Principles of Food Sanitation

Modifications of the contact plate method
include the agar slice (syringe extrusion and
agar sausage) and the use of selective and
differential media. Another assay technique
is the impression method. This technique
involves a piece of sterile cellophane tape,
which functions as a replicator to transfer cells
to a growth-support agar, with subsequent
incubation and counting. This approach
serves as only an approximate representation
of the contamination and does not distinguish
between particulate contamination containing
one cell or more.

Surface Rinse Method

This method uses elution of contamination
by rinsing to permit a microbial assay of the
resultant suspension. A sterile fluid is manu-
ally or mechanically agitated over an entire
surface. The rinse fluid is then diluted and
subsequently plated. When applicable, it is
more precise than the swab method because a
larger surface can be tested. The membrane
filter is an aid to the surface rinse method if
contamination is not excessive. The mem-
brane, bearing microorganisms, can be incu-
bated on a nutrient pad, stained in 4 to
6 hours, and examined under a microscope
with 8×to 100×magnification. Although the
surface rinse method is more accurate and
precise than the direct contact method and
has a higher recovery rate (approximately
70%) and the flexibility of interfacing with the
membrane fiber, it is restricted to horizontal
surfaces and usually limited to container type
equipment.

Direct Surface Agar Plating
(DSAP) Technique
This technique has utility for examining
contamination on surfaces in situ. Eating
utensils may be tested through pouring a
melted medium into a cup and allowing the
agar to solidify. The agar is transferred asep-
tically to sterile culture plates, with subse-

quent over-layering and incubation. The

agar slab may be protected by a cover and

counted after 28 to 48 hours.

Interpretation of Data from QA Tests

Microbial tests to evaluate hygienic condi-

tions of equipment and foodstuffs are dis-

cussed in Chapter 3. Additional information

on the tests that can be performed, is dis-

cussed in the following paragraphs.

Importance of a Monitoring Program

A monitoring program should be estab-

lished and implemented to provide an inter-

nal method of evaluating the overall

wholesomeness of the finished product and

the degree of sanitation. The main purpose

is to avoid problems related to product safety

and acceptability. The development of a pro-

gram should include determination of objec-

tives, techniques, and evaluation procedures.

In testing, the overall effectiveness of sanita-

tion-not just the quantification of microor-

ganisms on food-contact surfaces-should be

considered.

Products and surfaces to be tested should

be determined by type of products pro-

duced, production steps, and the importance

of the designated surface to sanitation prac-

tices and to the safety and/or overall accept-

ability of the food product. The monitoring

program should be based on desired accu-

racy, time requirements, and costs. The type

of food-contact surface to be tested should

also be considered in determination of the

monitoring technique.

To reduce the possibility of incorrect

interpretation of results, the monitoring pro-

gram should be designed so that data can be

statistically analyzed. Further misunder-

standing can be avoided through a thorough

comprehension of the benefits and limita-

tions of the test procedures-for example, rec-

ognizing that bacterial clumps from the

contact method of sampling should yield

Quality Assurance for Sanitation 127