This paper compared the effects of air and nitrogen on the freezing characteristics, color, and cell structures of chestnut kernels at different rates of heat transfer and adopted liquid nitrogen spray quick-freezing (NF-40 °C/-60 °C/-80 °C/-100 °C) and still air freezing (AF-20 °C/-40 °C) as the freezing methods. The ratio of heat transfer coefficients in N2 groups was two times as high as those in air groups, and NF-100 °C and NF-80 °C showed better freezing characteristics, good protection for cytoskeletons, and the color was similar to those of the fresh group. Taking both Multivariate Analysis of Variance (Principal Components Analysis and Cluster Analysis) and economic factors, NF-80 °C can be used as a suitable method for chestnut kernel freezing. When the ambient freezing temperature was lower than Tg, both NF and AF treatment groups presented poor quality. The rate and medium of heat transfer jointly influenced the freezing characteristics and quality. The former had a greater effect than the latter, however.
Keywords: cell structure; chestnut kernels; freezing characteristics; heat transfer medium; heat transfer rate.