Agriculture Reference
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of protein-based metal chelators such as glycoprotein, serum albumin, casein and
lactoferrin (Pihlanto 2006). Casein phosphopeptides are other milk-based
materials, derived from enzymatic hydrolysis of casein, and are believed to have
metal chelating abilities due to the presence of phosphate groups originating from
serine amino acids in the sequence. These polar functional groups create a medium
favorable for chelating metals such as calcium, zinc, copper, manganese and iron
(Kitts 2005). Casein hydrolysates and purifi ed casein phosphopeptides are
effective in inhibiting oxidation in a model system (Diaz et al. 2003) and in
cooked ground beef (Diaz and Decker 2004). Whey is also a milk-derived protein,
with antioxidant activity due to its bovine serum albumin (BSA) portion. BSA
was shown to function synergistically with certain phenolic compounds in oil-in-
water emulsions and the antioxidant effect was attributed to a protein-antioxidant
adduct that forms during storage (Almajano and Gordon 2004). Others, including
Tong et al. (2000), attributed the antioxidant activity to radical scavenging and
chelation of iron.
Vegetable proteins, such as those isolated from soybean, and their hydrolysis
products also exhibited antioxidant potential (Pena-Ramos and Xiong 2002).
Other antioxidant proteins and protein hydrolysis products can be obtained
from various sources such as potato (Hou et al. 2005; Wang and Xiong 2008),
chickpeas and white beans (Arkan and Yemenicioglu 2007), rapeseed (Yoshie-
Stark et al. 2008) and Sundakai shrub (Sivapriya and Srinivas 2007). All
these proteinaceous antioxidants hold considerable potential as natural metal
chelating and radical scavenging compounds, although they have not been
commercialized yet.
5.3.5 Maillard reaction antioxidants
The Maillard reaction takes place in food during cooking or processing and
is known for generating baked, toasted, roasted and broiled notes in cooked
foods. The reaction of amino acids and reducing sugars results in a cascade of
complicated reactions producing pigments responsible for food coloring as well
as chemical structures that constitute what we perceive as processed or cooked
food taste and aroma. Maillard reaction products (MRP) might also have
antioxidant activity.
Numerous studies have demonstrated the antioxidant effectiveness of MRP
either during food processing, or in model systems such as heated soybean oil and
pregelatinized starch containing a Maillard reaction reducing agent and amino
acid. It was found that the extent of browning correlated with the antioxidant
protection (Mastrocola and Munari 2000). The mechanism of action is not well-
defi ned. Potential explanations include radical scavenging activity, or metal
chelating potential, or to the ability of some of the intermediates to act as
reductases. The specifi c compounds responsible for the activity have not been
isolated nor identifi ed due to the complexity of the Maillard cascade of reactions
(Reische et al. 2008).
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