Characterization of water status and water soluble pectin from peaches under the combined drying processing.

Characterization of water status and water soluble pectin (WSP) from peach were evaluated after different stage of combined drying in which osmotic dehydration (OD) was considered as the pre-treatment prior to instant controlled pressure drop (DIC) - assisted infrared radiation drying (IRD) (IR-DIC). Results showed that the contents of free water and immobilized water decreased to 0 g after the combined drying. The content of bound water increased after IRD treatment. The residual PME activity in peach slices was 153.3-179.6% after OD treatment, while, the PG were totally inactivated after IRD. The degree of esterification (DE), WSP content and average molar mass (Mw) decreased significantly (from 75.00 to 43.74, from 156.00 to 74.91 mg/g AIR and from 2.28 to 0.49 × 10 Da, respectively) after the combined drying. The neutral sugar of WSP was mainly composed by galactose, arabinose and rhamnose, whose contents decreased after the combined drying. However, OD treatment would slow down the degradation. There was a low peak at 1740 cm in FT-IR spectrum observed for WSP after IRD and DIC treatment, which might illustrate the degradation of WSP during the combined drying.