20
RS may escape digestion due to various reasons. The compact molecular structure
of starch may limit the accessibility of hydrolytic enzymes (Haralampu 2000). The
starch may be physically inaccessible to the hydrolytic enzymes as in grains, seeds
and tubers. The starch granules may also be configured in such a manner which
prevents their digestion e.g., unripe bananas, raw potatoes, and high amylose maize
starch (Nugent 2005). When gelatinized starch is cooled retrograded starch (starch
crystals) is formed which is resistant to digestive enzymes. This form of ‘retrograded’ starch is found in foods like corn flakes, and cooked and cooled potatoes
(approximately 5%) (Haralampu 2000). Chemical modifications like esterification,
etherification and cross linking of starch also makes it resistant to enzymatic hydrolysis (Lunn and Buttriss 2007). RS has been further classified into five types: RS1,
RS2, RS3, RS4 and RS5.
RS1
This form of RS is physically inaccessible to hydrolytic enzymes because it is
entrapped within the food matrix such as partly milled grains and seeds. It can be
used in a variety of conventional foods as it is stable to most cooking operations
(Sajilata et al. 2006).
RS2
The RS2 comprises of native, uncooked granules like raw potato or banana starches,
whose crystallinity makes them resistant to enzymatic hydrolysis (Hernandez et al.
2008). These ungelatinized starches are resistant to digestion because of their compact structure (Sajilata et al. 2006). A particular type of RS2 called high amylose
maize starch (HAM) is unique because it is stable to most cooking operations
(Wepner et al. 1999).
RS3
RS3 is generally called retrograded starch (Wepner et al. 1999). It is formed when
starch is first gelatinized and then cooled for retrogradation. During retrogradation
the polymer chains reassociate by the formation of inter chain hydrogen bonds to
form double helices. The double helices are left handed, parallel stranded and one
turn of double helix is 20.8 Å. Retrograded starch has type A crystalline structure
(Eerlingen et al. 1993a, b). RS3 content is also affected by degree of polymerization
(DP) of amylose, with increase of DP, RS3 content increases, reaching maximum at
B. A. Ashwar et al.
RS may escape digestion due to various reasons. The compact molecular structure
of starch may limit the accessibility of hydrolytic enzymes (Haralampu 2000). The
starch may be physically inaccessible to the hydrolytic enzymes as in grains, seeds
and tubers. The starch granules may also be configured in such a manner which
prevents their digestion e.g., unripe bananas, raw potatoes, and high amylose maize
starch (Nugent 2005). When gelatinized starch is cooled retrograded starch (starch
crystals) is formed which is resistant to digestive enzymes. This form of ‘retrograded’ starch is found in foods like corn flakes, and cooked and cooled potatoes
(approximately 5%) (Haralampu 2000). Chemical modifications like esterification,
etherification and cross linking of starch also makes it resistant to enzymatic hydrolysis (Lunn and Buttriss 2007). RS has been further classified into five types: RS1,
RS2, RS3, RS4 and RS5.
RS1
This form of RS is physically inaccessible to hydrolytic enzymes because it is
entrapped within the food matrix such as partly milled grains and seeds. It can be
used in a variety of conventional foods as it is stable to most cooking operations
(Sajilata et al. 2006).
RS2
The RS2 comprises of native, uncooked granules like raw potato or banana starches,
whose crystallinity makes them resistant to enzymatic hydrolysis (Hernandez et al.
2008). These ungelatinized starches are resistant to digestion because of their compact structure (Sajilata et al. 2006). A particular type of RS2 called high amylose
maize starch (HAM) is unique because it is stable to most cooking operations
(Wepner et al. 1999).
RS3
RS3 is generally called retrograded starch (Wepner et al. 1999). It is formed when
starch is first gelatinized and then cooled for retrogradation. During retrogradation
the polymer chains reassociate by the formation of inter chain hydrogen bonds to
form double helices. The double helices are left handed, parallel stranded and one
turn of double helix is 20.8 Å. Retrograded starch has type A crystalline structure
(Eerlingen et al. 1993a, b). RS3 content is also affected by degree of polymerization
(DP) of amylose, with increase of DP, RS3 content increases, reaching maximum at
B. A. Ashwar et al.