4 Table 1. General characteristic of superior variety of sweet potato in Indonesia
Variety Physic form
Chemical content
Productivity Harvest
time Sari
Oval shaped tuber, short stalk tuber, red skin color, yellow
flesh, sweet an delicious taste Dry matter: 28
Starch content: 32 Beta carotene content:
381µg100 g 30-35 ton ha
3.5-4 months
Sukuh Ellipse and spherical tuber,
short stalk tuber, yellow skin color, white flesh color
Dry matter: 35 Starch content: 31
Beta carotene content: 36.59µg100g
25-30 tonha 4.0-4.5
months
Boko Long and ellipse tuber, very
shorter stalk tuber, red skin color, light-yellow flesh color
Dry matter: 32 Starch content: 32
Beta carotene content: 108µg100g
25-30 tonha 4.0-4.5
months
Jago Spherical tuber, short stalk
tuber, white skin color, yellow flesh color
Dry matter: 33 Starch content: 31
Beta carotene: 85µg100g 25-30 tonha
4.0-4.5 months
Kidal Spherical tuber, very short
stalk tuber, red skin color, yellow flesh color
Dry matter: 31 Starch content: 32.85
Beta carotene: 345µg100g 25-30 tonha
4.0-4.5 months
Source: RILET, 2008
2.2 RESISTANT STARCH
Starch defines as the major dietary source of carbohydrates, is the most abundant storage polysaccharides in plants, and occurs as granules in the chloroplast of green leaves and the amyloplast
of seeds, pulses, and tubers Ellis et al, 1998. Chemically, starches are polysaccharides, composed of a number of monosaccharides or sugar glucose molecules linked together with
α-D-1-4 and α-D- 1-6 linkages. The starch consist of 2 main structural components, amylose, which is essentially a
linier polymer in which glucose residues are α-D-1-4 linked typically constituting 15-20 of starch,
and amylopectin, which is a larger branched molecule with α-D-1-4 and α-D-1-6 linkages and is a
major component of starch BNF,1990 The term “resistant starch” was first coined by Englyst et al 1982 to describe a small
fraction of starch that was resistant to hydrolysis by exhaustive α-amylase and pullulanase treatment
in vitro after 120 minute incubation. However, because starch reaching the large intestine may be more or less fermented by the gut microflora, RS is now defined as the sum of the starch and product
of starch degradation which is not absorbed in the small intestine of healthy individuals Englyst et al, 1992.
There are four type of resistant starch. Type I represents starch that is resistant because it is in a physically inaccessible form, which is locked in the plant cell walls of some foodstuffs, such as
partially milled grains, seeds, and legumes Englyst et al, 1992, Sajilata, 2006. Figure 2 a shows microscopic view of the physically inaccessible RS1 in cell or tissue structures of partly milled grains,
seeds, and vegetable. Type II is a native starch granules, starch is tightly packed in a radial pattern and is relatively dehydrated. This compact structure limits the accessibility of digestive enzyme and
accounts for the resistant nature of RS2 such as, un-gelatinized starch. Figure 2 b shows the RS granules of type II resistant starch, that is raw potato, banana, high amylose starch Sajilata, 2006.
5 a
b
c d
Figure 2. Structure of Resistant Starch a Structure of type I resistant starch RS1, b Structure of type II resistant starch RS2, c Schematic presentation of enzyme type III resistant starch
RS3 Micelle model, d Preparation of cross-bended starch in modified starch of RS4 distarch
phosphate ester Sajilata et al, 2006
Type III resistant starch is made up retrograded starch or crystalline non-granular starch, like the starch found in cooked and cooled potatoes, bread crust, cornflakes, and high-amylose maize
starch Englyst et al, 1992; Eerlingen and Delcour, 1995. Schematic presentation of RS3 formed in aqueous amylose solutions depicted as micelle model is shown in Figure 2 c. Type IV refers to
specific chemically and thermally modified or re-polymerized starch Englyst et al, 1992; Eerlingen and Delcour, 1995. Structure of RS4 includes structure of modified starches obtained by chemical
treatments like distarch phosphate ester Figure 2 d. Table 2 outlines a summary of the different
types of RS, their classification criteria, and food sources. Type-III resistant starch is formed by thermal disruption of the granular structure of the
starch in water or gelatinization of the starch and re-crystallization of amylose and amylopectin retrogradation. Gelatinization will disrupt granular structure by heating starch with an excess of
water and amylose leaches from the granules into the solution as a random coil polymer. The gelatinized starch will be re-crystallized by cooling, which is the polymer chains begin to re-associate
as double helices, stabilized by hydrogen bonds Englyst et al., 1992; Eerlingen and Delcour, 1995. Formation is followed by enzymatic debranching of gelatinized starches followed by drying,
extrusion, or ion crystallization addition of salts Futch, 2009. Industrial production of resistant starch comes mainly from high amylose maize starches.
6 Table 2. Classification of type of RS, food sources, and factor affecting their resistance to digestion in
the colon
Type of RS Description
Food sources Resistance minimized
by RS1 Physically
protected Whole-or partly milled grains
and seeds, legumes Milling, chewing
RS2 Un-gelatinized resistant
granules with type B crystallinity, slowly hydrolyzed
by α-amylase
Raw potatoes, green bananas, some legumes, high amylose
corn Food processing and
cooking
RS3 Retrograded starch
Cooked and cooled potatoes, bread, cornflakes, food
products with repeated moist heat treatment
Processing conditions
RS4 Chemically modified starches
due to cross-linking with chemical reagents
Foods in which modified starches have been used for
example:breads, cakes Less susceptible to
digestibility in vitro Source: Nugent, 2005
Debranching enzyme using pullulanase has been applied to produce a starch with linier, low- molecular-weight and re-crystallizable polymer chains. Debranching enzymes such as pullulanase
rapidly hydrolyze only α-1,6-glucosidic bonds, releasing a mixture of long and shorter unit chains
from the parent amylopectin molecule. These fragments are linear polymers containing about 10 to 65 anhydroglucose units linked by
α-1,4-glucosidic bond. The debranched starch was then subjected to temperature cycling and incubation at a series of temperature and time to induce retrogradation and
yield the resistant starch Leong et al, 2007 A study on RS formation showed that as the amylose fraction increased, RS yield increased.
The formation was affected by the water content of the starting starch suspension, autoclaving temperature, condition of enzymatic reaction and cooling and drying process, as well as by the
presence of other ingredients such as lipids, sugars and salts Eerlingen and Delcour, 1995. Beside that, formation of resistant starch was also affected by several properties of starch, such as granular
structure, crystallinity, amylose and amylopectin ratio, and chain length Futch, 2009. Cummings et al 1987 also defined some factors associated with RS formation during the processes were the
physical state of the food materials whole or ground, water content, pH, heating time and temperature, composition substrate, number of heating and cooling cycles, freezing methods slow vs
rapid and drying method.
2.3 BENEFICIAL OF RESISTANT STARCH
