Page 324 - Natural Antioxidants, Applications in Foods of Animal Origin

Antioxidant Dietary Fiber: An Approach to Develop Healthy 303
VetBooks.ir polysaccharide chains represents a suitable way to cross-link them through

the formation of diferulates (Bunzel et al., 2001). The principal mechanism
for crosslinking cell wall polysaccharides is ferulate dehydrodimerization
via radical coupling reactions producing a number of different diferulates
(Bunzel et al., 2004). They form bridge structures between chains of poly-
saccharides. Moreover, ferulates have a significant role in cross-linking
polysaccharides to lignin; thus they deeply influence physical parameters
of DF determining its reticulation, molecular weight, and water solubility.
The amount of diferulates found in the SDF of different cereals is more than
100-fold lower than the amount present in the corresponding IDF (Bunzel
et al., 2001). The extent of diferulates severely affects the biological signifi-
cance of DF and it is believed that the amount of DF diferulates is inversely
correlated to the fermentability by intestinal microflora (Kroon, 2000; Wang
et al., 2004). The bacterial β-glucosidases and esterases cannot attack the
highly cross-linked IDF while their action is easier when the DF is less struc-
tured such as in SDF (Kroon et al., 1997; Zhao et al., 2003). Although it is
also reported that low to moderate levels of diferulates do not interfere with
hydrolysis of non-lignified cell walls by human gut microbiota (Funk et al.,
2007). It is generally accepted that higher the SDF/IDF ratio, the higher is
DF polyphenols bioaccessibility.

8.4 DIETARY FIBER PROCESSING AND QUALITY

The by-products from cereals as well as fruits and vegetables are subjected
different processing steps and conditions to prepare the DF or ADF. The
extent and intensity of these processing steps and conditions may affect
various properties and activity of this bioactive ingredient. The treatment
like extent and intensity of blanching and drying, nature of solvent used
should be taken into consideration while processing of ADF.
DF production typically involves pre-treatment methods, such as
blanching or chemical treatments depending on the type of raw material,
prior to drying, to inactivate enzymes responsible for degradation of many
active compounds (Wolfe & Liu, 2003). However, number of sensitive
compounds may degrade during blanching, depending on the type (steam-
or water-blanching) and conditions (Zhang & Hamauzu, 2004). Loss of SDF
and solubilization of structural polymers such as protopectin may happen
while blanching of high fiber products (Maté et al., 1998). Drying can
result in oxidation, thermal degradation and other events such as collapse of