Abstract:
The effects of gelatinization and gel storage conditions on the formation of canna resistant
starch (RS) were investigated. Starch slurries (10%, dwb) were autoclaved at 121 C for 30,60 and
120 min. The gels obtained were subsequently stored at different temperatures (4, 30 and 100 C)
and times (0, 1, 3, 5 and 7 d). Canna starch granules gelatinized for 30 min were entirely
disintegrated and dispersed into the solution, but some granule fragments could still be observed.
Extending the gelatinization time to 60 and 120 min resulted in a complete dispersion of the
granules. Analyses of the RS content in gelatinized starch samples in comparison with that in the
granular starch showed that the RS fraction in granular starch was very high (97.3% w/w), but a
substantial portion of RS was thermally instable as indicated by a great reduction in RS contents
(reduced to 1.9% w/w) after cooking at 100 C for 20 min. The RS contents in gelatinized starch
samples were 12.0-15.9% w/w and reduced to 7.9-10.8% w/w after cooking. Storage of gels
resulted in a significant increase in the amount of the thermally stable RS fraction, i.e. the thermally
stable RS content of 16.8% w/w was found in the gel sample gelatinized for 120 min and stored at
4 C for 3 d. This indicated that the ordered structures of RS portion were tightened under the
storage conditions. The crystals formed during storage displayed a B-type X -ray diffraction pattern
and the degree of crystallinity increased with increasing the storage time. The gelatinization
temperature of canna starch was 72.2 DC, whereas the RS products exhibited two melting
temperature ranges; 51.1-76.3 C and 163.1-165.1 DC, indicating that the newly formed crystals
were very strong. The canna RS products were soluble in water at room temperature and had
significantly lower viscosity, compared to the original canna starch.