Grape phenolic infusion into solid foods: studies on mass transfer and antioxidant capacity

Abstract

Osmotic Treatment (OT) enables to introduce controlled quantities of solution solutes into food and partially dehydrate it. The main aim of this study was to formulate intermediate-moisture solid foods with functional ingredients such as grape phenolics using OT. We evaluated how the source of phenolics and different types of binary mixtures of osmo-active solutes, 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. Fickian and empirical models were applied to characterise the mass transfer rate of grape phenolics during OT. 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 solid foods into which functional ingredients can be successfully incorporated. Under the conditions that maximized the phenolic infusion, the total phenolic content of the osmo-dehydrated 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 the kind and the concentration of osmo-active solute in the osmotic solution, food structure and the molecular weight of grape phenolics controlled their rate of infusion in the food. OT as a pre-treatment protected against grape phenolic degradation during further convective air drying.