THESIS

3.1 Processing condition on improvement of RS III content
In other process for producing amylase resistant rice starch, Shi and
Trzasko (1997) described a method in which a high amylose starch. Having at least
40% (w/w) of amylose and a water content of 10 to 80% (w/w), was heated to
temperature between 60 and 160 o C to provide a resistant granule starch with a total
dietary fiber content of at least 12%. The formation of non-waxy rice starch with
lower digestibility and therefore higher resistance to α- amylase on heating to 140 o C
may be attributed to the formation of several smaller molecular weight fractions from
hydrolysis of the starch on heating, with the different fraction re-crystallizing at
different temperatures on cool down. Cooling and re-crystallization of these smaller
starch fractions my not permit an orderly rearrangement of granules thereby
preventing access to α- amylase. When starch is gelatinized under high moisture
content and allowed to cool, alignment of ordered amylose molecules with each other
leads to the formation of a rigid gel. Resistant starch is produced as the insoluble
crystallite formed by the process of controlled retrogradation (Englyst et al. 1992).
Heat-moisture treated at the melting temperature (Tm) has been used to study the
digestibility and pasting properties of rice starch. Anderson et al. (2002) found that
starches (20% moisture) heated to the temperature of melting (Tm) and held for 60
min in the calorimeter showed a slow digestibility compared to unheated samples.
Digestibility decreased by 25% and 10%, respectively, for non-waxy and waxy rice
starches relative to non-treated starch (Lui et al. 1991)
Kim et al. (2006) carried out studies to determine resistant rice starch in
different ways, cooked as brown or white, boiled or steamed, whole grain or flour and
retrograded while grains and flour from the average amylose content was 22.25%.
They summarized that brown rice and retrograded rice appear to containing highest
amounts of resistant starch (Table 7). Unfortunately, boiled rice is low, and rice that
retrograde a lot are considered low quality. The material lost in boiling is also high in
RS, probably because amylose was selectively leached. Leaching of amylose would
less starch in the boiled rice and explain the loss in RS in boiled rice. The effect of
microwave treatment on the contents of total and enzyme resistant starch in white and
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