27
of granules. The crystalline lamellae are formed from the amylopectin short branch
chains arranged in clusters; these crystalline lamellae are interspersed with amorphous lamellae that consist of branching points of amylopectin and amylose molecules. The sub-chains of the amylopectin has been classified into three types. A
chains (outer chains) are the shortest among the three chains (CL 6–15) and are α-(1,
6)-linked to B chains. The B chains are linked in the same way and bear one or more
A chains and/or B chains. Depending on their respective length and the number of
clusters they span, B chains are further classified into B1, B2, B3 and B4 chains
(with one to four clusters). B1 and B2 chains have CL of 15–25 and 40–50, respectively, with B3 and B4 chains being much longer. The single C chain per amylopectin molecule contains the sole terminal reducing group and carries other chains
(Donald 2004). Within this structure, the linear chains lie in the region of high
molecular order, and the branch-points lie in the region of low molecular order.
These linear chains can form double helices to make up the crystalline structure. On
the basis of wide-angle X-ray diffraction scattering studies, native starch has been
classified into four types viz. A, B, C and V. The A type is characteristic of most
cereal starches, while the B type is characteristic of potato starch, other root starches,
amylomaize starch, and retrograded starch. The C type is a combination of A and B
types, and is found in smooth pea and various bean starches. The V type can be found
only in starch after gelatinization and the formation of amylose helical complexes
with lipids or related compounds.
Studies of X-ray diffraction of RS showed that chain fragments were packed in a
B type crystalline structure with enlarged crystal lattice which contributes to the
formation of RS. Any treatment that eliminates starch crystallinity (e.g., gelatinization) or damages the integrity of the plant cell or tissue structure (e.g., milling)
increases access to enzymes and reduces the RS content, whereas recrystallization
and chemical modifications increases the RS content (Englyst and Cummings 1986;
Adebowale et al. 2009; Kim and White 2013). Further high amylose content of
starch is known to lower starch digestibility (Chung et al. 2009). High amylose
maize starches with very long chains might be perfectly ordered into double helices
to form resistant starch (Ozturk et al. 2011). Higher contents of resistant starch were
found in Hylon VII than in Hylon V (high-amylose genetically modified corn
starches) which might be because of higher amylose content in Hylon VII (Dimantov
et al. 2004). Margareta Leeman et al. (2006) claimed that high amylose starch resists
enzymatic digestion due to its internal structure and B-type crystallinity. Native
cereal starch has been classified as an ideal SDS, since its structure makes it to be
digested slowly (Zhang et al. 2006a, b). They found that the A-type semicrystalline
structure of native cereal starch, including the distribution of perfect crystalline
regions in both crystalline and amorphous lamellae explains this slow digestion
property. The high proportion of SDS in cereal starch was also correlated with
higher proportion of short A chains with DP 5–10. The mechanism of slow digestion property of native cereal starch involves enzymatic digestion from inside out
and layer-by-layer. Enzymatic digestion begins in interior channels and at surface
pores, and then side-by-side digestion gradually enlarges the channel by simultaneously hydrolyzing crystalline and amorphous regions. Native starch is hydrolysed
Resistant Starch and Slowly Digestible Starch
of granules. The crystalline lamellae are formed from the amylopectin short branch
chains arranged in clusters; these crystalline lamellae are interspersed with amorphous lamellae that consist of branching points of amylopectin and amylose molecules. The sub-chains of the amylopectin has been classified into three types. A
chains (outer chains) are the shortest among the three chains (CL 6–15) and are α-(1,
6)-linked to B chains. The B chains are linked in the same way and bear one or more
A chains and/or B chains. Depending on their respective length and the number of
clusters they span, B chains are further classified into B1, B2, B3 and B4 chains
(with one to four clusters). B1 and B2 chains have CL of 15–25 and 40–50, respectively, with B3 and B4 chains being much longer. The single C chain per amylopectin molecule contains the sole terminal reducing group and carries other chains
(Donald 2004). Within this structure, the linear chains lie in the region of high
molecular order, and the branch-points lie in the region of low molecular order.
These linear chains can form double helices to make up the crystalline structure. On
the basis of wide-angle X-ray diffraction scattering studies, native starch has been
classified into four types viz. A, B, C and V. The A type is characteristic of most
cereal starches, while the B type is characteristic of potato starch, other root starches,
amylomaize starch, and retrograded starch. The C type is a combination of A and B
types, and is found in smooth pea and various bean starches. The V type can be found
only in starch after gelatinization and the formation of amylose helical complexes
with lipids or related compounds.
Studies of X-ray diffraction of RS showed that chain fragments were packed in a
B type crystalline structure with enlarged crystal lattice which contributes to the
formation of RS. Any treatment that eliminates starch crystallinity (e.g., gelatinization) or damages the integrity of the plant cell or tissue structure (e.g., milling)
increases access to enzymes and reduces the RS content, whereas recrystallization
and chemical modifications increases the RS content (Englyst and Cummings 1986;
Adebowale et al. 2009; Kim and White 2013). Further high amylose content of
starch is known to lower starch digestibility (Chung et al. 2009). High amylose
maize starches with very long chains might be perfectly ordered into double helices
to form resistant starch (Ozturk et al. 2011). Higher contents of resistant starch were
found in Hylon VII than in Hylon V (high-amylose genetically modified corn
starches) which might be because of higher amylose content in Hylon VII (Dimantov
et al. 2004). Margareta Leeman et al. (2006) claimed that high amylose starch resists
enzymatic digestion due to its internal structure and B-type crystallinity. Native
cereal starch has been classified as an ideal SDS, since its structure makes it to be
digested slowly (Zhang et al. 2006a, b). They found that the A-type semicrystalline
structure of native cereal starch, including the distribution of perfect crystalline
regions in both crystalline and amorphous lamellae explains this slow digestion
property. The high proportion of SDS in cereal starch was also correlated with
higher proportion of short A chains with DP 5–10. The mechanism of slow digestion property of native cereal starch involves enzymatic digestion from inside out
and layer-by-layer. Enzymatic digestion begins in interior channels and at surface
pores, and then side-by-side digestion gradually enlarges the channel by simultaneously hydrolyzing crystalline and amorphous regions. Native starch is hydrolysed
Resistant Starch and Slowly Digestible Starch