Freezing as pretreatment in instant controlled pressure drop (DIC) texturing of dried carrot chips: Impact of freezing temperature

Abstract

Instant controlled pressure drop (DIC) has been developed to impart a porous structure to partially dried pieces of fruits and vegetables by expanding them; however, the expansion was limited for carrots due to the compact tissue structure. The effects of freezing pretreatments with different freezing time on the texture and porous characteristics of DIC dried carrot chips were studied. Freezing curves and microstructure of the frozen carrots indicated that the tissues were severely damaged at freezing temperature of −18 °C and −40 °C, with freezing time of 84.2 and 45.0 min respectively. In addition, the samples also showed superior texture (hardness 38.45–39.60 N, crispness 1.18–1.95 mm) and higher volume ratio (0.59–0.71) than that of the −80 °C and −196 °C frozen samples. Moreover, the analysis of SEM and X-ray microtomography images demonstrated that the samples obtained more homogeneous porous microstructure with mode pore-size around 981 and 513 μm, respectively. In conclusion, selected and controlled freezing pretreatment before DIC drying could yield desirable and crispy carrot chips by controlling the growth of crystal, which would be a valid method to engineer the texture of DIC-dried vegetable and fruit chips.