Characteristics of apple juice and sugar infused fresh and frozen blueberries

• Osmotic dehydration (OD) prior to drying significantly reduces the moisture content of the frozen blueberry by about 30%.
• Sugar-based OD showed a shorter follow-up drying time (420 min) for blueberries than apple juice-based OD (480 min).
• Apple juice concentrates is a good substitute for sugar during OD without compromising yield of the dried blueberries.

Use of apple juice concentrate and standard sugar-based osmotic solution were compared during osmotic dehydration (OD) of fresh and frozen blueberries for solid gain and water loss. Additionally, fresh and frozen blueberries were characterized for moisture desorption using a thermo-gravimetric analyzer (TGA) at an isothermal temperature of 105 °C under dry nitrogen condition. Weight loss-time data generated from the TGA was used to calculate the overall liquid diffusion coefficient during moisture desorption. Results showed that the use of apple juice concentrate as an osmotic solution increased sugar concentration of frozen blueberries to 30.30 °Brix, which was similar to that obtained from the use of sugar-based osmotic solution (32.90 °Brix). Additionally, irrespective of the osmotic solution type, the osmotically dehydrated frozen blueberries reached the desired safe water activity (aw) range (0.40–0.50) in the 600 min drying time during follow-up drying at 74 °C. Moisture desorption characterization using TGA showed that fresh blueberries took about 53% additional drying time compared to frozen blueberries.