Abstract: In order to improve the quality of fresh in-shell peanut during hot air drying process, water migration characteristics and quality changes during hot air drying at different temperatures (40, 50 and 60 ℃) were investigated in the present study. The results showed that during the hot air drying process, the moisture content of fresh in-shell peanut changed significantly, and the content of weakly bound water decreased gradually. As the drying process progressed, the network structure of both peanut kernels and shells was deformed, and the porosity increased, which increased with increasing drying temperature. The drying process took place in the falling rate period. The drying time required to reach a moisture content within the safe limit was reduced by 45% when the drying temperature increased from 40 to 60 ℃, indicating that increasing temperature is helpful to accelerate the dehydration rate. In addition, under the influence of water content, the hardness of peanut kernels first increased, then decreased and finally increased once again at higher drying temperatures, and continuously increased at lower drying temperatures, while the hardness of peanut shells first decreased and then increased. According to the correlation analysis, the dry-basis moisture content was significantly positively correlated with the amplitude of low-field nuclear magnetic resonance signal (P < 0.01), negatively correlated with the porosity of peanut kernels and shells (P < 0.01) as well as the hardness of peanut kernels (P < 0.05). This paper provides a theoretical basis for the real-time monitoring of moisture during the hot air drying process of fresh in-shell peanuts and for high-quality drying.

Key words: fresh in-shell peanuts, low-field nuclear magnetic resonance, porosity, hardness