| Summary: | 碩士 === 輔仁大學 === 食品營養學系 === 84 === Dry cooked rice,being microwave-puffable and ready to eat,
was manufactured from polished rice in order to increase its
added value and shelf life. The objective of this study was to
search the optimal processingconditions on microwavable puffing
ratio of the dry cooked rice. TCW70,TC189 and TNuS19 rices
which amylose contents were respectively 1.4,18.3 and 25,4% were
used. They have been stored for more than six months at 4℃.
After beingsteam gelatinized,the rices dehydrated to a water
content of 12±1% by two-stepdrying at 90℃ and 70℃.
Subsequently, a response surface methodology(RSM) was used to
evaluate the effects of rice varieyt, storage time, alcohol and
sodium chloride addition on the microwave puffing ratio of the
dry cooked rice at 700W for 1 min. The microwave puffing
ratio of the dry cooked rice could be increased by extending
storage time, adding alcohol or sodium chloride. Among these,
addition of sodium chloride was the most effective,the next was
addition of alcohol andstorage time was the least effective to
the microwave puffing ratio. The optimalconditions for TCW70,
TC189 and TNus19 were respectively as follows,alcohol addition
of 5.1,4.1,4.2%,sodium chloride addition of 2.9,2.7,3.0%,and
storagetime for 20.3,16.6 and 0 day. The rehydration rate(y)
of the microwave puffed rices were further analyzed.The
rehydration rate could be elucidated by the equation, y=k tN,in
which t was the rehydration time, k was the isothermal
rehydration rate constant, n was related to the rehydration
temperature and the pore structure of the puffed rice.
Therehydratuibg rates were increased as the k values increased.
It was found that the k values of puffed TCW70 rice at 80℃ were
higher than those at 20℃, and both were linearly related to the
amounts of sodium chloried added. This was due to the high
puffing ratio and the pore structure of the puffed TCW70 rice.
The swelling powerfor the fuffed TCW70 rice was higher as
compared to both of the puffed TC189 and TNuS19 rices, was
likely due to its high amylopectin content.
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