2009_Book_FoodChemistry

8.14 Chelating Agents (Sequestrants) 455
application mode is by dipping or spraying the
fruit with a wax emulsion containing 0.1–0.45%
thiabendazole.
8.13 Antioxidants
(8.39)
Since lipids are widely distributed in food and
since their oxidation yields degradation products
of great aroma impact, their degradation is an important
cause of food deterioration by generation
of undesirable aroma. Lipid oxidation can be retarded
by oxygen removal or by using antioxidants
as additives. The latter are mostly phenolic
compounds, which provide the best results often
as a mixture and in combination with a chelating
agent. The most important antioxidants, natural
or synthetic, are tocopherols, ascorbic acid
esters, gallic acid esters, tert-butylhydroxyanisole
(BHA) and di-tert-butylhydroxytoluene (BHT).
They are covered in 3.7.3.2.2.
8.14 Chelating Agents
(Sequestrants)
Chelating agents have acquired greater importance
in food processing. Their ability to bind
metal ions has contributed significantly to stabilization
of food color, aroma and texture. Many
natural constituents of food can act as chelating
agents, e. g., carboxylic acids (oxalic, succinic),
hydroxy acids (lactic, malic, tartaric, citric),
polyphosphoric acids (ATP, pyrophosphates),
amino acids, peptides, proteins and porphyrins.
Table 8.14 lists the chelating agents utilized
by the food industry, while Table 8.15 gives
the stability constants for some of their metal
complexes.
Traces of heavy metal ions can act as catalysts
for fat or oil oxidation. Their binding by chelating
agents increases antioxidant efficiency and inhibits
oxidation of ascorbic acid and fat-soluble
vitamins. The stability of the aroma and color of
canned vegetables is substantially improved.
Table 8.14. Chelating agents used as additives in food
processing. (Compounds given in brackets are utilized
only as salts or derivatives)
(Acetic acid)
Na-, K-, Ca-salts
Citric acid
Na-, K-, Ca-salts,
monoisopropyl ester,
monoglyceride ester,
triethyl ester,
monostearyl ester,
EDTA
Na-, Ca-salts
(Gluconic acid)
Na-, Ca-salts
Oxystearin
Orthophosphoric acid Na-, K-, Ca-salts
(Pyrophosphoric acid) Na-salt
(Triphosphoric acid)
Na-salt
(Hexametaphosphoric acid,
10–15 residues) Na-, Ca-salts
(Phytic acid)
Ca-salt
Sorbitol
Tartaric acid
Na-, K-salts
(Thiosulfuric acid)
Na-salt
Table 8.15. Stability constants (pK-values) of some metal complexes
Chelating
agent Ca 2+ Co 2+ Cu 2+ Fe 2+ Fe 3+ Mg 2+ Zn 2+
Acetate 0.5 2.2 0.5 1.0
Glycine 1.4 5.2 8.2 4.3 10.0 3.5 5.2
Citrate 3.5 4.4 6.1 3.2 11.9 2.8 4.5
Tartrate 1.8 3.2 7.5 1.4 2.7
Gluconate 1.2 18.3 0.7 1.7
Pyrophosphate 5.0 6.7 22.2 5.7 8.7
ATP 3.6 4.6 6.1 4.0 4.3
EDTA 10.7 16.2 18.8 14.3 25.7 8.7 16.5