The Optimization Of Drying Process Of Instant Rice And Its Aging Characteristics During Storage

The effect of different drying methods on the quality of instant rice prepared with theprocedure of two times immersing, two times cooking were investigated in this paper. Theresults show that the instant rice which was dried with hot air in the condition oftemperature80℃for120min has well quality. Its rehydration time is7min, rehydrationrate is2.46, abram iodine value is0.568, enzyme hydrolysis rate is0.035, and its waterreabsorbing ratio is0.072. The instant rice which was dried with microwave power of450W for25min has well quality. Its rehydration time is8min, rehydration rate is2.28,abram iodine value is0.247, enzyme hydrolysis rate is0.057and its water reabsorbing ratiois0.020. The instant rice which was dried by vacuum freezing of temperature60℃for15hhas well quality. Its rehydration time is6min, rehydration rate is3.60, abram iodine value is0.381, enzyme hydrolysis rate is0.107, and its water reabsorbing ratio is0.924. The instantrice dried with vacuum freezing has the best suitable microscopic structure for rehydration,sensory quality and rehydration property. A suitable drying technology with thecombination of microwave and hot air was developed using single factor and orthogonalexperiment. This drying method was constituted of microwave drying with power450W for8min, then hot air drying under the temperature80℃for60min. The instant rice producedby this drying process has good quality. Its rehydration rate is2.50, abram iodine value is0.830, enzyme hydrolysis rate is0.044and the total time of drying is68min. This dryingmethod is most suitable for mass production. Its drying energy consumption is low and thetime is short.The influence of the addition of ethanol, citric acid, acetic acid, β-cyclodextrin andsucrose fatty acid ester on the on the quality of instant rice produced with above technologyof two times immersing, two times cooking was studied with the single factor andorthogonal test. The optimum additives constitution were ethanol mass concentration1.0%,acetic acid mass concentration0.6%, sucrose fatty acid ester mass concentration0.4%,β-cyclodextrin mass concentration of1.0%.The quality change of instant rice during the storage period was investigated and theresults show that there were little changes appeared of the indexes of retrogradation rate,gelatinization degree, rehydration characteristics, sensory quality, hardness and stickiness.All these changes were happened in the first15days of storage time, then less changes would be happened after15days. The Crystallization properties and thermal characteristicof instant rice during storage were analyzed with the X-ray diffraction and DSC, and theresults showed that the crystallinity of instant rice is0. But after18months, the crystallinityof instant rice increased to8.44%. The gathered form of instant rice changed less in theprocess of preservation. So the short-term aging of instant rice is mainly due to the rise ofits glass trasitio temperature.