Substituting wheat flour with rice flours significantly affected
the hardness of the cookies stored for 7 days (Fig. 2). The hardness
of the control wheat flour cookie increased significantly from
2239 g to 2771 g after 7 days of storage. This hardness increase is
typically observed for the cookies during their storage, and often
perceived as an undesirable change. The cookie undergoes spontaneous
changes in its structural matrix during a storage which is
induced with water migration (Youngquist & Brabbs, 1982).
Network formation as a result of starch retrogradation may cause
an increase in rigidity which appears as an increase in hardness of
cookie. For similar reasons, an increase in hardness during storage
has been observed in bread (Charoenthaikij et al., 2010).