Abstract: The effects of hot air puffing treatments at different temperatures and air velocities on the moisture and quality properties of potato-rice instant porridge developed by twin-screw extrusion technology were explored by measuring the dry basis moisture content, effective water diffusion coefficient and activation energy as well as the color, swelling degree, porosity and rehydration time. Furthermore, a kinetic model for the variation of the moisture content in the instant porridge was established during the puffing process. The results showed that both puffing temperature and air velocity affected the variation of the moisture content. The Page model was well fitted to the experimental values of moisture ratio, and it could accurately forecast the variation of the moisture content as a function of puffing temperature and air velocity. The effective water diffusion coefficient increased with increasing either puffing temperature or air velocity, and the activation energy was calculated as 18.96 kJ/mol. Puffing time, puffing temperature and air velocity all had a significant effect on the brightness value L*, yellowness-blueness value b*, expansion ratio, porosity and rehydration time of the instant porridge. According to the correlation analysis, the quality properties of the puffed instant porridge had significant correlations with each other (P < 0.01). The findings from this study may provide a theoretical basis for real-time monitoring of the variation of the moisture content in potato-rice instant porridge during hot air puffing for improved product quality.

Key words: potato-rice instant porridge; hot air puffing; kinetic model; quality properties