Drying efficiency and quality preservation of blackberries (Rubus spp. variety Tupy) in the near and mid-infrared-assisted freeze-drying

Abstract

The influence of infrared radiation-assisted freeze-drying (IRFD) on the process efficiency and quality of blackberries (Rubus spp. variety Tupy) was evaluated. Two lamp types were coupled in the freeze dryer to produce short-wavelength (NIRFD) and mid-wavelength (MIRFD). Treatments were: conventional freeze-drying (FD - control); continuous NIRFD, continuous MIRFD; NIRFD and MIRFD applied after 40 % weight reduction. IRFD reduced up to 42.51 % the drying time compared to FD, and NIRFD were the fastest treatments due to the greater penetration depth. ANOVA results of shrinkage, total color difference and hue angle were not significant (P < 0.05) and indicate that final volume reductions were not affected after IRFD and the surface colors were preserved with the same characteristic red color (mean hue of 32.9°) of FD. Results for hardness, total phenolic content (TPC), antioxidant capacity (AC) and anthocyanin content of freeze-dried blackberries were statistically different (P < 0.05) when using IRFD. MIRFD had higher hardness (10.13 N) compared to FD (6.98 N) and this result influenced the lower rehydration ratio. MIRFD also reduced the anthocyanin content. NIRFD significantly yielded higher values for TPC and has potential for the production of dried blackberries with good appearance, high nutritional content and faster rehydration capacity.

Keywords

• Infrared radiation-assisted freeze-drying
• Texture profile analysis
• Drying kinetics
• Bioactive compounds
• Microstructure