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
The slow hydrolysis of resistant starch makes it useful for the slow release of glucose, which can be especially useful in controlling glycaemic plasma responses Raben et al, 1994. Some other
benefits include increased faecal bulk, lowered faecal pH, and increased excretion of butyrate and acetate Phillip et al, 1995. Resistance starch was reported has physic character like un-soluble starch
but it has function like soluble starch. Resistant starch has a lower water-holding capacity. It has desirable physicochemical
properties such as swelling, viscosity increase, gel formation, and water-binding capacity, making it useful in a variety of foods Fausto et al, 1997. These properties make it possible to use most
7 resistant starch to replace flour on a 1-for-1 basis without significantly affecting dough handling or
rheology Sajilata, 2006. Beside that, RS is commercially use as a dietary fiber fortification in bread- making, as a texture modifier in baked goods, as a crisping agent, and as a functional ingredient in
other food.
2.4 Eubacterium rectale BACTERIA
Resistant starch can be utilized by microorganism present in the human large intestine. Consequently, the metabolites formed during the fermentation process, i.e., short chain fatty acid, may
serve as a main energy source for the colonocytes Mortensen, et al, 1996, including gases CO
2
, CH
4
, H
2
, lactate and branched fatty acids isobutyrate, isovalerate Macfarlene et al, 1991 and thus help to maintain colon health. The type and amount of by-product is dictated by the substrate
undergoing fermentation. Short chain fatty acids are the principal end-product of colonic fermentation and are produced in the approximate molar ratio of 60:25:15 acetate, propionate, and butyrate,
respectively Macfarlene et al, 1991. Among the genera of colonic bacteria, butyrate producing bacteria such as Eubacterium,
Peptostreptococci, Clostridia, Roseburia spp and Butyrofibriofibri- solvens are thought to have beneficial effect on the human host Purwani and Suhartono, 2009. Eubacterium is an obligately
anaerobic gram positive non-spore forming bacteria. It has road bacilli shape. The genus Eubacterium i.e. Eubacterium rectale which is the second most common genus in the human
intestine,also commonly found in the human fecal collected from a pilot study, including several known butyrate producers Schwiertz et al, 2002.
Several colonic bacterial groups produce amylase which hydrolyzes the starch into oligosaccharide Wang et al, 1999. It may induce the growth of useful bacteria including butyrate
producing bacteria. It is known that bacterial butyrate production is stimulated particularly by resistant starches Wang et al, 1999; Sharp and Macfarlene, 2000. Ability of several bacteria in using starch as
a substrate fermentation depend on the existence of degradation enzyme. Many species of Eubacterium is an obligately anaerobic gram positive non spore-forming.
Cells of Eubacterium rectale are slightly curved slender rods of moderate 0.5 x 2.0-5.0 µm length. Cells are gram positive, but decolorize readily to give a Gram-negative staining reaction. Cells from
early to mid-exponential phase cultures are clearly motile when examined by phase-contrast microscopy Duncan and Flint, 2008.
Eubacterium rectale possesses genes for the production of butyrate that show high similarity to genes from other Clostridia Mahowald, 2009. Metabolic pathway involves condensation of 2
molecules of acetylCoA to form butyrate and is accompanied by oxidation of NADH to NAD
+
. In vitro studies have shown that in the presence of carbohydrate, Eubacterium rectale consumes large
amounts of acetate for butyrate Duncan and Flint, 2008. The last step in Eubacterium rectale’s butyrate production pathway is catalyzed by the butyrylCoA dehydrogenaseelectron transfer
flavoprotein BcdEtf complex, and offers a recently discovered additional pathway for energy conservation, via a bifurcation of electrons from NADH to crotonylCoA and ferredoxin Li F, 2008.
Reduced ferredoxin, in turn, can be re-oxidizied via hydrogenases, or via the membrane-bound oxidoreductase, Rnf, which generates sodium-motive force.
Generally, metabolic pathway of Eubacterium rectale has a similarity with butyrate- producing Clostridia, because it possesses genes for the production of butyrate that show high
similarity to genes from other Clostridia Mahowald, 2009. The reaction involves a lot of enzymatic process and some factors may effects certain product forming. Glucose is metabolized to pyruvate via
Embden-Meyerhof-Parnas EMP pathway and produces two moles of ATP and NADH, from each
8 mole of glucose. Propionic acid is produced via 2 main pathways: 1 fixation of CO
2
to form succinate the dicarboxylic pathway; and 2 from lactate and acrylate. Pyruvate is an intermediate compound
for SCFA production, then can be metabolized to acetate, butyrate, and propionate.
2.5 BENEFICIAL OF SHORT CHAIN FATTY ACID ON COLON
