Dehydrated melon containing antioxidants and calcium from grape juice

Abstract

Background: Grape juice has a high antioxidant potential, capable of fighting oxidative processes in the body. The juice is mainly marketed in its concentrated form, which has a high content of glucose and fructose. The juice concentrate may then be used as an osmotic agent to dehydrated fruit with a relatively short shelf-life at room temperature, such as melon. The osmotic dehydration process can also be combined with conventional drying in order to further reduce the water activity (aw) of the product. Finally, the antioxidant-rich melon meets the consumers’ demand for foods which contain ingredients that may impart health benefits. Results: Melon dehydrated by osmotic process at 200, 400 and 600 mbar, using grape juice concentrate (GJC), showed no significant differences in physical characteristics (aw, °Brix, and moisture content). Higher efficiency was observed when dehydration was performed at 200 mbar. After osmotic dehydration with GJC, both plasmolysis of the melon cells and an increase in intercellular spaces were observed by optical microscopy, with no negative impact on the mechanical properties (True stress, Hencky’s strain and deformability modulus). Calcium present in GJC was impregnated into the melon matrix, thus contributing with the mineral composition and mechanical properties of the final product. No significant differences were observed for the antioxidant capacity of melon dehydrated both with GJC and GJC followed by air-drying at 50 and 70°C. This demonstrates that it is possible to combine the two processes to obtain a product with intermediate moisture without decreasing its antioxidant capacity. The samples scored above the acceptable limit (>5) varying between like slightly to like moderately, resulting in a purchase intent with average scores between 3 (maybe/maybe not buy) and 4 (probably would buy).Conclusions: A product with intermediate water activity, acidic, firm, high antioxidant capacity, rich in calcium and in naturally occurring sugars, and potential sensory acceptance can be obtained using grape juice concentrate in the osmotic dehydration process, followed by air-drying process.Keywords: osmotic dehydration, air-drying, fruit juice, optical microscopy, antioxidants, calcium.