| Summary: | 碩士 === 國立中興大學 === 食品科學系 === 91 === In addition to decorating the appearance, the basic purpose of packaging for a baked snack foods is to prevent its sorption of moisture from air, which will subsequently cause the deterioration of foods either in texture or flavor. The time in term of days, which requires for moisture absorption to reach to a maximum critical level is regarded as the shelf-life of the packaged foods. Therefore, how to properly choose a packaging material as well as how to determine the shelf-life of the packaged foods are the technology and concerns for most of the food manufacturers.
In this study, a rice cracker from non-glutinous rice, a bolo from potato starch, and a wafer-like biscuit from wheat flour are examined by sensory evaluation to determine the critical moisture level of the above-mentioned baked snack foods. Those unpackaged products as control are also examined by the method of absorptional isotherm curves. Calculating
enthalpy values is performed to understand the absorptional properties of those baked snack foods . The maximum water vapor permeability rate (max WVPR) and the predicted shelf-life (t) can be calculated from the information deduced from isothermal curves (25, 35, 45℃) and a mathematic model. The racticability of the mathematic formula are finally proofed by storage experimented on the packaged foods. The results are listed as follows :
1.The ANOVA statistics results of sensory evaluation getting
from the SAS system verify that the critical moisture level
of the above- mentioned baked snack foods are all found at 8%
dry basis.
2.From the sorptional isothermal characteristics of rice
cracker, bolo and wafer at 25℃, it is indicated that rice
cracker is more stable than bolo and wafer during experiment.
3.The enthalpy of rice cracker, bolo and wafer at different
moisture levels can indicate that absorptional properties
between those baked snack foods are different. In which, only
bolo with high water content can hold stable easily.
4.The predicted shelf-life (t) can be calculated with the
mathematic model :
t(day) = ln[(We-Wi)/(We-Wc)]×[(Xo.b)/(WVTRi.A)]
The maximum water vapor permeability rate (max WVPR) also can
be calculated with this mathematic model.
5.The experimented critical moisture levels (Wc%, db) after
storage for rice cracker, bolo and wafer were very close to
the predicted critical moisture levels and were not exceed
the critical value which can hold good quality of
products.The practicability of the deduced mathematic formula
for this study can be approved.
|
|---|
