Introduction
Food sampling is a process used to
check that a food is safe and it does not contain harmful contaminants, or
it contains only permitted additives at acceptable levels, or it
contains the right levels of key ingredients and its label declarations are
correct, or to know the levels of nutrients present. Food analysis is
carried out by exposing the food product to a chemical analysis. Analysis may
be undertaken by or on behalf of a manufacturer regarding their own product, or
for official food law enforcement or control purposes, or for research or
public information. To undertake any analysis, unless the whole amount of food
to be considered is very small so that the food can be used for testing in its
entirety, it is usually necessary for a portion of it to be taken (e.g. a small
quantity from a full production batch, or a portion of what is on sale in a
shop) – this process is known as food sampling.
In most cases, food to be analyzed are
having two levels of sampling – the first being selection of a portion from the
whole, which is then submitted to a laboratory for testing and the second being
the laboratory’s taking of the individual amounts necessary for individual
tests that may be applied. It is the former that is ‘food sampling’: the latter
is analytical laboratory ‘sub-sampling’, often relying upon initial
homogenization of the entire submitted sample. Where it is intended that the
results of any analysis to relate to the food as a whole it is crucially important
that the sample is representative of that whole – and the results of any
analysis can only be meaningful if the sampling is undertaken effectively. This
is true whether the ‘whole’ is a manufacturer’s entire production batch, or
where it is a single item but too large to all be used for the test. Factors
relevant in considering the representativeness of a sample include the
homogeneity of the food, the relative sizes of the sample to be taken and the
whole, the potential degree of variation of the parameter(s) in question
through the whole, and the significance and intended use of the analytical
result.
Food analysis is the discipline dealing
with the development, application and study of analytical procedures for
characterizing the properties of foods and their constituents. These analytical
procedures are used to provide information about a wide variety of different
characteristics of foods, including their composition, structure,
physicochemical properties and sensory attributes. This information is critical
to rational understanding of the factors that determine the properties of
foods, as well as the ability to economically produce foods that are
consistently safe, nutritious and desirable and for consumers to make informed
choices about their diet. The objective is to review the basic principles
of the analytical procedures commonly used to analyze foods and to discuss
their application to specific food components, e.g. lipids, proteins,
water, carbohydrates and minerals.
Sampling
The adequacy and condition of the sample or
specimen received for examination are of primary importance. If samples are
improperly collected and mishandled or are not representative of the sampled
lot, the laboratory results will be meaningless. Because interpretations about
a large consignment of food are based on a relatively small sample of the lot,
established sampling procedures must be applied uniformly. A representative
sample is essential when pathogens or toxins are sparsely distributed within
the food or when disposal of a food shipment depends on the demonstrated
bacterial content in relation to a legal standard. The number of units that
comprise a representative sample from a designated lot of a food product must
be statistically significant. The composition and nature of each lot affects
the homogeneity and uniformity of the total sample mass. The proper statistical
sampling procedure, according to whether the food is solid, semisolid, viscous,
or liquid, must be determined by the collector at the time of sampling by
considering the product is being sampled.
Whenever possible, submit
samples to the laboratory in the original unopened containers. If products are
in bulk or in containers too large for submission to the laboratory, transfer
representative portions to sterile containers under aseptic conditions. There
can be no compromise in the use of sterile sampling equipment and the use of
aseptic technique. Sterilize one-piece stainless steel spoons, forceps,
spatulas, and scissors in an autoclave or dry-heat oven. Use of a propane torch
or dipping the instrument in alcohol and igniting is dangerous and may be
inadequate for sterilizing equipment. Use containers that are clean, dry,
leak-proof, wide-mouthed, sterile, and of a size suitable for samples of the
product. Containers such as plastic jars or metal cans that are leak-proof may
be hermetically sealed. Whenever possible, avoid glass containers, which may
break and contaminate the food product. For dry materials, use sterile metal
boxes, cans, bags, or packets with suitable closures. Sterile plastic bags (for
dry, unfrozen materials only) or plastic bottles are useful containers for line
samples. Take care not to overfill bags or permit puncture by wire closure.
Identify each sample unit (defined later) with a properly marked strip of
masking tape. Do not use a felt pen on plastic because the ink might penetrate
the container. Whenever possible, obtain at least 100 g for each sample unit.
Submit open and closed controls of sterile containers with the sample.
Deliver samples to the laboratory promptly with the
original storage conditions maintained as nearly as possible. When collecting
liquid samples, take an additional sample as a temperature control. Check the
temperature of the control sample at the time of collection and on receipt at
the laboratory. Make a record for all samples of the times and dates of
collection and of arrival at the laboratory. Dry or canned foods that are not
perishable and are collected at ambient temperatures need not be refrigerated.
Transport frozen or refrigerated products in approved insulated containers of
rigid construction so that they will arrive at the laboratory unchanged.
Collect frozen samples in pre-chilled containers. Place containers in a freezer
long enough to chill them thoroughly. Keep frozen samples solidly frozen at all
times. Cool refrigerated samples, except shellfish and shell stock, in ice at
0-4°C and transport them in a sample chest with suitable refrigerant capable of
maintaining the sample at 0-4°C until arrival at the laboratory. Do not freeze
refrigerated products. Unless otherwise specified, refrigerated samples should
not be analyzed more than 36 h after collection. Special conditions apply to
the collection and storage of shucked, unfrozen shellfish and shell stock. Pack
samples of shucked shellfish immediately in crushed ice (no temperature
specified) until analyzed; keep shell stock above freezing but below 10C.
Examine refrigerated shellfish and shell stock within 6 h of collection but in
no case more than 24 h after collection.
No comments:
Post a Comment