2009_Book_FoodChemistry

3.7 Changes in Acyl Lipids of Food 219
ties are of importance in the use of BHA, TBHQ
and BHT in food processing. All three antioxidants
are steam distillable at higher temperatures.
Utilization of antioxidants is often regulated
by governments through controls on the use
of food additives. In North America incorporation
of antioxidants is permitted at a maximum level
of 0.01% for any one antioxidant, and a maximum
of 0.02% for any combination. The regulations
related to permitted levels often vary from
country to country.
The efficiency of an antioxidant can be evaluated
by a comparative assay, making use of an “antioxidative
factor” (AF):
a phenoxy radical (I):
(3.92)
which is then regenerated into the original
molecule by rapid interaction with BHT:
AF = I A /I 0 (3.91)
where I A = oxidation induction period for a fat or
oil (cf. 3.7.2.1.1) in the presence of an antioxidant
and I 0 = oxidation induction period of a fat or oil
without an antioxidant.
Hence, the efficiency of an antioxidant increases
with an increase in the AF value. As illustrated
by the data in Table 3.41, BHA in comparison
with BHT shows a higher efficiency in a lard sample.
This result is understandable since in BHT
both tertiary butyl substituents sterically hinder
the reaction with radicals to a certain extent (reaction
1 in Fig. 3.35). The effect on antioxidants
depends not only on the origin of fat or oil but,
also, on the processing steps used in the isolation
and refining procedures. Hence, data in Table
3.41 serve only as an illustration.
BHA and BHT together at a given total concentration
are more effective in extending shelf-life
of a fat or oil than either antioxidant alone at the
same level of use (Table 3.41).
To explain this, it is suggested that BHA, by
participating in reaction 1 (Fig. 3.35), provides
Table 3.41. Antioxidative factor (AF) values of some
antioxidants (0.02%) in refined lard
Antioxidant AF Antioxidant AF
d-α-Tocopherol 5 Octyl gallate 6
dl-γ-Tocopherol 12 Ascorbyl palmitate 4
BHA 9.5 BHAand
BHT 6 BHT a 12
a Each compound is added in amount of 0.01%.
(3.93)
On the other hand, the phenoxy radical (II) derived
from BHT can react further with an additional
peroxy radical:
(3.94)
Propyl gallate (PG) increases the efficiency
of BHA, but not that of BHT. Ascorbyl palmitate,
which is by itself a rather weak antioxidant,
substantially sustains the antioxidative activity of
γ,d,l-tocopherol.
3.7.3.2.3 Synergists
Substances which enhance the activity of antioxidants
are called synergists. The main examples
are lecithin, amino acids, citric, phosphoric, citraconic
and fumaric acids, i. e. compounds which