The effect of the molecular environment and the temperature dependence of hyperfine parameters in first principles calculations in alpha-D-glucose and beta-D-fructose crystal radicals have been investigated. More specifically, we show how static (0 K) cluster in vacuo hyperfine calculations, commonly used today, deviate from more advanced molecular dynamics calculations at the experimental temperature using periodic boundary conditions. From the latter approach, more useful information can be extracted, allowing us to ascertain the validity of proposed molecular models.