Impregnation-mediated Natural Fortification of Sliced Apples with Hypertonic Fruit Juices: Mass Transfer Kinetics and Product Quality

A natural fortification method was investigated for producing nutrition enhanced, shelf-stable apple chips. The fortification was facilitated by impregnation of nutrients in three hypertonic fruit juices (apple, grape, and cranberry) into apple tissues with an osmotic dehydration (OD) process with and without vacuum (VOD), which was followed by a hot air finish drying to obtain dried apply slices. The role played by the osmotic pressure difference between the osmotic solution and the apple tissue on dehydration rate was investigated. Quality attributes, including color, phenolic content (TPC) and antioxidant capacity (AOC) of the dried apples were evaluated. The results indicated that the grape juice was more effective in removal of moisture from apple tissues than the two other juices. The VOD speeded up the mass transfer but had no significant effect on nutrition enrichment. The VOD apple samples of grape juice had a water diffusion coefficient of 13.02 × 10-10 m2/s and a solid diffusion coefficient of 5.67 × 10-10 m2/s, while that of the OD-counterparts were 8.89 × 10-10 m2/s and 6.50 × 10-10 m2/s, respectively. The final products obtained by OD or VOD followed by hot air drying had a higher total phenol (TPC) and antioxidant content (AOC) than those of fresh apples. When grape juice was used as the osmotic solution, the sample produced by OD+AD had an AOC of 78.44 (%DDPH radical) and a TPC of 81.54 mg GAE / 100g of dry mass; whereas the sample treated by VOD+AD had an AOC of 81.13 (%DDPH radical) and a TPC of 86.09 mg GAE / 100g of dry mass. However, the TPC and AOC of fresh apple were 70.98 mg GAE / 100g of dry mass and 46.21 (%DDPH radical), respectively. Impregnation treatment with fruits juices was shown to be an effective method for enhancing the nutritional value of dried apples.