Abstract: In order to determine the crispness variation of microwave-freeze dried Chinese yam chips during the drying process, Chinese yam was dried in a microwave vacuum freeze dryer and the drying characteristics were evaluated. Meanwhile, changes in pore structure and texture characteristics during the drying process were analyzed by scanning electron microscopy, mercury porosimetry and puncture test, and a mathematical model describing the crispness of Chinese yam chips was developed to predict the quality change of Chinese yam chips during the drying process. The results showed that the whole drying process included acceleration and deceleration stages without a pronounced constant speed stage. The moisture content was lower with prolonged drying; the pore network structure was more compact. The higher the microwave intensity, the faster the drying rate, the lower the moisture content, and the denser the pore network structure. The best model was found to be the DoseResp model: y = A1 + (A2?A1)/(1 + 10((lg x0?x)p)) (R2 > 0.99), where x is the moisture content, y is crispness and A, x0 and p are coefficients. This model could better predict the crispness of Chinese yam chips.

Key words: puncture test, pore network structure, crispness, mathematical model