Heme proteins and oxidation in fresh and processed meats - Oxidation in Foods and Beverages and Antioxidant Applications - page 94

reduce ferric low molecular weight iron to ferrous iron (pro-oxidant property)
(Suh et al., 2003). Factors such as ascorbate concentration, metal concentrations,
pH, O 2 partial pressure, lipid hydroperoxide content, the presence or absence of
metal chelators, chelator-to-metal ratio, and type of metal chelator will
determine whether ascorbate inhibits or accelerates heme protein-mediated
lipid oxidation (Boyer et al., 1988; Lee et al., 2001; Tampo et al., 1994). It is
noteworthy that ascorbate can scavenge O 2 . This can be anti-oxidative if all the
O 2 is removed. It can be pro-oxidative if ascorbate lowers the oxygen
concentration to a level that accelerates Hb and Mb-mediated autooxidation
(Ledward, 1970). Ascorbate can also decompose lipid hydroperoxides at certain
conditions which can be pro-oxidative (Kanner and Mendel, 1977).
Tocopherol can inhibit Hb and Mb-mediated lipid by scavenging free radicals
that are produced by both heme proteins (Fig. 4.4). The ability of tocopherols to
physically modify cell membranes may be an additional mechanism that inhibits
lipid oxidation (Atkinson et al., 2008). Exogenous addition of tocopherol to
muscle (during meat processing) is often less effective at inhibiting lipid oxida-
tion compared to dietary addition. The poor ability of exogenous tocopherol to
inhibit lipid oxidation may be attributed to different orientations of the molecule
in cellular membranes compared to when tocopherol is metabolically incor-
porated into cellular membranes through dietary addition.
Rosemary extracts delayed color and flavor deterioration when added
exogenously to fresh and cooked sausages (Sebranek et al., 2005). The
mechanisms involved include free radical scavenging and possibly inactivation
of low molecular weight metals through chelation. An advantage of using
rosemary is that it can be labeled as a natural flavor. Synthetic free radical
scavengers such as butylated hydroxyanisole (BHA), butylated hydroxytolune
(BHT) and propyl gallate are less expensive and more effective than natural
extracts (on an added weight basis) yet some consumers object to having
synthetic antioxidants in food.
Temperature control is critical in delaying quality deterioration in muscle
foods. Muscle contains an extensive pool of endogenous antioxidants that
degrade more slowly at lower temperatures (Halliwell and Gutteridge, 1999;
Petillo et al., 1998). Added antioxidants will also be more effective if elevated
temperatures are avoided.
Sodium tripolyphosphate (STPP) and other polyphosphates are added to
increase water binding in meats but also can inactivate pro-oxidant metals via
chelation. STPP effectively inhibited met heme protein formation in ground beef
muscle containing 1.5% sodium chloride at pH 5.5 and 6.0 but not at pH 6.5 and
7.0 (Trout, 1990). Metals have enhanced solubility (and thus reactivity) at reduced
pH which may explain why STPP was effective only at the lower pH values.
4.7.1 Inhibiting pigment and lipid oxidation in a commercial product
Many cured and processed meat products (e.g., wieners and fermented sausages)
are exposed to light during retail display because consumers want to visually