Chemistry Reference
In-Depth Information
lower fat content but such products are not allowed to be labelled as butter. They
are marketed under special commercial names. The most widely used
emulsifiers are monoacylglycerols and diacylglycerols. Carotenes are added as
colouring agents, and tocopherols may be added, too. The oily phase of
margarines need not be very stable as they should be stored in a refrigerator and
for a restricted time, and only some products are stabilized with preservatives,
such as para-hydroxyphenolic acid.
Mayonnaises are oil-in-water emulsions. They can be stored for only limited
time and in a refrigerator so that antioxidants have no special importance.
15.5 Changes during culinary operations at ambient and low
temperatures
15.5.1 Changes in bulk fats and oils at ambient temperature
In bulk fats and oils, more polar antioxidants are usually more active than less
polar phenolic antioxidants (Cuvellier et al., 2000). Propyl gallate (PG) and di-
tert. butylhydroxytoluene (BHT), are typical examples. In food materials or in
model oil-in-water emulsions (Frankel et al., 1993, 1996), the activities may be
quite different, as shown on the example of tocopherol and Trolox (Frankel,
2007). Trolox has the same active group as tocopherols, but it is more polar as it
lacks the hydrophobic hydrocarbon chain of tocopherols. Therefore, it has the
same antioxidant activity as tocopherols in bulk oils. On the contrary, in emulsions
Trolox has more affinity towards water than tocopherols, and it concentrates on
the oil/water interface (Frankel, 1995). The same occurs in the case of synthetic
antioxidants, as polar antioxidants, like PG, accumulate at the W/O interface while
BHT remains in the oil droplet. Therefore, the data obtained in model experiments
in the systems free of water with polar natural antioxidants, such as caffeic acid or
catechin, cannot be applied to their activity in real foods, which regularly contain
water. Turkey meat lipids were oxidized on storage under evolution of off-odour
volatiles, especially on irradiation. Antioxidants, such as gallates, sesamol,
tocopherols reduced the off-odour intensity (Lee and Ahn, 2002).
Antioxidant enzymes of broccoli were stored at different temperatures
(Zhang et al., 2009), and the temperature of 10 ëC was found the most suitable
for storage. No effect of dietary antioxidants and free fatty acids was observed in
fresh cooked pork, but lipoprotein oxidation rose in prefrozen uncured cooked
meat under aerobic conditions (Haak et al., 2006).
Ground beef was irradiated at 84 ëC for up to seven days. On subsequent
storage, sesamol and tocopherols were more efficient than other antioxidants in
reducing the oxidation accompanied by evolution of off-odour volatiles (volatile
sulfur compounds appeared during the treatment and again disappeared) (Nam et
al., 2003).
Tryptophan bound in proteins reacts with phenolic aldehydes with formation
of tetrahydro--carbolins. Trolox showed better protection than a mixture of
Trolox and ascorbic acid (Herrais et al., 2003).
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