The effect of sucrose, fructose, and xylose on the retrogradation of waxy m
aize starch extrudates at relatively low moisture contents (20-50 g of wate
r/100 g of dry solid) at 277-353 K was investigated using X-ray diffraction
and H-1 nuclear magnetic resonance (NMR) relaxometry. The role of the suga
r depended on the type of sugar and its concentration, but most importantly
on the retrogradation conditions (water content and storage temperature).
For the isothermal retrogradation at 313 K, fructose considerably increased
the rate of retrogradation over the range of water contents investigated,
and the increase was proportional to the sugar concentration. The behavior
of xylose and sucrose was more complex. At 10% sugar content, both sugars e
nhanced starch retrogradation, while at 30% sugar content, xylose accelerat
ed the process at <35% (mc, dsb) but decreased the rate constant when more
water was present. This crossover took place at 42% me for sucrose. Sugars
enhanced the transformation of the A-type polymorph to a so-called pseudo-B
with an X-ray diffractogram similar to that of B-type starch, with the exc
eption of the 1.6-nm peak which was considerably depressed. The effects of
these sugars on the retrogradation kinetics in variable storage temperature
conditions mirrored those obtained when isothermal retrogradation was exam
ined in the water content domain.