- 3.09.
(3) Na citrate 2H 20 ----------------- 0.1g.

Solution A
(4) Mg S04.7H 20 --------------------- O.lg
(5) (NH4) 2SO4 ----------------------- - 1-09-
(6) Agar ---------------------------- 15.0g.
(7) Dist. H 2 0 ----------------------- 900 ml.
(1) Glucose ------------------------- 2g. Solution B
(2) Dist. H 2 0 ----------------------- 100 m

Add 10 ml. solu. B to solu. A before p1atin,g'

Crab Infusion Aqa@ r

(1) 200 g. crab meat + 500 ml. H 20
(2) Steam 1 hr.
(3) Filter
(4) 'Add 15g. agar & make up to I l4ter
(5) Add 10 g. NaCl
(6) Dispense
(7) Autoclave
(8) Store in refrigerator until needed

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