Studies On Influencing Factors Of Collapse Phenomenon For Freeze-dried Papasya Slices

Structural collapse phenomenon in the papaya freeze-drying process not only cause the rehydration characteristic and porosity of the freeze-dried papaya slices to decline, but also cost the company a fortune. In order to avoid or lighten the collapse level in the papaya freeze-drying process, a variety of papaya named" Da Bai Pi"was used as experimental material to study the factors causing papaya collapse in the freeze-drying process. The eutectic point、consolute point and glass transition temperature of raw or pretreated papaya was measured by Differential Scanning Calorimetry(DSC). The most effective freeze-drying conditions with the lowest collapse level was accomplished by comparing the influence of color、hardness、rehydration characteristic porosity and volume shrinkage, which caused by the maturity of raw material、 pretreatment method and the key technical parameters of the freeze-drying process. The main results are as follows:Firstly, the product of papaya with low ripeness may collapse seriously and pulps of papaya with high ripeness are so soft that they can’t be suitable for processing. The maturity of papaya with the total soluble solid content of8.46≈0.01Brix were most suitable for processing, and the collapse level of the product is lowest, whose shrinkage percentage was18.3±1%.Secondly, the balancing and harding pretreatment can bring down the collapse level of the product, however, the osmotic pretreatment harden the surface of the product and exacerbate the collapse level. It was concluded that the shrinkage percentage of the product was17.43±0.89%when the balancing temperature was95℃and time was60s by optimizing the balancing conditions. Meanwhile, Harding pretreatment can bring down the collapse level, and the shrinkage percentage of the product was16.45±1.02%when the material was pretreated by1.5%CaCl2solution, whose porosity and rehydration characteristic was enhanced significantly.Thirdly, in the key technical parameters of the freeze-dried processing, the frozen rate didn’t cause distinct influence on the quality of the product, on the contrary, inadequate frozen time might cause product to collapse. The shrinkage percentage of the blanched papaya frozen at-40℃for180min was18.06±2.19%.when the temperature procedure was set as follows:keep the temperature at80℃for4hours, and then keep the temperature at70℃for7hours, and at last keep the temperature at60℃for7hours, the shrinkage percentage of product under it was lowest with the value of19.02±0.43%by comparing to other procedures.