Studies of the Starch Pearl I：Combined Constant Temperature/Relative Humidity

• Main Authors: Li Dai, 戴俐
• Other Authors: Yi-Chung Fu
• Format: Others
• Language: zh-TW
• Published: 2002
• Online Access: http://ndltd.ncl.edu.tw/handle/37569757053052896177

碩士 === 國立中興大學 === 食品科學系 === 90 === Abstract Starch pearl is a traditional refreshment in Taiwan. The shelf life of fresh starch pearl is very short, and it usually preserved by refrigeration. Dried starch pearl can be stored at room temperature with at least one year shelf life. At present, the dried starchpearl is produced with Home-made type small scale factory. The drying condition is natural air-dry at room temperature. The relative humidity of the air is very high in Taiwan, this increase the difficulty for the drying processing and preservation of starch pearl-like products. Major disadvantages of conventional drying of foods are low energy efficiency and long drying time during the falling rate period. Because of the low thermal conductivity of food materials in this period, heat transfer to the inner sections of foods during conventional heating is limited. In order to eliminate this problem and achieve fast and effective thermal processing, the use of microwave for food drying is increase. Microwave drying is rapid, more uniform and energy efficient compared to conventional hot air drying. It is suggested that microwave energy should be applied in the falling rate period or at a low moisture content for finish drying. Our objective is to compare the drying rate during constant temperature/relative humidity drying and combined microwave finish drying. The quality of starch pearl after drying and rehydration will be also investigated. In this study, starch pearl is first dried by constant temperature/ relative humidity till the fraction of unremoved moisture content reaches 1/2 and 1/3, then final dried by microwave. At the period of constant temperature/relative humidity drying, starch pearl is dried during 27~57℃ and 60~80% relative humidity. The constant drying rate is positively correlated to drying temperature and negatively correlated to relative humidity. An equation of constant drying rate to explain the relationship between temperature and relative humidity is developed. It is found, before microwave finish drying, the moisture content of starch pearl is in the constant drying rate period. The results showed the microwave finish drying method cut 2/3 of traditional drying time. The results showed that the size of starch pearl cannot be too large. Appropriate diameter of starch pearl is about 6 mm. If the diameter is large than 6 mm the dried starch pearl will be very difficult to cook, and increase the cooking time. With no addition of CMC, the dried starch pearl is very easy to break and with higher cooking loss after drying and rehydration. It is believed that with addition of CMC is helpful for the quality of starch pearl and it can make dried starch pearl harder and not easily break. The dried starch pearl with microwave finishing drying have lower hardness and cooking loss than those drying at constant temperature/relative humidity. But the quality of dried starch pearl with microwave finishing drying is not different from commercial products. With no quality difference and significantly decreased drying time, the microwave finishing drying is promising for future commercial production.