Phytochemical stability in dried tomato pulp and peel as affected by moisture properties

Phytochemical stability was studied in dried tomato pulp and dried tomato peel stored at 30 °C with various water activity (a(w)) levels and related to glass transition temperature (T(g)) and water mobility. At a(w) < 0.32, the values for T(g) were >30 °C for both the pulp and peel, indicating that they were in the glassy state, with little molecular mobility. At a(w) = 0.56, T(g) was <30 °C, indicating the samples were in the rubbery state, with decreased viscosity and increased molecular mobility. The hydrophilic antioxidants (hydroxycinnamic acids and naringenin) were stable for samples in the glassy state, but were unstable for samples in the rubbery state. In contrast, the lipophilic antioxidants lycopene and α-tocopherol were mostly unstable for samples in the glassy state. These results could be used to optimize phytochemical contents in tomato products that must be dried prior to further processing.