1.3 Detection methods
The new regulation on food stuffs ('Lebensmittelgesetzgebung')
that became effective in Switzerland stipulates that all food
stuffs, food additives and processing aids that are derived
from or which contain GMOs require premarket approval (Article
15, LMV) and must be labelled as 'GVO-Erzeugnis' (GMO-product)
according to Articles 22k and 23, 'Lebensmittelverordnung' (LMV).
Products exempt from the labelling requirement need to be free
of the GMO itself and must have been purified from the (transgenic)
DNA (e.g. chemically defined substances like sugar). The novel
food regulations under discussion within the EC commission will
basically require labelling of GMO products if they are distinguishable
from conventional products by scientific methods.
All GMOs that are used in food stuffs in the United Kingdom have
to be approved by the ACNFP (Advisory Committee on Novel Foods
and Processes). The British FAC (Food Advisory Committee) has
developed a classification system that should be helpful in deciding
whether labelling of a product is necessary or desirable (Atkins
et al., 1992; Teuber, 1993):
- Nature-identical food products of genetically modified organisms:
foods that are the product of, or which contain products of a
GMO (but not the organism itself, its cells or DNA) and are identical
to products from conventional organisms traditionally consumed
(e.g. chymosin). The FAC concluded that labelling of chymosin
or cheese produced with it is not required.
- Foods containing recombinant DNA which were produced by introducing
genes only from the gene pool of its own species (self-cloning);
e.g. bakers' and brewers' yeast that have been approved in the
United Kingdom (Table 4, page 17). Again, the committee considered
labelling not to be absolutely necessary, but recommended a case-by-case
- Novel foods derived from GMOs but which contain neither the
GMO itself nor its cells nor DNA and which differ from products
conventionally consumed in Western Europe. Labelling of such products
- Foods containing recombinant DNA (or the GMO or its cells)
which were produced by introducing genes from the gene pool of
a different species. Labelling of such products may be required,
but the committee favoured a case-by-case examination.
The ongoing globalisation of trade is also affecting the food
sector. It is plausible that genetically engineered crops approved
only in foreign countries will make their way to the local market,
especially when the respective country is a major producer of
the crop. Current examples are the herbicide-tolerant soybean
(Roundup Ready, RR) from Monsanto and products from it or
insect-resistant corn from CIBA-GEIGY that arrived in Switzerland
and the EC, respectively, before approval of these products was
granted (Butler, 1996). The soybean has by now been approved for
food use in the United States, the European Community, Canada,
the United Kingdom, the Netherlands, Japan, Switzerland, Mexico
and Argentina. In the US, which is the main export country for
soybeans worldwide, no special labelling of the genetically engineered
soybean or products derived from it is required. Within the US
for the year 1996, RR soybeans have mostly been processed indiscriminately
from conventional soybean varieties. Some processing companies
such as Central Soya Co. (Fort Wayne, Indiana) apparently intended
to separate their products according to the soybean source (Wadman,
1996), but the bulk of the 1996 soybean harvest was not separated
and may contain up to 1-2 % genetically modified soybeans.
The observed relative ease with which genetically modified products
cross borders should be an added impetus for the EC and Swiss
authorities to develop adequate methodology for identifying GMOs
in food stuffs. This will facilitate controlling the adherence
to the respective regulatory guidelines. Accurate labelling would
also be an information service to consumers who want to exercise
their freedom of choice in the market place. In the past months
control authorities, trade and consumer organisations, as well
as groups such as Greenpeace, have shown increasing interest in
the development and increased availability of specific identification
methods for GMO-products. A recently founded company in Iowa,
USA provides analyses of predominantly raw, unprocessed food for
approximately $ 450 per sample (Sept. 1996). It was reported that
there has been tremendous interest in the analyses of the company
In contrast, there is only a very limited number of published
detection methods designed to identify approved genetically modified
food products such as the Flavr Savr tomato (Meyer, 1995a,b).
Development of proper product identification methods is made difficult
by the lack of specific information on the precise genetic changes
differentiating genetically engineered products from their conventional
counterparts. Therefore, it is not surprising that reviews published
within the last few years mainly discuss theoretical aspects dealing
with the identification of genetically engineered food products
(Bähler, 1994; Schulze, 1994; Hammes and Hertel, 1995; Engel
et al., 1995) or focus on the state-of-the-art in transgenic plant
research (Niederhauser et al., 1996).
One central objective of this paper is to review published methods
that have been designed for identifying genetically engineered
foods and methods which may be relevant for the design of new
methods. Information has been gathered from:
- Methods which have been (or soon will be) validated and published
in official collections of methods for the identification of products
in food derived from or consisting of GMOs.
- Methods which have been (or soon will be) published in scientific
journals for the identification of food products consisting of
or derived from GMOs.
- Publications in scientific journals describing the detection
of GMOs (mostly microorganisms) in the environment.
- Articles in scientific journals describing the identification
of DNA sequences or gene products that are also present as transgenes
or respective translation products in approved GMOs.
- Publications from the area of food science (e.g. authenticity
testing) containing information on the applicability of DNA-based
methods for the analysis of processed foods.
- Methods for detection of pathogens in food; methods in clinical
or veterinary diagnostics and other relevant areas.
- Highly specialised reports (e.g. annual reports from food
control authorities) covering the detection of GMOs in food that
are unavailable in common databases.
- Ongoing research projects concerning the detection or monitoring
The following compilation includes methods based on the detection
of proteins as well as RNA- (NASBA) and DNA-based amplification
techniques such as polymerase chain reaction (PCR), ligase chain
reaction (LCR), Q-beta-replicase. The main focus is on DNA-based methods,
in particular PCR, which represents the state-of-the-art technique for GMO
detection in food. PCR combines high specificity with wide applicability
with respect to the nature of the sample and suitability for laboratory
diagnostics. Therefore, this report will also consider several
articles dealing with specific problems which may arise when applying
PCR for the analysis of food stuffs, and several approaches to
prevent or counteract these problems.