349
ability to analyze complex mixtures, giving access to a theoretically unlimited mass
range. A basic characteristic of MALDI is mixing the analyte with a suitable matrix,
followed by application of the mixture on a MALDI plate and then irradiation by a
pulsed laser. During the irradiation, the analyte and matrix molecules are ablated
and ionized. A number of substances have been tested and applied as MALDI matrices, but there are no general rules for predicting the suitability of a substance as
matrix. The most frequently used matrices are derivatives of benzoic acid, e.g.,
2,5-dihydroxybenzoic acid (2,5-DHB), and derivatives of cinnamic acid, e.g.,
α-cyano-4-hydroxycinnamic acid (CHCA) or sinapic acid (SA). Fullerenes have
also been used as matrices, whereas the first application was for laser desorption of
biomolecules involving application of protein analyte solution directly onto the predeposited fullerene film. The most widely used sample preparation method for
MALDI analysis is the dried droplet technique when a mixed solution of sample or
analyte/s and matrix is deposited onto a MALDI plate and allowed to dry and the
sandwich method where the sample is placed “in a sandwich” between two matrix
layers (Ivanova et al. 2011b; Ivanova Petropulos et al. 2014a, b).
11.9 Application of Immunochemical Methods in Food
Analysis
As one of the tests for the detection of pathogens in food based on immunological
characteristics, the enzyme-linked immunosorbent assay (ELISA) is widely used
(Crowther 1995). The method is designed to replace detection or isolation on a solid
substrate, is relatively easy to perform, can be applied to a large number of pathogens, can be semiautomatic, and gives a quick result. Depending on the needs, the
goal of this test may be to detect the genus, species, or serotype of the microorganism. However, a positive result obtained by an ELISA test must be confirmed by a
conventional test. The biggest advantage of this method is the performance of negative screening, i.e., the possibility of including a significantly larger number of samples that can be tested for the presence or absence of a certain pathogen, assuming
that there is an acceptable level of false negative results (Crowther 1995). Positive
results obtained by ELISA techniques must be confirmed by analytical techniques
such as aqueous chromatography or gas chromatography and with fluorescent,
ultraviolet, or concentrated spectrophotometric detection techniques
(Crowther 1995).
The usefulness of the ELISA method has been confirmed by many authors in
proving the types of meat and various plant proteins often used as additional
ingredients in meat production, for the detection of enrofloxacin residues in chicken
muscle and liver. Using appropriate antibodies and standards, ELISA can be used to
quantify soy proteins, pea proteins, and gluten in heat-treated products. The ELISA
method has been tested several times for the purpose of qualitative and quantitative
determination of denatured soy proteins (Crowther 1995).
11 Chemical Composition and Nutritional Properties of Functional Food
ability to analyze complex mixtures, giving access to a theoretically unlimited mass
range. A basic characteristic of MALDI is mixing the analyte with a suitable matrix,
followed by application of the mixture on a MALDI plate and then irradiation by a
pulsed laser. During the irradiation, the analyte and matrix molecules are ablated
and ionized. A number of substances have been tested and applied as MALDI matrices, but there are no general rules for predicting the suitability of a substance as
matrix. The most frequently used matrices are derivatives of benzoic acid, e.g.,
2,5-dihydroxybenzoic acid (2,5-DHB), and derivatives of cinnamic acid, e.g.,
α-cyano-4-hydroxycinnamic acid (CHCA) or sinapic acid (SA). Fullerenes have
also been used as matrices, whereas the first application was for laser desorption of
biomolecules involving application of protein analyte solution directly onto the predeposited fullerene film. The most widely used sample preparation method for
MALDI analysis is the dried droplet technique when a mixed solution of sample or
analyte/s and matrix is deposited onto a MALDI plate and allowed to dry and the
sandwich method where the sample is placed “in a sandwich” between two matrix
layers (Ivanova et al. 2011b; Ivanova Petropulos et al. 2014a, b).
11.9 Application of Immunochemical Methods in Food
Analysis
As one of the tests for the detection of pathogens in food based on immunological
characteristics, the enzyme-linked immunosorbent assay (ELISA) is widely used
(Crowther 1995). The method is designed to replace detection or isolation on a solid
substrate, is relatively easy to perform, can be applied to a large number of pathogens, can be semiautomatic, and gives a quick result. Depending on the needs, the
goal of this test may be to detect the genus, species, or serotype of the microorganism. However, a positive result obtained by an ELISA test must be confirmed by a
conventional test. The biggest advantage of this method is the performance of negative screening, i.e., the possibility of including a significantly larger number of samples that can be tested for the presence or absence of a certain pathogen, assuming
that there is an acceptable level of false negative results (Crowther 1995). Positive
results obtained by ELISA techniques must be confirmed by analytical techniques
such as aqueous chromatography or gas chromatography and with fluorescent,
ultraviolet, or concentrated spectrophotometric detection techniques
(Crowther 1995).
The usefulness of the ELISA method has been confirmed by many authors in
proving the types of meat and various plant proteins often used as additional
ingredients in meat production, for the detection of enrofloxacin residues in chicken
muscle and liver. Using appropriate antibodies and standards, ELISA can be used to
quantify soy proteins, pea proteins, and gluten in heat-treated products. The ELISA
method has been tested several times for the purpose of qualitative and quantitative
determination of denatured soy proteins (Crowther 1995).
11 Chemical Composition and Nutritional Properties of Functional Food