The enrichment of fruits and vegetables with physiologically active compounds that have potential benefits in terms of health may be a key way of developing new functional foods. By-products of fruit processing, such as extracts from grape seeds and skins are widespread nutritional supplements, because of their high content of phenolic compounds. Considering that Osmotic Treatment (OT) enables to introduce controlled quantities of solution solutes into food and partially dehydrate it, it has been suggested as a feasible technology for exploiting jelly foods, fruit and vegetables as matrices into which bio-active compounds can be successfully incorporated. The main aim of this study was to formulate intermediate-moisture solid foods with functional ingredients such as grape phenolics using OT. To satisfy this main objective, we also evaluated how the source of phenolics, i.e. concentrated red grape juice and commercial extracts from grape seed and white grape marc, affects: (i) the penetration level of grape phenolics, (ii) the intake of low-molecular-weight phenolics, and (iii) antioxidant capacity in a model food made of agar during OT. Furthermore, the mass transfer rate of low-molecular-weight phenolics during OT in a model food with each source of grape phenolics was characterised at different operating conditions. To do so, Fickian and empirical models were applied. Besides, we determined how different types of binary mixtures of osmo-active solutes (sucrose and sodium chloride) affect the phenolic pattern and antioxidant capacity of the final product. Finally, the extent and rate of phenolic infusion into plant tissue (apple, banana and potato) was determined while their stability after a post-treatment such as convective air drying was evaluated. Our results confirm that OT is a suitable technology for the exploitation of jelly foods, fruits and vegetables as matrices into which functional ingredients can be successfully incorporated. Under the conditions that maximized the phenolic infusion, the total phenolic content of the osmo-dehydrated model food was close to the values reported in some rich-in-phenolic fruits and vegetables, while the TEAC was three times that of fresh fruit with the highest antioxidant capacity. The effective diffusion coefficients of total and individual phenolics showed that not only the concentration of soluble solids in the osmotic solution but also the molecular weight of grape phenolics controlled their rate of infusion in the model food. The penetration of phenolics with a molecular weight of over 612 g/mol was lower and made a poor contribution to total phenolic impregnation. By using more than one osmo-active solute (sucrose and NaCl) and adjusting the composition of the osmotic solution, OT can control not only the phenolics content but also the sensory properties of the end product. When infusing grape phenolic compounds into plant tissue, the extent of grape phenolic impregnation was controlled by food structure and the kind of osmo-active solute. Plant tissue showed a lower grape phenolic infusion than that of the model food. OT as a pre-treatment protected against grape phenolic degradation during further convective air drying, though the mechanisms controlling the chemical changes undergone by grape phenolics require further research.
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