Grape phenolic impregnation by osmotic treatment: influence of osmotic agent on mass transfer and product characteristics.

Osmotic treatment (OT) is applied to obtain high quality intermediate moisture products impregnated with particular solutes, for instance phenolics from commercial grape seed extracts. To investigate how the nature of osmo-active solutes affects mass transfer of grape phenolics in a solid model food, sucrose, sodium chloride and glycerol were used as osmo-active solutes. Mass transfer of total and individual grape phenolics of low molecular weight were characterized by the diffusional approach and Peleg’s model. Of all the osmo-active solutes investigated, sodium chloride led to the highest phenolic infusion rate for each individual phenolic analyzed. With all the osmo-active solutes, the non esterified flavan-3-ol monomers showed a higher initial rate of phenolic mass transfer (1/k1) than their corresponding gallate esters and flavan-3-ol dimers. The phenolic content in the osmo-treated model food was similar or higher than that of the richest fruits and vegetables in all the conditions tested, thus increasing the antioxidant capacity of the product.