Maillard reaction products for strengthening the recovery of trans-resveratrol from the muscat grape pomace by alkaline extraction and foam fractionation

In this study, the recovery of trans-resveratrol (trans-Res) from the muscat grape pomace had been investigated by alkaline extraction and foam fractionation with the assistance of Maillard reaction products. First, the conjugates of soy protein isolate (SPI) and dextran (Dex) were prepared by Maillard reaction, and they were characterized by SDS-PAGE and FTIR. The suitable Maillard reaction period of 10 h was determined by measuring glycation degree of SPI, foam stability and browning degree of reaction solution. Fluorescence spectrum showed that trans-Res could be assembled with SPI-Dex conjugates through intermolecular interaction. Response surface method (RSM) was used to establish the nonlinear multivariate relationship between process variables and response, thereby optimizing operation conditions. Response surface method (RSM) had been used to optimize the extraction conditions of trans-Res from the muscat grape pomace. The extraction percentage of trans-Res reached 88.2% under the optimal extraction conditions of temperature 80 °C, NaOH concentration 12 mM, SPI-Dex conjugates concentration 5.5 g/L and extraction time 86 min. Then, the supernatant of extracting liquor was separated and used to perform foam fractionation as the feeding solution. The SPI-Dex conjugates would play a role of collector for entraining trans-Res into the foam phase. At 30 °C of temperature, 150 mL/min of volumetric air flow rate, 0.3 M/kg of ionic strength and 400 mL of loading liquid volume, the recovery percentage and enrichment ratio of trans-Res were 90.3% and 6.2, respectively. Stability test results showed that SPI-Dex conjugates contributed to maintaining the stable structure of trans-Res by generating aggregates during foam fractionation.