26
studies showed, chemical modifications of starch can be used to prepare SDS and
RS, but clinical and toxicological trials needs to be performed in order to evaluate
the safety and efficacy of SDS and RS consumption.
Genetic Modification
Genetic modification of starch biosynthesis has been used to develop a strategy for
generating new cultivars with desired functionality through extensive breeding and
characterization of the resulting cultivars. Genetically controlled factors that affect
the starch functionality include structure of starch, content of starch, interaction of
cell components, and starch granule architecture. Waxy starches may be more suitable for developing SDS, since their fine amylopectin structure (i.e., the distribution
of branches and chain length) is more critical for SDS formation (Guraya et al.
2001b). In one study, SDS (long-chain amylopectin starch) was developed from
maize by over expressing a particular enzyme involved in starch biosynthesis
(Moallic et al. 2006). This starch, with high granule crystallinity, has few short
chains of amylopectin and more intermediate and long chains. Other study showed
that genetic mutants containing amylopectin molecules with either a high proportion of short chains with DP < 13 (particularly A chains with DP 5–9) or a high
proportion of long chains with DP ≥ 13 (particularly intermediate to long B chains
with DP > 30) contain greater proportions of SDS than wild type (Zhang et al.
2008). According to a study by Benmoussa et al. (2007), development of SDS and
RS is positively correlated with the presence of both long and intermediate/short
chains, respectively, while it is negatively correlated with the lowest proportion of
extremely short chains. They also found that the channels in starch granules can
regulate starch digestibility, since starch granules with channels are digested from
the interior, and more extensive channelization of starch gives more access to the
hydrolytic enzymes (Benmoussa et al. 2006). Therefore, genetic modification has
the potential to produce ideal starch with high contents of SDS and RS.
Factors Influencing the Formation of RS and SDS
Various factors have been reported to influence the formation of RS and SDS. These
are described as:
Starch Structure
Starch is semicrystalline in nature synthesized mostly as spherical granules in plant
tissues. These granules are composed of alternating concentric layers of ordered
crystalline and less-ordered amorphous lamellae extending from hilum to the surface
B. A. Ashwar et al.
studies showed, chemical modifications of starch can be used to prepare SDS and
RS, but clinical and toxicological trials needs to be performed in order to evaluate
the safety and efficacy of SDS and RS consumption.
Genetic Modification
Genetic modification of starch biosynthesis has been used to develop a strategy for
generating new cultivars with desired functionality through extensive breeding and
characterization of the resulting cultivars. Genetically controlled factors that affect
the starch functionality include structure of starch, content of starch, interaction of
cell components, and starch granule architecture. Waxy starches may be more suitable for developing SDS, since their fine amylopectin structure (i.e., the distribution
of branches and chain length) is more critical for SDS formation (Guraya et al.
2001b). In one study, SDS (long-chain amylopectin starch) was developed from
maize by over expressing a particular enzyme involved in starch biosynthesis
(Moallic et al. 2006). This starch, with high granule crystallinity, has few short
chains of amylopectin and more intermediate and long chains. Other study showed
that genetic mutants containing amylopectin molecules with either a high proportion of short chains with DP < 13 (particularly A chains with DP 5–9) or a high
proportion of long chains with DP ≥ 13 (particularly intermediate to long B chains
with DP > 30) contain greater proportions of SDS than wild type (Zhang et al.
2008). According to a study by Benmoussa et al. (2007), development of SDS and
RS is positively correlated with the presence of both long and intermediate/short
chains, respectively, while it is negatively correlated with the lowest proportion of
extremely short chains. They also found that the channels in starch granules can
regulate starch digestibility, since starch granules with channels are digested from
the interior, and more extensive channelization of starch gives more access to the
hydrolytic enzymes (Benmoussa et al. 2006). Therefore, genetic modification has
the potential to produce ideal starch with high contents of SDS and RS.
Factors Influencing the Formation of RS and SDS
Various factors have been reported to influence the formation of RS and SDS. These
are described as:
Starch Structure
Starch is semicrystalline in nature synthesized mostly as spherical granules in plant
tissues. These granules are composed of alternating concentric layers of ordered
crystalline and less-ordered amorphous lamellae extending from hilum to the surface
B. A. Ashwar et al.